PLANT-POPULATIONS AND MONSOON RAIN-FOREST IN THE NORTHERN-TERRITORY, AUSTRALIA

In the course of a comprehensive survey of rain forest vegetation in the Northern Territory, Australia, population size classes of presumed adults of each species present were censused at 394 mostly small (<2.5 ha) rain forest patches. It is found that populations of adult plants are typically very small; most species were represented by less than 50 adults in 81 percent of patches. Adult population size is dependent on patch size. Of 137 common rain forest species occurring at 10 percent or more sample sites, only 20 percent of species typically occurred in populations of more than 50 adults per patch. After characterizing the adult population profiles of each common species as either very small (1-6 individuals per patch; Type I), small (7-50 individuals; Type II), or large (>50 individuals; Type III), these data are modelled via logistic regression with life form, sexual reproductive mode (dioecious or cosexual individuals), diaspore dispersal agent, dispersability (vagility), diaspore dormancy, and vegetative reproductive capacity. It is found that species with typically small populations (Types I and II) are characterized by the tree habit and bird/bat dispersed diaspores. By contrast, species which typically occur in large populations (Type III) comprise disproportionately large numbers of vines and ferns, wind- and gravity-dispersed species, and clonally reproducing species. The representativeness of the sample sites, and implications for conservation, are considered in discussion. It is suggested that these data provide evidence of significant gene flow between isolated patches.