Optimum Area of Semi-Natural Grassland to Maintain Maximum Butterfly and Avian Species Richness in Japan

Optimum Area of Semi-Natural Grassland to Maintain Maximum Butterfly and Avian Species Richness in Japan

To evaluate the optimum area of semi-natural grassland to maintain maximum butterfly and avian species richness in Japan, digitalized grid data of butterfly and avian distribution, as well as vegetation distribution, throughout the country were used. After obtaining logistic regression models explaining the probabilities of occurrence of each species with semi-natural grassland area and latitude as variables, the optimum value was calculated. The expected maximum species richness of butterflies in the country was the highest in the case of about 40 square kilometers of semi-natural grassland per 100 square kilometers, though the value varied somewhat with latitude. The expected maximum species richness of birds was the highest in the case of about 60 square kilometers of semi-natural grassland per 100 square kilometers. This study showed that the decrease in semi-natural grassland in Japan has resulted in far from ideal conditions for many species.