Effects of declining understory vegetation on leaf litter decomposition in a Japanese cool-temperate forest

Understory vegetation, dominated by dwarf bamboo (Sasa spp.) in Japan, has been damaged by an overabundance of deer. Declining Sasa density may induce a decrease in litter decomposition due to the changes in soil environments. The effect of the environmental changes may also differ among litter from differenttree species. The objective of this study was to examine effects of declining Sasa density on litter decomposition in a cool-temperate mixed forest, with a focus on the effects of environmental factors and soil mesofauna on different litter species. The decomposition of three litter species was evaluated using litter bags with two different mesh sizes to consider different litter decomposability and control the accessibility of soil mesofauna. With decreasing Sasa density, soil water content increased whereas the number of soil mesofauna decreased. Litter mass loss decreased with declining Sasa density. Soil water content was negatively correlated with litter mass loss in the smaller mesh. Additionally, negative effects of Sasa degradation on litter decomposition did not change with litter species, but these effects changed among mesh sizes, suggesting that the effects of the decomposer community on litter decomposition changed with environmental conditions induced bySasadegradation. Complex interaction between decomposer communities and local environmental factors should be studied in further studies with longer periods over a wide range of areas.