Spatial and Temporal Variation in Bird Communities and Populations in North-Boreal Coniferous Forests: A Multiscale Approach

Abstract

north-boreal coniferous forests, was studied in detail. In north-boreal coniferous forests both larger and smaller scale phenomena affect patterns observed at a particular scale, and therefore, a multiscale approach is necessary in understanding the dynamics of avian biota. The sporadic occurrence of nomadic species such as two-barred crossbills and owls reflected the importance of the large biogeographic scale: ecological events occurring in the taiga belt far away affected bird communities in northern Finland. Regional variation of bird communities in old, virgin forests was similar to the overall regional variation of avian biota, because 70-80% of bird pairs in virgin forests are habitat generalists. Regional changes in the structure of forests and the increasing harshness of the climate to the north were important for the spatial dynamics of the bird communities. The local effects of habitat alteration (forestry) on bird populations were parallel to the long-term regional population trends of birds. The patterns of between-habitat changes in bird densities caused by forest management were connected with processes at the smaller, within-habitat scale. The long-term decline of the Siberian tit owing to heavy forest management could be explained by events at a local population scale, as the offspring production of the tit was poor in heavily thinned forests. Year-to-year variation in population densities of migratory species was similar in managed and virgin forests probably due to environmental unpredictability and harshness in the north.