We analyzed lichen species composition and biomass in 815 plots on 163 sites across wild reindeer regions in Norway, ranging from ranges with a long history of very low grazing pressure to heavily grazed sites. Reindeer density (1974–2000) and lichen biomass were well correlated for sites with comparable snow cover, altitude and terrain (R2 = 0.81, P = 0.006, n = 12). Absence of grazing for potentially several centuries has virtually resulted in a monoculture consisting of Cladina stellaris, Flavocetraria nivalis, and Alectoria ochroleuca (Syn. Bryocaulon ochroleuca). Light grazing in terms of 20 to 30% removal of initial lichen cover easily eroded Cladina stellaris from exposed ridges by cratering and trampling by reindeer through the snow, while Flavocetraria nivalis persisted longer. This decline in lichen cover observed along a historic grazing gradient further resulted in increasing cover of bare ground, but less than expected from lichen removal due to gradual colonization of other species, such as mosses (incl. Polytrichum piliferum), crustose and fruticose lichens, dwarf shrubs (Arctostaphylos spp., Empetrum nigrum, Loiseleuria procumbens), and graminoids, particularly rushes (Juncus trifidus). Moderate grazing may thus increase plant diversity on ridges compared to ungrazed lands, and hence strongly influence gradients in biomass, composition and abundance of ridge communities across the landscape.
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