Ecological restoration in boreal forest modifies the structure of bird assemblages

Ecological restoration is increasingly recognised as a useful tool for biodiversity conservation in boreal forests. Most restoration methods in this environment aim to emulate natural disturbances, and thereby promote the development of key ecological structures. However, research about forest ecosystem restoration is still in its infancy and the responses of many boreal species groups remain to be described. We established a large-scale field experiment to evaluate the short-term effects of two restoration treatments - prescribed burning and gap cutting involving the creation of dead wood - on breeding bird assemblages in boreal Sweden. We censused breeding birds using territory mapping during two years in forest stands subjected to the two restoration treatments, in untreated controls and in old-growth references (nature reserves) (n = 10 per treatment). Averaged over the two census years, we found 1145 territories of 36 bird species. Total bird species richness and abundance did not differ among treatments. However, prescribed burning led to clear changes in the structure of the bird assemblages. When dividing species according to four functional categorizations (migration, foraging, nesting and successional stage), we found that the abundance of long-distance migrants, ground breeders, strong cavity excavators and species preferring early-successional habitat was higher in burned stands than in untreated controls and gap-cut stands, as was the species richness of bark feeders and strong cavity excavators. In contrast, abundance of off-ground breeders and species richness of crown feeders were lower following prescribed burning than in the controls. The gap cutting treatment did not have any significant effects on the bird assemblages. Ecological restoration through prescribed burning can be a useful tool for the conservation of boreal forest birds, including the ecologically important strong cavity excavators (i.e. woodpeckers (Picidae)). Forest managers should therefore be encouraged to use prescribed burning as a restoration tool to quickly provide habitat for bird species adapted to natural disturbances in boreal forest.