| Despite their ecological importance and endemic status, little is known regarding the natural population dynamics of Hawaiian Cibotium. The primary goal of this research project was to determine the current population dynamics of the endemic tree fern, Cibotium chamissoi Kaulf. on Oahu Island. Demographic and molecular data were collected in order to determine recruitment, growth, mortality, and genetic diversity across existing size classes and natural habitats. Results indicate C. chamissoi demonstrates increasing growth with increasing size, and indeed can be considered slow growing species at an average of 3.8 cm/yr. Frond length and trunk top circumference were found to be better predictors of growth rate than total trunk length, although all morphological variables were significantly related to growth rate. Although recruitment was observed in half of our study sites, the rate of recruitment did not result in an increase in population size within any of the study plots at the conclusion of the study, due to greater observed rates of mortality. The oldest C. chamissoi that was measured had a trunk length of 428 cm at the conclusion of the study, and was calculated to be approximately 100 years old. In fact, it is likely that these tree ferns may be even older. Microsatellite results indicate that C. chamissoi is primarily outcrossing, with a breeding system that favors inter-gametophytic mating, as high levels of heterozygosity and genetic diversity were found within populations. Despite their high dispersal ability, however, several populations were found to have private alleles, indicating that gene flow among certain populations may be limited. |
