Landscape-level determinants of butterfly species richness in northern Europe: A country-wide survey reveals the paramount importance of forest land

Abstract

Human-induced changes in habitat amount and quality constitute the key driver behind negative trends in global biodiversity. Conservation actions must be based on solid knowledge of the factors affecting species richness in the remaining habitat fragments. Besides local characteristics, it is critical to consider a broader spatial context when evaluating habitat quality. Here we present an analysis of landscape-level determinants of butterfly species richness based on a country-wide survey in Estonia, representing the northern European forest zone. This study compares favourably to previous research in its scope (over 1200 systematically selected sites), and provides a relatively ‘natural’ reference point for the analyses based on areas with higher human population density. The number of butterfly species locally recorded was sought to be explained by variables describing the surroundings of the study sites at four spatial scales. The proportion of forest land was by far the strongest factor (positively) affecting the number of butterfly species recorded, followed by soil alkalinity. Notably, the effects of forest land area at the smallest (in a radius of 250 m) and largest (2000 m) spatial scales were partly independent of each other. The former likely reflects immediate habitat quality while the latter should be related to the colonisation-extinction balance in the metapopulation context. The correlates of anthropogenic pressure (e.g., urbanization, roads, agriculture) had little effect. The results highlight the key role of designing responsible forestry practices in the regional context of nature conservation.