Habitat quality, not patch isolation, drives distribution and abundance of two light-demanding butterflies in fragmented coppice landscapes

Abstract

Coppice forests are socio-ecological systems especially rich in biodiversity. They have been transformed into high forest and abandoned across large areas of Europe over the past 200 years. Coppice loss is likely an important driver of insect declines. It is currently unclear whether habitat quality or decreasing connectivity of the remaining fragments is more important for the survival of insect populations. We related the abundance of two coppice-attached butterflies of conservation concern, Satyrium ilicis and Melitaea athalia, to indicators of habitat quality and habitat connectivity. We estimated butterfly densities using Distance Sampling along a successional gradient (time since last cut: 1-9 years; N = 130 plots) across one of the largest remaining simple oak-birch coppice landscapes in Central Europe. Both species reached abundance peaks within four to six years after the last cut, declining rapidly in abundance with subsequent succession. We found no evidence that coupe size, coppice availability and patch (= coupe) connectivity were related to the density of the species. Besides stand age, the cover of larval foodplants explained predicted butterfly densities well. Only Satyrium ilicis benefitted from high Red Deer densities. Implications for insect conservation: Our results suggest that habitat quality and sufficient availability of coppice of suitable age matters more than coupe size and fragmentation within a traditional managed coppice landscape. Coppice restoration aiming at the study species should ensure a shifting mosaic of successional habitat to provide a large availability of resprouting oak stools and blueberry vegetation that holds dense Melampyrum pratense stands.