Aims In situ species survival involves persistence at current sites and/or colonization of new locations. Determining the likelihood of these events requires an understanding of population dynamics and dispersal. We address these issues in populations of a critically endangered tropical conifer Araucaria nemorosa and provide conservation recommendations.
Location Port Boise, island of Grand Terre, New Caledonia, Pacific Ocean.
Methods We characterize the demographic structure of six populations of A. nemorosa based upon size class frequencies and relative basal area compared to competing angiosperm trees. Using genotype data from 280 adult individuals at seven microsatellite loci, we indirectly estimate dispersal distances and project a maximal dispersal envelope around the extant populations.
Results Our survey detected marked differences in demographic parameters including the proportion of basal area occupied by A. nemorosa versus angiosperm trees (ranging from 25% to 77%), the size class frequency distributions of A. nemorosa and seedling densities (ranging from 500 to 37300 seedlings ha(-1)) among some populations. Wright's genetic neighbourhood ranged from 22 to 876 trees, and historic gene dispersal ranged from 10.8 to 82.4 m, indicating that most seed dispersal is < 100 m.
Main conclusions This study indicates that the risk of recruitment failure in remnant populations of Araucaria nemorosa is low in most of the stands but is high in the inland population Foret Nord. In situ natural regeneration appears to be constrained in this population, most likely as a consequence of competitive exclusion. Our results also suggest that the majority of seed dispersal is too short to allow A. nemorosa to disperse to new more hospitable sites within an ecologically relevant time-scale. Our findings have implications not only for this emblematic tree species but also for a wide range of fragmented and degraded plant species populations with limited dispersal that are vulnerable to competitive exclusion.
- natural regeneration
- New Caledonia
- seed dispersal