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  • Articles  (3,956)
  • Oxford University Press  (3,956)
  • 2010-2014  (3,681)
  • 1950-1954  (275)
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (3,501)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (455)
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  • Articles  (3,956)
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  • 1
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    Farmland Prices: Is This Time Different? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Description: The historical behavior of farmland prices, rental rates, and rates of return are examined by treating farmland as an asset with an infinitely long life. It is found that high (low) farmland prices relative to rents have historically preceded extended periods of low (high) net rates of return, rather than greater (smaller) growth in rents. Our analysis shows that this attribute is shared with stocks and housing, and the financial literature provides ample evidence that other assets feature it as well. The long-run relationship linking farmland prices, rents, and rates of return is analyzed. Based on this relationship, we conclude that recent trends are unlikely to be sustainable. The study explores the expected paths that farmland prices and rates of return might follow if they were to eventually conform to the average values observed in the historical sample, and concludes with a discussion of the policy implications. Recommendations for policy makers include close monitoring of farmland lending practices and institutions to allow early identification of potential problems, and identifying in advance appropriate interventions in case recent farmland market trends were to suddenly change.
    Keywords: Q14 - Agricultural Finance
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 2
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    Subscription Page (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 3
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    Some Comments on "Taxes, Subsidies, and Advertising Efficacy in Changing Eating Behavior: An Experimental Study" (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 4
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    Hispanic American Opinions toward Immigration and Immigration Policy Reform Proposals (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Description: This study presents evidence from a survey and choice experiment on the preferences of Hispanic immigrants who entered the United States illegally for different immigration reform proposal attributes. Key components of the current competing US Senate and House immigration reform bills are considered including pathways to legal permanent residence, temporary work visas, family visitation rights, and access to medical care. The results quantify the value Hispanic immigrants place on different policy attributes and suggest that longer-term work visas are highly valued. Ability to legally work in the United States and a pathway to citizenship are substantially more valued than social services such as medical care and social security benefits.
    Keywords: J15 - Economics of Minorities and Races ; Non-labor Discrimination, K37 - Immigration Law, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 5
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    What to Do about the "Cult of Statistical Significance"? A Renewable Fuel Application using the Neyman-Pearson Protocol (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Description: This research adapts the Neyman-Pearson testing protocol commonly used in biomedical research for ex post evaluation of the employment impacts of new ethanol bio-refineries in the U.S. Great Plains and the Midwest. By calculating the power of the test, the suggested protocol may provide policy-relevant information, even in the event of nonsignificant findings. The main obstacle to applying this protocol has been the need to posit an explicit alternative distribution, which runs counter to the empiricist tradition of mainstream econometrics. We resolve this problem by applying a data generating process with known parameters anchored to sample data to compute power.
    Keywords: C12 - Hypothesis Testing, Q42 - Alternative Energy Sources, R11 - Regional Economic Activity: Growth, Development, and Changes
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 6
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    Reply to Comment on Taxes, Subsidies, and Advertising Efficacy in Changing Eating Behavior: An Experimental Study (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Keywords: C91 - Laboratory, Individual Behavior, I18 - Government Policy ; Regulation ; Public Health
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 7
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    A Bayesian approach for modelling non-linear longitudinal/hierarchical data with random effects in forestry (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: Longitudinal or hierarchical data are often observed in forestry, which can pose both challenges and opportunities when performing statistical analyses. The current standard approach for analysing these types of data is mixed-effects models under the frequentist paradigm. Bayesian techniques have several advantages when compared with traditional approaches, but their use in forestry has been relatively limited. In this paper, we propose a Bayesian solution to non-linear mixed-effects models for longitudinal data in forestry. We demonstrate the Bayesian modelling process using individual tree height–age data for balsam fir ( Abies balsamea (L.)) collected from eastern Maine. Due to its frequent utilization in modelling dominant tree height growth over time, we choose to examine models based on the Chapman–Richards function. We established four different model formulations, each having varying subject-specific parameters, which we estimated using both frequentist and Bayesian approaches. We found the estimation results to be quite close between the two methods. In addition, an important feature of the Bayesian method is the unified manner in which estimation and prediction are handled. Specifically, local parameters can be predicted for a new dataset after setting the posterior distributions from the estimation stage as new priors in the prediction phase.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 8
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    Evaluating the profitability of selection cuts in irregular boreal forests: an approach based on Monte Carlo simulations (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: This study compares the financial return of converting old-growth boreal stands into even-aged stands to that of two approaches of selection cutting in Quebec (Canada). In this region, old-growth stands are usually harvested by completely removing the canopy while protecting the abundant advance regeneration, an approach known as careful logging around advance growth (CLAAG). These approaches were compared using a time frame of over 200 years. Consideration is given to the majority of the operating costs leading to end products. The financial analysis integrates Monte Carlo simulations, making it possible to consider the uncertainty associated with variables. The net present values (NPVs) are then associated with a distribution of probabilities. The results show that the probabilities of obtaining positive NPVs are high for all treatments, suggesting that selection cutting approaches can be appropriate alternatives to CLAAG for some stands. Depending on the criteria used, the CLAAG cut or one of the selection cuts show the best performances. In fact, the results of the financial study show that in the future, selection cutting approaches will be more profitable than CLAAG but still less than present CLAAG operations. This occurs because, according to the current yield curves and rotation ages, future stands managed with CLAAG will have smaller and less valuable trees than in the primary forest and in stands managed with the selection system.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 9
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    Examining growth dynamics of Pinus radiata plantations at old ages in New Zealand (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: There is a growing interest in the feasibility of establishing ‘Carbon’ forests where carbon sinks are created by maintaining forest stands out to considerable ages. In New Zealand, Pinus radiata (D. Don) is usually grown over 25- to 30-year rotations; the main aim of this paper is to examine the potential to maintain stands to 60 years or more. There were over 140 permanent sample plots in New Zealand that were maintained for at least 50 years. These data were examined to verify that growth can be sustained over this period. Net basal area per hectare and mean-top-height are graphically demonstrated to follow expected growth paths with no signs of senescence occurring. Stems per hectare loss is shown to be sometimes high, especially with dense stockings, but virtually all dying trees are small suppressed stems, so the impact on basal area yield at maturity is minimal. It is concluded that growing radiata pine on a rotation of 60 years is feasible, and it may be possible to use much longer rotations.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 10
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    The effects of site preparation practices on carbon dioxide, methane and nitrous oxide fluxes from a peaty gley soil (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: The effects of site preparation practices (drainage, mounding and fertilization) on the fluxes from the soil surface of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) were studied on an organic-rich peaty gley soil at Harwood Forest, north-east England. Drained plots had significantly higher CO 2 fluxes but significantly lower CH 4 fluxes compared with undrained plots, while N 2 O emissions were not affected by drainage. Mounding caused significantly higher CH 4 emissions, while it significantly reduced N 2 O emissions. Fertilization caused significant increases in emissions of CO 2 , CH 4 and N 2 O. In terms of overall greenhouse warming potential, drainage and fertilization increased CO 2 -equivalent emissions by ~18–29 and 7–23 per cent, respectively, while mounding reduced CO 2 -equivalent emissions by ~8 per cent in year 1, but had no effect on emissions in year 2 of study. Soil temperature was the main environmental variable controlling CO 2 emissions, while CH 4 was controlled primarily by water table depth. Nitrous oxide emissions responded to changes in soil temperature and water table depth. In the short term, drainage and fertilization contributed to accelerating greenhouse gas emissions significantly, although their long-term effects are likely moderated by accelerating carbon accumulation in the tree biomass. Long-term studies are required to assess the cumulative impacts of site preparation practices during the whole rotation cycle.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 11
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    Comparing field- and model-based standing dead tree carbon stock estimates across forests of the US (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: As signatories to the United Nation Framework Convention on Climate Change, the US has been estimating standing dead tree (SDT) carbon (C) stocks using a model based on live tree attributes. The USDA Forest Service began sampling SDTs nationwide in 1999. With comprehensive field data now available, the objective of this study was to compare field- and model-based estimates of SDT C stocks across the US to evaluate potential directions for improving National Greenhouse Gas Inventory (NGHGI) reporting and C dynamics research. Field inventory data indicated that most forests have relatively little SDT C stocks (〈1 Mg/ha), whereas large SDT C stocks (〉25 Mg/ha) are infrequent. Models used for past NGHGIs to predict SDT C stocks do not accurately reflect what was observed in inventory plots, resulting in an overestimation (~100 per cent) of SDT C stocks at the national scale. These results indicate that the current estimate of the Nation’s total forest C stock is overestimated by ~4.2 per cent due to overestimation of SDT C stocks that are a relatively small component of the total forest C stock. A field-based approach is suggested for use in future C reporting efforts to reduce estimation bias.
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 12
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    Comparative testing of single-tree detection algorithms under different types of forest (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: Airborne laser scanning data and corresponding field data were acquired from boreal forests in Norway and Sweden, coniferous and broadleaved forests in Germany and tropical pulpwood plantations in Brazil. Treetop positions were extracted using six different algorithms developed in Finland, Germany, Norway and Sweden, and the accuracy of tree detection and height estimation was assessed. Furthermore, the weaknesses and strengths of the methods under different types of forest were analyzed. The results showed that forest structure strongly affected the performance of all algorithms. Particularly, the success of tree detection was found to be dependent on tree density and clustering. The differences in performance between methods were more pronounced for tree detection than for height estimation. The algorithms showed a slightly better performance in the conditions for which they were developed, while some could be adapted by different parameterization according to training with local data. The results of this study may help guiding the choice of method under different forest types and may be of great value for future refinement of the single-tree detection algorithms.
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 13
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    Can overstorey retention be used to control bramble (Rubus fruticosus L. agg.) during regeneration of forests? (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: Silvicultural systems which retain canopy cover during the regeneration phase have become an increasingly important form of management, but their effectiveness in controlling weed species has not been extensively studied. The development of bramble, which is a widespread competitive weed species, was observed within a c . 35-year-old Corsican pine stand thinned to remove 10, 20, 40 and 80 per cent of basal area. Cover, height and numbers of inflorescences and berries were recorded in each of the 3 years following thinning and were generally ranked according to intensity of thinning, but there were no significant differences between treatments. Shoot length, estimated using a grid-intersection method, was significantly lower in the 10 per cent compared with the 40 and 80 per cent thinning treatments. The initial length of bramble shoot present, and basal area and number of trees remaining could be used in various combinations to predict cover, height and shoot length. Although the bramble thicket was generally less well developed in the less-intense thinning treatments, these did not appear to enhance the establishment of trees. Seedlings grew best in the 80 per cent treatment and overall their mean heights were generally lower than that of bramble. Retention of overstorey cover in order to suppress bramble growth and promote tree seedling establishment during forest regeneration may not succeed.
    Print ISSN: 0015-752X
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 14
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    The effects of whole-tree harvesting on three sites in upland Britain on the growth of Sitka spruce over ten years (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: Three experiments were established in the 1990s to examine the impact of complete residue (brash) and above-ground biomass removal (i.e. ‘whole-tree harvesting’, WTH) at clearfelling on the subsequent growth and yield of replanted Sitka spruce ( Picea sitchensis ). The sites were of varying fertility; two would now be considered to be of ‘medium’ risk for brash removal, while one would be a ‘high’-risk site. The interactions between brash removal and regular remedial fertilizer applications and weed control regimes were also investigated at each site. After 10 years, trees had been successfully established at all sites, and in most cases, the treatments were close to canopy closure. The main effects observed at all sites were due to brash retention and fertilizer application. The benefits from the former were not evident until the last stages of the establishment period, whereas benefits from fertilizer application were evident once the trees had reached 5–6 years of age. The impacts of weed control were inconsistent, providing temporary benefits on the more fertile sites, and having a negative effect on the poorest site, primarily because the herbicide regime favoured the development of ericaceous vegetation which competed with the planted trees for nutrients. After 10 years at the two medium-risk sites, the difference in growth between plots with brash retained and those where brash was removed was 5–9 per cent for height growth and 5–7 per cent for diameter. However, at the poorest site, the equivalent differences were ~9 per cent and 19 per cent. The results show that the impact of brash removal due to WTH are significantly affected by site type and soil fertility and also that it may take nearly a decade before the impacts of such practices are evident.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 15
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    Comparing a top-down and bottom-up approach in the identification of criteria and indicators for sustainable community forest management in Nepal (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Description: Policy makers, scientists and civil society are involved in the development of criteria and indicators for sustainable forest management (SFM), reflecting the growing worldwide demand for addressing sustainable development and environmental governance management goals. Such frameworks have been largely derived from expert-led or community-based approaches. This article details the identification process of criteria and indicators (C & I) based on the international principles of SFM through the analysis of a hybrid approach that uses both a top-down (TD) and a bottom-up (BU) approach. The aim of this article is to discuss how the two approaches have worked to incorporate the different views, opinions and experiences of experts and stakeholders. National-level C & I are then compared with those at the local level, making specific reference to sustainable community forest (CF) management. For the TD approach, a Delphi survey was conducted where 121 experts shared their knowledge, experience and judgements in assessing a set of 72 indicators with regard to the applicability, practicality and importance of national, regional and CF management in Nepal. For the BU approach, C & I for CF management were developed with the direct involvement of various stakeholders. It was shown that such a hybrid approach is feasible from a methodological point of view, but a framework is needed by the government to more fully utilize the opportunities of the C & I development process in the SFM context. The results of this study also help to bridge the gap between the ad hoc planning of decision makers and the requirement for a holistic management system, which includes participatory processes. Based on the conclusions of this study, general recommendations for the methodological design of C & I development in similar studies are given.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 16
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    Editor's Note (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-02-11
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 17
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    Collection of papers on hydrogen and fuel cells for low carbon energy (2012)
    Oxford University Press
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    Publication Date: 2012-02-17
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 18
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    Characterization of Ni-Cu-based catalysts for multi-fuel steam reformer (2012)
    Oxford University Press
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    Publication Date: 2012-02-17
    Description: Low-temperature methane and methanol steam-reforming catalysts Ni/Al 2 O 3 , Cu/Al 2 O 3 and Ni–Cu/Al 2 O 3 with various loadings of Ni and Cu were prepared using a wet impregnation method. The samples were characterized using scanning electron microscope, surface area (BET) test, X-ray diffraction (XRD), infrared test, CO chemisorption test and temperature-programmed reduction tests. XRD testing showed that NiO and CuO were present. Ni–Cu-alloyed catalyst shows a significant change in the catalyst characteristics compared with those of individual metals. The results presented in this paper show the main changes in the catalyst properties using ex situ testing.
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 19
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    Synthesis of new Mn/Ti containing perovskites and examination of their potential for use as solid oxide fuel cell electrodes (2012)
    Oxford University Press
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    Publication Date: 2012-02-17
    Description: In this paper we report the synthesis of a series of new Mn/Ti containing perovskites, La 1– x Mn x Mn 1– x Ti x O 3– , for investigation of their potential for use as solid oxide fuel cell electrodes, particularly anodes. Single-phase samples could be achieved for x ≤ 0.4. Above this level, La 2 Ti 2 O 7 impurities were found. Conductivity measurements showed electronic conductivity up to a maximum of 12 S cm –1 at 850°C in air. While the samples were shown to be stable in both air and 5% H 2 /N 2 , the conductivities in the latter were significantly lower (0.4 S cm –1 ), which would be an issue for potential anode applications.
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 20
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    Traceability, recalls, industry reputation and product safety (2012)
    Oxford University Press
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    Publication Date: 2012-12-28
    Description: Sometimes, authorities are unable to rapidly identify the origin of a tainted product. In such cases, recalls or warnings often apply to all suppliers, even to those that had not contributed to the contamination. Traceability enables more targeted recalls by identifying the product's origin more specifically. In this article, we show how increased traceability protects the reputation of industries by limiting the size of recalls. We show the relationships between traceability and the level of food safety with many identical small farms in a competitive industry and for an industry using collective action to set rules and standards.
    Keywords: D21 - Firm Behavior, Q10 - General, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 21
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    Product quality in the agri-food chain: do cooperatives offer high-quality wine? (2012)
    Oxford University Press
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    Publication Date: 2012-12-28
    Description: We investigate the impact of decentralised decision-making on product quality. Comparing a cooperative and an investor-owned firm suggests that members of the cooperative have an incentive to produce too much and to free-ride on quality. Whether or not cooperatives deliver higher quality products depends on the way in which the quality of the final product is determined from the quality levels of the inputs delivered (quality aggregation) as well as the number of members of the cooperative. Empirical evidence on the Austrian wine market suggests that wines produced by cooperatives tend to be of significantly lower quality, ceteris paribus .
    Keywords: D22 - Firm Behavior: Empirical Analysis, D23 - Organizational Behavior ; Transaction Costs ; Property Rights, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 22
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    Hydraulic time constants for transpiration of loblolly pine at a free-air carbon dioxide enrichment site (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: The impact of stored water on estimates of transpiration from scaled sap flux measurements was assessed in mature Pinus taeda (L.) at the Duke Free-Air CO 2 Enrichment (FACE) site. We used a simple hydraulic model with measurements of sap flux ( J ) at breast height and the base of the live crown for 26 trees over 6 months to examine the effects of elevated CO 2 (eCO 2 ) and fertilization (N F ) treatments, as well as temporal variation in soil moisture ( M ( t ) ), on estimates of the hydraulic time constant (). At low M ( t ) , there was little (〈12%) difference in of different treatments. At high M ( t ) , differences were much greater, with reductions of 27, 52 and 34% in eCO 2 , N F and eCO 2 x N F respective to the control. Incorporating with these effects into the analysis of a larger data set of previous J measurements at this site (1998–2008) improved agreement between modeled and measured values in 92% of cases. However, a simplified calibration of that neglected treatment and soil moisture effects performed more dependably, improving agreement in 98% of cases. Incorporating had the effect of increasing estimates of reference stomatal conductance at 1 kPa vapor pressure deficit (VPD) and saturating photosynthetic active radiation (PAR) an average of 12–14%, while increasing estimated sensitivities to VPD and PAR. A computationally efficient hydraulic model, such as the one presented here, incorporated into a hierarchical model of stomatal conductance presents a novel approach to including hydraulic time constants in estimates of stomatal responses from long-term sap flux data sets.
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 23
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    Climatic control of tracheid production of black spruce in dense mesic stands of eastern Canada (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: Inferences on climate change effects are reliable only if they are based on a causal relationship rather than simple statistical predictive capacity. To assess for causal links between climate and mature black spruce ( Picea mariana (Mills.) BSP) radial growth, we combined the use of wood anatomy, cambium phenology, climate and soil measurements (air temperature and humidity, precipitations, soil temperature and water content, photosynthetically active radiation), and a model selection approach proceeding backwards from a full model. Results show that the number of tracheids is responsible for 88% of the variation in ring width whereas mean tracheid diameter accounts for the remaining 12%. The number of tracheids produced depends on factors related to photosynthesis during tracheid production, i.e., daily light intensity and maximum temperature between the day of initiation and the day of cessation of tracheid production, plus soil temperature during August of the previous year which is an important period for determining the number of new needles produced. It is also important to consider duration of the period for tracheid production. These results imply that short-term climate change should increase black spruce radial growth. They also suggest that the typical use of post-growth ring width sampling individually linked to air temperature and precipitations is not sufficient to infer climate change effects accurately on radial growth where there is no strong single climatic limitation but multiple limitations instead.
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 24
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    Changes in wood density, wood anatomy and hydraulic properties of the xylem along the root-to-shoot flow path in tropical rainforest trees (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-21
    Description: It is generally assumed that the largest vessels are occurring in the roots and that vessel diameters and the related hydraulic conductance in the xylem are decreasing acropetally from roots to leaves. With this study in five tree species of a perhumid tropical rainforest in Sulawesi (Indonesia), we searched for patterns in hydraulic architecture and axial conductivity along the flow path from small-diameter roots through strong roots and the trunk to distal sun-canopy twigs. Wood density differed by not more than 10% across the different flow path positions in a species, and branch and stem wood density were closely related in three of the five species. Other than wood density, the wood anatomical and xylem hydraulic traits varied in dependence on the position along the flow path, but were unrelated to wood density within a tree. In contrast to reports from conifers and certain dicotyledonous species, we found a hump-shaped variation in vessel diameter and sapwood area-­specific conductivity along the flow path in all five species with a maximum in the trunk and strong roots and minima in both small roots and twigs; the vessel size depended on the diameter of the organ. This pattern might be an adaptation to the perhumid climate with a low risk of hydraulic failure. Despite a similar mean vessel diameter in small roots and twigs, the two distal organs, hydraulically weighted mean vessel diameters were on average 30% larger in small roots, resulting in ~ 85% higher empirical and theoretical specific conductivities. Relative vessel lumen area in percent of sapwood area decreased linearly by 70% from roots to twigs, reflecting the increase in sclerenchymatic tissue and tracheids in acropetal direction in the xylem. Vessel size was more closely related to the organ diameter than to the distance along the root-to-shoot flow path. We conclude that (i) the five co-occurring tree species show convergent patterns in their hydraulic architecture despite different growth strategies, and (ii) the paradigm assuming continuous acropetal vessel tapering and decrease in specific conductance from fine roots towards distal twigs needs reconsideration.
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    The effects of elevated CO2 and nitrogen fertilization on stomatal conductance estimated from 11 years of scaled sap flux measurements at Duke FACE (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: In this study, we employ a network of thermal dissipation probes (TDPs) monitoring sap flux density to estimate leaf-specific transpiration ( E L ) and stomatal conductance ( G S ) in Pinus taeda (L.) and Liquidambar styraciflua L. exposed to +200 ppm atmospheric CO 2 levels (eCO 2 ) and nitrogen fertilization. Scaling half-hourly measurements from hundreds of sensors over 11 years, we found that P. taeda in eCO 2 intermittently (49% of monthly values) decreased stomatal conductance ( G S ) relative to the control, with a mean reduction of 13% in both total E L and mean daytime G S . This intermittent response was related to changes in a hydraulic allometry index ( A H ), defined as sapwood area per unit leaf area per unit canopy height, which decreased a mean of 15% with eCO 2 over the course of the study, due mostly to a mean 19% increase in leaf area ( A L ). In contrast, L. styraciflua showed a consistent (76% of monthly values) reduction in G S with eCO 2 with a total reduction of 32% E L , 31% G S and 23% A H (due to increased A L per sapwood area). For L. styraciflua , like P. taeda , the relationship between A H and G S at reference conditions suggested a decrease in G S across the range of A H . Our findings suggest an indirect structural effect of eCO 2 on G S in P. taeda and a direct leaf level effect in L. styraciflua . In the initial year of fertilization, P. taeda in both CO 2 treatments, as well as L. styraciflua in eCO 2 , exhibited higher G S with N F than expected from shifts in A H , suggesting a transient direct effect on G S . Whether treatment effects on mean leaf-specific G S are direct or indirect, this paper highlights that long-term treatment effects on G S are generally reflected in A H as well.
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    Using electrical resistivity tomography to differentiate sapwood from heartwood: application to conifers (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: Estimating sapwood area is one of the main sources of error when upscaling point scale sap flow measurements to whole-tree water use. In this study, the potential use of electrical resistivity tomography (ERT) to determine the sapwood–heartwood (SW–HW) boundary is investigated for Pinus elliottii Engelm var. elliottii x Pinus caribaea Morelet var. hondurensis growing in a subtropical climate. Specifically, this study investigates: (i) how electrical resistivity is correlated to either wood moisture content, or electrolyte concentration, or both, and (ii) how the SW–HW boundary is defined in terms of electrical resistivity. Tree cross-sections at breast height are analysed using ERT before being felled and the cross-section surface sampled for analysis of major electrolyte concentrations, wood moisture content and density. Electrical resistivity tomography results show patterns with high resistivities occurring in the inner part of the cross-section, with much lower values towards the outside. The high-resistivity areas were generally smaller than the low-resistivity areas. A comparison between ERT and actual SW area measured after felling shows a slope of the linear regression close to unity (=0.96) with a large spread of values ( R 2 = 0.56) mostly due to uncertainties in ERT. Electrolyte concentrations along sampled radial transects (cardinal directions) generally showed no trend from the centre of the tree to the bark. Wood moisture content and density show comparable trends that could explain the resistivity patterns. While this study indicates the potential for application of ERT for estimating SW area, it shows that there remains a need for refinement in locating the SW–HW boundary (e.g., by improvement of the inversion method, or perhaps electrode density) in order to increase the robustness of the method.
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    A comparison of the hydraulic efficiency of a palm species (Iriartea deltoidea) with other wood types (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: Palms are an important component of tropical ecosystems, living alongside dicotyledonous trees, even though they have a very different growth pattern and vascular system. As monocots, vessels in palms are located within vascular bundles and, without a vascular cambium that many dicotyledonous trees possess, palms cannot add additional vessels to their vascular system as they get older and taller. This means that hydraulic architecture in palms is more predetermined, which may require a highly efficient hydraulic system. This preset nature, along with the decoupling of hydraulic and mechanical functioning to different cell types, may allow palms to have a more efficient hydraulic system than dicotyledonous trees. Therefore, this study seeks to determine the efficiency of the hydraulic system in the palm Iriartea deltoidea (Ruiz & Pav.) and compare this efficiency with other tree forms. We measured cross-sectional areas of roots, stems and fronds as well as leaf areas of I. deltoidea saplings. Likewise, cross-sections were made and vessel diameters and frequencies measured. This allowed for the calculation of theoretical specific conductivity ( K S,calc ), theoretical leaf-specific conductivity ( K L,calc ), and vessel diameter and vessel number ratios between distal and proximal locations in the palms. Iriartea deltoidea palms were found to have the largest, least frequent vessels that diverged most from the square packing limit (maximum number of vessels that fit into a given area) compared with other major tree forms, and they therefore invested the least space and carbon into water transport structures. Likewise, conduits tapered by ~1/3 between ranks (root, bole and petiole), which represents an efficient ratio with regard to the trade-offs between safety and efficiency of the conducting system. Conduits also exhibited a high conservation of the sum of the conduit radii cubed ( r 3 ) across ranks, thereby approximating Murray's law patterning. Therefore, our results indicate that the palm I. deltoidea has a very efficient hydraulic system in terms of maintaining a large conducting capacity with a minimal vascular investment. This efficiency may allow palms to compete well with dicotyledonous trees in tropical and subtropical climates but other developmental factors largely restrict palms from regions that experience prolonged freezing temperatures.
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    Nitrogen nutrition and drought hardening exert opposite effects on the stress tolerance of Pinus pinea L. seedlings (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: Functional attributes determine the survival and growth of planted seedlings in reforestation projects. Nitrogen (N) and water are important resources in the cultivation of forest species, which have a strong effect on plant functional traits. We analyzed the influence of N nutrition on drought acclimation of Pinus pinea L. seedlings. Specifically, we addressed if high N fertilization reduces drought and frost tolerance of seedlings and whether drought hardening reverses the effect of high N fertilization on stress tolerance. Seedlings were grown under two N fertilization regimes (6 and 100 mg N per plant) and subjected to three drought-hardening levels (well-watered, moderate and strong hardening). Water relations, gas exchange, frost damage, N concentration and growth at the end of the drought-hardening period, and survival and growth of seedlings under controlled xeric and mesic outplanting conditions were measured. Relative to low-N plants, high-N plants were larger, had higher stomatal conductance (27%), residual transpiration (11%) and new root growth capacity and closed stomata at higher water potential. However, high N fertilization also increased frost damage (24%) and decreased plasmalemma stability to dehydration (9%). Drought hardening reversed to a great extent the reduction in stress tolerance caused by high N fertilization as it decreased frost damage, stomatal conductance and residual transpiration by 21, 31 and 24%, respectively, and increased plasmalemma stability to dehydration (8%). Drought hardening increased tissue non-structural carbohydrates and N concentration, especially in high-fertilized plants. Frost damage was positively related to the stability of plasmalemma to dehydration ( r = 0.92) and both traits were negatively related to the concentration of reducing soluble sugars. No differences existed between moderate and strong drought-hardening treatments. Neither N nutrition nor drought hardening had any clear effect on seedling performance under xeric outplanting conditions. However, fertilization increased growth under mesic conditions, whereas drought hardening decreased growth. We conclude that drought hardening and N fertilization applied under typical container nursery operational conditions exert opposite effects on the physiological stress tolerance of P. pinea seedlings. While drought hardening increases overall stress tolerance, N nutrition reduces it and yet has no effect on the drought acclimation capacity of seedlings.
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    Ecotypic variation in response to light spectra in Scots pine (Pinus sylvestris L.) (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: We investigated Scots pine adaptive responses to the light spectra by measuring hypocotyl length in seeds sampled from three natural Scots pine ecotypes across a latitudinal cline ranging from 63° to 68° N in Sweden where the adaptive cline is known to be steeper. Seeds were germinated under dark (D) and three monochromatic continuous light wavelengths: blue (B), red (R) and far-red (FR). Analysis of variance revealed a northward decrease in the inhibitory effect of FR with respect to D, the so-called far red high irradiance response. Ecotypic variation for hypocotyl development was observed under the FR and D treatments, while the trends for the B and R treatments were not statistically significant. Under FR the ecotypic variation showed an increase in hypocotyl length northwards, in contrast to the treatment under D which showed a decrease in the hypocotyl length northwards. These results could be interpreted in view of the previously reported northward increase in FR requirement to maintain growth in Norway spruce and Scots pine. Prior to the performance of the main light experiment, the maternal effect on progeny performance was investigated, which showed the absence of maternal environment effect on the performance of the seedlings.
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    Differences in the responses of photosystem I and photosystem II of three tree species Cleistanthus sumatranus, Celtis philippensis and Pistacia weinmannifolia exposed to a prolonged drought in a tropical limestone forest (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: Drought stress can induce closure of stomata, thus leading to photoinhibition. The effects of prolonged severe drought under natural growing conditions on photosystem I (PSI), photosystem II (PSII) and cyclic electron flow (CEF) in drought-tolerant tree species are unclear. In spring 2010, southwestern China confronted severe drought that lasted several months. Using three dominant evergreen species, Cleistanthus sumatranus (Miq.) Muell. Arg. (Euphorbiaceae), Celtis philippensis Bl. (Ulmaceae) and Pistacia weinmannifolia J. Poisson ex Franch. (Anacardiaceae) that are native to a tropical limestone forest, we investigated the influence of this stress on PSI and PSII activities as well as light energy distribution in the PSII and P700 redox state. By the end of the drought period, predawn leaf water potential ( pd ) largely declined in each species, especially in C. sumatranus . Photosystem I activity strongly decreased in the three species, especially in C. sumatranus which showed a decrease of 65%. The maximum quantum yield of PSII after dark adaptation remained stable in P. weinmannifolia and C. philippensis but significantly decreased in C. sumatranus . Light response curves indicated that both linear electron flow and non-photochemical quenching were severely inhibited in C. sumatranus along with disappearance of CEF, resulting in deleterious excess light energy in PSII. We conclude that PSI is more sensitive than PSII to prolonged severe drought in these three drought-tolerant species, and CEF is essential for photoprotection in them.
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    Electron transport efficiency at opposite leaf sides: effect of vertical distribution of leaf angle, structure, chlorophyll content and species in a forest canopy (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
    Description: We investigated changes in chlorophyll a fluorescence from alternate leaf surfaces to assess the intraleaf light acclimation patterns in combination with natural variations in radiation, leaf angles, leaf mass per area (LMA), chlorophyll content (Chl) and leaf optical parameters. Measurements were conducted on bottom- and top-layer leaves of Tilia cordata Mill. (a shade-tolerant sub-canopy species, sampled at heights of 11 and 16 m) and Populus tremula L. (a light-demanding upper canopy species, sampled at canopy heights of 19 and 26 m). The upper canopy species P. tremula had a six times higher PSII quantum yield ( II ) and ratio of open reaction centres (qP), and a two times higher LMA than T. cordata . These species-specific differences were also present when the leaves of both species were in similar light conditions. Leaf adaxial/abaxial fluorescence ratio was significantly larger in the case of more horizontal leaves. Populus tremula (more vertical leaves), had smaller differences in fluorescence parameters between alternate leaf sides compared with T. cordata (more horizontal leaves). However, optical properties on alternate leaf sides showed a larger difference for P. tremula . Intraspecifically, the measured optical parameters were better correlated with LMA than with leaf Chl. Species-specific differences in leaf anatomy appear to enhance the photosynthetic potential of leaf biochemistry by decreasing the interception of excess light in P. tremula and increasing the light absorptance in T. cordata . Our results indicate that intraleaf light absorption gradient, described here as leaf adaxial/abaxial side ratio of chlorophyll a fluorescence, varies significantly with changes in leaf light environment in a multi-layer multi-species tree canopy. However, this variation cannot be described merely as a simple function of radiation, leaf angle, Chl or LMA, and species-specific differences in light acclimation strategies should also be considered.
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    Understanding stomatal conductance responses to long-term environmental changes: a Bayesian framework that combines patterns and processes (2013)
    Oxford University Press
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    Publication Date: 2013-02-21
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Speculative bubbles in agricultural commodity markets (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: Numerous factors have been proposed in the literature as explaining the recent commodity price movements. In this paper we focus on one of the most widely discussed factors, the impact of speculative bubbles. We investigate whether commodity prices during the spike of 2007–2008 might have deviated from their intrinsic values based on market fundamentals. To do this, we use a bootstrap methodology to compute the finite sample distributions of recently proposed tests. Monte-Carlo simulations show that the bootstrap methodology works well, and allows us to identify explosive processes and collapsing bubbles for wheat, corn and rough rice. There was less evidence of exuberance in soya bean prices.
    Keywords: C12 - Hypothesis Testing, C15 - Simulation Methods, G14 - Information and Market Efficiency ; Event Studies, Q14 - Agricultural Finance
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Farmers' satisfaction and intention to continue membership in agricultural marketing co-operatives: neoclassical versus transaction cost considerations (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: The survival of agricultural marketing co-operatives depends on their capability of satisfying and maintaining their base of farmer members. Hypotheses regarding these two success factors are developed in neoclassical economics and transaction cost economics. They are tested with a survey of 321 members of marketing co-operatives specialising in fresh fruits and vegetables. Our results show support for both perspectives. Price paid to farmers is important for their satisfaction with the co-operative. Farmers' perceptions of transaction costs are even more important.
    Keywords: D22 - Firm Behavior: Empirical Analysis, D23 - Organizational Behavior ; Transaction Costs ; Property Rights, P13 - Cooperative Enterprises, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness
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    Preference reversals in Contingent and Inferred valuation methods (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: We examine inconsistencies in preference orderings using the Contingent valuation (CV) and the Inferred valuation (IV) methods. We find that in the context of a food market we do not observe strong inconsistencies. Weak inconsistencies are observed for the IV method, indicating that IV is slightly more susceptible to inconsistent preference orderings than the CV method. We also find that the IV method generates higher valuations than CV in the case of consumers with high commitment costs (that is, low familiarity with the product) but successfully mitigates social desirability bias in the case of low commitment costs and high normative motivations.
    Keywords: C93 - Field Experiments, D12 - Consumer Economics: Empirical Analysis
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    Local Agri-food Systems in a Global World: Market, Social and Environmental Challenges (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Combining discrete and continuous mixing distributions to identify niche markets for food (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: This paper explores the demand and willingness to pay (WTP) for value-added services to chicken. Since the demand for such services are likely to be highly segmented and often applies only to a market niche, models based on assumptions of homogeneity among consumers are likely to be inappropriate. For this reason, this paper combines discrete and continuous mixing distributions to concurrently identify the size of the niche market and the heterogeneity among consumers within the market niche. Failing to account for the niche market nature of value-added services is shown to have implications for predictions of WTP, demand and total revenue.
    Keywords: C25 - Discrete Regression and Qualitative Choice Models, D12 - Consumer Economics: Empirical Analysis, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness
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    Farm Incomes, Wealth and Agricultural Policy: Filling the CAP's Core Information Gap (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
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    Experimental auctions, collective induction and choice shift: willingness-to-pay for rice quality in Senegal (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: We propose a collective induction treatment as an aggregator of information and preferences, which enables testing whether consumer preferences for food quality elicited through experimental auctions are robust to aggregation. We develop a two-stage estimation method based on social judgement scheme theory to identify the determinants of social influence in collective induction. Our method is tested in a market experiment aiming to assess consumers' willingness-to-pay for rice quality in Senegal. No significant choice shift was observed after collective induction, which suggests that consumer preferences for rice quality are robust to aggregation. Almost three quarters of social influence captured by the model and the variables was explained by social status, market expertise and information.
    Keywords: C24 - Truncated and Censored Models, C91 - Laboratory, Individual Behavior, C92 - Laboratory, Group Behavior, D12 - Consumer Economics: Empirical Analysis, D71 - Social Choice ; Clubs ; Committees ; Associations
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    Selection bias in a gravity model of agrifood trade (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: In the analysis of bilateral trade flows, reported trade of zero or missing observations is quite common and this is a problem when estimating log-linear gravity equations. This has caused many researchers to either ignore the zero trade flows or replace the zero with a small positive number. Both of these actions bias the resulting parameter estimates of the gravity equation. In this study, we correct for this misspecification by using the Heckman selection model to estimate bilateral trade flows for 46 agrifood products, for the period 1990–2000, for 52 countries. In our sample, selection bias rarely affects the signs of variables but often has a substantial effect on the magnitude, statistical significance and economic interpretation of the marginal effects. Hence, treating zero trade flows properly is important from both a statistical and an economics perspective.
    Keywords: F10 - General, F12 - Models of Trade with Imperfect Competition and Scale Economies, F19 - Other, Q17 - Agriculture in International Trade, R12 - Size and Spatial Distributions of Regional Economic Activity
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    Estimating risk preferences in the presence of bifurcated wealth dynamics: can we identify static risk aversion amidst dynamic risk responses? (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: Estimating risk preferences is tricky because controlling for confounding factors is difficult. Omitting or imperfectly controlling for these factors can attribute too much observable behaviour to risk aversion and bias estimated preferences. Agents often modify risky decisions in response to dynamic wealth or asset thresholds, where such thresholds exist. Ignoring this dynamic risk response introduces an attribution bias in static estimates of risk aversion. We demonstrate this pitfall using a simple model and a Monte Carlo simulation to explore the implications of this problem for empirical estimation. While an approach that jointly estimates risk preferences and wealth dynamics may remedy the problem by extracting dynamic risk responses from observed behaviour, it is likely to be challenging to implement in broader empirical settings for reasons we discuss.
    Keywords: D81 - Criteria for Decision-Making under Risk and Uncertainty, D90 - General, O12 - Microeconomic Analyses of Economic Development
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    Willingness to pay for environmental attributes of non-food agricultural products: a real choice experiment (2013)
    Oxford University Press
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    Publication Date: 2013-02-26
    Description: This paper investigates consumers'willingness to pay a price premium for two environmental attributes of a non-food agricultural product. We study individual preferences for roses associated with an eco-label and a carbon footprint, using an economic experiment combining discrete choice questions and real economic incentives involving real purchases of roses against cash. The data are analysed with a mixed logit model and reveal significant premiums for both environmental attributes of the product.
    Keywords: C90 - General, D12 - Consumer Economics: Empirical Analysis, Q10 - General
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    Characterization and performance of novel modified silica gel/molecular sieve composite (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: In this paper, using lithium chloride and calcium chloride as modifying agents, the modified silica gel and molecular sieve composite based on ceramic fiber was prepared by treating ceramic fiber paper with sequential impregnation of the suspension of waterglass and molecular sieve and the aqueous solution of salt. The composition of the modified composite was characterized by using Fourier transform infrared spectroscopy (FTIR). Thermogravimetry (TG) and temperature programmed desorption (TPD) were used to evaluate the desorption performance of the composite. FTIR spectra indicated that impregnation salt has no effect on the composition of molecular sieve. TG and TPD analysis indicated that desorption activated energy of modified composite was lower than that of molecular sieve. The result of the dynamic and static adsorption experiment showed that the adsorption performance of molecular sieve enhanced greatly through the modification.
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Enhanced Heat Transfer and Energy Conservation: A review of the selected papers from ISHTEC2012 (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Optimization of a two-step process for biodiesel production from Jatropha curcas crude oil (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: In the present work, the process of synthesis of methyl esters from Jatropha curcas crude oil as an alternative vegetable oil, using a two-step catalyzed process is shown. In the first step, sulfuric acid was used as a catalyst for the esterification reaction of free fatty acid (FFA) and methanol in order to reduce the FFA content to ~0.2%. In the second step, the product from the first step was further reacted with methanol using potassium metoxide as a catalyst. The two-step processes have been developed and optimized by application of the factorial design and response surface methodology. The optimum conditions for biodiesel production were obtained when using methanol to FFA contents of Jatropha crude oil molar ratio (MR) of 20:1, 5 wt% of sulfuric acid, at 60°C with a reaction time of 60 min in the first step, followed by using an MR of methanol to product from the first step of 6:1, 0.95 wt% of KOCH 3 , at 45°C with a reaction time of 60 min in the second step. The percentage of methyl ester in the obtained product was more than 98%. The model has been found to describe the experimental range studied adequately and allows us to scale-up the process. In addition, the fuel properties of the produced biodiesel were in the acceptable ranges according to EN14214 European biodiesel standards.
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    Composites 'salt inside porous matrix' for adsorption heat transformation: a current state-of-the-art and new trends (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Adsorption heat transformation (AHT) is one of the challenging technical approaches for supporting the world community initiatives to alleviate or reverse the gravity of the problems arising from CO 2 emissions and global warming. The key tool for enhancement of the AHT efficiency and power is a harmonization of adsorbent properties with working conditions of the AHT cycles. It can be realized by means of target-oriented designing the adsorbent specified for a particular AHT cycle. Two-component composites ‘salt in porous matrix’ (CSPMs) offer new opportunities for nano-tailoring their sorption properties by varying the salt chemical nature and content, porous structure of the host matrix and synthesis conditions. CSPMs have been recognized as promising solid sorbents for various AHT cycles, namely adsorption chilling, desiccant cooling, heat storage and regeneration of heat and moisture in ventilation systems. In this review, we survey a current state-of-the-art and new trends in developing efficient CSPMs for various AHT cycles.
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    Modeling of micro/meso-scale reactive transport phenomena in catalyst layers of proton exchange membrane fuel cells (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: In this article, we outline and review the methods that are currently used to simulate the micro/meso-scale flow and reactive transport processes in the porous catalyst layers (CLs) of a fuel cell. The approaches beyond the atomic scale (molecular dynamics) and below the conventional continuum scale (Navier–Stokes solvers) use coarse-grained pseudo-particles which can either move on a fixed lattice or continuously in space. The focus is mainly put on the development of the off-lattice pseudo-particle models, such as coarse-grained molecular dynamics (CG-MD), dissipative particle dynamics (DPD) and smoothed particle hydrodynamics (SPH) methods. As an example, a CG-MD method is performed as a microscopic structure reconstruction technique to reflect the self-organized phenomena during the formation steps of a CL. In addition, we also highlight the combined nano-scale elementary kinetic processes and the issues on the coupling of DPD and SPH to finite element (FE) modeling techniques. This article also highlights the critical aspects and addresses the future trends and challenges for these models.
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    Preparation, hydrothermal stability and thermal adsorption storage properties of binderless zeolite beads (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Novel binderless zeolite beads of types A and X have been synthesized and characterized by scanning electron microscopy, mercury intrusion, nitrogen adsorption, thermogravimetry, water adsorption isotherm measurements, cyclic hydrothermal treatments and storage tests. The binderless molecular sieves show an improved adsorption capacity, sufficient hydrothermal stability, higher specific energies and the potential for a better performance density of the storage. Both open and closed storage tests have shown comparable adsorption capacities and specific energies for the binderless molecular sieves. A significantly higher discharging temperature, however, could be realized with the open storage system.
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    Impact of climate change on ventilation load and energy use of air conditioning systems in buildings of Hong Kong (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Climate change may seriously affect the energy consumption of buildings by influencing their air conditioning loads, especially the ventilation loads which vary directly with the local weather conditions. Research on how the ventilation load responds to climate change is of great significance, especially in coastline subtropical regions like Hong Kong. This paper investigated the impacts of climate change on buildings' ventilation load and building energy use in Hong Kong with the hourly meteorological data from 1950 to 2007. Results have been well validated by the simulation of a typical local hotel building during this period. The results show that climate warming increases both sensible and latent parts of the cooling ventilation load. The latent part, which occupies ~80% of the total ventilation load, increases at a higher rate, about twice of that of the sensible one. Furthermore, it is found that the urban heat island (UHI) effect causes a much higher growth rate of the ventilation load at night, which is about three times compared with that in the daytime. The latent part of the cooling ventilation load at night, which is found to be the most sensitive component to the climate change, plays a most significant role in the energy consumption increase. The possible measures were thus suggested to avoid negative changes of the ventilation load. Besides, reducing the UHI effect by better urban planning also significantly benefits the local buildings with a long air-conditioning operation time.
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    Problems involved in the shell-side performance of a longitudinal-flow shell-and-tube heat exchanger with decrease in L/D and its solutions (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: This paper presents a numerical simulation of the fluid flow and heat transfer in the shell-side of a large-scale shell-and-tube heat exchanger with longitudinal flow through porous-medium and distributed-resistance model. Such characteristics as flow field distribution, shell-side pressure drop, heat transfer performance and overall performance factor of the shell-side were studied with change in L / D and Re . It was shown that when L / D decreased from 6.0 to 1.5 with the same Re , the fluid flow maldistribution became intense, pressure drop increased sharply, and that the overall performance factor decreased sharply. Particularly, when L / D ≤ 2.0, the problems became more and more serious. Through a detailed analysis of the pressure field distribution, it was discovered that 〉80% of the total pressure drop occurred in the region of the inlet and the outlet, where the fluid flow mainly cross the tube bundle. In order to solve the problems, the use of a novel structure of multi-parallel-channel inlet and outlet (MPC) in the shell-side was proposed. A comprehensive investigation showed that MPC is very effective not only in optimizing the fluid flow distribution of the shell-side and enhancing the global heat transfer performance of a heat exchanger, but also in decreasing shell-side pressure drop.
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    Review of thermal processing of biomass and waste in molten salts for production of renewable fuels and chemicals (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Renewable energy has gained great attention and interest in recent years due to growing energy consumption and greater environmental concerns. Biomass is regarded as a promising candidate for replacing fossil-derived products, through either thermal, biological, or physical processes. This review focuses on thermal processing of biomass in molten salts for production of renewable fuels and chemicals, concepts based on dispersion of biomass or waste particles in a molten salt bath. Inorganic salts have very high heat capacities and good thermal stability at high temperatures. Some molten salts have catalytic properties, and in thermal processing of biomass, the product yields and compound compositions of products can be adjusted by varying compositions and amount of molten salts. In addition, molten salts will retain noxious contaminants, and it is thus possible to use difficult convertible- and/or contaminated biomass as feedstock.
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    Biochemical processing of reed canarygrass into fuel ethanol (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Reed canarygrass is a temperate perennial grass of interest as a bioenergy crop. The canarygrass was evaluated for conversion to bioethanol using liquid hot water and dilute ammonia pretreatments prior to fermentation. The resulting hydrolysates were evaluated for production of ethanol, xylose and soluble xylans. Dilute ammonia gave higher yield efficiencies than liquid hot water. The optimal condition for dilute ammonia (4% w/v) pretreatment was 170°C for 20 min. Hydrolysates were converted to ethanol using Saccharomyces in the presence of a blend of commercial cellulases and additional carbohydrases. The final ethanol conversion efficiency was 84% based upon total hexosans, with 72% of the xylan converted to soluble xylan oligomers.
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    Adaptation to climate change of dioecious plants: does gender balance matter? (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Print ISSN: 0829-318X
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Norway maple displays greater seasonal growth and phenotypic plasticity to light than native sugar maple (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Norway maple ( Acer platanoides L), which is among the most invasive tree species in forests of eastern North America, is associated with reduced regeneration of the related native species, sugar maple ( Acer saccharum Marsh) and other native flora. To identify traits conferring an advantage to Norway maple, we grew both species through an entire growing season under simulated light regimes mimicking a closed forest understorey vs. a canopy disturbance (gap). Dynamic shade-houses providing a succession of high-intensity direct-light events between longer periods of low, diffuse light were used to simulate the light regimes. We assessed seedling height growth three times in the season, as well as stem diameter, maximum photosynthetic capacity, biomass allocation above- and below-ground, seasonal phenology and phenotypic plasticity. Given the north European provenance of Norway maple, we also investigated the possibility that its growth in North America might be increased by delayed fall senescence. We found that Norway maple had significantly greater photosynthetic capacity in both light regimes and grew larger in stem diameter than sugar maple. The differences in below- and above-ground biomass, stem diameter, height and maximum photosynthesis were especially important in the simulated gap where Norway maple continued extension growth during the late fall. In the gap regime sugar maple had a significantly higher root : shoot ratio that could confer an advantage in the deepest shade of closed understorey and under water stress or browsing pressure. Norway maple is especially invasive following canopy disturbance where the opposite (low root : shoot ratio) could confer a competitive advantage. Considering the effects of global change in extending the potential growing season, we anticipate that the invasiveness of Norway maple will increase in the future.
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    Impact of ectomycorrhizal colonization and rust infection on the secondary metabolism of poplar (Populus trichocarpa x deltoides) (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Fungal colonization can significantly affect the secondary metabolism of the host plants. We tested the impact of a common below-ground symbiosis, i.e., ectomycorrhiza formation, on poplar leaf chemical components that are involved in the defence against a common disease, i.e., rust fungi, in N-deficient soil. A rust-susceptible poplar clone ( Populus trichocarpa x deltoides ‘Beaupré’) was (a) non-associated with ectomycorrhizal fungus (EM) Hebeloma mesophaeum (Pers.) Quélet MÜN and non-infected with rust fungus Melampsora larici-populina Kleb. (isolate 98AG31), (b) associated with EM, (c) inoculated with rust fungus and (d) associated with EM and inoculated with rust fungus. Poplar leaves were analysed by photometric and mass spectrometric techniques (liquid chromatography–tandem mass spectrometry (LC-MS/MS), pyrolysis–field ionization mass spectrometry (Py-FIMS)). Both rust infection and mycorrhiza formation led to increased proportions of condensed tannins in relation to total phenolics (13% in the control, 18–19% in the fungal treatments). In contrast, salicylic acid concentration (6.8 µg g –1 in the control) was higher only in the rust treatments (17.9 and 25.4 µg g –1 with rust infection). The Py-FIMS analysis revealed that the rust-infected treatments were significantly separated from the non-rust-infected treatments on the basis of six flavonoids and one lipid. The relative abundance of these components, which have known functions in plant defence, was decreased after rust infection of non-mycorrhizal plants, but not in mycorrhizal plants. The results indicate that the ectomycorrhizal formation compensated the rust infection by a decrease in the flavonoid syntheses. The study provides new evidence for an interactive response of mycorrhizal colonization and infection with rust fungi in the metabolism of poplar.
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    A gene expression analysis of cell wall biosynthetic genes in Malus x domestica infected by 'Candidatus Phytoplasma mali' (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Apple proliferation (AP) represents a serious threat to several fruit-growing areas and is responsible for great economic losses. Several studies have highlighted the key role played by the cell wall in response to pathogen attack. The existence of a cell wall integrity signaling pathway which senses perturbations in the cell wall architecture upon abiotic/biotic stresses and activates specific defence responses has been widely demonstrated in plants. More recently a role played by cell wall-related genes has also been reported in plants infected by phytoplasmas. With the aim of shedding light on the cell wall response to AP disease in the economically relevant fruit-tree Malus x domestica Borkh., we investigated the expression of the cellulose ( CesA ) and callose synthase ( CalS ) genes in different organs (i.e., leaves, roots and branch phloem) of healthy and infected symptomatic outdoor-grown trees, sampled over the course of two time points (i.e., spring and autumn 2011), as well as in in vitro micropropagated control and infected plantlets. A strong up-regulation in the expression of cell wall biosynthetic genes was recorded in roots from infected trees. Secondary cell wall CesA s showed up-regulation in the phloem tissue from branches of infected plants, while either a down-regulation of some genes or no major changes were observed in the leaves. Micropropagated plantlets also showed an increase in cell wall-related genes and constitute a useful system for a general assessment of gene expression analysis upon phytoplasma infection. Finally, we also report the presence of several ‘knot’-like structures along the roots of infected apple trees and discuss the occurrence of this interesting phenotype in relation to the gene expression results and the modalities of phytoplasma diffusion.
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    Genetic transformation of European chestnut somatic embryos with a native thaumatin-like protein (CsTL1) gene isolated from Castanea sativa seeds (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: The availability of a system for direct transfer of antifungal candidate genes into European chestnut ( Castanea sativa Mill.) would offer an alternative approach to conventional breeding for production of chestnut trees tolerant to ink disease caused by Phytophthora spp. For the first time, a chestnut thaumatin-like protein gene ( CsTL1 ), isolated from chestnut cotyledons, has been overexpressed in three chestnut somatic embryogenic lines. Transformation experiments have been performed using an Agrobacterium tumefaciens Smith and Townsend vector harboring the neomycin phosphotransferase ( NPTII ) selectable and the green fluorescent protein ( EGFP ) reporter genes. The transformation efficiency, determined on the basis of the fluorescence of surviving explants, was clearly genotype dependent and ranged from 32.5% in the CI-9 line to 7.1% in the CI-3 line. A total of 126 independent transformed lines were obtained. The presence and integration of chestnut CsTL1 in genomic DNA was confirmed by polymerase chain reaction (PCR) and Southern blot analyses. Quantitative real-time PCR revealed that CsTL1 expression was up to 13.5-fold higher in a transgenic line compared with its corresponding untransformed line. In only one of the 11 transformed lines tested, expression of the CsTL1 was lower than the control. The remaining 115 transformed lines were successfully subjected to cryopreservation. Embryo proliferation was achieved in all of the transgenic lines regenerated and the transformed lines showed a higher mean number of cotyledonary stage embryos and total number of embryos per embryo clump than their corresponding untransformed lines. Transgenic plants were regenerated after maturation and germination of transformed somatic embryos. Furthermore, due to the low plantlet conversion achieved, axillary shoot proliferation cultures were established from partially germinated embryos (only shoot development), which were multiplied and rooted according to procedures already established. Transgenic plants were acclimatized and grown in a greenhouse. No phenotypic differences were found with control plants, suggesting no potential cytotoxic effects of the green fluorescent protein. The results reported in the present work could be considered as a first step toward the production of fungal-disease tolerant cisgenic chestnut plants.
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    Using the compensated heat pulse method to monitor trends in stem water content in standing trees (2012)
    Oxford University Press
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    Publication Date: 2012-11-09
    Description: Studying the dynamics of stem water content (   ) in living trees has an outstanding physiological interest but all the available techniques to measure exhibit major drawbacks. In this work, we present a new methodology to estimate variations in along with sap velocity using the compensated heat pulse (CHP) technique. One lab experiment was performed on several wooden blocks obtained from three different tree species. Samples were slowly dried and their moisture loss was monitored by both gravimetric approaches and time-domain reflectometry (TDR) or CHP probes in order to contrast the validity of our methodology (volumetric specific heat (VSH)-CHP) over a range of water contents. In addition, a field experiment was conducted to monitor fluctuations in standing olive trees ( Olea europaea L. cv. ‘Arbequina’) growing under three different irrigation regimes. In the lab test, the actual values deduced gravimetrically differed from the estimates yielded by the VSH-CHP method. However, it could successfully track relative changes in the water stored for the range of expected in living wood. Furthermore, the field experiment showed a seasonal change in , which was similar in shape and magnitude to those reported in the literature for olive and other Mediterranean tree species. On the other hand, differences in the seasonal patterns of between irrigation treatments strongly corresponded with those of sap flow and some leaf water potential measurements. The results of this work suggest that the CHP technique could be employed to monitor the dynamics of both and sap flow simultaneously in standing trees and evidence that seasonal changes in might be used as a long-term water status indicator.
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    Nutritional attributes of ash (Fraxinus spp.) outer bark and phloem and their relationships to resistance against the emerald ash borer (2012)
    Oxford University Press
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    Publication Date: 2012-12-15
    Description: The emerald ash borer ( Agrilus planipennis Fairmaire, EAB) is an alien, invasive wood-boring insect that is responsible for killing millions of ash trees since its discovery in North America in 2002. All North American ash species ( Fraxinus spp.) that EAB has encountered have shown various degrees of susceptibility, while Manchurian ash ( Fraxinus mandshurica Ruprecht), which shares a co-evolutionary history with this insect, is resistant. Recent studies have looked into constitutive resistance mechanisms in Manchurian ash, concentrating on the secondary phloem, which is the feeding substrate for the insect. In addition to specialized metabolism and defense-related components, primary metabolites and nutritional summaries can also be important to understand the feeding behavior of insect herbivores. Here, we have compared the nutritional characteristics (water content, total protein, free amino acids, total soluble sugars and starch, percent carbon and nitrogen, and macro- and micronutrients) of outer bark and phloem from black, green, white and Manchurian ash to determine their relevance to resistance or susceptibility to EAB. Water content and concentrations of Al, Ba, Cu, Fe, K, Li, tryptophan and an unknown compound were found to separate black and Manchurian ash from green and white ash in a principal component analysis (PCA), confirming their phylogenetic placements into two distinct clades. The traits that distinguished Manchurian ash from black ash in the PCA were water content and concentrations of total soluble sugars, histidine, lysine, methionine, ornithine, proline, sarcosine, tyramine, tyrosol, Al, Fe, K, Na, V and an unknown compound. However, only proline, tyramine and tyrosol were significantly different, and higher, in Manchurian ash than in black ash.
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    Interacting effects of elevated CO2 and weather variability on photosynthesis of mature boreal Norway spruce agree with biochemical model predictions (2012)
    Oxford University Press
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    Publication Date: 2012-12-15
    Description: According to well-known biochemical and biophysical mechanisms, the stimulation of C 3 photosynthesis by elevated atmospheric CO 2 concentration ([CO 2 ]) is strongly modified by changes in temperature and radiation. In order to investigate whether a static parameterization of the commonly used Farquhar et al. model of photosynthesis (i.e., without CO 2 -induced seasonal or thermal acclimation of photosynthetic capacity) can accurately predict these interactions in mature boreal Norway spruce ( Picea abies (L.) Karst.) during the frost-free part of the growing season, shoot gas exchange was continuously measured on trees during their second/third year of exposure to ambient or doubled [CO 2 ] inside whole-tree chambers. The relative CO 2 -induced enhancement of net photosynthesis ( A n ) at a given temperature remained stable over the study period, but increased strongly with temperature and radiation, in agreement with predictions by the model. Light-saturated A n (+67% at 20 °C), dark respiration (+36%) and intercellular to ambient [CO 2 ] ratio ( c i / c a ; +27%) were significantly increased by CO 2 treatment. Stomatal conductance ( g s ) was not significantly affected. Our results demonstrate that the Farquhar et al. model of photosynthesis has the capability to predict interactions between [CO 2 ] and seasonal weather variability on A n in Norway spruce during the non-frost growing season without accounting for CO 2 -induced seasonal and/or thermal photosynthetic acclimation. However, stomatal model assumptions of reduced g s and constant c i / c a under rising atmospheric [CO 2 ] did not hold.
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    Decoupling of agricultural support payments: the impact on land market participation decisions (2012)
    Oxford University Press
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    Publication Date: 2012-08-03
    Description: This paper analyses the impact of the recent decision by the European Union to ‘decouple’ agricultural support payments from agricultural production on Irish farmers' land market decisions. The land market participation decisions of Irish farmers are modelled using a dynamic probit model, while the extent of participation decisions is modelled using a dynamic tobit model. Decoupling does not appear to have significantly altered farmers' land market decisions. One likely explanation for this is the cross-compliance obligation for farmers to maintain land in a state fit for agricultural production in order to receive their full payments.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Methods to Analyse Agricultural Commodity Price Volatility (2012)
    Oxford University Press
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    Publication Date: 2012-08-03
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Dynamics of productivity and technical efficiency in Russian agriculture (2012)
    Oxford University Press
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    Publication Date: 2012-08-03
    Description: This paper analyses regional productivity and technical efficiency development in Russian agriculture. We formulate a regional stochastic frontier model by assuming that producers maximise return to the outlay. We control for regional heterogeneity and endogeneity/simultaneity in input decisions, technical efficiency and technical change by employing a two-step estimation procedure. In the first step, we use the system Generalized Method of Moments approach (system GMM), which gives consistent estimates of the production technology parameters. In the second step, we apply the standard stochastic frontier approach to estimate technical efficiency and its determinants.
    Keywords: D24 - Production ; Cost ; Capital and Total Factor Productivity ; Capacity, Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Understanding the Common Agricultural Policy (2012)
    Oxford University Press
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    Publication Date: 2012-08-03
    Print ISSN: 0165-1587
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Interactions of thinning and stem height on the drought response of radial stem growth and isotopic composition of Norway spruce (Picea abies) (2012)
    Oxford University Press
    Details
    Publication Date: 2012-10-18
    Description: Radial stem growth and the isotopic composition of growth rings are commonly used to quantify the effects of droughts on trees. However, often these parameters are quantified only at one stem height, e.g., 1.3 m, and it is not known how representative this is for the whole stem. This study investigated radial growth at four stem heights (1.3, 5.5, 9.8 and 14 m) of 21, and wood 13 C and 18 O at two heights (1.3 and 14 m) of 10 (co-)dominant Norway spruce trees from heavily (HT) and moderately thinned (MT) stands to assess whether different thinning intensities influenced the drought response of stems at different tree heights. Annual basal area increments (BAIs) and stable isotopes in earlywood and latewood were compared between thinning treatments and among the different stem heights. For BAIs, linear correlations with climate were analysed as well. The response of radial growth and isotopic composition to drought was similar at different stem heights in HT trees, but varied with height in MT trees, which were also more sensitive to climatic variations. Recovery of radial growth after drought was more rapid in trees from HT compared with MT stands, except for the topmost height. Basal area increments at breast height (1.3 m) provided good estimates of the volume growth response to drought for the whole stem, but not for its recovery. The faster recovery of radial growth at 1.3 m height of HT compared with MT trees after the 2003 drought was not accompanied by differences in recovery of isotopic composition. However, this is likely to be related to differences between treatments in remobilization of stored C and in tree structure (leaf area, root systems).
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    Importance of crown architecture for leaf area index of different Populus genotypes in a high-density plantation (2012)
    Oxford University Press
    Details
    Publication Date: 2012-10-18
    Description: Crown architecture is an important determinant of biomass production and yield of any bio-energy plantation since it determines leaf area display and hence light interception. Four Populus genotypes—of different species and hybrids and with contrasting productivity and leaf area—were examined in terms of their branch characteristics in relation to crown architecture during the first and second growing seasons after plantation establishment. The trees were planted at high density (8000 ha –1 ) on two different former land use types, cropland and pasture. We documented significant differences in branch architecture among the genotypes and for the first year among the former land use types. Land use effects only affected factors not related to canopy closure and wood production, and decreased after the first growing season. This suggested that both former land use types were equally suited for the establishment success of a poplar bio-energy plantation. Tree height and branch dimensions—branch diameter and branch length—were the most important determinants of wood production and maximum leaf area index. Despite the secondary importance of the number of sylleptic branches, these branches contributed significantly to the total leaf area in three out of the four studied genotypes. This indicated that enhanced syllepsis accelerates leaf area development and hence carbon assimilation, especially in the early stages of a high-density plantation with poplar.
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    Polyamine metabolism during exponential growth transition in Scots pine embryogenic cell culture (2012)
    Oxford University Press
    Details
    Publication Date: 2012-10-18
    Description: Polyamine (PA) metabolism was studied in liquid cultures of Scots pine ( Pinus sylvestris L.) embryogenic cells. The focus of the study was on the metabolic changes at the interphase between the initial lag phase and the exponential growth phase. PA concentrations fluctuated in the liquid cultures as follows. Putrescine (Put) concentrations increased, whereas spermidine (Spd) concentrations decreased in both free and soluble conjugated PA fractions. The concentrations of free and soluble conjugated spermine (Spm) remained low, and small amounts of excreted PAs were also found in the culture medium. The minor production of secondary metabolites reflected the undifferentiated stage of the embryogenic cell culture. Put was produced via the arginine decarboxylase (ADC) pathway. Futhermore, the gene expression data suggested that the accumulation of Put was caused neither by an increase in Put biosynthesis nor by a decrease in Put catabolism, but resulted mainly from the decrease in the biosynthesis of Spd and Spm. Put seemed to play an important role in cell proliferation in Scots pine embryogenic cells, but the low pH of the culture medium could also, at least partially, be the reason for the accumulation of endogenous Put. High Spd concentrations at the initiation of the culture, when cells were exposed to stress and cell death, suggested that Spd may act not only as a protector against stress but also as a growth suppressor, when proliferative growth is not promoted. All in all, Scots pine embryogenic cell culture was proved to be a favourable experimental platform to study PA metabolism and, furthermore, the developed system may also be beneficial in experiments where, e.g., the effect of specific stressors on PA metabolism is addressed.
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    Effects of drought acclimation on the mechanical properties of Ochroma pyramidale, Betula pendula and Acacia karroo tree seedling stems (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-04-05
    Description: Drought acclimation in woody plants tends to be associated with the development of denser vascular tissue. As wood density may be correlated with the mechanical properties of the tissue, we hypothesized that seedlings subjected to drought would develop stems that had a higher density as well as stiffer and stronger tissue. We tested our hypothesis on establishing trees of the species Betula pendula , Acacia karroo and Ochoma pyramidale . The seedlings were grown for 1 year under well-watered as compared with cyclically droughted conditions. The modulus of elasticity in bending, yield stress, density and pith- and bark fractions of the stems at different heights were measured. In all three species, individuals grown under drought conditions had on average stiffer and stronger stems than the well-watered individuals, though non-significantly so in A. karroo . These differences were associated with a higher density in O. Pyramidale but not in the other species. In B. pendula , the differences in mechanical properties appear to be associated with other factors, e.g. modifications of the micro fibril angle in the S2 cell wall layer. Our results indicate that drought acclimation in seedlings affects the mechanical properties of the stem but that the causal acclimational processes may vary between species.
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    A gap-based approach for regenerating pine species and reducing surface fuels in multi-aged mixed conifer stands in the Sierra Nevada, California (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-04-05
    Description: Multi-aged stands in a mixed conifer forest of California were treated to mitigate harvest-related increases in surface fuels and to prepare sites for natural regeneration of Pinus species. The study was designed to (1) assess effectiveness of small gap fuel treatments (piling and burning in 0.04 ha gaps) on surface fuel and modelled fire behaviour; (2) test the effect of substrate quality on germination of Pinus species; (3) measure the influence of gap creation on light availability and stand-level light heterogeneity. While the fuel treatment only covered 10 per cent of stand area, it was effective in avoiding increases in stand-level surface fuel following harvests. Fire behaviour was predicted to be moderate following the treatments. The harvest coupled with the gap surface fuel treatments did not change predicted fire behaviour compared with the pretreatment stands. There was a significant but variable increase in germination of Pinus ponderosa seed when sowed on ash substrates compared with bare soil. No substrate effect was detected for Pinus lambertiana . The 0.04-ha gaps created distinct pockets of light and greatly increased stand-level light heterogeneity. This gap-based approach to regenerating multi-aged stands coupled with small-scale fuel treatments is promising for reducing fire hazard and regenerating shade-intolerant species.
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    A broad-scale analysis of the main factors determining the current structure and understory composition of Catalonian sub-alpine (Pinus uncinata Ram.) forests (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-04-05
    Description: A broad-scale analysis of the structure and understory composition of Pyrenean mountain pine ( Pinus uncinata Ram.) stands was performed using data from the Spanish National Forest Inventory. Twelve structure-based forest typologies were defined from variables related to tree size, stand density, vertical structure and standing deadwood, using cluster analysis techniques. These typologies were adequately classified (accuracy 〉75 per cent) by a dichotomous key obtained from classification and regression trees. Multiple regression models were then used to analyse relationships between the main stand structural variables and a set of climatic and physiographic factors. The models showed significant correlations between winter temperature, slope and continentality (among other variables) and the current structure of mountain pine stands. The relationships between the understory composition of mountain pine forests and different environmental and structural overstory factors were found to be driven by an elevation-pH gradient and a stand density-soil stoniness gradient. The results of this study can be directly used for forest planning at different scales and could help forest managers to establish strategies designed to facilitate a given habitat for species of conservation interest.
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    Boreal forest soil carbon: distribution, function and modelling (2012)
    Oxford University Press
    In: Forestry
    Details
    Publication Date: 2012-04-05
    Description: Increasing accumulation of CO 2 in the atmosphere has led to calls for terrestrial mechanisms for CO 2 abatement and given that soils represent the largest terrestrial body of C on Earth, there is a great deal of interest in soils as a sink for atmospheric C. This emphasis on sequestration in boreal forest soils is understandable given the sheer mass of this C reservoir (~1700 Pg of C) but diverts our attention from the importance of soil C in soil physical, chemical and biotic functions, and importantly, it ignores the possibility that soils may also represent a source of C. In this review, we address these issues through a discussion of the size and character of boreal forest soil C pool, its role in ecosystem function, the potential impacts of climate change on soil C, efforts to model these processes and the role of soil C in boreal resilience to the impacts of climate change. Soil C is fundamental to ecosystem function in terms of improving soil physical properties, increasing soil biotic activity and enhancing insulation all of which improve site productivity. Managing upland soils for C sequesteration will achieve little in terms of offsetting fossil fuel emissions but would likely improve soil quality. Most of the C stored in the boreal biome is found in permafrost and wetland soils and events related to climatic change could shift these soils from C sink to C source. Melting of permafrost soils with predicted warming trends within the circumpolar region could result in the release of 30–60 Pg C by the year 2040. Such predictions, however, are limited by uncertainty in both climatic changes and soil response to these changes. Prediction of shifts in soil C dynamics with climate change relies on our ability to link C transformations to N dynamics and climatic variables. Improvement in ecosystem models will advance our ability to assess the resilience of the boreal biome under future climatic conditions.
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    Effect of solution temperature and absorber pressure in R134a-DMAC system using horizontal tubular absorbers (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-09
    Description: Investigations are carried out to study the heat and mass transfer characteristics of a falling film horizontal absorber by employing a two-dimensional numerical technique. The potential refrigerant, R134a (1,1,1,2-tetrafluroethane), is absorbed by the falling film of the R134a–DMAC (dimethylacetamide) solution. The variations of performance parameters along the tube surface are presented for different solution inlet temperatures and absorber pressures. The mass flux at the interface is observed to be higher at higher solution temperature and absorber pressure. The variation of the interface to bulk fluid and bulk fluid to wall heat transfer coefficient, overall heat transfer coefficient and mass transfer coefficient are studied for different solution temperatures and absorber pressures.
    Print ISSN: 1748-1317
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    Solar absorber tube analysis: thermal simulation using CFD (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: Solar–thermal power plants are being deployed world-wide. These plants have traditionally used steel absorber pipes. Two types of fluids have been used in such ventures, synthetic aromatic fluid or water. Fluid flow in parabolic trough systems leads to instability in the tube due to the concentrated solar flux on only one-half of the absorber tube, resulting in temperature asymmetricity. The resulting stresses cause deflection and bending of the tube. This paper deals with direct steam systems and proposes incorporation of internal helical fins within the tube to reduce temperature variation. The fins provide an orderly distribution of flow from the ‘hot’ to the ‘cold’ side of the tube. A CFD simulation was carried out for three fin pitches, and an aluminium pipe without fins. The effect on heat transfer improvement and temperature asymmetry is presently reported. It is shown that the thermal gradient between the upper and lower temperature for the pipe without a helical fin (20 K) is considerably higher compared with the pipes with 100, 200 and 400 mm pitch helical fins, i.e. 10.8, 13, 14.9 K, respectively. Also, the thermal gradient for the aluminium pipe was also much lower when compared with the steel pipe.
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    A review of state-of-the-art aerogel applications in buildings (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-09
    Description: Aerogels are a special type of solid material with nanometre-scale pores 〈1/3000th the width of a human hair. Porosity is in excess of 90%, in some cases as high as 99.9%, and densities can be as low as 3 kg/m 3 . Aerogels are essentially ‘puffed-up sand’ and are often termed ‘frozen smoke’. Their thermal conductivity (0.014 W/m K at room temperature) is the lowest of any solids, and they also have good transparency. The acoustic properties of aerogels make them effective insulators against noise, and aerogels have the lowest refractive index, and dielectric constant of all solid materials. The unusual properties of aerogels open the way to a new range of opportunities for their application in buildings. This paper provides information on their unique features and reviews the potential applications for aerogels in buildings as well as latest developments in the field.
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    Energy co-operatives in the UK (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-09
    Description: The UK is implementing different types of policies to encourage the use of renewable energy for electricity generation. Currently, the UK is falling behind other European countries in this respect. Hence, co-operatives play an important role in helping the UK to move forward. Co-operatives are of interest to the Government in respect of economic development in the community. Co-operatives keep both the business, or entity, and the wealth it creates locally, which also supports the local economy. Survival rates are higher for co-operatives, which will make them a more sustainable choice for businesses and have a positive impact upon employment opportunities. Co-operatives can be adapted to suit all types of situations, especially during difficult times such as the world economic downturn. This article explores the role energy co-operatives can play within the context of electricity generation in the UK. A review of the degree of exploitation of two leading and currently deployed renewable energy technologies is presented for key member states within the EU. This is followed by a discussion on the growth of the co-operatives and their role in meeting the aims of achieving a low-carbon economy.
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    Investigations of emission characteristics and thermal efficiency in a spark-ignition engine fuelled with natural gas-hydrogen blends (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: This paper presents the experimental results of a single cylinder Enfield engine using an electronically controlled fuel injection system which was developed to carry out exhaustive tests using neat compressed natural gas (CNG), and mixtures of hydrogen in CNG (HCNG) as 5, 10, 15 and 20% by energy. Experiments were performed at 2000, 2400 and 2800 rpm with wide open throttle and varying the equivalence ratio. Hydrogen, which has a fast burning rate, when added to CNG, enhances its flame propagation rate. The emissions of HC, CO, decreased with increasing percentage of hydrogen but NO x was found to increase. The results indicated a marked improvement in the brake thermal efficiency with the increase in percentage of hydrogen added. The improved thermal efficiency was clearly observed to be more in lean regions when compared with rich regions.
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    Experimental investigation on green roofs over buildings (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: Green roof is a passive cooling technique that stops incoming solar radiation from reaching the building structure below. Many studies have been conducted over the past 10 years to consider the potential building energy benefits of green roofs and have shown that they can offer benefits in energy reduction for winter heating as well as summer cooling. Green roofs have many benefits over conventional roofs: they reduce storm water run-off, the heat island effect in cities and energy requirements for cooling; all of this while sequestering some CO 2 from the atmosphere. But because of their expense, the building industry has yet to fully embrace their large-scale implementation. Over the summer', two test structures, one with a green roof and the other with an RCC roof, were built and tested at the Ujjain Engineering College, Ujjain, RGPV University, to determine their cooling potential. Results indicate that the test cell with the green roof consistently performs better than those with the conventional cement RCC roof.
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    Performance of solid desiccant-based evaporative cooling system under the climatic zones of India (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: For better use of evaporative cooling techniques in humid climate, a desiccant cooling system (DCS) can be an alternative option in place of a conventional cooling system. This paper presents a theoretical comparative study of the performance of a DCS for four different climatic conditions of India (i.e. hot and dry, warm and humid, moderate and composite climates). From the analysis, it was found that the performance of a DCS is suitable in warm and humid climate. The thermodynamic equations of intermediate states of the desiccant cooling cycle are also presented. Effects of some parameters such as outdoor specific humidity, R / P ratio (regeneration air flow/process air flow) and power required to regenerate the desiccant wheel have been studied. The theoretical minimum R / P ratio has been computed for the maximum coefficient of performance (COP) of a DCS and its value was found to be 0.55 in Mumbai (warm and humid climate) for the 80% effectiveness of ECW. This paper also presents the relationship between COP and regeneration power with the different values of R / P ratios.
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    Sorption, permeation and selective transport of moisture/VOCs through a CA membrane for total heat recovery (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: This article studies in detail the permeation properties of highly permeable and highly selective polymer membrane for water vapor/volatile organic compound (VOC). A dense cellulose acetate (CA) membrane is prepared by the dry method. The sorption and permeation properties of water vapor and VOCs (acetic acid, formaldehyde, acetaldehyde, toluene and ethane) are experimentally investigated. Besides, the mass transfer coefficient of self-membrane can be separated from the total mass transfer coefficient. Using sorption and permeation data of gases, diffusion coefficient is calculated based on a solution–diffusion mechanism. The selectivity for water vapor/VOC is discussed and analyzed. The permeability selectivities of water vapor/VOC are all over 100. The result shows that the novel CA sense membrane is suitable for air dehumidification and total heat recovery.
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    Yaw analysis of a micro-scale horizontal-axis wind turbine operating in turbulent wind conditions (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: Building-mounted micro-wind turbines are capable of contributing a significant proportion of a building's energy needs. However, the introduction of this technology in built-up areas has been limited due to a number of issues, such as lower wind speeds, high turbulence and noise. This study presents an investigation into the effect of turbulence, which is more prominent in the built environment, on the operation of a micro-scale horizontal-axis wind turbine. For this purpose, an innovative method of sensing the yaw position of the wind turbine is required, which is discussed along with detailed methodology and the results obtained. The wind turbine used in the experiment uses a swing rudder system, and the effectiveness of this in turbulent conditions was also investigated. This study concluded that the wind turbine missed ~20% of the total power available in the wind and that the swing rudder system was suited to high wind speeds, while the fixed rudder suited to low wind speeds.
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    Off-design analysis of ORC and CO2 power production cycles for low-temperature surplus heat recovery (2013)
    Oxford University Press
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    Publication Date: 2013-02-09
    Description: Electricity production with an organic Rankine cycle and a transcritical Rankine cycle is investigated in this paper with R-123 and CO 2 as working fluids, respectively. The analysis focuses on the off-design behavior with different control strategies to show some of the occurring difficulties. It was found that both cycles need an advanced control strategy to avoid non-feasible operation (R-123) or significant losses in work output (CO 2 ). A challenge for the advanced control is the required large change in expander speed, which can lead to compatibility problems with the grid.
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    Improving sap flux density measurements by correctly determining thermal diffusivity, differentiating between bound and unbound water (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: Several heat-based sap flow methods, such as the heat field deformation method and the heat ratio method, include the thermal diffusivity D of the sapwood as a crucial parameter. Despite its importance, little attention has been paid to determine D in a plant physiological context. Therefore, D is mostly set as a constant, calculated during zero flow conditions or from a method of mixtures, taking into account wood density and moisture content. In this latter method, however, the meaning of the moisture content is misinterpreted, making it theoretically incorrect for D calculations in sapwood. A correction to this method, which includes the correct application of the moisture content, is proposed. This correction was tested for European and American beech and Eucalyptus caliginosa Blakely & McKie. Depending on the dry wood density and moisture content, the original approach over- or underestimates D and, hence, sap flux density by 10% and more.
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    Stomatal patchiness in the Mediterranean holm oak (Quercus ilex L.) under water stress in the nursery and in the forest (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: The evergreen holm oak Quercus ilex L. is the most representative tree in Mediterranean forests. Accurate estimation of the limiting factors of photosynthesis for Q. ilex and the prediction of ecosystem water-use efficiency by mechanistic models can be achieved only by establishing whether this species shows heterogenic stomatal aperture, and, if so, the circumstances in which this occurs. Here, we collected gas-exchange and chlorophyll fluorescence data in Q. ilex leaves from a nursery to measure the effects of stomatal oscillations on PSII quantum yield ( PSII ) under water stress. Stomatal conductance ( g s ) was used as an integrative indicator of the degree of water stress. Images of chlorophyll fluorescence showed heterogeneous PSII when g s was 〈50 mmol H 2 O m –2 s –1 , representative of severe drought and corresponding to a container capacity 〈45%. Stomatal patchiness was related to a coefficient of variation (CV) of PSII values 〉2.5%. A parallel study in the forest confirmed heterogeneous PSII values in leaves in response to declining water availability. Three kinds of Q. ilex individuals were distinguished: those resprouting after a clear-cut (resprouts, R); intact individuals growing in the same clear-cut area as resprouts (controls, C); and intact individuals in a nearby, undisturbed area (forest controls, CF). Patchiness increased in C and CF in response to increasing drought from early May to late July, whereas in R, PSII values were maintained as a result of their improved water relations since the pre-existing roots were associated with a smaller aerial biomass. Patchiness was related to a % CV of PSII values 〉4 and associated in the summer with mean g s values of 30 mmol H 2 O m –2 s –1 . Under milder drought in spring, PSII patchiness was less strictly related to g s variations, pointing to biochemical limitants of photosynthesis. The occurrence of heterogenic photosynthesis caused by patchy stomatal closure in Q. ilex during severe drought should be taken into account in ecosystem modelling in which harsher water stress conditions associated with climate change are predicted.
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    Freezing pattern and frost killing temperature of apple (Malus domestica) wood under controlled conditions and in nature (2012)
    Oxford University Press
    Details
    Publication Date: 2012-07-17
    Description: The freezing pattern and frost killing temperatures of apple ( Malus domestica Borkh.) xylem were determined by differential thermal analysis and infrared differential thermal analysis (IDTA). Results from detached or attached twigs in controlled freezing experiments and during natural field freezing of trees were compared. Non-lethal freezing of apoplastic water in apple xylem as monitored during natural winter frosts in the field occurred at –1.9 ± 0.4 °C and did not change seasonally. The pattern of whole tree freezing was variable and specific to the environmental conditions. On detached twigs high-temperature freezing exotherms (HTEs) occurred 2.8 K below the temperature observed under natural frosts in the field with a seasonal mean of –4.7 ± 0.5 °C. Microporous apple xylem showed freezing without a specific pattern within a few seconds in IDTA images during HTEs, which is in contrast to macroporous xylem where a 2D freezing pattern mirrors anatomical structures. The pith tissue always remained unfrozen. Increasing twig length increased ice nucleation temperature; for increased twig diameter the effect was not significant. In attached twigs frozen in field portable freezing chambers, HTEs were recorded at a similar mean temperature (–4.6 ± 1.0 °C) to those for detached twigs. Upon lethal intracellular freezing of apple xylem parenchyma cells (XPCs) low-temperature freezing exotherms (LTEs) can be recorded. Low-temperature freezing exotherms determined on detached twigs varied significantly between a winter minimum of –36.9 °C and a summer maximum –12.7 °C. Within the temperature range wherein LTEs were recorded by IDTA in summer (–12.7 ± 0.5 to –20.3 ± 1.1 °C) various tiny clearly separated discontinuous freezing events could be detected similar to that in other species with contrasting XPC anatomy. These freezing events appeared to be initially located in the primary and only later in the secondary xylem. During the LTE no freezing events in the bark and central pith tissue were recorded. Attached twigs were exposed to various freezing temperatures at which LTEs occur. Even if 60% of XPCs were frost-damaged twigs were able to recuperate and showed full re-growth indicating a high regeneration capacity even after severe frost damage to XPCs.
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    From lab to nature: assessing injury in xylem parenchyma cells (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
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    Gross nitrogen retranslocation within a canopy of Quercus serrata saplings (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: Nitrogen (N) retranslocation within tree canopies has been intensively studied and assumed to function as a one-way process (e.g., from older to newer leaves). However, recent studies have found that both N output and input occur in individual leaves, suggesting that ‘gross’ N retranslocation exists behind ‘net’ N retranslocation. In the present study, the amount and direction of gross N retranslocation within a canopy of deciduous oak Quercus serrata Thunb. ex. Murray saplings were investigated. Labeling was conducted with leaves of Q. serrata saplings cultivated under conditions of low-N (LN) or high-N (HN) fertility. Subsequently, N movement within the canopy was traced. Leaves at two different positions in the canopy (top and lateral) were labeled to determine the direction of gross N retranslocation. To detect seasonal differences, the leaf-labeling experiment was conducted twice during the early and late phases of the growing season. In addition, to compare the quantitative importance of gross N retranslocation and root N uptake, the latter was determined by labeling Q. serrata roots. The N-labeling experiment revealed gross N retranslocation among leaves, i.e., from top to lateral, lateral to top and lateral to lateral positions. Gross N retranslocation was quantitatively more important than root uptake, especially for plants cultivated at LN fertility. Season also affected the amount of gross N retranslocation, and these effects differed between LN and HN fertilities. These findings suggest that N allocation within a canopy is controlled dynamically by both gross N output and input. The mechanisms controlling gross N output and input likely function as key determinants of N allocation within a tree canopy.
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    Novel, cyclic heat dissipation method for the correction of natural temperature gradients in sap flow measurements. Part 1. Theory and application (2012)
    Oxford University Press
    Details
    Publication Date: 2012-07-17
    Description: Natural temperature gradient (NTG) can be a significant problem in thermal sap flow measurements, particularly in dry environments with sparse vegetation. To resolve this problem, we propose a novel correction method called cyclic heat dissipation (CHD) in its thermal dissipation probe (TDP) application. The CHD method is based on cyclic, switching ON/OFF power schema measurements and a three-exponential model, extrapolating measured signal to steady state thermal equilibrium. The extrapolated signal OFF represents NTG, whereas the extrapolated signal ON represents standard TDP signal, biased by NTG. Therefore, subtraction of the OFF signal from the ON signal allows defining the unbiased TDP signal, finally processed according to standard Granier calibration. The in vivo Kalahari measurements were carried out in three steps on four different tree species, first as NTG, then as standard TDP and finally in CHD mode, each step for ~1–2 days. Afterwards, each tree was separated from its stem following modified Roberts' (1977) procedure, and CHD verification was applied. The typical NTG varying from ~0.5 °C during night-time to –1 °C during day-time, after CHD correction, resulted in significant reduction of sap flux densities ( J p ) as compared with the standard TDP, particularly distinct for low J p . The verification of the CHD method indicated ~20% agreement with the reference method, largely dependent on the sapwood area estimate. The proposed CHD method offers the following advantages: (i) in contrast to any other NTG correction method, it removes NTG bias from the measured signal by using in situ, extrapolated to thermal equilibrium signal; (ii) it does not need any specific calibration making use of the standard Granier calibration; (iii) it provides a physical background to the proposed NTG correction; (iv) it allows for power savings; (v) it is not tied to TDP, and so can be adapted to other thermal methods. In its current state, the CHD data processing is not yet fully automated.
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    Observation of the scale of patchy stomatal behavior in leaves of Quercus crispula using an Imaging-PAM chlorophyll fluorometer (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: Patchy stomatal closure occurs in plants with heterobaric leaves, in which vertical extensions of bundle sheath cells delimit the mesophyll and restrict the diffusion of CO 2 . The scale of patchy stomatal behavior was investigated in this study. The distribution of PSII quantum yield ( II ) obtained from chlorophyll fluorescence images was used to evaluate the scale of stomatal patchiness and its relationship with leaf photosynthesis in the sun leaves of 2-year-old saplings of Quercus crispula Blume. Fluorescent patches were observed only during the day with low stomatal conductance. Comparison of numerical simulation of leaf gas exchange and chlorophyll fluorescence images showed that heterogeneous distribution of electron transport rate through PSII ( J ) was observed following stomatal closure with a bimodal manner under both natural and saturated photosynthetic photon flux densities. Thus, fluorescence patterns can be interpreted in terms of patchy stomatal closure. The mapping of J from chlorophyll fluorescence images showed that the scale of stomatal patchiness was approximately 2.5-fold larger than that of anatomical patches (lamina areas bounded by bundle sheath extensions within lamina). Our results suggest the spatial scale of stomatal patches in Q. crispula leaves.
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    Effects of predicted future and current atmospheric temperature and [CO2] and high and low soil moisture on gas exchange and growth of Pinus taeda seedlings at cool and warm sites in the species range (2012)
    Oxford University Press
    Details
    Publication Date: 2012-07-17
    Description: Predicted future changes in air temperature and atmospheric CO 2 concentration ([CO 2 ]), coupled with altered precipitation, are expected to substantially affect tree growth. Effects on growth may vary considerably across a species range, as temperatures vary from sub-optimal to supra-optimal for growth. We performed an experiment simultaneously at two locations in the current range of loblolly pine, a cool site and a warm site, to examine the effect of future climate conditions on growth of loblolly pine seedlings in contrasting regions of the species range. At both sites 1-year-old loblolly pine seedlings were grown in current (local ambient temperature and [CO 2 ]) and predicted future atmospheric conditions (ambient +2 °C temperature and 700 mol mol –1 [CO 2 ]). Additionally, high and low soil moisture treatments were applied within each atmospheric treatment at each site by altering the amount of water provided to the seedlings. Averaged across water treatments, photosynthesis ( A net ) was 31% greater at the cool site and 34% greater at the warm site in elevated temperature and [CO 2 ] compared with ambient temperature. Biomass accumulation was also stimulated by 38% at the cool site and by 24% at the warm site in that treatment. These results suggest that a temperature increase of 2 °C coupled with an increase in [CO 2 ] (predicted future climate) will create conditions favorable for growth of this species. Reduced soil moisture decreased growth in both current and predicted atmospheric conditions. Biomass accumulation and A net were reduced by ~39 and 17%, respectively, in the low water treatment. These results suggest that any benefit of future atmospheric conditions may be negated if soil moisture is reduced by altered precipitation patterns.
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    Nutritional and pathogenic fungi associated with the pine engraver beetle trigger comparable defenses in Scots pine (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: Conifer bark beetles are often associated with fungal complexes whose components have different ecological roles. Some associated species are nutritionally obligate fungi, serving as nourishment to the larvae, whereas others are pathogenic blue-stain fungi known to be involved in the interaction with host defenses. In this study we characterized the local and systemic defense responses of Scots pine ( Pinus sylvestris L.) against Ophiostoma brunneo-ciliatum Math. (a blue-stain pathogen) and Hyalorhinocladiella macrospora (Franke-Grosm.) Harr. (a nutritional fungus). These fungi are the principal associates of the pine engraver beetle, Ips acuminatus (Gyll.). Host responses were studied following inoculation with the fungi, singly and as a fungal complex, and by identifying and quantifying terpenoids, phenolic compounds and lignin. Although the length of the necrotic lesions differed between control (wound) and fungal treatments, only two compounds (pinosylvin monomethyl ether and (+)-α-pinene) were significantly affected by the presence of the fungi, indicating that Scots pine has a generic, rather than specific, induced response. The fact that both nutritional and blue-stain fungi triggered comparable induced defense responses suggests that even a non-pathogenic fungus may participate in exhausting host plant defenses, indirectly assisting in the beetle establishment process. Our findings contribute to the further development of current theory on the role of associated fungal complexes in bark beetle ecology.
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    Hydraulic differences along the water transport system of South American Nothofagus species: do leaves protect the stem functionality? (2012)
    Oxford University Press
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    Publication Date: 2012-07-17
    Description: Hydraulic traits were studied for six Nothofagus species from South America (Argentina and Chile), and for three of these species two populations were studied. The main goal was to determine if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems, consistent with the theory of hydraulic segmentation along the vascular system of trees in ecosystems subject to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density and leaf water relations were examined. Large variations in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency ( P 50 ) ranged from –0.94 to –2.44 MPa in leaves and from –2.6 to –5.3 MPa in stems across species and populations. Populations in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared with stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance ( K Leaf ) were observed. Both traits were functionally related: species with higher wood density had lower K Leaf . Other stem and leaf hydraulic traits were functionally coordinated, resulting in Nothofagus species with an efficient delivery of water to the leaves. The integrity of the more expensive woody portion of the water transport pathway can thus be maintained at the expense of the replaceable portion (leaves) of the stem–leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolism formation in the trees more vulnerable to cavitation.
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    Novel, cyclic heat dissipation method for the correction of natural temperature gradients in sap flow measurements. Part 2. Laboratory validation (2012)
    Oxford University Press
    Details
    Publication Date: 2012-07-17
    Description: Sap flow measurements conducted with thermal dissipation probes (TDPs) are vulnerable to natural temperature gradient (NTG) bias. Few studies, however, attempted to explain the dynamics underlying the NTG formation and its influence on the sensors' signal. This study focused on understanding how the TDP signals are affected by negative and positive temperature influences from NTG and tested the novel cyclic heat dissipation (CHD) method to filter out the NTG bias. A series of three experiments were performed in which gravity-driven water flow was enforced on freshly cut stem segments of Fagus sylvatica L., while an artificial temperature gradient (ATG) was induced. The first experiment sought to confirm the incidence of the ATG on sensors. The second experiment established the mis-estimations caused by the biasing effect of the ATG on standard TDP measurements. The third experiment tested the accuracy of the CHD method to account for the ATG biasing effect, as compared with other cyclic correction methods. During experiments, sap flow measured by TDP was assessed against gravimetric measurements. The results show that negative and positive ATGs were comparable in pattern but substantially larger than field NTGs. Second, the ATG bias caused an overestimation of the standard TDP sap flux density of ~17 cm 3 cm –2 h –1 by 76%, and the sap flux density of ~2 cm 3 cm –2 h –1 by over 800%. Finally, the proposed CHD method successfully reduced the max. ATG bias to 25% at ~11 cm 3 cm –2 h –1 and to 40% at ~1 cm 3 cm –2 h –1 . We concluded that: (i) the TDP method is susceptible to NTG especially at low flows; (ii) the CHD method successfully corrected the TDP signal and resulted in generally more accurate sap flux density estimates (mean absolute percentage error ranging between 11 and 21%) than standard constant power TDP method and other cyclic power methods; and (iii) the ATG enforcing system is a suitable way of re-creating NTG for future tests.
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    Indications of heightened constitutive or primed host response affecting the lignin pathway transcripts and phenolics in mature Norway spruce clones (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: Two mature clones of Norway spruce ( Picea abies (L.) Karst.) that have previously been shown to have differential degrees of resistance towards the necrotrophic pathogen Heterobasidion parviporum (Niemelä & Korhonen) were compared with respect to the primed defense expression of transcripts related to biosynthesis of lignin, stilbenes and other phenolic compounds from one year to the next. The host's response to physical wounding and pathogen inoculation was examined in the initial year, whereas indications of heightened basal defense level or primed response, and responses to re-wounding, were examined the following year. The responses of the two clones to wounding and pathogen inoculation, examined in the initial year, differed; the increases in lignin and phenolics were more distinct in response to the pathogen than to wounding alone. The more resistant clone 589 had higher initial lignin concentrations in the cell walls when compared with clone 409, and these remained higher in clone 589 over both years and increased after the treatments. Both clones responded at the transcriptional and chemical levels to wounding; changes were evident both in the initial wounds and when re-wounded the following year. There were distinct differences in the basal transcript levels of the lignin pathway-related genes, phenolics and total lignin levels in healthy tissue from the initial year to the following year indicative of a primed host response or at least altered constitutive level of defense expression.
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    Estimating sap flux densities in date palm trees using the heat dissipation method and weighing lysimeters (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: In a world of diminishing water reservoirs and a rising demand for food, the practice and development of water stress indicators and sensors are in rapid progress. The heat dissipation method, originally established by Granier, is herein applied and modified to enable sap flow measurements in date palm trees in the southern Arava desert of Israel. A long and tough sensor was constructed to withstand insertion into the date palm's hard exterior stem. This stem is wide and fibrous, surrounded by an even tougher external non-conducting layer of dead leaf bases. Furthermore, being a monocot species, water flow does not necessarily occur through the outer part of the palm's stem, as in most trees. Therefore, it is highly important to investigate the variations of the sap flux densities and determine the preferable location for sap flow sensing within the stem. Once installed into fully grown date palm trees stationed on weighing lysimeters, sap flow as measured by the modified sensors was compared with the actual transpiration. Sap flow was found to be well correlated with transpiration, especially when using a recent calibration equation rather than the original Granier equation. Furthermore, inducing the axial variability of the sap flux densities was found to be highly important for accurate assessments of transpiration by sap flow measurements. The sensors indicated no transpiration at night, a high increase of transpiration from 06:00 to 09:00, maximum transpiration at 12:00, followed by a moderate reduction until 08:00; when transpiration ceased. These results were reinforced by the lysimeters' output. Reduced sap flux densities were detected at the stem's mantle when compared with its center. These results were reinforced by mechanistic measurements of the stem's specific hydraulic conductivity. Variance on the vertical axis was also observed, indicating an accelerated flow towards the upper parts of the tree and raising a hypothesis concerning dehydrating mechanisms of the date palm tree. Finally, the sensors indicated reduction in flow almost immediately after irrigation of field-grown trees was withheld, at a time when no climatic or phenological conditions could have led to reduction in transpiration.
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    Two decades of sunfleck research: looking back to move forward (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
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    Needle metabolome, freezing tolerance and gas exchange in Norway spruce seedlings exposed to elevated temperature and ozone concentration (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: Northern forests are currently experiencing increasing mean temperatures, especially during autumn and spring. Consequently, alterations in carbon sequestration, leaf biochemical quality and freezing tolerance (FT) are likely to occur. The interactive effects of elevated temperature and ozone (O 3 ), the most harmful phytotoxic air pollutant, on Norway spruce ( Picea abies (L.) Karst.) seedlings were studied by analysing phenology, metabolite concentrations in the needles, FT and gas exchange. Sampling was performed in September and May. The seedlings were exposed to a year-round elevated temperature (+1.3 °C), and to 1.4 x ambient O 3 concentration during the growing season in the field. Elevated temperature increased the concentrations of amino acids, organic acids of the citric acid cycle and some carbohydrates, and reduced the concentrations of phenolic compounds, some organic acids of the shikimic acid pathway, sucrose, cyclitols and steroids, depending on the timing of the sampling. Although growth onset occurred earlier at elevated temperature, the temperature of 50% lethality (LT 50 ) was similar in the treatments. Photosynthesis and the ratio of photosynthesis to dark respiration were reduced by elevated temperature. Elevated concentrations of O 3 reduced the total concentration of soluble sugars, and tended to reduce LT 50 of the needles in September. These results show that alterations in needle chemical quality can be expected at elevated temperatures, but the seedlings' sensitivity to autumn and spring frosts is not altered. Elevated O 3 has the potential to disturb cold hardening of Norway spruce seedlings in autumn, and to alter the water balance of the seedling through changes in stomatal conductance ( g s ), while elevated temperature is likely to reduce g s and consequently reduce the O 3 -flux inside the leaves.
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    Sunflecks in trees and forests: from photosynthetic physiology to global change biology (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: Sunflecks are brief, intermittent periods of high photon flux density (PFD) that can significantly improve carbon gain in shaded forest understories and lower canopies of trees. In this review, we discuss the physiological basis of leaf-level responses to sunflecks and the mechanisms plants use to tolerate sudden changes in PFD and leaf temperature induced by sunflecks. We also examine the potential effects of climate change stresses (including elevated temperatures, rising CO 2 concentrations and drought) on the ability of tree species to use sunflecks, and advocate more research to improve our predictions of seedling and tree carbon gain in future climates. Lastly, while we have the ability to model realistic responses of photosynthesis to fluctuating PFD, dynamic responses of photosynthesis to sunflecks are not accounted for in current models of canopy carbon uptake, which can lead to substantial overestimates of forest carbon fixation. Since sunflecks are a critical component of seasonal carbon gain for shaded leaves, sunfleck regimes and physiological responses to sunflecks should be incorporated into models to more accurately capture forest carbon dynamics.
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    Differences in ascorbate and glutathione levels as indicators of resistance and susceptibility in Eucalyptus trees infected with Phytophthora cinnamomi (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: In this study we investigated the role that ascorbate (AA) and glutathione (GSH) play in the plant pathogen interaction of susceptible Eucalyptus sieberi L. A. Johnson and resistant Eucalyptus sideroxylon Woolls with Phytophthora cinnamomi Rands root infection. In a glasshouse study, seedlings were grown in soil-free plant boxes to facilitate the inoculation of the root systems by a P. cinnamomi zoospore solution. Ascorbate and GSH concentrations were measured in infected roots and leaves, along with leaf gas exchange, chlorophyll fluorescence and carbohydrate concentrations over a time course up to 312 h (13 days) post-inoculation (pi). At the early stages of infection (from 24 h pi), significant decreases in AA and GSH concentrations were observed in the infected roots and leaves of the susceptible E. sieberi seedlings. At the later stage of infection (312 h pi), the earlier AA decreases in the leaves of infected plants had become significant increases. In contrast, late, significant AA increases in the absence of any GSH changes were observed in the infected roots of the resistant E. sideroxylon seedlings. In E. sideroxylon leaves, a significant GSH increase occurred at 24 h pi; however, by 312 h pi the earlier increase had become a significant decrease, while no changes occurred in AA. In E. sieberi , photosynthesis ( A ), stomatal conductance ( g s ) and PSII quantum efficiency ( PSII ) were reduced by ~60, 80 and 30%, respectively, in infected plants and remained significantly lower than uninfected controls for the duration of the experiment. Significant reductions in these parameters did not occur until later (120 h pi for g s and 312 h pi for A and PSII ), and to a lesser extent in the resistant species. Non-structural carbohydrate analysis of roots and leaves indicate that carbohydrate metabolism and resource flow between shoots and roots may have been altered at later infection stages. This study suggests that reduced antioxidant capacity, leaf physiological function and carbohydrate metabolism are associated with susceptibility in E. sieberi to P. cinnamomi infection, while AA increases and new root formation were associated with resistance in E . sideroxylon .
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    The diversification of terpene emissions in Mediterranean oaks: lessons from a study of Quercus suber, Quercus canariensis and its hybrid Quercus afares (2012)
    Oxford University Press
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    Publication Date: 2012-09-14
    Description: Interspecific gene flow is common in oaks. In the Mediterranean, this process produced geographical differentiations and new species, which may have contributed to the diversification of the production of volatile terpenes in the oak species of this region. The endemic North African deciduous oak Quercus afares (Pomel) is considered to be a stabilized hybrid between the evergreen Quercus suber (L.) and the deciduous Quercus canariensis (Willd.), presumably being monoterpene and isoprene emitters, respectively. In a common garden experiment, we examined the terpene emission capacities, terpene synthase (TPS) activities and nuclear genetic markers in 52 trees of these three oak species. All but one of the Q. suber and Q. canariensis trees were found to be genetically pure, whereas most Q. afares trees possessed a mixed genotype with a predominance of Q. suber alleles. Analysis of the foliar terpene emissions and TPS activities revealed that all the Q. canariensis trees strongly produced isoprene while all the Q. suber trees were strong monoterpene producers. Quercus afares trees produced monoterpenes as well but at more variable and significantly lower rates, and with a monoterpene pattern different than that observed in Q. suber . Among 17 individuals tested, one Q. afares tree emitted only an insignificant amount of terpenes. No mixed isoprene/monoterpene emitter was detected. Our results suggest that the capacity and pattern of volatile terpene production in Algerian Q. afares populations have strongly diverged from those of its parental species and became quantitatively and qualitatively reduced, including the complete suppression of isoprene production.
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    Herbivore and human impacts on woody species dynamics in Maputaland, South Africa (2012)
    Oxford University Press
    In: Forestry
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    Publication Date: 2012-09-08
    Description: Maputaland’s woodlands are under utilization pressure inside and outside conserved areas due to mounting densities of mammals in the former and increasing human utilization of vegetation in the latter. Conservation of this biodiversity hotspot requires a better understanding of vegetation dynamics. To this purpose, woodland vegetation structure was evaluated at three sites through size class distribution analysis and grain determination, a forestry concept here applied to woodlands. The three sites represented animal disturbance/utilization, human disturbance/utilization and no disturbance/utilization regimes for comparable periods. Common species occurrence patterns differed between sites. The woodlands of all three sites were mostly fine-grained forest-like vegetation units and followed fine-grained forest dynamics closely. The grain model performed successfully for the region’s woodlands and proved a good tool to improve vegetation dynamics understanding. In general, people and herbivores led to local extirpation of species and threatened both ecological structure and function of Maputaland’s woodlands. However, the fine grain status was considered positive, as it facilitated future management options by reducing time frames and scale of management actions to be applied.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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