The abundance of five rare tree species in forests on limestone hills of northern Vietnam

Abstract

Rare tree species may become endangered as a result of forest conversion and disturbance. The availability of reliable ecological information on such tree species may help in conservation efforts, but such data is often limited. We studied the abundance of five red-listed tree species in an old-growth forest growing on limestone hills in northern Vietnam and identified potentially relevant ecological factors. Three of the studied species are largely restricted to limestone hills and regarded as specialists (Excentrodendron tonkinense, Chukrasia tabularis and Garcinia fagraeoides), while the two other species (Parashorea chinensis and Melientha suavis) are more widely distributed. The study species were recorded across 40 initial random plots at a range of frequencies (13 - 60%) and at relatively low stem densities (0.4 - 4% of the total stems). Using the adaptive cluster sampling method (ACS), we found all species to be relatively abundant across the site. The density of the three specialist species tended to increase from lower to upper slope positions, which was consistent with an increase in rockoutcrop cover, steepness of the slope, and a reduced soil depth. However, even on rocky, steep sites we found a high variation in tree densities of these species among plots, which could not be explained by the recorded ecological factors. The non-specialist species did not occur on mostly rocky sites. We regard these results as a potential baseline from which impacts of logging can be addressed and to inform potential management.