Global Change Abstracts The Swiss Contribution - SCNAT

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102 production during the course of the dry season was highly variable among the tree species. Tree diversity significantly affected litter production, and the majority of the intermediate diverse mixtures had higher litter yields than expected based on yields in monoculture. In contrast, high diverse mixtures did not show such overyielding in litter production. Litter decomposition rates were also highly species-specific, and were related to various measures of litter quality (C/N, lignin/N, fibre content). We found no overall effect of litter diversity if the entire litter mixtures were analyzed, i.e. mixing species resulted in pure additive effects and observed decomposition rates were not different from expected rates. However, the individual species changed their decomposition pattern depending on the diversity of the litter mixture, i.e. there were species-specific responses to mixing litter. The analysis of temporal C and N dynamics within litter mixtures gave only limited evidence for nutrient transfer among litters of different quality. At this early stage of our tree diversity experiment, there are no coherent and general effects of tree species richness on both litter production and decomposition. Within the scope of the biodiversityecosystem functioning relationship, our results therefore highlight the process-specific effects diversity may have. Additionally, species-specific effects on ecosystem processes and their temporal dynamics are important, but such effects may change along the gradient of tree diversity. Oikos, 2007, V116, N12, DEC, pp 2108-2124. 08.1-169 Exploring the functional significance of forest diversity: A new long-term experiment with temperate tree species (BIOTREE) Scherer Lorenzen M, Schulze E D, Don A, Schumacher J, Weller E Switzerland, Germany Ecology , Plant Sciences , Biodiversity , Forestry Effects of biodiversity on ecosystem functioning have been mainly studied in experiments that artificially create gradients in grassland plant diversity. Woody species were largely excluded from these early experiments, despite the ecological and socioeconomic importance of forest ecosystems. We discuss conceptual aspects of mechanistically driven research on the biodiversity-ecosystem functioning relationship in forests, including the comparison of scientific approaches like ‘observational studies’, ‘removal experiments’, and ‘synthetic-assemblage experiments’. We give a short overview on the differences between herbaceous and forest ecosystems, focusing on can- Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems opy characteristics, and the possibilities for individual versus population-based investigations. We present detailed information about the first large-scale, multisite and long-term biodiversityecosystem functioning experiment with tree species of temperate forests (BIOTREE - BIOdiversity and ecosystem processes in experimental TREE stands). At three sites of differing geology and local climate, we planted 200,000 saplings on a total area of 70 ha. At two sites, diversity gradients were established by varying the number of tree species (BIOTREE-SPECIES). At a third site, only functional diversity at a constant level of tree species richness was manipulated by selecting mixtures that differ in the functional trait values of the corresponding species (BIOTREE-FD). Additional experimental treatments at the subplot level include silvicultural management options, the addition of subdominant species, and the reduction of genetic diversity. Response variables focus on productivity, biogeochemical cycles and carbon sequestration, and resource use complementarity. We explore the use of different measures of functional diversity for a posteriori classifications of functional richness and their use in the analysis of our tree diversity experiment. The experiment is thought to provide a long-term research platform for a variety of scientific questions related to forest biodiversity and ecosystem processes. Perspectives in Plant Ecology Evolution and Systematics, 2007, V9, N2, pp 53-70. 08.1-170 Patterns of variation of a common fern (Athyrium filix-femina; Woodsiaceae): Population structure along and between altitudinal gradients Schneller J, Liebst B Switzerland Plant Sciences , Ecology , Biodiversity Genetic variability of Athyrium filix-femina populations was evaluated with regard to phenotypic, allozyme, and RAPD variation in 20 Swiss populations along five altitudinal gradients at four different elevations in the northern Swiss Alps. Additionally, allozyme and phenotypic variations in one Italian and two Spanish populations were compared with the variation in the Swiss populations. We hypothesized that there will be statistically significant genetic differences among populations of different altitudes and sites. The results showed no substantial correlation between genetic variation and phenotypic variation among Swiss populations. These results imply that outbreeding and effective gene exchange (long-distance spore dispersal) are the keys to population structure
Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems 103 in this fern species, and as a consequence, phenotypic plasticity is assumed to be favored. This contrasts with results found in similar studies of herbaceous flowering plants where genetic adaptation to gradients like altitude is common. However, when data from the more distant Italian and Spanish populations of A. filix- femina were included, significant variation was detected. American Journal of Botany, 2007, V94, N6, JUN, pp 965-971. 08.1-171 Examining native and exotic species diversity in European riparian forests Schnitzler A, Hale B W, Alsum E M Switzerland, France, USA Plant Sciences , Ecology , Biodiversity , Forestry This study performs a meta-analysis of existing studies of European riparian forests to investigate which exotic species have successfully established in intact riparian forests and which characteristics of these forests correspond with successful establishment. We used analysis of covariance models to investigate the relationship between community species richness, percent exotic species, and several environmental variables. We found a total richness of 1380 species, of which 45 (3.3%) were exotic. Species- rich communities generally had the higher percentage of exotics, but were not significantly related to latitude or environmental variables. Exotics, in contrast, were at generally higher levels at lower latitudes and were more abundant in large river plains and communities with intermediate levels of disturbance. These results suggest that future climate change and human actions that mimic intermediate levels of disturbance may further enhance the spread of exotic species. Biological Conservation, 2007, V138, N1-2, AUG, pp 146-156. 08.1-172 Speciation reversal and biodiversity dynamics with hybridization in changing environments Seehausen O, Takimoto G, Roy D, Jokela J Switzerland, USA Biodiversity , Ecology A considerable fraction of the world’s biodiversity is of recent evolutionary origin and has evolved as a by-product of, and is maintained by, divergent adaptation in heterogeneous environments. Conservationists have paid attention to genetic homogenization caused by human-induced translocations (e.g. biological invasions and stocking), and to the importance of environmental heterogeneity for the ecological coexistence of species. However, far less attention has been paid to the consequences of loss of environmental heterogeneity to the genetic coexistence of sympatric species. Our review of empirical observations and our theoretical considerations on the causes and consequences of interspecific hybridization suggest that a loss of environmental heterogeneity causes a loss of biodiversity through increased genetic admixture, effectively reversing speciation. Loss of heterogeneity relaxes divergent selection and removes ecological barriers to gene flow between divergently adapted species, promoting interspecific introgressive hybridization. Since heterogeneity of natural environments is rapidly deteriorating in most biomes, the evolutionary ecology of speciation reversal ought to be fully integrated into conservation biology. Molecular Ecology, 2008, V17, N1, JAN, pp 30-44. 08.1-173 Altitudinal and horizontal shifts of the upper boundaries of open and closed forests in the Polar Urals in the 20th century Shiyatov S G, Terentev M M, Fomin V V, Zimmermann N E Russia, Switzerland Meteorology & Atmospheric Sciences , Forestry , Plant Sciences , Ecology In the Polar Urals (the Rai-Iz massif and Mounts Tchernaya and Malaya Tchernaya), altitudinal and horizontal shifts of the upper boundary of open and closed larch forests in the 20th century have been studied. Spatiotemporal parameters of these shifts have been assessed with the aid of the ARC/ INFO geographic information system (ESRI Inc., United States), using our original large-scale geobotanical maps showing the distribution of different types of forest-tundra communities in the early 1910s and 2000s. The results show that tree vegetation has been actively expanding to higher elevations over the past 90 years. On average, the upper boundaries of open and closed forests have ascended 26 and 35 m and shifted horizontally 290 and 520 m, respectively. These shifts have been conditioned by climate warming and increasing humidity observed since the 1920s. Russian Journal of Ecology, 2007, V38, N4, JUL, pp 223-227. 08.1-174 Temperate grasslands and global atmospheric change: a review Soussana J F, Lüscher A France, Switzerland Meteorology & Atmospheric Sciences , Plant Sciences , Ecology , Agriculture, Soil Sciences
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Global Change Abstracts The Swiss Contribution - SCNAT

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