The importance of micro-topographic heterogeneity in determining species diversity of alpine plant communities of Glacier National Park, MT

Alpine plant communities can be exceptionally diverse at a fine scale, and they often exhibit fine scale topographic variability. High species diversity is often attributed to spatial and temporal heterogeneity in the environment. The goal of this study was to test for a positive relationship between microtopographic heterogeneity and species diversity of alpine plants. Species diversity of vascular plants was sampled at 8 sites in Glacier National Park, MT during the summer of 2009. Species richness was assessed both within a 1 x 1 m plot and at 100 points spaced 10 cm apart within the plot. To quantify topographic heterogeneity and variability, the relative elevation was measured for all 100 points in the plot as well. Similarity in species composition between study plots was investigated using Non-Metric Multidimensional Scaling. The study plots separated into two groups based on the presence/absence of Dryas octopetala. This difference is most likely due to plots occupying different positions along the mesotopographical gradient and therefore experiencing different moisture regimes. Regression for all 1 m2 plot data found a negative relationship between topographic heterogeneity and species richness, and no relationship between topographic variability and species richness. Quantile regression was used to assess the relationship between point measures of species richness and topographic variability. There is evidence for topographic variability imposing a limit on species richness for all sites grouped together and for sites that do not contain D. octopetala. This limit is most likely due to the interaction of soil disturbance and the productivity of a site.