Population size of the endangered narrow-range endemic tree <i>Semecarpus Calcicola</i> Kochummen (Anacardiaceae), Mantanani Island, Malaysia

Abstract Semecarpus calcicola is an endangered tree restricted to Pulau Mantanani, Malaysia. New data of population size and structure was used to reassess the IUCN threat category of this species. Results are based on twenty-six 400 m 2 plots in a 26.5 ha area that included the majority of Semecarpus calcicola ’s known population. GLMs were used to investigate the relationship between the number of individuals and elevation. Estimates of the population size for each size class were determined using Horvitz-Thompson estimators, generalised regression estimators and spatial linear models and extrapolated to the study area. Elevations of the plots were obtained from a digital elevation model as auxiliary data. Significant relationships were found between the number of individuals and elevation. Mature individuals are more common at higher elevations, whilst seedlings, saplings and poles are more abundant in the lower elevation plots. Land-use change due to the increase of tourism activities and the local community drives the significant decreases of mature individuals within the lower elevation. Introduced cattle, tourism-related land-use change and plantation activities further threaten the population of S. calcicola, particularly smaller individuals due to herbivory. The estimate of population size varied among the methods and size classes. The estimated number of mature individuals ranged from 509 to 764.