Effects of reindeer on boreal forest floor vegetation: Does grazing cause vegetation state transitions?

Intensive reindeer grazing has been hypothesized to drive vegetation shifts in the arctic tundra from a low-productive lichen dominated state to a more productive moss dominated state Although the more productive state can potentially host more herbivores, it may still be less suitable as winter grazing grounds for reindeer, if lichens, the most preferred winter forage, are less abundant Therefore, such a shift towards mosses may have severe consequences for reindeer husbandry if ground-growing lichens have difficulties to recover We tested if reindeer cause this type of vegetation state shifts in boreal forest floor vegetation, by comparing plant species composition and major soil processes inside and outside of more than 40-year-old exclosures Lichen biomass was more than twice as high inside exclosures than in grazed controls and almost 5 times higher than in heavily grazed patches Contrary to our predictions, net N mineralization and plant production were higher in the exclosures than in the grazed controls The lack of response of phytometer plants in a common garden bioassay indicated that changed soil moisture may drive effects of reindeer on plant productivity in these dry Pine forest ecosystems