Plants as indicators of snow layer duration in southern Norwegian mountains

The main aim of this paper was to study the responses of mountain plants in relation to the time of snowmelt. Three mountain areas situated along an oceanic-continental gradient were selected as study sites, and the sample plots ranged from 182 m below to 473 m above the climatic forest limit. in total, 185 quadrats (2 m x 2 m), stratified to include only oligotrophic and mesotrophic mountain vegetation types, were selected to represent a topographic range along altitudinal gradients. In each quadrat, the percentage groundcover of the species was recorded. From the beginning of April until July 2004, snow thickness was monitored, and the Julian day when the snow had completely melted was determined for all plots. The relationship between species abundances and Julian day of snowmelt were analysed by two different numerical methods: (1) relative values for species optimum and tolerance were given by Detrended Canonical Correspondence Analysis (DCCA) with Julian day of snowmelt as the constraining variable. (2) Species responses were modelled by Generalized Linear Models (GLM). For species with significant unimodal responses, optimum and tolerance were calculated. For species with significant linear models, different species response models were identified by the regression intercepts. One hundred and twenty six species (taxa) were tested, and 103 evidenced statistically significant (p < 0.05) distribution responses. Several common alpine plants had a distribution that appeared to be independent of snow. On the basis of the results of the numerical methods, the species were separated into nine Snow Indicator (SI) classes, as a parallel to the Ellenberg indicator values. The species' SI values were used to calculate weighted average SI values to examine the relationships between previously described plant communities and vegetation transects which experience different snow conditions. (C) 2007 Elsevier Ltd. All rights reserved.