Abstract
Forest damage occurs in the common cormorant's (Phalacrocorax carbo) colony or roost. The relationship between colonization of the common cormorant and forest decline was studied at the Isaki Peninsula which faces Lake Biwa, Shiga Prefecture. The forest was classified into 5 types according to both number of nests and the extent of forests. Individual trees were classified into 5 -damage degree from healthy to death. Five plots, 0.25ha each, were established for examining the influence of the nesting on individual trees. Tree species, DBH, the number of nests and the extent of the trees healthy were checked up in each plot. An 2,000 m belt transect was set to estimate the situation of forest decline, the total number of nests and vegetation cover in the whole study area. At the most part, nests were found on declining trees, and no nest was observed at dead trees in all plots. The analysis of increment core sampled from about 40 trees showed that the dam- age degree of tree can be an index for the tree's physiological decline. The number of common cormorant's nests have been increasing and forest decline have been proceeing in the peninsula since 1996.
