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  • 1
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: The impacts of climate change on Mediterranean-type ecosystems may result from complex interactions between direct effects on water stress and subsequent modifications in flammability and fire regime leading to changes in standing biomass and plant species composition. We analysed these interrelations through a simulation approach combining scenarios of climate change developed from GCM results and a multispecies functional model for vegetation dynamics, SIERRA. A fire risk procedure based on weekly estimates of vegetation water stress has been implemented. Using climate data from 1960 to 1997, simulations of a typical maquis woodland community have been performed as baseline and compared with two climate scenarios: a change in the rainfall regime alone, and changes in both rainfall and air temperature. Climate changes are defined by an increase in temperature, particularly in summer, and a change in the rainfall pattern leading to a decrease in low rainfall events, and an increase in intense rainfall events. The results illustrate the lack of drastic changes in the succession process, but highlight modifications in the water budget and in the length of the drought periods. Water stress lower than expected regarding statistics on the current climate is simulated, emphasizing a long-term new equilibrium of vegetation to summer drought but with a higher sensibility to rare events. Regarding fire frequency, climate changes tend to decrease the time interval between two successive fires from 20 to 16 years for the maquis shrubland and from 72 to 62 years in the forested stages. This increase in fire frequency leads to shrub-dominated landscapes, which accentuates the yield of water by additional deep drainage and runoff.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Drought control over conductance and assimilation was assessed using eddy flux and meteorological data monitored during four summer periods from 1998 to 2001 above a closed canopy of the Mediterranean evergreen oak tree Quercus ilex. Additional discrete measurements of soil water content and predawn leaf water potential were used to characterize the severity of the drought.Canopy conductance was estimated through the big-leaf approach of Penman–Monteith by inverting latent heat fluxes. The gross primary production (GPP) was estimated by adding ecosystem respiration to net ecosystem exchange. Ecosystem respiration was deduced from night flux when friction velocity (u*) was greater than 0.35 m s−1. Empirical equations were identified that related maximal canopy conductance and daily ecosystem GPP to relative soil water content (RWC), the ratio of current soil water content to the field capacity, and to the predawn leaf water potential. Both variables showed a strong decline with soil RWC for values lower than 0.7. The sharpest decline was observed for GPP. The curves reached zero for RWC=0.41 and 0.45 for conductance and GPP, respectively. When the predawn leaf water potential was used as a surrogate for soil water potential, both variables showed a hyperbolic decline with decreasing water potential.These results were compared with already published literature values obtained at leaf level from the same tree species. Scaling up from the leaf to ecosystem highlighted the limitation of two big-leaf representations: Penman–Monteith and Sellers' Π factor. Neither held completely for comparing leaf and canopy fluxes. Tower measurements integrate fluxes from foliage elements clumped at several levels of organization: branch, tree, and ecosystem. The Q. ilex canopy exhibited non-random distribution of foliage, emphasizing the need to take into account a clumping index, the factor necessary to apply the Lambert–Beer law to natural forests.Our results showed that drought is an important determinant in water losses and CO2 fluxes in water-limited ecosystems. In spite of the limitations inherent to the big-leaf representation of the canopy, the equations are useful for predicting the influence of environmental factors in Mediterranean woodlands and for interpreting ecosystem exchange measurements.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 1432-1939
    Schlagwort(e): Key words Pine needles ; Litter ; Nutrient ; Prescribed burning ; Global versus local calibrations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The aim of this study was to produce calibration equations between near-infrared reflectance (NIR) spectra and the concentrations of carbon, nitrogen, and phosphorus in heterogeneous material: from living needles to litter in Pinus halepensis stands subjected to prescribed burnings. The aim was to determine whether calibrations should be conducted within each stage in the transformation of needles (local calibrations), giving relationships that were accurate but valid only for each particular stage, or whether it was possible to integrate the various forms of variation in needles (global calibrations) while retaining an acceptable accuracy. A principal component analysis calculated from the sample spectral data was used to distinguish three different sets, each sharing spectral characteristics and corresponding to three categories of needle: needles collected on the pines (N), falling needles (F), and litter (L), and each containing samples collected from the burnt sites and a control site. Samples representative of all the forms of variation in spectral properties were selected from within each category and their carbon, nitrogen, and phosphorus concentrations were measured using standard wet chemistry methods; these constituted the calibration sets n, f, and l. Calibrations were produced between the nutrient concentrations and the NIR spectra of the calibration sets n, f, and l and the grouped sets (n+f, f+l, n+f+l). The results of local calibrations made from each individual category showed that the carbon, nitrogen, and phosphorus concentrations were accurately predictable by NIR spectra. The global calibrations made by lumping together several categories were valid for a wider range of concentrations and for spectrally heterogeneous materials and in most cases were just as accurate as the local calibrations produced from each individual category.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1572-9680
    Schlagwort(e): Dehesa ; oak trees (Quercus spp.) ; mediterranean region ; agrosilvopastoral system ; Sierra Morena ; effect of trees on soils
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract A multidisciplinary team undertook a six-year investigation on the agro-ecological and socio-economic aspects of the dehesa system in the Sierra Norte area, a part of the Sierra Morena of the Sevilla Province, Western Andalusia, Spain. This paper summarizes its findings on the various agro-ecological features of the system and evaluates the system's functional aspects vis-a-vis the trends and developments in land use in the region over the past few centuries. The synergistic effects of tree cover on understorey grassland vegetation is discussed in terms of soil fertility build-up and favourable micro-climatic and hydrological features, and the potential use of this information in future research and development programmes to improve the dehesa system in the Mediterranean region is outlined.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 1572-9680
    Schlagwort(e): Dehesa ; oak trees (Quercus spp.) ; mediterranean region ; agrosilvopastoral system ; Sierra Morena ; effect of trees on soils
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract A multidisciplinary team undertook a six-year investigation on the agro-ecological and socio-economic aspects of the dehesa system in the Sierra Norte area, a part of the Sierra Morena of the Sevilla Province, Western Andalusia, Spain. This paper summarizes its findings on the various agro-ecological features of the system and evaluates the system's functional aspects vis-a-vis the trends and developments in land use in the region over the past few centuries. The synergistic effects of tree cover on understorey grassland vegetation is discussed in terms of soil fertility build-up and favourable micro-climatic and hydrological features, and the potential use of this information in future research and development programmes to improve the dehesa system in the Mediterranean region is outlined.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2008-12-01
    Beschreibung: The intrinsic variability of volatile organic compound emissions and photosynthetic parameters in response to two drying cycles was investigated on Quercus suber L. saplings originating from three Tunisian populations native to contrasting climates. Emissions mainly included monoterpenes plus traces of sesquiterpenes and methylsalicylate that steadily decreased during the experiment unrelated to treatments. Instead, monoterpene emissions increased by 30% during a first moderate drought and remained enhanced after rewatering, while CO2–H2O gas exchange was reduced by 30%. A second severe drought decreased monoterpene emissions to about two third of controls, strongly inhibited gas exchange and photochemical efficiency, and caused a partial loss of chlorophyll. Rewatering led to only partial recovery of emissions and photosynthetic parameters of stressed plants whose biomasses and leaf nitrogen and chlorophyll contents were lower than in control plants. There was no clear difference among populations in volatile organic compound emissions or photosynthetic parameters. However, the population inhabiting the most arid region had intrinsically smaller leaves with lower specific leaf masses and higher drought-related leaf losses than populations native to less arid climates. These results indicate an adaptive shift from stress-tolerating towards stress-avoiding ecotypes under arid climates involving mainly morphological adaptations without apparent differentiation in volatile organic compound production, probably because of its high phenological plasticity.
    Print ISSN: 0045-5067
    Digitale ISSN: 1208-6037
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 1993-12-01
    Beschreibung: To study mineral cycling in forest ecosystems, it is essential to know the decomposition rate of the litter. This study attempted to predict directly, by near infrared reflectance spectroscopy, the stage of decomposition of leaf litter expressed as the percentage of ash-free litter mass remaining (LMR). Leaf litter of 10 different species, with varied initial compositions and at different stages of decomposition produced by incubation in the laboratory under controlled conditions, were used in this study. The LMR calibrations were carried out on half of the samples of the various populations (all species, woody species, broad-leaved species, trees, broad-leaved trees, oaks, deciduous trees, and evergreen trees). The standard error of cross validation varied between 1.69 and 3.01. Predictions were carried out on the other half of the samples of each population; the standard error of prediction varied between 2.35 and 3.77, with a r2 (coefficient of determination) of 0.97 to 0.99. The calibration equations obtained from the laboratory samples were applied to samples that had decomposed in the field in litter bags. The standard error of prediction varied between 4.46 and 5.97, with a r2 of 0.90 to 0.93. Near infrared reflectance spectroscopy thus provides a direct prediction of the LMR in leaf litter of different species, during the decomposition stage studied (i.e., between 100 and 20% of litter mass remaining). The possibilities of using near infrared reflectance spectroscopy in decomposition studies are discussed.
    Print ISSN: 0045-5067
    Digitale ISSN: 1208-6037
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2009-02-01
    Print ISSN: 0013-936X
    Digitale ISSN: 1520-5851
    Thema: Chemie und Pharmazie , Energietechnik
    Publiziert von American Chemical Society
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2011-04-01
    Print ISSN: 1286-4560
    Digitale ISSN: 1297-966X
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2003-09-01
    Print ISSN: 1286-4560
    Digitale ISSN: 1297-966X
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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