The impacts of deer on woodland butterflies: the good, the bad and the complex

Deer grazing is an important feature of many key butterfly habitats in Brit ain, yet few data are available on its impacts. Butterfly populations can b e affected in a number of ways, through effects on the local availability o f larval food-plants or nectar sources, to larger-scale changes in habitat structure and management. Many woodland butterflies have historically relie d on clearings in coppiced woodland, but current high numbers of roe deer ( Capreolus capreolus), and to a lesser extent fallow deer (Dama dama), can s everely reduce tree regrowth and are now a major disincentive to the mainte nance of this traditional form of management. In contrast, deer grazing may be very beneficial in some woodland habitats. In Scotland, most colonies o f the threatened pearl-bordered fritillary (Boloria euphrosyne) rely to som e extent on grazing by deer, to slow down natural regeneration and maintain open bracken (Pteridium aquilinum) habitats in canopy gaps and along woodl and edges. Such areas have recently been targeted by schemes to encourage n ative woodland, but the fencing out of deer and other grazing animals can l ead to rapid loss of these crucial woodland habitats. Far more research is needed to determine the full extent of these impacts and implications for c onservation programmes.