Ecological Gradient of Avian Community on Lower Limit in Subalpine Coniferous Forests

Abstract

The bird communities of subalpine coniferous forest in Shiga-Kogen, central Japan were studied in nine breeding seasons from 1973 to 1981 and were compared with some bird communities of several subalpine coniferous and temperate deciduous forests. The census data were analyzed in relation to three parts, which are: coniferous part, deciduous part and the ecotone between the above two parts. The characteristic feature for the bird communities of subalpine coniferous forest is the extremely high and stable population densities of a few species. In the coniferous part, four species showed the high and stable population densities. These birds are Parus ater, Regulus regulus, Phylloscopus borealis and Tarsiger cyanurus. At lower fringe of subalpine coniferous forest, the bird community showed: high number of species, high bird density, high diversity index and low dominance index. These phenomena are due to invaded species from deciduous forest, such as Parus major, Ficedula narcissina and Erithacus cyane, and existence of ecotone preferring edge species, such as Emberiza variabilis and Phylloscopus tenellipes. Excepting Parus ater, remaining main three species of coniferous part suddenly disappear through ecotone in the deciduous part. For analysis of the structure of bird community, the concept of adaptive space (Nakamura 1978•1980) was applied. About 70% out of overall population density of bird community in coniferous part consisted of main three groups of adaptive spaces, that are the titmice, warbler and thrush types. Especially, the adaptive space of warbler type, which includes two high density species, Regulus regulus and Phylloscopus borealis, has the largest volume of adaptive space in the subalpine coniferous forest studied.