Burning and mowing as habitat management for capercaillie Tetrao urogallus: An experimental test

In Scots pine Pinus sylvestris forests, the important ecological effects of natural fires could be emulated using prescribed fire. Species that may benefit from fire effects include capercaillie Tetrao urogallus, a large forest grouse. A key component of forest habitats for capercaillie is the ericaceous shrub, bilberry Vaccinium myrtillus, which is eaten by capercaillie, and supports abundant arthropods, taken by young chicks. We carried out an experiment testing whether prescribed burning would be a valuable technique for capercaillie habitat management. The study took place at Abernethy Forest, the largest ancient native pinewood in Britain, and a key capercaillie site, holding c 8-20% of the British population. Prescribed fire in woodland is highly novel in Britain. We therefore also tested mowing, which might replicate some fire effects more cheaply and safely. Twenty-five experimental blocks were established within open pine stands with ground vegetation including bilberry, but dominated by heather Calluna vulgaris. Each block held three 700 m² plots, randomly assigned to control, mow and burn. Vegetation, arthropods and capercaillie dung were monitored over a 7-year period, including 1 year prior to treatment. Mean bilberry cover, initially around 12%, increased in mown and burnt areas, but there were also increases in controls, following unusual natural die-back of heather. By the sixth season after treatment, bilberry cover was significantly higher in burnt and mown areas than controls, averaging 27% (95% confidence intervals 24-30), compared to 20% (19-21) in controls. Biomass of spiders, an important dietary group for capercaillie chicks, as measured by pitfall trapping, was significantly higher in burnt and mown plots than controls, by about 56% (38-76). However, biomass of caterpillars, often considered a more important dietary group, did not show clear differences between treatments. An alternative analysis was used to ‘statistically remove’ natural heather die-back; this enhanced the treatment differences in bilberry cover and spider biomass. Capercaillie dung counts suggested that burnt, and especially mown areas, had more summer capercaillie usage than controls. Capercaillie conservation at sites similar to Abernethy is likely to benefit from either prescribed fire or mowing, because these techniques increase bilberry and spider abundance. This study illustrates the value of collaboration between researchers and land-managers, in developing and testing novel management techniques. We support the idea that ‘dominance reduction’, delivered through managed disturbance, offers a general principle to guide land-managers wishing to maintain biodiversity, particularly where key species, like capercaillie, are strongly associated with sub-dominant plant species like bilberry.