Changes in the abundance and species diversity of Collembola community along with dwarf bamboo density gradient in a mountainous temperate forest of Japan

Abstract

Understory vegetation plays an important role in forest ecosystems by providing protection from soil physicochemical stresses or disturbance. Consequently, this type of vegetation may help maintain soil biodiversity and functions. However, the effects of understory degradation on soil faunal communities is not well understood. This study investigated the effects of the declining understory dwarf bamboo density in cool-temperate Japanese deciduous forests on the community composition of soil Collembola; by comparing partitioned community dissimilarity indices and trait components to detect the processes shaping community under understory degradation. For the species richness and diversity of Collembola community, unimodal quadratic model to dwarf bamboo density was selected as best model among all measured environmental properties, whereas, for Collembola abundance, linear negative relationship to dwarf bamboo density was selected as best model. For Collembola trait compositions, dwarf bamboo density model was not selected, although those of soil C and hardness were selected. The nestedness component in community dissimilarity increased with greater dwarf bamboo density differences between plots, whereas the replacement component was not significant. This suggests that the decreasing dwarf bamboo density might induce reduced niche space of whole Collembola community. In the range of mid to high density of dwarf bamboo, the higher density of dwarf bamboo declined the species diversity of the Collembola community, whereas the abundance still increased, probably because of the competitive exclusion by the dominant Folsomia octoculata under less disturbed habitat condition in high understory and litter coverage. Our results implied that the changes in the abundance and species diversity of Collembola community to understory density gradient were controlled both by abiotic niche reduction and biotic competitive exclusion without life-form trait selection.