Witches - broom of bamboo is the most destructive disease in bamboo in Japan, and its causative agent is Aciculosporium take MIYAKE (Cavicipitaceae). We investigated the influence of the witches - broom of bamboo on the structure, species composition, and species richness of bamboo forests, particularly in the Phyllostachys bambusoides and P. pubescens forests. We found that most of the P. bambusoides forests were affected by this disease, and more than 50% of their patch areas were covered with dead culms in a quarter of the investigation spots. On the other hand, the P. pubescens forests were completely unaffected by the disease. The species composition in the diseased bamboo forests was more diverse than that of the healthy bamboo forests, and the species richness of the former was higher than that of the latter. We suggest that the disease had a negative impact on the structure of the P. bambusoides forests and a positive impact on its species composition and species richness. Further, it had an unusual influence on the P. pubescens forests.
