The relationship between diversity of insect assemblages and stand condition in deciduous broad-leaved forests in Hokkaido, northern Japan

The relationship between diversity of insect assemblages and stand condition was investigated in middle-aged and old-aged deciduous broad-leaved forests in Hokkaido, northern Japan. Eight 0.1-ha sample plots (two plots at each stand in northern, eastern, central and southern part of Hokkaido) were selected for investigation of stand condition and insect assemblages using collision traps baited with benzyl acetate. Samples were collected from the end of May to the beginning of September in 2002 and 2003. We selected the following insects in our analyses: (1) longicorn beetle (Coleoptera: Disteniidae, Cerambycidae), (2) false darkling beetle (Coleoptera: Melandryidae), (3) ground beetle (Coleoptera: Carabidae), (4) butterfly (Lepidoptera: Papilionidae, Pieridae, Nymphalidae, Lycaenidae, Hesperiidae). We analyzed the relationship between each insect variables (number of species, number of individuals, species diversity (H')) and selected stand variables (basal area density ( m2/ha) and stem density (trees/ha) of total, weakened, standing dead, overstory, midstory and understory trees; mean diameter at breast height (DBH) of total, high-ranking forty trees; number of woody plant species, species diversity (H') of woody plant; number and total diameter of fallen dead trees and branches using transect method (50m x 4 routes per one plot)). (1) Longicorn beetle: A total of 1762 individuals belonging to 43 species were caught. Most of them generally depend on dead or dying wood; nevertheless, species richness, abundance, species diversity were not correlated with basal area and stem density of standing dead trees, number and total diameter of fallen dead trees and branches. Whereas species richness had a significant negative correlation with basal area density of weakened trees, and species diversity had a significant positive correlation with basal area density of midstory and understory trees. (2) False darkling beetle: A total of 160 individuals belonging to 18 species were caught. Most of them generally depend on dead or dying wood. Species richness and abundance had a significant positive correlation with number of freshly fallen dead trees and branches, and had a significant negative correlation with mean DBH. Species diversity had a significant negative correlation with basal area density of standing dead trees. (3) Ground beetle: A total of 285 individuals belonging to 22 species were caught. Most of them are very important predators of other arthropods, invertebrates and small creatures. Species richness had a significant positive correlation with mean DBH of high-ranking forty trees, basal area density of midstory and understory trees, and had a significant negative correlation with number of freshly fallen dead trees and branches. Abundance had a significant positive correlation with basal area density of midstory and understory trees. Species diversity had a significant positive correlation with species diversity of woody plant. (4) Butterfly: A total of 159 individuals belonging to 22 species were caught. Most of them are herbivores of living plants. Abundance had a significant negative correlation with number of woody plant species. Species diversity had a significant positive correlation with basal area density of weakened trees.