Ecophysiological and community-level constraints to the invasion of Myrica faya, an alien tree in Hawaii Volcanoes National Park.

摘要

Myrica faya is an alien tree invading the montane and submontane forest and submontane grassland communities of Hawaii Volcanoes National Park. The goals of my research were to identify possible community-level constraints to Myrica establishment in rain forest communities within the current range of Myrica in the park and to determine the potential for further range expansion of Myrica.;Seed germination, seedling mortality and seedling growth were monitored in Metrosideros rain forest communities with dense understory cover of the ferns, Dicanopteris linearis and Cibotium glaucum. These fern understories reduced incoming light to less than 1% of full sun, resulting in low germination, high mortality and low growth rates of seedlings. Myrica seedling recruitment appeared to occur primarily in gaps in the understory fern cover. Within the current invasion range of Myrica, low light availability in the understory of intact rain forest communities is a predominant factor restricting Myrica invasion of these habitats.;The potential for the invasion of Myrica beyond its current range was investigated near two invasion fronts; one in the wet montane rain forest and the other in the seasonally dry submontane grassland. Seed inputs, seed germination, seedling survival and growth rates were determined. While seed inputs were low beyond both invasion fronts, constraining the potential rate of invasion, the response of Myrica to particular characteristics of each habitat also limited establishment. In the wet, montane rain forest, seed germination was greatly inhibited, probably due to the interaction of low light availability in the understory and high soil water content. In contrast, establishment in the high light environment of the seasonal submontane grassland was restricted by the susceptibility of seeds and young germinants to high moisture stress during the summer, which resulted in low seed germination and high seedling mortality. Though seedlings growth rates were high during the wet season, growth rates were significantly reduced during the dry summer period.