Effects of Habitat Quality and Isolation on the Colonization of Restored Heathlands by Butterflies

Abstract

In areas with intensive land use, such as the Netherlands, habitat fragmentation and loss of habitat quality due to eutrophication and drainage are major threats to the preservation of species-rich communities of heathland and acid grassland. Restoration of such nutrient-poor habitats may be carried out by removing the topsoil from ex-arable land, in order to lower the nutrient levels. However, the establishment of target plant communities is known to be fragmentary. The current study shows that this also applies to butterflies. Ten years after topsoil removal in eight study areas, on average, only 3.5 of 10 characteristic heathland species were recorded on the sites. Species that did colonize had a significantly lower density than in the source populations. Our study indicates that although isolation effects were limiting colonization, poor habitat quality was the main limiting factor, mainly due to lack of host plants, hydrological conditions, and, to a lesser extent, lack of nectar plants and excessive residual nutrient levels. An experiment with the introduction of cut heather in one study area showed a significantly higher abundance of both target and nontarget butterflies in manipulated sites than in control sites. It can be concluded that habitat restoration by topsoil removal can be successful for butterflies of especially wet heathland habitats, provided that source populations are at close range and care is taken that complete plant communities are restored.