The importance of date of snowmelt for the separation of different oligotrophic and mesotrophic mountain vegetation types in Southern Norway
Odland, Arvid; Munkejord, Hans; Kristian
The main aim of this paper was to quantify the explanatory power of different "snow variables" for the separation of different mountain vegetation types. Three mountain areas situated along an oceanic-continental gradient were selected as study sites, and the sample plots ranged from 785 to 1440 m a.s.l. (182 m below to 473 m above the climatic forest limit) and included both the Northern boreal zone (NB), the Low alpine zone (LA) and the Middle alpine zone (MA). In total, 185 quadrates (2×2 m) were selected by a stratified random sampling procedure to represent a range of topography and different vegetation cover. Soil samples were analysed from each quadrate, and the variation in snow melt and soil temperature was monitored during the spring/summer. The three main floristic gradients identified by a DCA analysis were best explained by Julian day of snowmelt (r = 0.83), relative altitude (r = −0.62), and precipitation (regional climate) (r = −0.42) respectively. 16 vegetation types were separated by the use of TWINSPAN, and these were related to the environmental variables and compared with earlier phytosociological studies. A CVA analysis and Monte Carlo Permutation tests showed that the separated vegetation types were different in terms of all measured environmental variables, but Julian day of snowmelt explained the differences best, followed by altitude. Floristical and environmental variations were small between the NB and the LA zones. Vegetation stands in the MA zone (more than 250-300 m above the climatic forest limit) showed a relatively small floristic variation, and the vegetation stands were here limited to areas where maximum snow thickness (in April) varied between 0.5 and 2.5 m, and where Julian day of snowmelt occurred later than the middle part of May. On the basis of the present relationship between vegetation composition, Julian day of snowmelt and altitude, possible vegetational changes of global warming are predicted.