Phenology, reproductive potential, seed dispersal and predation, and seedling establishment of three invasive plant species in a Hawaiian rain forest.

摘要

The objective of this study was to investigate phenology, reproductive potential, seed dispersal and predation, and seedling establishment of three important weed species (Clidemia hirta, Hedychium gardnerianum, Psidium cattleianum) of Hawaiian rain forests. The phenology results revealed that Clidemia ripe fruit production was highest from October through January, Hedychium from October through December, and Psidium in November. Compared to Psidium of similar sizes at lower elevations, the production of ripe fruit by Psidium at the study site appeared limited. Clidemia was estimated to produce more than four orders of magnitude more seeds than Hedychium and Psidium of equal cover. Individual Clidemia plants, which averaged 0.37 m2 cover, produced an average of 3,815,552 seeds/yr. Birds, especially two common non-native species (Zosterops iaponicus and Leiothrix lutea ), are dispersing all three weed species as well as at least six native plant species, one non-native species, and four unidentified species. Under experimental conditions, the passage time for Clidemia seeds was as long as 210 minutes, for Hedychium seeds as long as 270 minutes, and with limited results, for Psidium seeds less than 60 minutes. Non-native rats (Rattus spp.) were discovered to be dispersing viable Clidemia seeds that did not differ significantly in germinability or germination rate from control seeds. Non-native rats were also discovered to have caused a 48.3% reduction in Hedychium seed production through flower bud, flower, and pre-dispersal seed predation. The final objective of this investigation was to determine which sites are suitable for germination and initial seedling growth of the study species. Results from Clidemia sites (but not Hedvchium and Psidium) indicated a large, viable seed bank and/or substantial seed rain. Clidemia produced the greatest number and heights of seedlings in scalped and grassy sites. Hedychium produced the greatest number of seedlings in epiphytic sites and the least in grassy sites. Psidium were found in three site types, with the tallest seedlings being found in fernland sites. Data from the last part of this investigation suggest that Clidemia is disturbance-adapted and less adapted to protected, shaded sites, whereas Hedychium and Psidium are greater threats to recovering and intact rain forests.