Subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests with an understorey vegetation of dwarf shrubs, lichens and mosses form an important habitat for semi-domestic reindeer (Rangifer tarandus). In the summer ranges, reindeer browse mountain birches, whereas in the winter ranges, reindeer leave mountain birches intact and feed on lichens and evergreen dwarf shrubs. Here, we re-analyzed forest structure and understorey vegetation after 12 years in northern Finnish reindeer herding co-operatives where winter and summer ranges had been separated since the 1980’s. We found that the number of mountain birches and the biomass of evergreen and deciduous dwarf shrubs had increased substantially. Yet, the increases in many plant groups varied with seasonal range and habitat, revealing that the seasonal use of reindeer ranges was a major driver for the ongoing subarctic ecosystem change. For example, tall mountain birch seedlings had increased twice as fast in winter than summer ranges. Evergreen dwarf shrub mountain crowberry (Empetrum nigrum ssp. hermaphroditum) had increased to a greater extent in winter ranges in a semidry habitat, but to a greater extent in summer ranges in a dry habitat.
These vegetation trends revealed the cumulative effect of climate warming and grazing regimes, which gave insights into the vegetation we may expect to see in the future. This information helps predicting forage availability for the reindeer under warming climate.
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Reference: Stark, S., Ylänne, H. and Kumpula, J., Recent changes in mountain birch forest structure and understory vegetation depend on the seasonal timing of reindeer grazing. Journal of Applied Ecology.
Text written by Sari Stark.
Picture: Subarctic forest‐tundra ecotones dominated by mountain birch (Betula pubescens ssp. czerepanovii) (photo credit: Sari Stark)