Global Change Abstracts The Swiss Contribution - SCNAT

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80 08.1-115 Effects of an extended drought period on grasslands at various altitudes in Switzerland Feller U, Signarbieux C Switzerland Plant Sciences , Meteorology & Atmospheric Sciences , Ecology Photosynthesis Research, 2007, V91, N2-3, FEB- MAR, p 294. 08.1-116 Secondary succession and loss in plant diversity following a grazing decrease in a wooded pasture of the central Swiss Alps Frelechoux F, Meisser M, Gillet F Switzerland Plant Sciences , Agriculture, Soil Sciences , Biodiversity , Ecology Reduced cattle grazing pressure in the Alps has caused the reforestation of many subalpine pastures during the last decades. To understand the dynamics of natural reforestation and to evaluate how this change affects plant species diversity, we described the vegetation of a wooded pasture in the central Swiss Alps (Sembrancher, Valais) using the integrated synusial method. Based on stratified vegetation releves in 27 plots, we defined 11 community types at the synusial level (two tree-layer, five shrub-layer, and four herb-layer synusiae), and four community types at the phytocoenosis level (pasture, tall forbs and scrub, wooded pasture and forest). The spatial distribution of these four phytocoenoses suggests that they represent successional stages after abandonment, and that the pathway of vegetation succession depends on the aspect. We suppose that on northern oriented, cool and shady locations, abandoned pastures first develop towards tall-forb meadows and scrub with Alnus viridis, and then to a preforested stage with Picea abies and Larix decidua. In contrast, on western oriented, warm and sunny location, Larix decidua (mainly) and Picea abies directly colonize the abandoned pastures, but further succession finally leads to the same pre-forested stage as on northern slopes. Plant species richness was highest in open areas and decreased by 25 % as tree cover increased from 6 % to 65 %. According to our successional model, plant species diversity is lost more rapidly on northern slopes (with speciespoor green alder scrub) than on western slopes (with species- rich young larch forests), suggesting that northern slopes most urgently need an appropriate grazing management. Botanica Helvetica, 2007, V117, N1, JUN, pp 37-56. Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems 08.1-117 Changes of photosynthetic traits in beech saplings (Fagus sylvatica) under severe drought stress and during recovery Galle A, Feller U Switzerland Plant Sciences , Forestry In the context of an increased risk of extreme drought events across Europe during the next decades, the capacity of trees to recover and survive drought periods awaits further attention. In summer 2005, 4- year-old beech (Fagus sylvatica L.) saplings were watered regularly or were kept for 4 weeks without irrigation in the field and then re- watered again. Changes of plant water status, leaf gas exchange and Chl a fluorescence parameters, as well as alterations in leaf pigment composition were followed. During the drought period, stomatal conductance (g(s)) and net photosynthesis (P-n) decreased in parallel with increased water deficit. After 14 days without irrigation, stomata remained closed and P-n was almost completely inhibited. Reversible downregulation of PSII photochemistry (the maximum quantum efficiency of PSII (F-v/F-m)), enhanced thermal dissipation of excess excitation energy and an increased ratio of xanthophyll cycle pigments to chlorophylls (because of a loss of chlorophylls) contributed to an enhanced photo-protection in severely stressed plants. Leaf water potential was restored immediately after re- watering, while g(s), P-n and F-v/F-m recovered only partially during the initial phase, even when high external CO 2 concentrations were applied during the measurements, indicating lasting non-stomatal limitations. Thereafter, P-n recovered completely within 4 weeks, meanwhile g(s) remained permanently lower in stressed than in control plants, leading to an increased ‘intrinsic water use efficiency’ (P-n /g(s)). In conclusion, although severe drought stress adversely affected photosynthetic performance of F. sylvatica (a rather drought-sensitive species), P-n was completely restored after re- watering, presumably because of physiological and morphological adjustments (e.g. stomatal occlusions). Physiologia Plantarum, 2007, V131, N3, NOV, pp 412-421. 08.1-118 Stochastic gene expression in switching environments Gander M J, Mazza C, Rummler H Switzerland Microbiology , Ecology Organisms are known to adapt to regularly varying environments. However, in most cases, the
Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems 81 fluctuations of the environment are irregular and stochastic, alternating between favorable and unfavorable regimes, so that cells must cope with an uncertain future. A possible response is population diversification. We assume here that the cell population is divided into two groups, corresponding to two phenotypes, having distinct growth rates, and that cells can switch randomly their phenotypes. In static environments, the net growth rate is maximized when the population is homogeneously composed of cells having the largest growth rate. In random environments, growth rates fluctuate and observations reveal that sometimes heterogeneous populations have a larger net growth rate than homogeneous ones, a fact illustrated recently through Monte-Carlo simulations based on a birth and migration process in a random environment. We study this process mathematically by focusing on the proportion f (t) of cells having the largest growth rate at time t, and give explicitly the related steady state distribution pi. We also prove the convergence of empirical averages along trajectories to the first moment Epsilon pi (f), and provide efficient numerical methods for computing Epsilon pi (f). Journal of Mathematical Biology, 2007, V55, N2, AUG, pp 249-269. 08.1-119 Natural forest regrowth as a proxy variable for agricultural land abandonment in the Swiss mountains: a spatial statistical model based on geophysical and socio-economic variables Gellrich M, Baur P, Zimmermann N E Switzerland Forestry , Agriculture, Soil Sciences , Plant Sciences Modelling In many European mountain regions, natural forest regrowth on abandoned agricultural land and the related consequences for the environment are issues of increasing concern. We developed a spatial statistical model based on multiple geophysical and socio-economic variables to investigate the pattern of natural forest regrowth in the Swiss mountain area between the 1980s and 1990s. Results show that forest regrowth occurred primarily in areas with low temperature sum, intermediate steepness and soil stoniness as well as close to forest edges and relatively close to roads. Model results suggest that regions with weak labor markets are favored in terms of land abandonment and forest regrowth. We could not find an effect of population change on land abandonment and forest regrowth. Therefore, we conclude that decision makers should consider non-linearities in the pattern of forest regrowth and the fact that labor markets have an effect on land abandonment and forest regrowth when designing measures to prevent agricultural land abandonment and natural forest regrowth in the Swiss mountains. Environmental Modeling Assessment, 2007, V12, N4, NOV, pp 269-278. 08.1-120 Challenges to the uptake of the ecosystem service rationale for conservation Ghazoul J Switzerland Biodiversity , Ecology Conservation Biology, 2007, V21, N6, DEC, pp 1651-1652. 08.1-121 What you see is where you go? Modeling dispersal in mountainous landscapes Graf R F, Kramer Schadt S, Fernandez N, Grimm V Germany, Switzerland, Spain Modelling , Ecology Inter-patch connectivity can be strongly influenced by topography and matrix heterogeneity, particularly when dealing with species with high cognitive abilities. To estimate dispersal in such systems, simulation models need to incorporate a behavioral component of matrix effects to result in more realistic connectivity measures. Interpatch dispersal is important for the persistence of capercaillie (Tetrao urogallus) in central Europe, where this endangered grouse species lives in patchy populations embedded in a mountainous landscape. We simulated capercaillie movements with an individual-based, spatially explicit dispersal model (IBM) and compared the resulting connectivity measure with distance and an expert estimation. We used a landscape comprising discrete habitat patches, temporary habitat, non-habitat forests, and non-habitat open land. First, we assumed that dispersing individuals have perfect knowledge of habitat cells within the perceptual range (null model). Then, we included constraints to perception and accessibility, i.e., mountain chains, open area and valleys (three sub-models). In a full model, all sub-models were included at once. Correlations between the different connectivity measures were high (Spearman’s rho > 0.7) and connectivity based on the full IBM was closer to expert estimation than distance. For selected cases, simple distance differed strongly from the full IBM measure and the expert estimation. Connectivity based on the IBM was strongly sensitive to the size of perceptual range with higher sensitivity for the null model compared to the full model that included context dependent perceptu-
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