Impacts on tree diversity in a malagasy lowland rainforest of soil type, a devastating cyclone and an invading pioneer

Abstract

At Manombo Reserve Speciale, lowland rainforest occurs both on ferralitic soil of volcanic (basaltic) origin, and, just a few kilometers eastward, on white sand. Much of the forest on basaltic soil was devastated by cyclone Gretelle on 24 January 1997. In some parts of this forest the cyclone snapped or knocked over most trees over 10 m tall. Introduced Cecropia peltata recruited copiously in devastated areas, and seemed poised to take over the forest. In October 2005, we censused stems ¡Y 5 cm dbh on two plots of approximately 0.25 ha apiece, one in devastated forest on basaltic soil, one in less damaged, intensely managed forest on white sand, to assess diversity and species composition on the two soil types. This paper centers on three questions: (1) How does soil quality affect diversity and species composition? (2) Did cyclone Gretelle diminish tree diversity in devastated areas of the reserve? (3) Is Cecropia peltata simply an early successional species, which more shade-tolerant native species will replace