Recent changes in mountain birch forest structure and understory vegetation depend on the seasonal timing of reindeer grazing

Subarctic forest-tundra ecotones dominated by mountain birch (Betula pubescens ssp. czerepanovii) are an important habitat for semi-domestic reindeer Rangifer tarandus. The seasonal timing of grazing may direct vegetation trajectories in these systems, because the summer ranges, birches subjected to browsing, while winter feed on understorey and arboreal lichens but leave intact. Based earlier research, we predicted that (a) browsing dampens ongoing ‘shrubification’ semi-dry dry forests (b) is accompanied a decline lichens. We tested predictions through re-analysing forest structure after 12 years areas where ranges had been separated since 1980s. also how changes lichen abundances align with shrub correlation analyses. number tall seedlings increased twice as fast than big ranges. dominant evergreen dwarf crowberry (Empetrum nigrum hermaphroditum) greater extent semidry habitat, habitat. Deciduous graminoid biomass similarly found no evidence support increasing contributed lichens; instead, cover seedlings. Synthesis application. subarctic depend greatly whether area used or range reindeer. recent likely lead improved forage availability reindeer, opposite be true availability.