Impacts of moso bamboo (Phyllostachys pubescens) invasion on dry matter and carbon and nitrogen stocks in a broad-leaved secondary forest located in Kyoto, western Japan

In western and central Japan, the expansion of exotic moso bamboo (Phyllostachys pubescens Mazel ex J. Houz.) populations into neighboring vegetation has become a serious problem. Although the effects of bamboo invasion on biodiversity have been well studied, shifts in nutrient stocks and cycling, which are fundamental for ecosystem functioning, are not fully understood. To explore the effects of P.pubescens invasion on ecosystem functions we examined above- and below-ground dry matter and carbon (C) and nitrogen (N) stocks in a pure broad-leaved tree stand, a pure bamboo stand, and two tree-bamboo mixed stands with different vegetation mix ratios in the secondary forest of Kyoto, western Japan. In the process of invasion, bamboo shoots offset broad-leaved tree deaths; thus, no clear trend was apparent in total above- or below-ground biomass or in plant C and N stocks during invasion. However, the ratio of above-ground to below-ground biomass (T/R ratio at the stand level) decreased with increasing bamboo dominance, especially in the early stages of invasion. This shift indicates that rapid bamboo rhizomatous growth is a main driver of substantial changes in stand structure. We also detected rises in the C/N ratio of forest-floor organic matter during bamboo invasion. Thus major impacts of P.pubescens invasion into broad-leaved forests include not only early shifts in biomass allocation, but also changes in the distribution pattern of C and N stored in plants and soil.