PARENT SESSION
Poster Session #41: Invasive Species Ecology: Woodlands.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Alteration of secondary-successional pathways in northwestern Pacific islands by the invasion of Leucaena leucocephala.

YOSHIDA, KEIICHIRO^*,1, OKA, SHUICHI², ¹ National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan² Tokyo Metropolitan University, Hachioji, Tokyo, Japan

ABSTRACT- It is commonly believed that plant communities on continental islands are less susceptible to invasion by exotic plant species than are those on oceanic islands, due to their greater native diversity. To test this hypothesis, we compared the successional pathways in abandoned fields invaded by Leucaena leucocephala on Haha-jima Island, an oceanic island, and Miyako-jima Island, a continental island. Interpretation of aerial photographs and field investigation indicated that Leucaena leucocephala scrub became established on both subtropical islands immediately after agricultural abandonment. There was, however, a significant difference in the secondary-successional pathways on the two islands. On Haha-jima Island, the invasion of this alien species altered the secondary-successional pathway irreversibly, because Leucaena leucocephala scrub restricted the establishment of indigenous species. By contrast, Leucaena leucocephala invasion did not affect the secondary-successional pathway as seriously on Miyako-jima Island, where dense thickets of Leucaena leucocephala were replaced directly by indigenous species of fast-growing secondary trees (Macaranga tanarius and Melanolepis multiglandulosa). These results provide evidence for the hypothesis that simple communities on oceanic islands are more susceptible to invasion by Leucaena leucocephala than diverse communities on continental islands. It is possible that the greater susceptibility to Leucaena leucocephala invasion was due to the scarcity of fast-growing secondary-forest species in the indigenous flora.

KEY WORDS: biological invasion, Leucaena leucocephala, subtropical islands, successional pathway