Invasion of Leucaena leucocephala and its Effects on the Native Plant Community in the Ogasawara (Bonin) Islands1

摘要

To examine the effect of biological invasion by early-successional exotic plant species on the secondary succession of native plant species, we compared secondary forests with and without koa haole invasion, which became established in fields that were abandoned for 55 yr on Chichi-jima and Haha-jima in the Ogasawara (Bonin) Islands, in the northwestern Pacific. A comparison of the forest structure and the composition of secondary forest showed that the species richness of native plant species was significantly lower, and the basal area of late-successional alien plants (bischofia and Korean mulberry) was significantly larger in secondary forests with koa haole invasion than in those without koa haole invasion. The secondary forests in areas that had been invaded by koa haole had a significantly smaller basal area of native plant species and a greater area of late-successional alien plants in the understory than those in areas that had not been invaded by koa haole. These results suggest that in the Ogasawara Islands, the native species are incapable of replacing dense koa haole thickets directly and that invasion by koa haole promotes invasion and establishment of more aggressive alien plant species. Consequently, the invasion and expansion of koa haole has had a severe effect on the native plant community in the Ogasawara (Bonin) Islands and may alter the secondary succession.