Impacts of local and regional factors on vegetation of boreal semi-natural grasslands

Using data from 46 sites in southern Finland and ordination methods, we examined plant-environment relationships in boreal mesic semi-natural grasslands at two spatial scales (grain sizes), using plots of 0.25 ha and 1 x 1 m. We applied the variation partitioning approach to determine the pure fractions of environmental variable groups and their joint effects on plant species compositional variation in the studied grasslands. The variables related to land-use intensity and high nutrient level (especially phosphorus) had a major role in explaining the species composition at both scales, although soil heterogeneity and habitat characteristics also accounted for a notable amount of the species compositional variation at the 0.25 ha grain size. At the 1 x 1 m grain size, the majority of the species compositional variation was related to the pure spatial differences between the studied grasslands (i.e. the site identity (dummy 0/1) variable), whereas the impacts of within-site variation of local environmental factors were considerably smaller. High nutrient levels and variables related to low land-use intensity, e.g. litter accumulation, were also significantly correlated with floristic variation at the 1 x 1 m grain size. Rare and declining grassland species are associated with low-nutrient grassland sites and patches. The main recommendation for the management planning of boreal semi-natural grasslands is that the first restoration attempts should be targeted to areas where nutrient levels, particularly that of phosphorus, are relatively low. Soil properties and plant species composition can provide useful guidelines for defining the correct management procedures for different sites.