Effects of Canopy Gap Disturbance on Forest Birds in Boreal Forests

We studied the effects of small-scale disturbance on breeding, forest passerine birds in an old-growth and managed boreal forests in northern Finland. Small-scale disturbance (< 2 ha) in an old-growth and managed forests originated from wind falls and small clear cuts. Continuous forest without gaps was used as a control for both management types (old-growth and managed forests). Passerines' response to disturbance was examined by estimating species richness and abundance of different ecological groups. Species richness and the total abundance of birds did not differ between gap and non-gap plots, neither did the abundance of most ecological groups. Management type or study year were the most important factors explaining abundances. Our results differ from studies conducted in temperate forests, mainly in North America, where small-scale disturbance have been found to increase avian diversity and abundance. Differences between boreal and temperate forests or in avian assemblages between continents may explain observed differences.