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  • Articles  (26,355)
  • 2005-2009  (26,355)
  • 2007  (26,355)
  • Mathematics  (16,837)
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (9,552)
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  • 2005-2009  (26,355)
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  • 1
    Electronic Resource
    Electronic Resource
    Multiple Imputation and Random Forests (MIRF) for Unobservable, High-Dimensional Data (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 12 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Understanding the genetic underpinnings to complex diseases requires consideration of sophisticated analytical methods designed to uncover intricate associations across multiple predictor variables. At the same time, knowledge of whether single nucleotide polymorphisms within a gene are on the same (in cis) or on different (in trans) chromosomal copies, may provide crucial information about measures of disease progression. In association studies of unrelated individuals, allelic phase is generally unobservable, generating an additional analytical challenge. In this manuscript, we describe a novel approach that combines multiple imputation and random forests for this high-dimensional, unobservable data setting. An application to a cohort of HIV-1 infected individuals receiving anti-retroviral therapies is presented. A simulation study is also presented to characterize method performance.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/12
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  • 2
    Electronic Resource
    Electronic Resource
    Phase Variation in Child and Adolescent Growth (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 9 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Child growth is characterised by increases in height, and increases in maturational status. Functional data analysis provides a tool to separate these two sources of variation (registration) and differentiates between the variation in maturational tempo (temporal, or "phase" variation) and the variation in height (amplitude variation). We extended this concept by combining Principal Component Analysis (PCA) and the Maximum Likelihood Principle. Longitudinal data on height were obtained from two large growth studies from Lublin, Poland, and Zurich, Switzerland, with altogether 361 children. Variation in amplitude monotonically rises with age; variation in phase peaks during puberty. During mid-puberty, phase variation is large and explains up to 40 percent of total height variance in girls, and up to 50 percent in boys. Eight amplitude and 4 phase components appeared biologically significant. The largest amplitude component explained 91% of the amplitude variance and is characterised by an almost horizontal pattern. The largest phase component explained 66% (boys) and 63% (girls) of phase variance, rises throughout childhood and reaches up to 0.85 years in adolescent boys, and up to 0.75 years in adolescent girls. Phase components significantly correlated with the clinical signs of puberty. The combination of PCA and the Maximum Likelihood Principle provides a new, powerful and automatic tool for growth modelling that includes estimates of future growth, adult stature and developmental tempo. Preliminary results indicate that this approach can be used for automatised screening purposes.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/9
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  • 3
    Electronic Resource
    Electronic Resource
    An Integrated Analysis of Individual and Aggregated Health Data Using Estimating Equations (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 10 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Analyses of individual disease-exposure data within a population are useful when exposure of interest varies sufficiently within the population. When the within-population variance of exposure is limited, however, power of the individual-data analysis is reduced. In such situations, aggregated-data analyses of disease data across populations, with a sample of individual exposure data from each population, can be powerful in estimating the exposure effect if between-population variation of exposure is large. In this paper, we consider a new analytical framework that is a combination of the individual- and aggregated-data analyses, based on an estimating equation approach. The proposed analysis utilizes strengths from individual data and aggregated data in the estimation of the exposure effect of interest, depending on which of the exposure variations (within- versus between-population) dominates. Simulation studies under various different scenarios were performed to show the strengths of the proposed approach in the estimation of the exposure effects of interest.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/10
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  • 4
    Electronic Resource
    Electronic Resource
    Conditional Volatility and Distribution of Exchange Rates: GARCH and FIGARCH Models with NIG Distribution (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art1 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper extends the Fractionally integrated GARCH (FIGARCH) model by incorporating Normal Inverse Gaussian Distribution (NIG). The proposed model is flexible and allows one to model time-variation, long memory, fat tails as well as asymmetry and skewness in the distribution of financial returns. GARCH and FIGARCH models for daily log exchange rate returns with Normal, Student's t and NIG error distributions as well as GARCH/FIGARCH-in-mean models with t errors are estimated and compared both in terms of sample fit as well as out-of-the-sample predictive ability in several dimensions. The FIGARCH model with symmetric and asymmetric NIG errors outperform alternatives both in-sample fit and 1-day and 5-day ahead predictions of the quartiles of the exchange rate return distributions.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss3/art1
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamic Multinomial Ordered Choice with an Application to the Estimation of Monetary Policy Rules (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 4, art2 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: We present a novel specification of a dynamic multinomial ordered choice model, where the latent variable is a function of strictly stationary exogenous variables and lags of the choice variable. We prove that such a model with weakly dependent errors will have a strictly stationary solution which is L-2 near epoch dependent. We also derive consistency and asymptotic normality of the maximum likelihood estimator for a probit specification of the model. We illustrate a possible application of the model by estimating a discrete version of a robust ``difference" monetary policy rule for the period 1990:2006 at a monthly frequency.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss4/art2
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  • 6
    Electronic Resource
    Electronic Resource
    Jump-and-Rest Effect of U.S. Business Cycles (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 4, art3 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: One of the most familiar empirical stylized facts about output dynamics in the United States is the positive autocorrelation of output growth. This paper shows that positive autocorrelation can be better captured by shifts between business cycle states rather than by the standard view of autoregressive coefficients. The result is extremely robust to different nonlinear alternative models and applies not only to output but also to the most relevant macroeconomic variables.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss4/art3
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  • 7
    Electronic Resource
    Electronic Resource
    Wavelet Instruments for Efficiency Gains in Generalized Method of Moment Models (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 4, art4 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: We propose a simple computational method in the context of generalized method of moments for improving the efficiency of regression coefficient estimates. The gains in efficiency arise by incorporating additional moment conditions in the estimation framework based on maximal overlap wavelet packet transforms of the continuous explanatory variables. A major advantage of the proposed method is that it does not require additional exogenous auxiliary information but relies on wavelet packet transforms of the existing continuous explanatory variables. Based on existing theory, we provide theoretical arguments for the proposed methodology, for both linear and non-linear models, and demonstrate its advantages with both an empirical application concerning two brand demand models and a Monte Carlo simulation study.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss4/art4
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  • 8
    Electronic Resource
    Electronic Resource
    Fractionally Integrated Long Horizon Regressions (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art6 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: We consider long horizon regression models where the disturbance and the predictor are possibly fractionally integrated. Asymptotic distributions of the OLS estimator and of the test statistic are given. It is found that the t-statistic diverges at the rate of square root of T, where T is the sample size. Thus, it is desirable to use the scaled test statistic, as it converges to a well-defined limit, which depends on the memory parameters through the functionals on the fractional Wiener processes. Simulation studies present some empirical distributions of the scaled test statistic according to different values of the memory parameters. The proposed model with fractional processes is empirically more tractable than the model with local to unity processes, since memory parameters are consistently estimable unlike localizing parameters in the latter model.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss1/art6
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  • 9
    Electronic Resource
    Electronic Resource
    Technical and Financial Feasibility Analysis of Distributed Bioprocessing Using Regional Biomass Pre-Processing Centers (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art10 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Research indicates that large biorefineries capable of handling 5000-10000MT of biomass per day are necessary to achieve process economies. However, such large biorefineries also entail increased costs of biomass transportation and storage, high transaction costs of contracting with a large number of farmers for biomass supply, potential market power issues, and local environmental impacts. We propose a network of regional biomass preprocessing centers (RBPC) that form an extended biomass supply chain feeding into a biorefinery, as a way to address these issues. The RBPC, in its mature form, is conceptualized as a flexible processing facility capable of pre-treating and converting biomass into appropriate feedstocks for a variety of final products such as fuels, chemicals, electricity, and animal feeds. We evaluate the technical and financial feasibility of a simple RBPC that uses ammonia fiber expansion pretreatment process and produces animal feed along with biorefinery feedstock.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/jafio/vol5/iss2/art10
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  • 10
    Electronic Resource
    Electronic Resource
    A Doubly Robust Censoring Unbiased Transformation (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 4 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: We consider random design nonparametric regression when the response variable is subject to right censoring. Following the work of Fan and Gijbels (1994), a common approach to this problem is to apply what has been termed a censoring unbiased transformation to the data to obtain surrogate responses, and then enter these surrogate responses with covariate data into standard smoothing algorithms. Existing censoring unbiased transformations generally depend on either the conditional survival function of the response of interest, or that of the censoring variable. We show that a mapping introduced in another statistical context is in fact a censoring unbiased transformation with a beneficial double robustness property, in that it can be used for nonparametric regression if either of these two conditional distributions are estimated accurately. Advantages of using this transformation for smoothing are illustrated in simulations and on the Stanford heart transplant data.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/4
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  • 11
    Electronic Resource
    Electronic Resource
    Modeling the Effect of Alzheimer's Disease on Mortality (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 13 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Mortality rate ratios and the associated proportional hazards models have been used to summarize the effect of Alzheimer's disease on longevity. However, the mortality rate ratios vary by age and therefore do not provide a simple parsimonious summary of the effect of the disease on lifespan. Instead, we propose a new parameter that is defined by an additive multistate model. The proposed multistate model accounts for different stages of disease progression. The underlying assumption of the model is that the effect of disease on mortality is to add a constant amount to death rates once the disease progresses from an early to late stage. We explored the properties of the proposed model; in particular the behavior of the mortality rate ratio and median survival that is induced by the model. We combined information from several data sources to estimate the parameter in our model. We found that the effect of Alzheimer's disease on longevity is to increase the absolute annual risk of death by about 8% once a person progressed to late stage disease. Most importantly, we find that this additive effect is the same regardless of the patients' age or gender. Thus, the proposed additive multi-state model provides a parsimonious and clinically interpretable description of the effects of Alzheimer's disease on mortality.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/13
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  • 12
    Electronic Resource
    Electronic Resource
    Conditional Likelihood Inference in a Case-Cohort Design: An Application to Haplotype Analysis (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 1 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Under the setting of a case-cohort design, covariate values are ascertained for a smaller subgroup of the original study cohort which typically is a representative sample from a population. Individuals with a specific event outcome are selected to the second stage study group as cases and an additional subsample is selected to act as a control group. We carry out analysis of such a design using conditional likelihood where the likelihood expression is conditioned on the ascertainment to the second stage study group. Such likelihood expression involves the probability of ascertainment which need to be expressed in terms of the model parameters. We present examples of conditional likelihoods for models for categorical response and time-to-event response. We show that the conditional likelihood inference leads to valid estimation of population parameters. Our application considers joint estimation of haplotype-event association parameters and population haplotype frequencies based on SNP genotype data collected under a case-cohort design.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/1
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  • 13
    Electronic Resource
    Electronic Resource
    Regression Analysis of Mean Lifetime: Exploring Nonlinear Relationship with Heteroscedasticity (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 5 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: As a generalization of the accelerated failure time models, we consider parametric models of lifetime Y, where the conditional mean E(Y|X;beta) can depend nonlinearly on the covariates X and some parameters beta. The error distribution can be heteroscedastic and dependent on X. With observed data subject to right censoring, we propose regression analysis for beta based on Kaplan-Meier estimates of the means over several regions of X. Consistency and asymptotic distributional properties of the estimators are established under general conditions. A resulting estimator of beta is shown to be the sum of two possibly dependent asymptotic normal quantities, based on which conservative confidence intervals and tests are derived. Simulation studies are conducted to investigate the performance of the proposed estimator and to compare it with Buckley-Jame's method. To illustrate the methodology, we study an example with kidney transplant data, where a nonlinear relationship called "mixtures-of-experts", proposed in the neural networks literature, is used to model the relationship between the survival time and the age of the patients.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/5
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  • 14
    Electronic Resource
    Electronic Resource
    The Benjamini-Hochberg Method in the Case of Discrete Test Statistics (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 11 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: We present a reformulation of the Benjamini-Hochberg method that is useful in 'large-scale' multiple testing problems based on discrete test statistics and derive its basic asymptotic (as the number of hypotheses tends to infinity) properties, subsuming earlier results. A set of gene expression data is used to illustrate the workings of the method in a multiple testing problem based on Kolmogorov-Smirnov and Mann-Whitney statistics.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol3/iss1/11
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  • 15
    Electronic Resource
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    A Threshold Model of Real U.S. GDP and the Problem of Constructing Confidence Intervals in TAR Models (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art4 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: We estimate real US GDP growth as a threshold autoregressive process, and construct confidence intervals for the parameter estimates. However, there are various approaches that can be used in constructing the confidence intervals. We construct confidence intervals for the slope coefficients and the threshold using asymptotic results and bootstrap methods, finding that the results for the different methods have very different economic implications. We perform a Monte Carlo experiment to evaluate the various methods. Surprisingly, the confidence intervals are wide enough to cast doubt on the assertion that the time-series responses of GDP to negative growth rates are different than the responses to positive growth rates.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss3/art4
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  • 16
    Electronic Resource
    Electronic Resource
    A Smooth Transition Autoregressive Conditional Duration Model (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art5 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This study presents a novel model for analyzing duration data, called the smooth transition autoregressive conditional duration model of price and duration, which considers past price changes and durations. The model enables the process of the conditional expected duration to switch in a smooth transition way, broadening the autoregressive conditional duration (ACD) model in Engle and Russell (1998). The model is applied to empirical data, and estimation results indicate that the process of the expected duration is nonlinear. The expected trade duration behavior on the market opening is affected by past trade durations, while the expected trade duration behavior during the trading hours is affected by past price changes and trade durations. Expected trade durations are much more persistent in the upward market compared to the downward market. Shocks to trade durations are more persistent on the market opening and gradually decrease in the downward market.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss1/art5
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  • 17
    Electronic Resource
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    Which Are the World's Wobblier Currencies? Reference Exchange Rates and Their Variation (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art5 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: Measuring country exchange rates relative to a common reference basket results in a set of no-arbitrage prices, unlike trade-weighted indexes, the usual method of comparing country exchange rate histories. The reference basket is analogous to a portfolio, and its choice can be resolved by drawing on required economic interpretations or uses. We use currency reference rates to examine the historical variability of different currencies over designated cyclical bands. The temporal decompositions used are those provided by wavelet analysis, which is light on maintained assumptions about data generating processes. Some countries, notably Japan and New Zealand do exhibit a powerful but irregular medium term cycle, while others are much more stable. Implications are briefly examined for investment, hedging, monetary policy and common currency studies.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss3/art5
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  • 18
    Electronic Resource
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    Wavelet Variance Analysis of Output in G-7 Countries (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art6 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: The large decline in output volatility experienced by most industrialized countries in the last decades has been thoroughly analyzed using standard time and frequency domain methods. In this paper we investigate the issue of moderation of volatility in G-7 economies and its sources, applying a multi-scaling approach to the industrial production indices of G-7 countries between 1961:1-2006:10. Using the MODWT estimates of wavelet variance we provide a scale-based analysis of variance that allows us to characterize the decline in volatility and to detect the importance of the various explanations of the moderation. The main scale-by-scale results stemming from multi scale analysis of variance are: i) a reduction in volatility which, although displayed by all the G-7 countries, is not uniform across time scales (as the decline is larger at short-term scales than at business cycle scales for France and Italy, and quite uniform across scale for the UK and the US) nor countries (as the decline is significant for a subset of countries only, i.e. France, Italy, the UK and the US); and ii) the moderation has to be attributable to the decline in the variance of both common (in the 1970s) and country-specific (in the 1960s) exogenous disturbances hitting the economy.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/snde/vol11/iss3/art6
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  • 19
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    Contract Selectivity, Food Safety, and Traceability (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art2 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Contracts are an increasingly common method for coordinating exchange in the food industry. Contracts often include specifications for product attributes including food safety. One of the goals of explicit safety specifications is to discourage or deter suppliers who would deliver unsafe food. In this article, we use a principal-agent model in the context of adverse selection to examine how contracts that include traceability can be used to select against producers who cannot meet a processor's safety specifications. We find that the motivation to select against unsafe producers depends on the magnitude of the failure costs and the proportion of the failure costs allocated to producers. We also identify the conditions under which the processor selects against unsafe producers regardless of traceability. Our results are important to regulators and negotiators who want to support safe producers and deter unsafe producers.
    Type of Medium: Electronic Resource
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  • 20
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    Measuring the Degree of Retail Competition in U.S. Cheese Markets (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art1 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: The objective of this article is to measure the degree of competition among retail stores to sell a specific brand of a product. For this purpose, we estimate brand-specific demand equations along with first order conditions from stores' profit maximization. In stores' profit maximization, we account for three sources of conjectural variation: within a store but across brands, across stores for the same brand, and across stores for other brands. Data on U.S. retail store price and sales data on cheese products from ACNielsen Homescan database are used in our empirical analysis. A set of indices representing concentration of purchases across brands within each store and across stores for each brand are used to estimate conjectural elasticities. Results show the existence of price markups suggesting imperfectly competitive behavior in retail cheese markets.
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  • 21
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    Market and Welfare Effects of Collusion with Reference to Multi-Product Food Oligopoly and Oligopsony (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art5 
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    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Among the dominant firms in the US meat and grain business, many produce several products, some of which are demand-related. Yet, virtually all research on collusion among those firms focuses on a single product. This paper uses a game-theoretic model to investigate the conditions under which multi-product food firms producing demand-related goods have incentives to collude, and examines the welfare implications of collusion for participants in a vertical marketing chain. I show that multi-product food firms have a greater incentive to collude when they become more efficient. In contrast to previous work, I find that the effect of the degree of product substitutability on collusion sustainability hinges on the cost effect arising from joint production. From a policy standpoint, I show that mergers between single-product firms producing demand-related goods under certain conditions may hinder collusion.
    Type of Medium: Electronic Resource
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  • 22
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    Cherry Picking: Should Sellers Let Buyers Sort? (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art11 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Agricultural goods sold in supermarkets often vary significantly in quality. Yet, when these goods are sold at a single price, consumers may expend significant time and effort to sort goods for quality. From the standpoint of sellers, the resources expended on sorting only serve to reallocate high quality goods to consumers who sort intensively and low quality goods to consumers who sort minimally or not at all. Because these lower quality goods are less attractive to consumers who do not sort, sellers may be forced to lower prices. Why then do sellers allow sorting when they might prevent it? This paper presents a demand model where sellers choose whether to allow sorting. Sellers may allow consumer sorting when it fosters the distribution of qualities that occurs under quality discrimination, despite the associated reduction in the total gains to trade through sorting costs and quality efficiency loss. In general, sorting may allow sellers to improve the quality of goods for marginal consumers who constrain price-setting for sellers with market power. The total effect on price, amount sold and welfare is ambiguous due to the role of market power. Simulations are provided to demonstrate these effects.
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  • 23
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    Biofuels Policies in Asian Countries: Impact of the Expanded Biofuels Programs on World Agricultural Markets (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art8 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: The governments of Asian countries are promoting biofuels programs to deal with energy security and environmental problems, and to increase farm income. However, securing raw materials for biofuels is a crucial problem, because these raw materials comprise various agricultural products which are used as food sources in Asian countries. Increasing biofuel consumption is exacerbating this problem. To address it, the governments of Asian countries are working on biofuel programs which will not compete with food security. Most of the Asian countries are food-importing countries. Increasing food prices, due to competition, could lead to social unrest. It is expected that the introduction and development of second-generation biofuels can mitigate the competition between food and energy. As various countries develop second-generation biofuels, international cooperation is needed to maximize such development in Asia and other regions. Establishing international cooperation to develop second-generation biofuels is urgently needed in Asian countries.
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    Estimating the Welfare Effects of U.S. Distortions in the Ethanol Market Using a Partial Equilibrium Trade Model (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art5 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: In this paper the impact of distortions on U.S. imports of ethanol from Brazil are calculated. This is achieved by using two-stage least squares to estimate a partial equilibrium trade model based on annual data from 1975 to 2006. From this the derived export supply and import demand elasticities are used to derive "back-of-the-envelope" measures of the static and cumulative deadweight losses, assuming the distortions are not eliminated. The results presented support the hypothesis that the U.S. and Brazil would reap gains from trade if distortions in the U.S. ethanol market were eliminated.
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    Consumer Response to Information and Second-Generation Genetically Modified Food in India (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art8 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: This study investigates the Indian market for GM wheat. First, we address the obvious valuation and acceptance questions for Indian consumers. Then we investigate the extent to which the provision of information about GM wheat has any significant effect on consumers' willingness to pay and the degree to which the effect varies based on the information treatment. Finally, we consider whether the type of primary beneficiary of GM wheat production affects valuation. Specifically, we assess the conjecture that consumers' willingness to pay for GM wheat changes according to whether the crop is portrayed as producer-friendly or consumer-friendly.
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    The Value of Collective Reputation for Environmentally-Friendly Production Methods: The Case of Val di Gresta (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art7 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: In this paper we investigate consumers' preferences for various environment-friendly production systems for carrots. We use discrete-choice multi-attribute stated-preference data to explore the effect of collective reputations from growers of an Alpine valley known for its environment-friendly production: Val di Gresta 'the valley of organic orchards'. Data analysis of the panel of discrete responses identifies unobserved taste heterogeneity for organic, bio-dynamic and place of origin, while observed heterogeneity for income is addressed by a piece-wise linear function. The implied sample distributions of individual-specific WTP for each of these random attributes are then compared. Results indicate that Integrated Pest Management is preferred to biodynamic as an emerging method. The presence of a premium for Val di Gresta produce is confirmed. The use of an experimental design to identify the relevant second order effects reveals the presence of a reputation effect which can be decomposed into a generic effect from place of origin and a specific one for each EFPMs. Farmers operating in geographically limited marginal areas, such as mountain valleys, may find it useful to invest in collective reputation through high quality standard to achieve higher returns. This strategy may compensate for the dwindling public support to farm income from EU programmes.
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    Generic Advertising and Product Differentiation Revisited (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art3 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: This paper revisits the analysis of generic commodity advertising under product differentiation by Crespi and Marette. Crespi and Marette had shown that a dominant firm producing high-quality goods and facing a competitive fringe of lower quality producers could be harmed by a generic advertising campaign while the fringe was left unaffected. Under this dominant-firm model, a question remained why these producers might support a program for which they were indifferent. In this paper we show that under a duopoly model a high-quality firm may be harmed while its lower-quality rival may be made better off by a generic program, thus helping to explain why some producers might favor a program while others do not. Further, this paper dismisses the claim made by some litigants that increased branded advertising is the result of a deleterious effect of generic advertising.
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    Fair Trade Labeling: Inside or Outside Supermarkets? (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art9 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: This article is a theoretical contribution to the debate surrounding the introduction of Fair Trade products into large-scale retail distribution. In the model, a Fair Trade certifier and a traditional producer compete to supply their product to a single retailer, consumers who are Fair Trade likers are willing to pay an "ethical" premium for the Fair Trade product, and the premium depends on the revenue of Fair Trade product producers. The conditions of existence of an equilibrium where the Fair Trade product coexists with the traditional brand product on the retailer's shelves are highlighted. In particular, we show that a Fair Trade certifier implements this equilibrium if his preferences are such that the weight devoted to the price paid to producers is smaller than the weight he grants to the quantities of Fair Trade product sold. We also show that a retailer's decision to sell the Fair Trade product is not based on the percentage of consumers who are willing to pay for it, but on how much the Fair Trade likers are willing to pay.
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    Policy Alternatives for the Future Biofuels Industry (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art2 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: US and state governments have subsidized ethanol since 1978, and the rationale for these subsidies has varied over time from supporting farm prices and income, to environmental quality, and more recently to energy security and reduction of greenhouse gas emissions. The recent boom in ethanol investment and production can be considered as an unintended consequence of an ethanol subsidy keyed to $20 crude oil and fixed at 51 cents per gallon combined with oil surging to $70/bbl. Thus, in the 2005-07 period, ethanol was extremely profitable inducing substantial new investment. For the future, different political action groups and political figures propose renewable fuels targets or standards ranging from 35 to 100 billion gallons per year. To achieve anything like these levels, it is likely that the current policy set will need to be reconsidered. In addition to the current policy, this paper considers using a subsidy tied to the energy security gains and greenhouse gas emission reductions provided by renewable fuels, subsidies targeted specifically at cellulose ethanol, and different versions of a renewable fuel standard such as the one passed by the US Senate. It is clear that we must develop a better understanding of the consequences of these alternative policy pathways.
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    Ethanol Expansion in the Food versus Fuel Debate: How Will Developing Countries Fare? (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art6 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: This paper examines the impact of ethanol expansion in the United States, brought about by higher crude oil prices, on agricultural commodity prices. Given the United States's stature as a major producer and exporter of many agricultural commodities, the resulting increase in commodity prices has spillover effects into the global market. Using the price changes estimated within a multi-commodity, multi-country agricultural modeling system, this paper attempts to show how an increase in world commodity prices would affect the costs of food baskets around the world and how higher food costs will impact food security, particularly in developing countries. In general, we find that countries where corn is the major food grain experience larger increases in food basket cost while countries where rice is the major food grain have smaller food basket cost increases. Countries where wheat and/or sorghum are the major food grains fall in between. Consequently, the highest percentage increases are seen in Sub-Saharan Africa and Latin America where food basket costs are estimated to increase by at least 10%. The lowest percentage increases are seen in Southeast Asia, with cost increases of less than 2.5%.
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    Explorations in Biofuels Economics, Policy, and History: Introduction to the Special Issue (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art1 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Biofuels are prominent in current discussion both as a solution to problems and as a creator of problems. They have promise as a substitute for fossil fuels, particularly for petroleum as the raw material for transportation fuel. But biofuels also have pitfalls, especially when produced at a scale sufficient to replace a significant proportion of the world's use of petroleum. The articles in this special issue analyze key aspects of both the promise and pitfalls of biofuels. They address issues in the technology of producing raw materials for biofuels and converting these raw materials into fuel, resource constraints facing expansion of biofuel production, and the demand for fuels. Particular attention is paid to the relationship between expanded biofuel production and the cost of food. The economics of biofuels is inherently linked to policy issues as well as market analysis because biofuels in every country have received subsidies from governments. Consequently several articles address the welfare economics of governmental efforts to promote biofuels, with a focus on U.S. ethanol subsidies. These subsidies generate net social losses (deadweight costs) on a global scale, although not necessarily from the U.S. national viewpoint. Governmental promotion of biofuels can be justified on the grounds of externalities created by the use of fossil fuels, most notably in recent debates on global warming caused by the release of sequestered carbon in the form of carbon dioxide. This justification is weakened and perhaps even nullified by externalities in the production and use of biofuels. The articles in this issue consider a range of topics concerning these matters, and the welfare losses caused by biofuel subsidies absent net environmental gains from biofuels.
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    A Resampling-Based Approach to Multiple Testing with Uncertainty in Phase (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 2 
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    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Characterizing the genetic correlates to complex diseases requires consideration of a large number of potentially informative biological markers. In addition, attention to alignment of alleles within or across chromosomal pairs, commonly referred to as phase, may be essential for uncovering true biological associations. In the context of population based association studies, phase is generally unobservable. Preservation of type-1 error in a setting with multiple testing presents a further analytical challenge. This manuscript combines a likelihood-based approach to handling missing-ness in phase with a resampling method to adjust for multiple testing. Through simulations we demonstrate preservation of the family-wise error rate and reasonable power for detecting associations. The method is applied to a cohort of 626 HIV-1 infected individuals receiving highly active anti-retroviral therapies, to ascertain potential genetic contributions to abnormalities in lipid profiles. The haplotypic effects of 2 genes, hepatic lipase (HL) and endothelial lipase (EL), on high-density lipoprotein cholesterol (HDL-C) are tested.
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    Gains from Synchronization (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art2 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper investigates the transmission mechanisms of structural shocks and volatility between economies through trade links, and the effects of synchronization on business cycles. We investigate the transmission of outside structural shocks and the fluctuations that the shocks generate. We identify conditions under which international economic links reduce the volatility and unpredictability of economic output emanating from shocks within the individual economies. Under certain conditions, devaluation of a country's currency causes reduction in the unpredictability of the business cycle and its volatility as seen by that country's exporters, while increased valuation of a country's currency produces higher unpredictability and volatility, as seen by the country's importers.
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    The Transmission of Aggregate Supply and Aggregate Demand Shocks in Japan: Has There Been a Structural Change? (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 4, art5 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: Despite expansionary fiscal and monetary policies, the Japanese real economy has been stagnating since the bubble bursting in the early nineties. Within a multivariate setup, this paper proposes to test for and date apossible structural shift in the response of Japanese macroeconomic fluctuations to aggregate supply and aggregate demand shocks. The econometric methodology directly derives from Andrews (1993) and Bai, Lumsdaine and Stock (1998) theoretical results. Our empirical study from monthly post-1980 observations reveals i) a significant structural break in the end of 1991, and ii) a sharp decrease in the influence of demand shocks on Japanese output fluctuations after this date.
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    Change-Points in U.S. Business Cycle Durations (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art6 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper develops a change-point model that can endogenously detect a structural shift in a time series of durations. The model is applied to NBER data on U.S. business cycle durations for expansions and contractions. There are two primary results. First, the change-point model endogenously detects a shift in the distribution for the phases of the U.S. business cycle around WWII. The pattern of duration dependence for both contractions and expansions correspond to earlier work, such as Diebold and Rudebusch (1990), Sichel (1991) and Zuehlke(2003), that exogenously split the sample at WWII. The second result is that the change-points for expansions and contractions generally occur earlier than WWII when controlling for various factors, such as the duration of the preceding half-cycle, wars and a trend variable. For expansions, the only significant explanatory variable is a trend, resulting in each successive expansion's hazard rate uniformly shifting down. For contractions, both a trend and the lagged duration of the preceding expansion are found, when estimated separately, to be significant. Controlling for a trend, contractions no longer exhibit positive duration dependence following the estimated change-point.
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    Complex Dynamics in the Neoclassical Growth Model with Differential Savings and Non-Constant Labor Force Growth (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art3 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: In this paper we analyze the dynamics shown by the neoclassical one-sector growth model with differential savings as in Bohm and Kaas (2000) while assuming CES production function and the labour force dynamic described by the Beverton Holt equation (see Beverton and Holt, 1957). The resulting dynamic system is bidimensional, autonomous and triangular: we investigate its qualitative and quantitative dynamic properties. The study herewith presented aims at confirming that the system can exhibit cycles or even a chaotic dynamic pattern, if shareholders save more than workers, when the elasticity of substitution drops below one (so that capital income declines). The analytical results are supplemented by numerical experiments.
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    Detecting Multiple Changes in Persistence (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 3, art2 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper considers the problem of testing for and dating changes (at unknown points) in the order of integration of a time series between different trend-stationary and difference-stationary regimes. While existing procedures in the literature are designed for processes displaying only a single such change in persistence, our proposed methodology is also valid in the presence of multiple changes in persistence. Our procedure is based on sequences of doubly-recursive implementations of the regression-based unit root statistic of Elliott et al. (1996). The asymptotic validity of our procedure is demonstrated analytically. We use Monte Carlo methods to simulate both finite sample and asymptotic critical values for our proposed testing procedure and to simulate the finite sample behaviour of our procedure against a variety of single and multiple persistence change series. The procedure is shown to work well in practice. The impact of deterministic level and trend breaks on our procedure is also discussed. An empirical application of the procedure to interest rate data is considered.
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    A New Application of Exact Nonparametric Methods to Long-Horizon Predictability Tests (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art7 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: Empirical results from long-horizon regression tests have been influential in the finance literature. Yet, it has come to be understood that traditional long-horizon tests may be unreliable in finite samples when regressors are persistent and when the horizon is long relative to sample size. Recent research has provided valid alternative inference procedures in long-horizon regression in the case for which the regressor follows a near-unit root autoregressive process. However, in small samples, such processes may sometimes be difficult to distinguish with confidence from other persistent data generating processes, such as those displaying long-memory or structural breaks. In this paper, we demonstrate a simple means by which existing nonparametric sign and signed rank tests may be applied to provide exact inference in long-horizon predictive tests, without requiring any modeling assumptions on the regressor. Employing this robust approach, we find evidence of stock return predictability at moderate horizons using short-term interest rates, but little evidence of either short or long-run predictability using dividend-price ratios.
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    A Dynamic Semiparametric Proportional Hazard Model (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art1 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper proposes a dynamic proportional hazard (PH) model with non-specified baseline hazard for the modelling of autoregressive duration processes. By employing a categorization of the underlying durations we reformulate the PH model as an ordered response model based on extreme value distributed errors. In order to capture persistent serial dependence in the duration process, we extend the model by an observation driven ARMA dynamic based on generalized errors. We illustrate the maximum likelihood estimation of both the model parameters and discrete points of the underlying unspecified baseline survivor function. The dynamic properties of the model as well as the estimation quality are investigated in a Monte Carlo study. It is illustrated that the model is a useful approach to estimate conditional failure probabilities based on (persistent) serially dependent duration data which might be subject to censoring mechanisms. In an empirical study based on financial transaction data we apply the model to estimate conditional asset price change probabilities. An evaluation of the forecasting properties of the model shows that the proposed approach is a promising competitor to well-established ACD type models.
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    A Class Test for Fractional Integration (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art5 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: Diebold and Rudebusch (1991) and Haubrich (1993) argue that, when income follows a fractionally differenced process, the Deaton's excessive smoothness paradox can be resolved. A key to the success of their result relies on a valid test for fractional integration. However, most of the tests in the literature are nested within fractional alternatives. This paper designs a new test for a more general hypothesis that the true data generating process is indeed fractionally integrated. The test is applied to the real disposable income per capita of the U.S. and the real quarterly GDP data of the G7 industrial countries.
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    Equilibrium Efficiency in the Ramsey Model with Habit Formation (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art2 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper analyzes the equilibrium efficiency in a Ramsey model with habit formation. Uniqueness and saddle-path stability of the steady state is proved analytically. The competitive equilibrium is efficient at the steady state. However, the presence of externalities arising from average past consumption renders the competitive equilibrium inefficient off the steady state because agents do not take (fully) into account the indirect effect that consumption has in utility through its influence on habits. The efficient equilibrium can be decentralized by means of a consumption tax that converges to an arbitrary constant value, or by means of an income tax that converges to zero.
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    Spurious Inference in the GARCH (1,1) Model When It Is Weakly Identified (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art1 
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    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: This paper shows that the Zero-Information-Limit-Condition (ZILC) formulated by Nelson and Startz (2006) holds in the GARCH (1,1) model. As a result, the GARCH estimate tends to have too small a standard error relative to the true one when the ARCH parameter is small, even when sample size becomes very large. In combination with an upward bias in the GARCH estimate, the small standard error will often lead to the spurious inference that volatility is highly persistent when it is not. We develop an empirical strategy to deal with this issue and show how it applies to real datasets.
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    Scale and Transaction Costs in the U.S. Biopower Industry (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art10 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: With increasing interest in renewable energy from agriculture, including biopower and cellulose ethanol, there is a need for better understanding of the economic organization of this emerging industry. Study of the organization of the biopower industry represents an under-researched area and a new application of transaction cost theory to an emerging industry. Refinement of the theory can also result from challenging applications. This article provides an application of transaction cost economics to the existing United States biopower industry while challenging the empirical convention of excluding production cost variables from transaction cost analysis. Utilizing survey data from 53 biopower generators we study the relationship between physical asset specificity, site specificity, and scale in explaining firms' decisions to procure inputs internally, externally, or to use both methods. Consistent with transaction cost theory, both site specificity and scale are good predictors of organizational form. Given this evidence, this article reconsiders the impact of scale and transaction costs on the choice of organizational from.
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    Ethanol: No Free Lunch (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art3 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: The sharp rise in energy prices in the 1980s triggered a strong interest in the production of ethanol as an additional energy component. Economists are divided as to the payoffs from ethanol derived corn in part because of the complex interrelationship between energy produced from ethanol and energy from fossil fuels. Using a welfare economic framework, we calculate that there can be treasury savings from ethanol using tax credits as these subsidies can be smaller than direct payments to corn farmers which are essentially eliminated from the expansion of ethanol. Also, to the extent that ethanol dampens fuel prices there can be a net welfare gain from ethanol production in the presence of ethanol subsidies.
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    Fueling the Automobile: An Economic Exploration of Early Adoption of Gasoline over Ethanol (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art11 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: When the automobile was developed near the beginning of the last century, it was the relatively new fuel gasoline, not the familiar ethanol that became the fuel of choice. We examine the intersections of the early development of the automobile and the petroleum industry and consider the state of the agriculture sector during the same period. Through this process, we find a series of influences, such as relative prices and alternative markets, that help to explain how in the early years of automobile development, gasoline won out over the equally likely technical alternative ethanol. We also examine the industrial relations in the automobile industry that seem to have influenced the later adoption of leaded gasoline, rather than ethanol, as a solution to the problem of engine knock.
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    Potential Land Use Implications of a Global Biofuels Industry (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art9 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: In this paper we investigate the potential production and implications of a global biofuels industry. We develop alternative approaches to consistently introduce land as an economic factor input and in physical terms into a computable general equilibrium framework. The approach allows us to parameterize biomass production consistent with agro-engineering information on yields and a "second generation" cellulosic biomass conversion technology. We explicitly model land conversion from natural areas to agricultural use in two different ways: in one approach we introduced a land supply elasticity based on observed land supply responses and in the other approach we considered only the direct cost of conversion. We estimate biofuels production at the end of the century could reach 221 to 267 EJ in a reference scenario and 319 to 368 EJ under a global effort to mitigate greenhouse gas emissions. The version with the land supply elasticity allowed much less conversion of land from natural areas, forcing intensification of production, especially on pasture and grazing land, whereas the pure conversion cost model led to significant deforestation. These different approaches emphasize the importance of somehow reflecting the non-market value of land more fully in the conversion decision. The observed land conversion response we estimate may be a short turn response that does not fully reflect the effect of long run pressure to convert land if rent differentials are sustained over 100 years.
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  • 47
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    Survival Instantaneous Log-odds Ratio from Empirical Functions (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 7 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: The objective of this work is to introduce a new method called the Survivorship Instantaneous Log-odds Ratios (SILOR); to illustrate the creation of SILOR from empirical bivariate survival functions; to also derive standard errors of estimation; to compare results with those derived from logistic regression. Hip fracture, AGE and BMI from the Third National Health and Nutritional Examination Survey (NHANES III) were used to calculate empirical survival functions for the adverse health outcome (AHO) and non-AHO. A stable copula was used to create a parametric bivariate survival function, that was fitted to the empirical bivariate survival function. The bivariate survival function had SILOR contours which are not constant. The proposed method has better advantages than logistic regression by following two reasons. The comparison deals with (i) the shapes of the survival surfaces, S(X1, X2), and (ii) the isobols of the log-odds ratios. When using logistic regression the survival surface is either a hyper plane or at most a conic section. Our approach preserves the shape of the survival surface in two dimensions, and the isobols are observed in every detail instead of being overly smoothed by a regression with no more than a second degree polynomial. The present method is straightforward, and it captures all but random variability of the data.
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  • 48
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    Causal Effect Models for Realistic Individualized Treatment and Intention to Treat Rules (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 3 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Marginal structural models (MSM) are an important class of models in causal inference. Given a longitudinal data structure observed on a sample of n independent and identically distributed experimental units, MSM model the counterfactual outcome distribution corresponding with a static treatment intervention, conditional on user-supplied baseline covariates. Identification of a static treatment regimen-specific outcome distribution based on observational data requires, beyond the standard sequential randomization assumption, the assumption that each experimental unit has positive probability of following the static treatment regimen. The latter assumption is called the experimental treatment assignment (ETA) assumption, and is parameter-specific. In many studies the ETA is violated because some of the static treatment interventions to be compared cannot be followed by all experimental units, due either to baseline characteristics or to the occurrence of certain events over time. For example, the development of adverse effects or contraindications can force a subject to stop an assigned treatment regimen.In this article we propose causal effect models for a user-supplied set of realistic individualized treatment rules. Realistic individualized treatment rules are defined as treatment rules which always map into the set of possible treatment options. Thus, causal effect models for realistic treatment rules do not rely on the ETA assumption and are fully identifiable from the data. Further, these models can be chosen to generalize marginal structural models for static treatment interventions. The estimating function methodology of Robins and Rotnitzky (1992) (analogue to its application in Murphy, et. al. (2001) for a single treatment rule) provides us with the corresponding locally efficient double robust inverse probability of treatment weighted estimator. In addition, we define causal effect models for "intention-to-treat" regimens. The proposed intention-to-treat interventions enforce a static intervention until the time point at which the next treatment does not belong to the set of possible treatment options, at which point the intervention is stopped. We provide locally efficient estimators of such intention-to-treat causal effects.
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  • 49
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    Statistical Learning of Origin-Specific Statically Optimal Individualized Treatment Rules (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 6 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Consider a longitudinal observational or controlled study in which one collects chronological data over time on a random sample of subjects. The time-dependent process one observes on each subject contains time-dependent covariates, time-dependent treatment actions, and an outcome process or single final outcome of interest. A statically optimal individualized treatment rule (as introduced in van der Laan et. al. (2005), Petersen et. al. (2007)) is a treatment rule which at any point in time conditions on a user-supplied subset of the past, computes the future static treatment regimen that maximizes a (conditional) mean future outcome of interest, and applies the first treatment action of the latter regimen. In particular, Petersen et. al. (2007) clarified that, in order to be statically optimal, an individualized treatment rule should not depend on the observed treatment mechanism. Petersen et. al. (2007) further developed estimators of statically optimal individualized treatment rules based on a past capturing all confounding of past treatment history on outcome. In practice, however, one typically wishes to find individualized treatment rules responding to a user-supplied subset of the complete observed history, which may not be sufficient to capture all confounding. The current article provides an important advance on Petersen et. al. (2007) by developing locally efficient double robust estimators of statically optimal individualized treatment rules responding to such a user-supplied subset of the past. However, failure to capture all confounding comes at a price; the static optimality of the resulting rules becomes origin-specific. We explain origin-specific static optimality, and discuss the practical importance of the proposed methodology. We further present the results of a data analysis in which we estimate a statically optimal rule for switching antiretroviral therapy among patients infected with resistant HIV virus.
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    The Analysis of Bivariate Truncated Data Using the Clayton Copula Model (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 8 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: In individuals infected with human immunodeficiency virus (HIV), distributions of quantitative HIV RNA measurements may be highly left-censored due to values falling below assay detection limits (DL). It is of the interest to find the relationship between plasma and semen viral loads. To address this type of problem, we developed an empirical goodness-of-fit test to check the Clayton model assumption for bivariate truncated data. We also used truncated tau to estimate the dependence parameter in the Clayton model for this type of data. It turns out that the proposed methodology works for both truncated and fixed left censored bivariate data. The proposed test procedure is demonstrated using an HIV data set, and statistical inference is drawn based on corresponding test result.
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    Preference-Based Instrumental Variable Methods for the Estimation of Treatment Effects: Assessing Validity and Interpreting Results (2007)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 14 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: Observational studies of prescription medications and other medical interventions based on administrative data are increasingly used to inform regulatory and clinical decision making. The validity of such studies is often questioned, however, because the available data may not contain measurements of important prognostic variables that guide treatment decisions. Recently, approaches to this problem have been proposed that use instrumental variables (IV) defined at the level of an individual health care provider or aggregation of providers. Implicitly, these approaches attempt to estimate causal effects by using differences in medical practice patterns as a quasi-experiment. Although preference-based IV methods may usefully complement standard statistical approaches, they make assumptions that are unfamiliar to most biomedical researchers and therefore the validity of such an analysis can be hard to evaluate. Here, we describe a simple framework based on a single unobserved dichotomous variable that can be used to explore how violations of IV assumptions and treatment effect heterogeneity may bias the standard IV estimator with respect to the average treatment effect in the population. This framework suggests various ways to anticipate the likely direction of bias using both empirical data and commonly available subject matter knowledge, such as whether medications or medical procedures tend to be overused, underused, or often misused. This approach is described in the context of a study comparing the gastrointestinal bleeding risk attributable to different non-steroidal anti-inflammatory drugs.
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    Short-Run Patience and Wealth Inequality (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art4 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: The quasi-geometric (hyperbolic) literature typically assumes that agents are short-run impatient. In this paper, we deviate from this assumption by considering an economy in which a fraction of the population is short-run patient and the remaining population is short-run impatient. In a calibrated version of a neoclassical growth model with uninsurable risk and liquidity constraints, we find that the presence of few short-run patient and many short-run impatient agents leads to empirically plausible degrees of wealth inequality.
    Type of Medium: Electronic Resource
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    The Dynamic Behaviour of an Endogenous Growth Model with Public Capital and Pollution (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art4 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: In this paper we present an endogenous growth model with environmental pollution and public capital. As to pollution we assume that it is a by-product of aggregate production and that it negatively affects utility of the household but not production possibilities directly. The paper studies the dynamics of the model and demonstrates that there exists either a unique balanced growth path which is a saddle point or there exist two balanced growth paths with one being locally saddle point stable and one being asymptotically stable.
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    Time Series Models for Forecasting: Testing or Combining? (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 1, art3 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: In this paper we systematically compare forecasting accuracy of hypothesis testing procedures with that of a model combining algorithm. Testing procedures are commonly used in applications to select a model, based on which forecasts are made. However, besides the well-known difficulty in dealing with multiple tests, the testing approach has a potentially serious drawback: controlling the probability of Type I error at a conventional level (e.g., 0.05) often excessively favors the null, which can be problematic for the purpose of forecasting. In addition, as shown in this paper, testing procedures can be very unstable, which results in high variability in the forecasts.Selecting a candidate forecast by testing and combining forecasts are both useful but for complementary situations. Currently, there seems to be little guidance in the literature on when combining should be preferred to selecting. We propose instability measures that are helpful for a forecaster to gauge the difficulty in selecting a single optimal forecast.Based on empirical evidences and theoretical considerations, we advocate the use of forecast combining when there is considerable instability in model selection by testing procedures. On the other hand, when there is little instability, testing procedures could work well or even better than forecast combining in terms of forecast accuracy.
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    Volatility Components and Long Memory-Effects Revisited (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 2, art3 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: The goal of this paper is to illuminate the capability of the component GARCH model of Ding and Granger (1996) and Engle and Lee (1999) to reproduce the long memory-type behavior of financial volatility. The potential of this model to capture the long memory dynamics observed in measures of financial volatility has been documented recently by Maheu (2005) and Deo et al. (2006), who base their conclusions on simulation techniques and a forecasting exercise, respectively. In this paper, a simple explanation for these observations is provided, which is based on the theoretical autocorrelation function (ACF) of the component GARCH model. We also elucidate why even higher-order GARCH models with Bollerslev's (1986) nonnegativity constraints enforced cannot mimic the long memory effects. The reasoning is supported with several empirical examples, for which we explicitly calculate the theoretical ACF implied by a couple of different fitted models, and find that their structure is just as predicted by our argument. To conveniently conduct these computations, a general simple method for computing the theoretical ACF of GARCH models is suggested, which is easier to use than the formulas developed so far, and particularly so for higher lag-orders. The ability of the component model to approximate long memory is also validated on the basis of a visual comparison between the empirical and the implied theoretical ACFs.
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    Movements in the Equity Premium: Evidence from a Time-Varying VAR (2007)
    Cambridge, Mass. : Berkeley Electronic Press (now: De Gruyter)
    Studies in nonlinear dynamics and econometrics 11.2007, 4, art1 
    Details
    ISSN: 1081-1826
    Source: Berkeley Electronic Press Academic Journals
    Topics: Mathematics , Economics
    Notes: Previous literature has recognized the importance of regime changes in the calculation of ex-ante equity premia. However, the methodologies used to estimate equity premia only allow for very restrictive forms of regime transitions. This paper addresses the issue by postulating an evolving model for the law of motion of dividend growth, consumption growth and dividend-price ratio. Model parameters are then used to compute conditional and unconditional U.S. equity premia. We substantially extend and confirm previous work on the declining equity premium, and uncover important macroeconomic factors driving the equity premium. We find that the equity premium has declined, particularly from 1950 to 1971 and from 1988 to 2000. Our results point to changing consumption volatility as an important priced factor. We find that volatility of consumption growth is a good indicator of economic uncertainty and, as such, its changes are reflected in expected returns, and are priced by the market. We also find that not accounting for parameter time variation induces large pricing errors, as too little variation in dividend yields is attributed to changes in expected dividend growth.
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    Got Organic Milk? Consumer Valuations of Milk Labels after the Implementation of the USDA Organic Seal (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art4 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: This paper investigates consumer reactions to changes in information provision regarding organic production. Quantitative analyses focus on the actual implementation of mandatory labeling guidelines under the National Organic Program. The unique nature of the fluid milk market in combination with these regulatory changes allows us to place a value on information sets under different labeling regimes. Hedonic price functions provide an initial reference point for analyses of individual responses. A random utility discrete choice model serves as the primary econometric specification and allows consideration of consumer preference heterogeneity along observable household demographics. Our results indicate that the USDA organic seal increases the probability of purchasing organic milk. An initial hedonic price function approach, as well as simulations within the discrete choice framework, suggests that consumers value the change in labeling regulations with regard to organic production. Our results further suggest that consumers substitute away from milk carrying the rBGH-free label. This may indicate that consumers pay less attention to these labels in the time period investigated compared to results found in studies that use earlier time periods.
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    Generic and Brand Advertising in Markets with Product Differentiation (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 1, art6 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: In this paper, we analyze how generic advertising affects brand advertising and firm profits in differentiated oligopoly markets. We show that in the Crespi (2007) model only the high quality firm will use brand advertising when differentiation is vertical. We also demonstrate that when differentiation is horizontal, the equilibrium is likely to be more symmetric in terms of firm profits, spending on brand advertising, and firm response to generic advertising. Finally, we point out that generic advertising will increase expenditures on brand advertising when firms play a supermodular game. The results confirm that there are many reasons why generic advertising may increase firm spending on brand advertising.
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    Fuel Ethanol Subsidies and Farm Price Support (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art4 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: Ethanol subsidies are well established in U.S. policy and have high priority in corn growers' political agenda. This paper develops a vertical market model of ethanol, byproducts, and corn which is used to analyze whether corn growers would prefer the government's subsidy dollar to be spent directly on corn subsidies (though deficiency payments) rather than on a subsidy on ethanol made from corn. Because the subsidy dollar has to be shared with ethanol manufacturers under the ethanol subsidy, it is to be expected, and the model confirms, that a dollar spent on a direct corn subsidy increases corn growers' producer surplus more than an a dollar spent on an ethanol subsidy under many plausible values of the relevant parameters. But there are equally plausible parameter values under which the ethanol subsidy is preferred by corn growers. The economics of this result turn mainly on the price discrimination an ethanol subsidy creates between ethanol and corn used for feed and export purposes, reducing the buyers' price of ethanol and byproducts but increasing the price of corn fed and exported. This enables producers of corn and ethanol to increase their joint producer surpluses above the total value of subsidies paid. The paper also analyzes the social cost (deadweight loss) of these subsidies, and finds the ethanol subsidy to generate deadweight losses likely to be in the billions of dollars annually.
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    European Union Policy on Bioenergy and the Role of Sustainability Criteria and Certification Systems (2007)
    Lincoln, Neb. : Berkeley Electronic Press (now: De Gruyter)
    Journal of agricultural & food industrial organization 5.2007, 2, art7 
    Details
    ISSN: 1542-0485
    Source: Berkeley Electronic Press Academic Journals
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Notes: The EU has set ambitious targets to raise the share of renewable energies, particularly biofuels. With an increasingly controversial public debate and more scientific evidence about the downsites of biofuels, recently the European Unions biofuel targets have been bound to the condition that they have to be produced sustainable. Therefore the European Commission is currently developing sustainability criteria for biofuels. Establishing certification schemes is a possible strategy to ensure that bioenergy crops are produced in a sustainable manner. However, many questions with regard to the design and implementation of sustainability criteria and certification schemes remain unsolved. This article discusses the role that bioenergy plays in the European policy context and the approach the EU is currently following in order to ensure the sustainability of biofuels. It addresses the limits of the chosen approach, concluding that certification schemes can not serve as the only safeguard for sustainable bioenergy, but need to be complemented by other tools and policies.
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    Coulomb potential in one dimension with minimal length: A path integral approach (2007)
    American Institute of Physics
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    Publication Date: 2007-11-01
    Print ISSN: 0022-2488
    Electronic ISSN: 1089-7658
    Topics: Mathematics , Physics
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    Closed-form summation of the Dowker and related sums (2007)
    American Institute of Physics
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    Publication Date: 2007-04-01
    Print ISSN: 0022-2488
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    Topics: Mathematics , Physics
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    Exact and quasiexact solvability of second order superintegrable quantum systems. II. Relation to separation of variables (2007)
    American Institute of Physics
    Details
    Publication Date: 2007-02-01
    Print ISSN: 0022-2488
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    Topics: Mathematics , Physics
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    New solution family of the Jacobi equations: Characterization, invariants, and global Darboux analysis (2007)
    American Institute of Physics
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    Publication Date: 2007-02-01
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    On the noncommutative and nonassociative geometry of octonionic space time, modified dispersion relations and grand unification (2007)
    American Institute of Physics
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    Publication Date: 2007-07-01
    Print ISSN: 0022-2488
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    Gauge transformations for the constrained CKP and BKP hierarchies (2007)
    American Institute of Physics
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    Publication Date: 2007-11-01
    Print ISSN: 0022-2488
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    A shift in the gap dynamics of Betula alleghaniensis in response to single-tree selection (2007)
    Canadian Science Publishing
    Details
    Publication Date: 2007-03-01
    Description: We investigated yellow birch ( Betula alleghaniensis Britt.) growth patterns and disturbance frequency before and after the advent of selection harvesting at the Ford Forestry Center in the Upper Peninsula of Michigan, USA, through the use of tree-ring analysis. Based on the boundary-line release detection procedure, 88% of the trees in our sample (n = 67) displayed evidence of at least one moderate or major release. Prior to active forest management, releases were infrequent, and trees that originated during that period had growth histories consistent with establishment after large-scale disturbances (i.e., large canopy gaps, 〉200 m2). Conversely, tree cohorts that recruited to the canopy more recently displayed a growth pattern suggestive of periodic small gap expansion. Given the declining representation of yellow birch in these forests, the latter strategy, although probably sufficient to prevent extirpation, is unlikely to ensure a sustainable and harvestable population of this and other midtolerants in managed uneven-aged forests. Our results highlight the importance of considering the cumulative influence of infrequent disturbances and chance events on the maintenance of tree species diversity.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Backhauling in forest transportation: models, methods, and practical usage (2007)
    Canadian Science Publishing
    Details
    Publication Date: 2007-12-01
    Description: In this paper, we consider a tactical transportation planning problem in forestry to decide the destination of logs. This problem is generally solved by finding the flow between a set of supply points and demand points. It can be formulated as a linear programming problem involving direct flows between supply and demand points. However, better solutions can be found by using additional flow variables representing flow in potential backhaul routes. However, the number of such variables is often very large. In this article, we provide the basis for backhaul flow planning in forestry. This includes defining the underlying operations research models for both the flow problem and the subproblem to find backhaul routes. The size of the problem in terms of the number of variables increases rapidly with the number of supplies and demands and we describe a column generation approach for its solution. We report on some case studies and industrial systems where the approach has been used.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Modeling corewood–outerwood transition in loblolly pine using wood specific gravity (2007)
    Canadian Science Publishing
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    Publication Date: 2007-06-01
    Description: A modified logistic function was used for modeling specific-gravity profiles obtained from X-ray densitometry analysis in 675 loblolly pine ( Pinus taeda L.) trees in four regeneration trials. Trees were 21 or 22 years old at the time of the study. The function was used for demarcating corewood, transitional, and outerwood zones. Site and silvicultural effects were incorporated into the model. Heteroscedasticity and within-group correlation were accounted for by specifying the variance and serial-correlation structure, respectively. The estimated transition zone was located between rings 5 and 15, and the outerwood demarcation point varied from rings 12 to 15. No effects of treatments on the demarcation points were observed; however, site preparation and fertilization affected the lower asymptotes of the curves in all sites. A geographical trend for the demarcation point was observed, with the northern site requiring more time to reach a plateau in specific gravity compared with the southern sites. The diameter of the juvenile core was increased as a result of the treatments. However, the amount of corewood was not statistically affected, ranging from 55% in the north to 75% in the south, except at one site where fertilization decreased the percentage of corewood.
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    Forest dynamics following spruce budworm outbreaks in the northern and southern mixedwoods of central Quebec (2007)
    Canadian Science Publishing
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    Publication Date: 2007-04-01
    Description: The effects of 20th century spruce budworm ( Choristoneura fumiferana (Clem.)) outbreaks on forest dynamics was examined in the southern and northern parts of the mixedwood forest zone in central Quebec, Canada. In each region, three study areas were placed in unmanaged stands that had not burned for more than 200 years. Disturbance impacts and forest succession were evaluated using aerial photographs and dendrochronology. Spruce budworm outbreaks occurred around 1910, 1950, and 1980 in both regions. The 1910 outbreak seemed to have limited impact in both regions, and the 1950 outbreak caused heavy mortality in conifer stands (mostly of balsam fir, Abies balsamea (L.) Mill.) in the southern region. The 1980 outbreak caused major mortality in the northern region, but had little impact in the southern region. Successive spruce budworm outbreaks led to a massive invasion by hardwood species in the last century in the southern region but not in the northern region. The reason for such contrasting dynamics between regions is unknown, but we hypothesize that differences in disturbance intensities, influenced by climate, played a major role. Results from this study emphasize that generalizations about the effect of spruce budworm outbreaks on forest dynamics cannot be derived from observations made during a single outbreak or at a single location.
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    Long-term calcium addition increases growth release, wound closure, and health of sugar maple (Acer saccharum) trees at the Hubbard Brook Experimental Forest (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: We surveyed and wounded forest-grown sugar maple ( Acer saccharum Marsh.) trees in a long-term, replicated Ca manipulation study at the Hubbard Brook Experimental Forest in New Hampshire, USA. Plots received applications of Ca (to boost Ca availability above depleted ambient levels) or Al (to compete with Ca uptake and further reduce Ca availability). We found significantly greater total foliar and membrane-associated Ca in foliage of trees in plots fertilized with Ca when compared with trees from Al-addition and control plots (P = 0.005). Coinciding with foliar Ca differences, trees exhibited a significant difference in crown vigor and in percent branch dieback among treatments (P 〈 0.05), with a trend towards improved canopy health as Ca levels increased. Annual basal area increment growth for the years following treatment initiation (1998–2004) was significantly greater in trees subjected to Ca addition compared with trees in control and Al treatments. Treatment-related improvements in growth were particularly evident after overstory release following a 1998 ice storm. The amount of wound closure was also greatest for trees in Ca-addition plots relative to Al-addition and control plots (P = 0.041). These findings support evidence that ambient Ca depletion is an important limiting factor regarding sugar maple health and highlight the influence of Ca on wound closure and growth following release from competition.
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    Changes in understory light regime in a beech–maple forest after a severe ice storm (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: We assessed canopy openness (%) in an old-growth beech–maple forest immediately before and in the 3 years following a severe ice storm. We estimated canopy openness using hemispherical photographs taken at a height of 0.6 m above the soil surface in 101 permanent plots. Mean canopy openness increased from a prestorm value of 7.7% to 16.6% in the summer immediately following the storm. However, the mean canopy openness returned to prestorm levels within 3 years. The changes in canopy openness immediately after the storm were significantly influenced by canopy openness prior to the storm and also by species composition; plots with lower canopy openness prior to the storm and plots that consisted of more shade-tolerant species had greater canopy damage. While canopy gaps are often considered to promote the establishment of shade-intolerant species in the deciduous forests of eastern North America, gaps created by ice storms at our study site may not persist long enough to promote the establishment of these species.
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    Interactive effects of condensed tannin and cellulose additions on soil respiration (2007)
    Canadian Science Publishing
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    Publication Date: 2007-10-01
    Description: Plant polyphenolics are receiving increased attention for their influences on belowground processes. Tannins are of particular interest because of their predominance in natural systems, their wide variation in both quality and quantity, and their protein-binding abilities. Current theory holds that simple phenolics increase microbial activity by acting as carbon substrates, while larger tannins decrease microbial activity by binding with organic nitrogen such as proteins. Here, we present results from a simple microcosm experiment that demonstrates that the influence of condensed tannins on soil respiration depends on the availability of additional carbon substrates. We purified tannins from trembling aspen ( Populus tremuloides Michx.) and crossed three levels of tannin additions with three levels of cellulose additions in laboratory microcosms. Soil respiration was measured over 36 days. In the absence of cellulose, high amounts of condensed tannins increased cumulative soil respiration. In the presence of abundant cellulose, condensed tannins decreased cumulative soil respiration. The positive and negative effects of purified tannins on soil respiration are time dependent, such that initial respiration is likely tannin induced, while later respiration is cellulose induced and tannin limited.
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    Growth of epiphytic old forest lichens across climatic and successional gradients (2007)
    Canadian Science Publishing
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    Publication Date: 2007-10-01
    Description: This paper aims to assess the influence of canopy cover on lichen growth in boreal forests along a regional forest gradient. Biomass and area gain, and some acclimation traits, were assessed in the old-forest lichens Lobaria pulmonaria (L.) Hoffm., Pseudocyphellaria crocata (L.) Vain., and Usnea longissima Ach. transplanted 110 days in three successional Norway spruce ( Picea abies (L.) Karst.) forest stands (clearcut, young, and old forest) repeated along a rainfall gradient (continental, suboceanic, and Atlantic zones) in Scandinavia. Lichen growth peaked in Atlantic rainforests with mean dry matter (DM) gain up to 36%–38%. The alectorioid lichen U. longissima showed the widest range of growth responses and no signs of chlorophyll degradation. Its highest DM gain consistently occurred in clearcuts, whereas the DM gain was close to zero in the shadiest young forest. The two foliose lichens L. pulmonaria and P. crocata exhibited maximal growth rates in old forests, but apparently growth was limited by low light even in old forests. Their DM gain was reduced in the most sun-exposed clearcuts due to chlorophyll degradation and was relatively high under closed young canopies, suggesting a better adaptation to shade. The lichen responses show that a high frequency and dominance of young and dense fast-growing forest stands at a landscape level are not compatible with large populations of these old-forest lichens and that a lack of lichens under an industrial forestry regime may not necessarily be determined by low dispersal efficiency only.
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    Optimization based planning tools for routing of forwarders at harvest areas (2007)
    Canadian Science Publishing
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    Publication Date: 2007-11-01
    Description: The forwarding of logs at harvest areas once the harvesting is done is planned manually by experienced operators. To improve their efficiency and simplify the planning we have developed and tested a decision support system at a major Swedish forest company. The system is based on a combination of a geographic information system (GIS), global positioning system (GPS), and optimization routines to solve the underlying vehicle routing problem. The routes for the forwarders are found by using a repeated matching algorithm. The solution time is short, and it is possible to find routes dynamically in a real-time environment. The geographic information required is found by using a GPS together with data obtained from the bucking software in the harvesters. To show the routes and location of the forwarder, we make use of a GIS that is connected to the GPS. We report on a study with savings in the distance travelled of 8% and numerical tests on the solution methodology. We also compare the proposed solution method with some well-known routing methods.
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    Overstory tree mortality resulting from reintroducing fire to long-unburned longleaf pine forests: the importance of duff moisture (2007)
    Canadian Science Publishing
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    Publication Date: 2007-08-01
    Description: In forests historically maintained by frequent fire, reintroducing fire after decades of exclusion often causes widespread overstory mortality. To better understand this phenomenon, we subjected 16 fire-excluded (ca. 40 years since fire) 10 ha longleaf pine ( Pinus palustris Mill.) stands to one of four replicated burning treatments based on volumetric duff moisture content (VDMC): wet (115% VDMC); moist (85% VDMC); dry (55% VDMC); and a no-burn control. During the first 2 years postfire, overstory pines in the dry burns suffered the greatest mortality (mean 20.5%); pine mortality in the wet and moist treatments did not differ from the control treatment. Duff reduction was greatest in the dry burns (mean 46.5%), with minimal reduction in the moist and wet burns (14.5% and 5%, respectively). Nested logistic regression using trees from all treatments revealed that the best predictors of individual pine mortality were duff consumption and crown scorch (P 〈 0.001; R2 = 0.34). Crown scorch was significant only in dry burns, whereas duff consumption was significant across all treatments. Duff consumption was related to moisture content in lower duff (Oa; R2 = 0.78, P 〈 0.001). Restoring fire to long-unburned forests will require development of burn prescriptions that include the effects of duff consumption, an often overlooked fire effect.
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    A computer approach to finding an optimal log landing location and analyzing influencing factors for ground-based timber harvesting (2007)
    Canadian Science Publishing
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    Publication Date: 2007-02-01
    Description: Locating a log landing is an important task in forest operations planning. Several methods have been developed to find an optimal landing location and compute a mean skidding distance, but they simplify harvest unit attributes and do not simultaneously consider multiple design factors influencing optimal landing locations. In this study, we introduce a computerized model developed to determine the optimal landing location for ground-based timber harvesting. Using raster-based GIS data, the model finds skid trails from stump to each of candidate landings and selects the best landing location that minimizes total skidding and spur road costs. The model is applied to several hypothetical harvest units with different terrain and harvest volume attributes to analyze the effects of design factors influencing optimal landing locations. Unit boundary shapes, volume distribution, the presence of obstacles, terrain conditions, and spur road construction are considered as influencing design factors.
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    Abundance, diversity, and resilience of nematode assemblages in forest soilsThis article is one of a selection of papers published in the Special Forum on Towards Sustainable Forestry — The Living Soil: Soil Biodiversity and Ecosystem Function. (2007)
    Canadian Science Publishing
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    Publication Date: 2007-02-01
    Description: Forest litter and soil may contain 〉10 × 106 individual nematodes·m–2 and, regionally, 〉400 species. Root-feeding nematodes may be pathogenic to young plants; microbial-feeding nematodes may increase turnover of the microbial pool; predacious and omnivorous nematodes represent higher trophic levels. The spatial distribution and abundance of nematode species in forests reflect soil type, soil fertility, climate, canopy and understorey plant species, litter depth, forest age, and management. Nematodes may be important in forest nurseries; they occur throughout the rooting depth of forest trees; hyphal-feeding species may influence mycorrhizae; and insect-vectored Bursaphelenchus species are a quarantine risk. Nematode populations interact with those of other soil animals (e.g., mites, tardigrades, enchytraeids, and protozoa). The diversity and abundance of the nematode assemblage make nematodes a useful indicator of soil condition and soil processes. Information available from forest systems suggests that, as long as physical disturbance is minimized and remaining trees or herb layer moderate the microclimate, logging and other forestry operations have only transitory effects on nematode populations. Extreme disturbance, such as bulldozing and slash-and-burn management, can significantly reduce nematode abundance and diversity. In contrast, management that enhances growth of understorey or herb layer can stimulate nematode populations. Each of these changes can be related to changes in food resource availability and environmental conditions, such as soil temperature and moisture. Although details of soil nematode contributions to nutrient processes in forest soils are sparse, that their populations are maintained through cycles of moderate management practices suggest that their beneficial contributions will also be maintained.
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    Structure and regeneration dynamics of three subtropical midmontane moist evergreen broad-leaved forests in southwestern China, with special reference to bamboo in the forest understories (2007)
    Canadian Science Publishing
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    Publication Date: 2007-12-01
    Description: Two midmontane moist evergreen broad-leaved forests on the Ailao Mountains, Yunnan, and one on Mount Emei, Sichuan, southwestern China were studied to characterize the forest structure and dynamics as manifested in size, age, canopy gaps, regeneration modes, and the survival of seedlings. The most dominant canopy trees were species of Lithocarpus and Castanopsis of Fagaceae along with species of Machilus of Lauraceae and of Schima of Theaceae. The vertical structures of the forests were multilayered. All the canopy species had multimodal-shaped size and age distributions. In each forest of the study sites, the mean size of a canopy gap, caused mainly by the death of canopy trees, was smaller than 65 m2. No surviving seedlings of Fagaceae species were found in understories having bamboo with a coverage greater than 25% in any quadrat of the three forests. The poor seedling bank in the study forests is apparently due to the presence of bamboo in the understory. The tree regeneration may be synchronously related to the bamboo flowering event (interval approximately 55–60 years).
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    The reduction of organic-layer depth by wildfire in the North American boreal forest and its effect on tree recruitment by seed (2007)
    Canadian Science Publishing
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    Publication Date: 2007-06-01
    Description: We compared prefire and postfire organic-layer depths in boreal forest types (14 fires) across Canada, and examined tree recruitment as a function of depth. There was extensive within-stand variation in depth, much of it due to clustering of thinner organic layers around boles. There were no significant differences in postfire organic-layer depth among sites with different prefire forest species composition, but sites in the eastern boreal region had thicker postfire organic layers than those in the western boreal region. Mean organic-layer depth was much greater in intact stands than after fires; overall, fire reduced organic-layer depth by 60%, largely because of increases in the area of thin (
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    Impacts of postfire salvage logging on understory plant communities of the boreal mixedwood forest 2 and 34 years after disturbance (2007)
    Canadian Science Publishing
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    Publication Date: 2007-12-01
    Description: We compared understory vegetation composition and richness in aspen-dominated boreal mixedwood forest stands in Alberta, Canada, that had been burned by wildfire with those that burned and were subsequently salvage logged. Stands were examined at early and midsuccessional (2 and 34 years after disturbance(s), respectively) developmental stages. In comparison with wildfire stands, understory communities of early successional salvage-logged stands were characterized by greater species richness, weedy species presence, higher shrub abundance, and lower abundances of fire-specialist seed bank species. In constrained ordination, the understory community of early successional wildfire stands was related to greater canopy cover, sapling density, and moss depth, whereas that of salvage-logged stands was related to greater light, volume of downed deadwood, and litter and organic matter. Longer term effects of salvage logging on the understory community were minimal and, instead, reflected the influence of forest canopy redevelopment. In midsuccessional stands, understory composition was related to conifer density, litter cover, soil moisture, organic layer depth, tall shrub density, and bryophyte-covered microsite cover. Postfire salvage logging can have substantial short-term effects on the postfire understory plant community; in the longer term, effects will depend to a large extent on the influence of harvesting and subsequent management on canopy redevelopment.
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    Linking forests and economic well-being: a four-quadrant approach (2007)
    Canadian Science Publishing
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    Publication Date: 2007-10-01
    Description: This paper has three main objectives: (i) to investigate whether the four-quadrant approach introduced by     J.S. Maini reveals a useful typology for grouping countries by gross domestic product (GDP) and forest cover per capita, (ii) to determine if the framework can enhance our understanding of the relationship between forest cover and GDP per capita, and (iii) to investigate why countries in the four-quadrant world occupy different quadrants and to determine the principal factors affecting country movement across and within the individual quadrants. The examination reveals that countries can be classified into four broad categories and that GDP and forest cover per capita have a low but consistent level of negative association. After regressing economic, institutional, social capital, and other variables on a country’s occupancy and movement in the four-quadrant world, the results suggest that countries in each quadrant share different characteristics and that factors underlying country movement vary according to the quadrant being observed. Overall, countries with less corruption and higher education are likely to experience increases in both forest cover and GDP per capita, while countries exporting a significant proportion of forest products have a reduced probability of increasing both variables.
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    Partial cutting as an analogue to stem exclusion and dieback in trembling aspen (Populus tremuloides) dominated boreal mixedwoods: implications for deadwood dynamicsThis article is one of a selection of papers published in the Special Forum IUFRO 1.05 Uneven-Aged Silvicultural Research Group Conference on Natural Disturbance-Based Silviculture: Managing for Complexity. (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: In the winter of 1998–1999, two partial harvesting treatments that removed 33% (1/3) and 61% (2/3) of stand basal area were applied to even-aged trembling aspen ( Populus tremuloides Michx.) stands and compared with unharvested control stands. Stands in the 1/3 treatment were low thinned, while stands in the 2/3 removal were crown thinned. Coarse woody debris dynamics were assessed during the following 6 years by means of permanent sampling plots and downed wood inventories. Between 1999 and 2004, tree mortality was, respectively, 18%, 17%, and 32% in control stands and 1/3 and 2/3 harvesting treatments. Although total snag density was similar between controls and partial cutting treatments, total snag basal area was significantly higher in controls in 2004. Between 1999 and 2004, net change in aspen snag density was positive for controls and negative for both partial cutting treatments. Partial cutting also exacerbated mortality of small-diameter white birch ( Betula papyrifera Marsh.). Downed wood volume increased by 35 m3·ha–1 in controls and by 25 m3·ha–1 in the 2/3 harvesting treatment, while it decreased by 7 m3·ha–1 in the 1/3 harvesting treatment. Coarse woody debris goals can be established in silviculture prescriptions; type, timing, and intensity of partial cutting are crucial to the outcome.
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    Plastic and adaptive response to weather events: a pilot study in a maritime pine tree ring (2007)
    Canadian Science Publishing
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    Publication Date: 2007-11-01
    Description: This work proposes a novel approach to describing intraring wood density characteristics as functions of annual weather events. This approach was tested using three different maritime pine clonal experiments, in which X-ray microdensitometry has revealed conspicuous within-ring patterns affecting most of the trees in 1996. This pattern has been interpreted as the variation of tree response to weather-controlled changes of water balance during the 1996 growing season. The level of tree response was estimated using an original norm of reaction obtained from the microdensity profiles. A 1996 site drought index profile was synchronized with the 1996 microdensity profile by pairing conspicuous points of abrupt change in both profiles (breakpoints). Regression of density breakpoints on drought breakpoints describes the norm of reaction of radial increment to water availability, and the plasticity of radial increment to changes in soil moisture is described by the slope of the regression. The slope showed moderate levels of genetic control that depended on the site and could potentially be used as criteria for the evaluation of tree adaptation to weather.
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    Fuels on disturbed and undisturbed sites in the southern Appalachian Mountains, USA (2007)
    Canadian Science Publishing
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    Publication Date: 2007-06-01
    Description: Fuel distribution in the southern Appalachian Mountain region was measured in over 1000 study plots that were stratified by topographic position (aspect and slope position) and disturbance history. Few fuel differences occurred among topographic positions for undisturbed plots, indicating that fuel accumulation is no greater on highly productive sites than on less productive sites. Litter was slightly higher on undisturbed upper slopes (4.2 t/ha) than on lower slopes (3.7 t/ha) but woody fuels showed no significant differences. Rhododendron ( Rhododendron spp.) and mountain laurel ( Kalmia latifolia L.) were less common than expected, occurring on 25% and 42% of sampled plots, respectively. Disturbance history and type played a greater role in determining fuel loads than did topographic position. Disturbances had occurred on 30% of sample plots within the past 10 years and were most common on exposed slopes. Litter was significantly lower in burned plots (3.5 t/ha vs. 4.0 t/ha in undisturbed plots). One-hour fuels (1.0 t/ha) were significantly higher on beetle-killed plots than on undisturbed plots (0.7 t/ha) while larger woody fuels tended to be greater in plots subjected to beetle attack, fire, and wind.
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    Modeling long-term tree growth curves in response to warming climate: test cases from a subtropical mountain forest and a tropical rainforest in Mexico (2007)
    Canadian Science Publishing
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    Publication Date: 2007-05-01
    Description: The Earth’s temperature has increased 0.6 °C over the last 100 years, and further climate change is predicted to potentially raise it by 3.5 °C over the next century. More than half of the global annual net primary production of biomass is estimated to occur in the tropics, especially tropical evergreen forest. In temperate forests, increasing temperature may extend the non-frost growing season, and thus increase the CO2 sequestration rate, but some authors have also suggested a negative impact of warming in tropical forests from decreased photosynthetic activity. Using the PL model (Ricker and del Río 2004), we forecast growth of two Mexican tree species after climate warming. The model predicts the high-mountain species Pinus hartwegii Lindl. to decrease its expected relative growth throughout its lifetime by 10.6% as a consequence of a 0.6 °C temperature increase; in contrast, the tropical rainforest species Diospyros digyna Jacq. is predicted to increase its expected relative growth throughout its lifetime by 25.4%. The key factor appears to be the expected relationship between temperature and precipitation, rather than temperature alone. While one cannot expect a universal response across sites, some standing tropical rainforests such as those at Los Tuxtlas in Mexico may constitute a carbon sink in a changing climate.
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    Modelling of wood density and fibre dimensions in mature Norway spruce (2007)
    Canadian Science Publishing
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    Publication Date: 2007-08-01
    Description: Basic density (BD), fibre length (FL), fibre width (FW), and fibre wall thickness (FWT) were investigated in 46 Norway spruce ( Picea abies (L.) Karst.) trees from five different stands in eastern Norway. From each tree, wood samples were collected in different radial and longitudinal positions. Random coefficient mixed models were used to investigate variation within as well as among trees, both within and among stands. The R2 with random effects included, describing the best possible (individual) fit of the observed data to the models, were 0.90 for BD, 0.99 for FL, 0.88 for FW, and 0.91 for FWT. With only fixed effects, the best model explained 56% of the total variation for BD, 94.5% for FL, 61% for FW, and 63% for FWT. A common model for all trees, without tree and site information, predicted FL well but BD, FW, and FWT poorly. Adding site index, breast height diameter, and tree height to the models reduced the residual variance considerably for FW, FWT, and particularly BD, whereas only a minor improvement was gained for FL. The latter type of models might be easier to use for industrial purposes. Although information about ring width gave further improvements, ring width measurements are time consuming and difficult to perform in the forest and in industrial environments.
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    Yield decline in Chinese-fir plantations: a simulation investigation with implications for model complexity (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: A variety of competing hypotheses have been described to explain yield decline in Chinese-fir ( Cunninghamia lanceolata (Lamb.) Hook.) plantations. The difficulty in implementing field experiments suggests ecosystem modeling as a viable option for examining alternative hypotheses. We present a conceptual model of Chinese-fir yield decline and explore its merits using the ecosystem-based FORECAST model. Model results suggest that yield decline is caused primarily by a decline in soil fertility, largely as a consequence of slash burning in conjunction with short rotations. However, as tree leaf area declines, there is a transition (over subsequent rotations) from seed rain based competition to bud bank based competition, increasing the competitive impact of minor vegetation on tree growth. Short rotations increase understory survival between rotations and may cause a gradual shift from tree dominance to shrub/herb dominance over subsequent rotations. These effects are most evident on nutrient-poor sites, but understory competition poses a significant yield decline risk on good sites as well. We conclude that sustainable production in Chinese-fir plantations requires the avoidance of activities that compromise soil fertility and increase understory competition. The risk and severity of yield decline would be reduced by increasing rotation lengths and avoiding plantations on infertile sites.
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    Dead wood dynamics in declining balsam fir and spruce stands in New Brunswick, Canada (2007)
    Canadian Science Publishing
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    Publication Date: 2007-04-01
    Description: Forest management prescriptions increasingly incorporate snag and downed dead wood (DDW) guidelines. This study utilizes permanent inventory plots to determine dead wood dynamics in 33 balsam fir ( Abies balsamea (L.) Mill.) – spruce ( Picea spp.) (BFSP) and 17 spruce – balsam fir (SPBF) stands in New Brunswick, Canada. Stands were declining, unmanaged, and had a history of recurrent spruce budworm ( Choristoneura fumiferana (Clem.)) outbreaks and aerial insecticide spraying. Fixed-area sampling matched remnants of 1165 dead trees and 864 corresponding pieces of DDW to plot trees that died over the last 15–18 years with known year and cause of death. Declining BFSP stands had the highest accumulation of dead wood (196 m3/ha) compared with SPBF and nondeclining BFSP (122 m3/ha and 77 m3/ha, respectively). Dead wood dynamics were influenced by cause of death, as a function of differences in tree height at death affecting snag decay, fragmentation, and fall. One-half of all dead trees never made a significant contribution to the snag population (25% uprooted and 25% stem breakage), and attrition resulted in only 50% of snags standing with a mean height of 6 m 15–20 years after death. This study will be of direct value to those managing or modeling dead wood dynamics in similar forests.
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    Relationships between climate and double rings in Quercus ilex from northeast Spain (2007)
    Canadian Science Publishing
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    Publication Date: 2007-10-01
    Description: The influence of climatic factors on tree-ring width and the formation of double rings was studied in Quercus ilex L. growing in a coppice stand left unmanaged for 22 years. Ten trees were felled and discs were taken every 30 cm from bole and dominant branches. Dendrometer bands were installed on 10 nearby trees and the data recorded were used to confirm the accuracy of our tree-ring identification. They were also used to relate the seasonal radial growth pattern to double-ring formation. Double rings were frequent and occurred consistently along the stem. Two types of double rings could be recognized according to their width: type I, with the extra growth band accounting for approximately 50% of the tree ring; and type II, with a narrow extra growth band. Type I double rings were formed when approximately 1/2 of the growing-season precipitation occurred during the second growth period of the season and after the summer drought. Type II double rings occurred when approximately 1/3 of the precipitation in the growing season occurred after the summer drought. The formation of double rings was triggered by rainfall in summer and the extra growth-band width was related to summer and autumn environmental conditions. Double rings in Q. ilex can potentially be used in dendroclimatological studies, as they are formed in response to climatic conditions within the growing season.
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    Comparison of fire scars, fire atlases, and satellite data in the northwestern United States (2007)
    Canadian Science Publishing
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    Publication Date: 2007-10-01
    Description: We evaluated agreement in the location and occurrence of 20th century fires recorded in digital fire atlases with those inferred from fire scars that we collected systematically at one site in Idaho and from existing fire-scar reconstructions at four sites in Washington. Fire perimeters were similar for two of three 20th century fires in Idaho (1924 and 1986). Overall spatial agreement was best in 1924 (producer’s accuracy = 94% and 68% and user’s accuracy = 90% and 70% for the 1924 and 1986 fires, respectively). In 1924, fire extent from the atlas was greater than for fire scars, but the reverse was true for 1986. In 1986, fire extent interpreted from the delta normalized burn ratio derived from pre- and post-fire satellite imagery was similar to that inferred from the fire-scar record (producer’s accuracy = 92%, user’s accuracy = 88%). In contrast, agreement between fire-scar and fire-atlas records was poor at the Washington sites. Fire atlases are the most readily available source of information on the extent of late 20th century fires and the only source for the early 20th century. While fire atlases capture broad patterns useful at the regional scale, they should be field validated and used with caution at the local scale.
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  • 92
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    The introduced bark beetles Hylurgus ligniperda and Hylastes ater (Coleoptera: Scolytidae) in Chile: seasonal flight and effect of Pinus radiata log placement on colonization (2007)
    Canadian Science Publishing
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    Publication Date: 2007-01-01
    Description: The seasonal flight of Hylurgus ligniperda (Fabr.) and Hylastes ater (Paykull) and the effect of log placement in Pinus radiata D. Don plantations on colonization by these species in Chile are described. Seasonal flight activity was monitored with α-pinene and ethanol-baited traps at three sites and colonization synchrony with trap logs. In two experiments with individual logs and log decks, data were recorded on adults found under the logs, attacks on the bark surface, and adults beneath the bark of logs in three storage treatments: individual logs and log decks (1) touching the soil; (2) elevated above the soil; and (3) touching other logs (individual logs) or logs separated with spacers (log decks). Each treatment was replicated in a plantation and a clearcut. At San José (region IX) and Peña Blanca (region VIII), H. ligniperda flew primarily in spring and H. ater flew in spring and fall. At Brasil (region VIII), H. ligniperda and H. ater flew primarily in summer through fall. The flight of H. ligniperda was more synchronized with colonization of logs than was that of H. ater. The mean number of attacks was significantly higher on individual logs and log decks stored on the soil than on those elevated above the soil, and significantly higher in the clearcut than in the plantation. Mean numbers of adults beneath the bark did not vary significantly among individual-log treatments, but were significantly lower in the log decks separated by spacers. Logging during nondispersal periods (June–August in regions VIII–X) and storing log decks above the soil could reduce beetle colonization of newly cut logs. With this information, management of recently cut logs (harvesting, transport, and storage operations) could be scheduled and executed so as to reduce the risk of these species being introduced into log-importing countries.
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    Effect of gap harvesting on epiphytes and bark-dwelling arthropods in the Acadian forest of central Maine (2007)
    Canadian Science Publishing
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    Publication Date: 2007-11-01
    Description: Using a long-term silvicultural experiment, we (i) investigated how epiphyte and arthropod communities were affected by height on the stem, bark texture, and stem diameter of red maple ( Acer rubrum L.) trees, (ii) examined how harvest gaps influenced epiphyte and arthropod communities on red maple boles, and (iii) explored whether these effects influenced the relationship between the epiphyte and arthropod communities. Arthropod and epiphyte assemblages dwelling on the bark of red maple trees located in undisturbed forest and harvest gaps varied with height. Bryophytes, Cladonia spp., and cyanolichens were most abundant near the base of the tree, while noncyano, foliose lichens and fruticose lichens were most abundant 4–6 m above the ground. Acari, Araneae, and Collembola were most abundant near the base of the tree, while Diptera were most abundant above 2 m. A previously undocumented assemblage of dipterans (flies), primarily in the suborder Nematocera, was found. Gap harvesting reduced the abundance of bryophytes, Collembola (springtails), Araneae (spiders), and total arthropods on the bark of red maple. Canonical correlation analysis revealed a positive association between bryophytes, Collembola, and Araneae. A strong correlation between Collembola and Araneae suggested a possible trophic interaction that may be affected by gap harvesting through a reduction in bryophyte abundance.
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    Black spruce (Picea mariana) foliage hosts numerous and potentially endemic fungal endophytes (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: Fungal foliar endophytes (hereinafter endophytes) were isolated on malt agar from black spruce ( Picea mariana (Mill.) BSP) needles from the Quebec boreal forest during 2 successive years to study their distribution along a latitudinal transect. Twenty sites were sampled in 2002, 8 of which were sampled again in 2003, in an area located between 47°N and 54°N in the province of Quebec. The endophytes were named whenever possible, using homologies of ITS rDNA sequences from GenBank. In 2002, 232 morphotypes were classified in 40 operational taxonomic units (OTUs), and in 2003, 93 morphotypes were classified in 16 OTUs, for a total of 44 OTUs. Isolation frequencies of the most common endophyte species were 28% for Lophodermium piceae (Fuchel) Höhn., 17% for Darkera parca Whitney, Reid & Piroz, and 9% for Dwayaangam colodena Sokolski & Bérubé. Of the 44 OTUs identified, 18 were unique to P. mariana and found on one site only, possibly constituting rare endemic species. There was some evidence that needles colonized with rare endophyte species were more abundant in the western and southern regions than in the northern region. This supports our hypothesis that as the diversity of tree species surrounding the P. mariana decrease from the southern region to the northern region, the diversity of endophytes also decreases.
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    Gas exchange and resource utilization in two alpine oaks at different altitudes in the Hengduan Mountains (2007)
    Canadian Science Publishing
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    Publication Date: 2007-07-01
    Description: The evergreen sclerophyllous broadleaf forests composed of alpine oaks in the Hengduan Mountains of southwest China are mainly distributed at altitudes of 1700–4800 m. Gas exchange and related leaf traits of Quercus guyavifolia H. Lév. and Quercus pannosa Hand.-Mazz. were measured at eight sites along an altitudinal gradient to understand their physiological adaptabilities. Both Q. guyavifolia and Q. pannosa showed a significant midday depression in the photosynthesis rate (PN) due to a high vapor pressure deficit and high temperature around noon. The optimum temperature for photosynthesis for the two oak species ranged from 17 to 23 °C depending on altitude. When the temperature exceeded 25 °C, PN decreased sharply. However, PN was not depressed by high irradiance. As altitude increased, the leaf dry mass per unit area of the two oaks increased but the chlorophyll content decreased, while the maximum values of daily mean photosynthesis rate (Pd), maximum photosynthesis rate (Pmax), Pd/Pmax, water-use efficiency, and photosynthetic nitrogen use efficiency occurred at altitudes of 3240–3610 m. Although the photosynthetic capacities of the two oaks were higher in August than in May, altitudinal trends did not change with season. The altitudinal range from 3240 to 3610 m would be optimal for the growth and development of these two alpine oaks in the Hengduan Mountains.
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    Species-specific response to climate reconstruction in upper-elevation mixed-conifer forests of the western Sierra Nevada, California (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: Dendrochronology climate reconstruction studies often sample dominant, open-grown trees to reduce competition effects and isolate annual climate influences on radial increment growth. However, there has been no examination of how species respond as stand densities increase or which species in mixed-conifer forests provide a better record of past climate. We sampled 579 trees representing five upper montane mixed-conifer species at the Teakettle Experimental Forest in California’s southern Sierra Nevada to determine species-specific responses to annual climatic fluctuations. Using the Kalman filter, we examined the affect of local stand density on growth response and whether the growth–climate relationship improved with a time lag. The Kalman filter iteratively calculates error for predicted versus actual radial growth and accounts for this variation in the corrector equation. Under current high-density conditions, shade-tolerant white fir ( Abies concolor (Gord. & Glend.) Lindl.) provided the best model for climate reconstruction. Shade-intolerant Jeffrey pine ( Pinus jeffreyi Grev. & Balf.) had a lagged response to annual climatic fluctuations, possibly because its roots may tap water reserves in granitic bedrock fissures. Open-grown trees provided more accurate records of climate. Changes in forest density in this forest may have resulted in changes in species-specific response to annual climatic fluctuations.
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    Impacts of elevated ozone and nitrogen on growth and photosynthesis of European aspen (Populus tremula) and hybrid aspen (P. tremula × Populus tremuloides) clones (2007)
    Canadian Science Publishing
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    Publication Date: 2007-11-01
    Description: Impacts of elevated tropospheric ozone and soil nitrogen amendment on two native European aspen ( Populus tremula L.) and eight hybrid aspen (P. tremula L. × Populus tremuloides Michx.) clones were studied in a free-air ozone exposure system. Potted saplings were exposed to ambient (ca. 20 ppb) or 1.5× ambient ozone and two levels of soil nitrogen (39 and 78 kg N·ha–1·year–1 in the first year, 60 and 140 kg N·ha–1·year–1 in the second year for low-nitrogen and high-nitrogen treatments, respectively) over two growing seasons. The plants were measured for photosynthesis, chlorophyll fluorescence, and biomass accumulation. Ozone decreased leaf-level net photosynthesis (Asat) in particular early in the growing season and maximum quantum yield of photosystem II (Fv/Fm) at the end of the growing season. Nitrogen amendment increased the growth of all plant parts and mitigated the adverse ozone effects. There were significant differences in ozone responses among the clones, and we were able to cluster the clones into sensitivity groups based on their growth responses. The most ozone-tolerant genotypes were hybrid aspen clones, indicating that populations that have already experienced selection for ozone-tolerant genotypes should be used to cross-breed with ozone-sensitive populations to achieve tolerance of a climate with increasing tropospheric ozone concentrations.
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    The regeneration decision: a sequential two-option approach (2007)
    Canadian Science Publishing
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    Publication Date: 2007-02-01
    Description: Real option theory has for some decades been used in forest economics to analyse problems that involve irreversible and stochastic decisions. One of these problems is when to harvest a stand and with what species to regenerate. This problem is analysed here, assuming that the value development of both the present and the next stand is stochastic and that the regeneration species must be chosen. The latter decision is assumed asymmetric, as natural regeneration can be exchanged for a planted regeneration but not vice versa. Consequently, the decision can be postponed for some time if natural regeneration is foreseen, making a species change possible if favoured by the value development or if regeneration of the present species proves unsuccessful. This is an extension of the traditional two-option problem, by involving several stochastic elements that are nested in another option problem: when to harvest a stand. Thus the decision on when to harvest a stand depends on its present value as well as on the value of the future stand, both values evolving stochastically. The problem is formulated as a sequential two-option problem and solved numerically.
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    Natural canopy gap disturbances and their role in maintaining mixed-species forests of central Quebec, CanadaThis article is one of a selection of papers published in the Special Forum IUFRO 1.05 Uneven-Aged Silvicultural Research Group Conference on Natural Disturbance-Based Silviculture: Managing for Complexity. (2007)
    Canadian Science Publishing
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    Publication Date: 2007-09-01
    Description: Until recently, natural dynamics of mixedwood stands have been largely ignored, resulting in the transformation of many North American mixedwoods into conifer- or hardwood-dominated stand types. The goal of this study was to examine canopy gap dynamics in balsam fir ( Abies balsamea (L.) Mill.) – yellow birch ( Betula alleghaniensis Britt.) mixedwoods to better understand possible mechanisms for species coexistence. Gap proportion in 12 study stands varied between 9% and 30% of the total stand area, while gap size varied from 20 to 2100 m2. Balsam fir mortality was the primary cause of gap formation. Balsam fir and mountain maple ( Acer spicatum Lamb.) dominated the tree and shrub regeneration layers, respectively. Shrub competition slows the natural filling of gaps by tree species. Our results indicate that yellow birch is most abundant in gaps over 800 m2 and balsam fir in those under 200 m2. Transition models showed that the greater longevity of yellow birch than balsam fir ensured its maintenance as a dominant. Dominant species coexistence thus results from divergent use of available resources through time and space. Forest management should maintain variability in harvest timing and size because the use of one gap size or a single rotation age will lead to an imbalance in species proportion relative to natural stands.
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    Frost hollows of the boreal forest as extreme environments for black spruce tree growth (2007)
    Canadian Science Publishing
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    Publication Date: 2007-02-01
    Description: An extensive survey of spruce growth forms was conducted in frost hollows of the Parc national des Grands-Jardins located in the highlands of the Charlevoix region (Quebec). Frost hollows studied were situated within lichen woodlands, which are a favourable environment for the formation of cold air masses. The mean number of frosts recorded 1 m aboveground during the growing seasons of 1997–2002 indicates that there is no frost-free period in frost hollows. Based on the records of minimum temperature in two frost hollows, the critical threshold for frost-ring formation is a nocturnal temperature below 0 °C for 6.4 h with a climax at around –5.7 °C, i.e., at a cooling rate of 1.78 °C/h under the freezing point for at least 3.2 h. Frequent and severe nocturnal frosts slow down the colonization of black spruce in frost hollows, and are at the origin of the inverted tree line that surrounds frost hollows. Mean stem height of black spruce in frost hollows is 1.97 m ± 2.15. A comparative analysis of aerial photographs between 1950 and 1996 showed a 34% reduction in frost hollow area due to the progressive colonization of black spruce. Massive tree establishment occurred in frost hollows between 1970 and 1980 because of the reduced frequency of freezing temperatures during the growing season.
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