Grazing and soil pH are biodiversity drivers of vascular plants and bryophytes in boreal wood-pastures

Wood-pastures have been formed by traditional low-intensity livestock grazing in wooded areas. They host high biodiversity values that are now threatened by both management abandonment (ceased grazing) and agricultural intensification, and therefore these habitats are of conservation interest in Europe. In order to explore the effects of grazing on the biodiversity of boreal wood-pastures, we studied the communities of vascular plants and bryophytes in 24 currently grazed and 24 abandoned sites. In addition to the current management situation, we studied the effects of soil pH and moisture, tree density, historical land-use intensity, time since abandonment (in abandoned sites) and grazing intensity (in grazed sites). Grazed sites had higher species richness of both species groups and rare species were also slightly more numerous. Grazing impacted the community composition of vascular plants more than that of bryophytes. For both species groups soil pH (which ranged from 3 to 5) was the most important variable in determining species richness, the number of rare species and the composition of communities. The responses of the two species groups varied somewhat, but generally species richness was maximized on sites with higher soil pH, moisture and grazing intensity, but lower tree cover. We conclude that more effort should be paid on maintaining currently grazed sites under management. If a site has been abandoned, it could be restored into a wood-pasture if it still retains some structural features such as openness and typical species of a wood-pasture. Highest biological conservation values for both management and protection can be found among those sites that are naturally most fertile, but attention should also be paid on the landscape-scale versatility of managed sites.