Seasonal grazing effects by semi-domesticated reindeer on subarctic mountain birch forests

In northern Fennoscandia, the spatial and temporal grazing practices of semi-domesticated reindeer (Rangifer tarandus tarandus) vary, which implies different grazing effects dependent on natural conditions as well as management regime (i.e., timing and intensity of grazing). We compared density and biomass of main plant groups in semi-dry mountain birch forests exposed to either long-term summer or winter grazing in three reindeer herding districts in the northernmost Finland. Percent plant cover, height, and biomass of reindeer lichens (Cladonia spp.) and dwarf shrubs (Vaccinium uliginosum, Calluna vulgaris, and Betula nana) were lower on summer ranges compared with winter ranges. The biomass of other dwarf shrubs (Vaccinium myrtillus and V. vitis-idaea), and graminoids and herbs, and the % cover of non-vegetated bare soil and litter were, however, higher on summer ranges than on winter ranges. Young mountain birch shoots (Betula pubescens ssp. czerepanovii) were less frequent on summer ranges than on winter ranges. The total leaf biomass under the browsing height of reindeer (