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Prediction of Vegetation Patterns at the Limits of Plant Life: A New View of the Alpine-Nival Ecotone
Michael Gottfried, Harald Pauli and Georg Grabherr
Arctic and Alpine Research
Vol. 30, No. 3 (Aug., 1998), pp. 207-221
Published by: INSTAAR, University of Colorado
Stable URL: http://www.jstor.org/stable/1551968
Page Count: 15
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The distribution pattern of individual plant species, as well as of plant communities, at the transition between the alpine and the nival environment (= alpine-nival ecotone) is likely to be drastically affected by climate change. Currently, the best way to explore the vegetation structure and to detect possible changes is the application of spatial modeling to predict vegetation patterns over larger areas combined with dynamic modeling techniques. Schrankogel in Tyrol, Austria, was selected as a typical high alpine mountain to establish and test such models. As a first step, the predictive model for the spatial pattern of species and plant communities is presented here. Direct and indirect gradient analyses (CA, CCA) were combined with GIS-techniques based on a fine-grained Digital Elevation Model (DEM; pixel size: 1 m2). Approximately 1000 field samples (vascular plant species and cover within 1 m2 squares) distributed over the alpine-nival ecotone of the mountain were taken as the vegetation data input. Topographic descriptors were derived from the DEM as habitat characters of those samples. Using the correlations between vegetation samples and habitat characters, single plant species as well as community distribution could be predicted for the pixels of the whole model area (the studied ecotone area contained a total of 650,000 pixels) for which habitat characters were known from the DEM. Distinct distribution patterns at different spatial resolutions appeared for individual species, species groups, and communities in relation to the relief. Descriptors of relief curvature and roughness explained more of the variability than "classical" terrain attributes, such as elevation or exposure. Nevertheless, the altitudinal gradient was clearly reflected by the CCA ordination. As species richness of vascular plants was recorded in each sample plot, biodiversity distribution patterns could be modeled. These patterns showed the general trend of decline of biodiversity with altitude, but with a maximum of species richness at the ecotone itself. Since the relief modifies the high mountain climate remarkably, this differentiated relief dependency of vegetation supports the view that this type of environments will be affected significantly by climate change.