Forest expansion in Scotland and its potential effects on black grouse Tetrao tetrix conservation

Abstract

Increasing forest cover has been the policy of various countries in recent decades. The Scottish government aims to increase national forest cover from 18% to 25% by 2050. Mid-altitude upland areas above farmland and below the natural tree line will be targeted for planting, which could impact black grouse Tetrao tetrix, a species of conservation concern which is most abundant in this zone. We used lek counts, counts of black grouse shot on sporting estates and habitat data in the Tay region to investigate distributions of black grouse in relation to forest and non-forest habitat composition. Moorland was generally selected relative to forest habitats. Planting of new forests was linked to establishment of leks and maturing of forests was linked to lek extinctions. Between 1945 and 2010, including a previous period of incentivised forest expansion, shooting densities (birds shot per km²) were significantly correlated with the area of pre-thicket (<14 years) forestry in the Tay study area, increasing as it was planted but decreasing as it matured to a closed-canopy structure. Across three Scottish regions (Argyll, Inverness and Galloway) habitat composition within 1 km of leks was similar at 45-60% moorland and 10-15% young forest suggesting this habitat composition may provide a template for designing mosaics that can sustain viable populations in the face of forest expansion. Protection of moorland patches and provision of young forest over a smaller but more consistent area may benefit the species' conservation.