Geographical variation in bird communities of old, intact forests in northern Finland

Abstract

Regional variation in the structure of bird communities in northern Finnish primeval forests was studied using line transects. Birds were censused both in spruce- and pinedominated forests in five areas of Lapland from 1982-86. The habitat structure of the census areas was defined by using habitat variables of silvicultural maps. The northward decrease in the bird density of pine forests correlated positively with the latitudinal decrease in the cubic volume of the stand. There were no clear regional trends in the bird density of spruce forests, presumably, owing to the northward increase in the proportion of birch in these forests . This increase in the proportion of birch is probably advantageous to migratory foliage insectivores and seed eaters, such as Carduelis flammea. Species numbers decreased significantly to the north in spruce forests, which can partly be explained by the northward decrease in the number and density of southern bird species favouring spruce forests . Within-habitat regional variation in the structure of bird communities agreed with an omithogeographic zonation that is also affected by the regionally varying proportions of different habitats . The main reason for the agreement was that the density variation of forest habitat generalists (Frangilla montifringilla, Phylloscopus trochilus, C. fiammea, Anthus trivialis, Muscicapa striata) in old forests seemed to be similar to the overall regional density trends of these species in northern Finland. Species preferring old forests are probably more affected by differences in local factors between the study areas, such as size of the primeval forest area (e .g. Parus cinctus) and hunting (Tetrao urogallus).