Arthropods inhibiting dead wood (saproxylic arthropods) contribute to nutrient cycle in forest ecosystems via participating wood decomposition and trophic processes following it. However, almost studies in urban fragments dealt with limited taxa such as endangered species. In this study, we compared the saproxylic arthropod communities in urban fragments and mature large forests.
We surveyed forests in warm-temperate zone in Japan. Forest size was ranged from 0.01km2 to 62.16km2 (area of inscribed circle), vegetation types were deciduous coppice forest and evergreen old-growth forest. Sampling of arthropods was conducted on three 10m square plots in each forest and by breaking up to 10 woody debris in each plot.
By sampling on 15 plots, 89 species and 1274 individuals were collected. Surveyed forests were classified into two saproxylic arthropod communities based on two-dimensional NMDS using dissimilarity of species composition. Environment of these community types had a significant difference in the forest area (P<0.001, T-test for log transferred value); saproxylic arthropod communities in large forest and those in fragmented urban forests.
According to rare-faction curve and functional trait composition, urban saproxylic arthropod community showed lower species diversity with high abundance by few species, high dominance of omnivore and fungivore guild, and dominated by generalists using both dead-wood and fallen leaves. The saproxylic arthropod community in large forest showed high species diversity with low individual density, abundant in carnivore. Consequently, large forest had the properties of stable and mature community common to various organisms as plants and large animals, but urban fragments had unstable one. Our results suggest that decomposition process might be different between urban fragments and large forests.