Conservation and sustainable use of tropical trees in the genus Aquilaria I. Status and distribution in Indonesia Original Research Article

Tropical trees in the genus Aquilaria Lam. are the principal source of gaharu, one of the most valuable forest products traded internationally. Although these species are the focus of increasing conservation concern, information on their status and distribution is lacking. Information from herbarium accessions, a national forest inventory (NFI), field surveys and gaharu traders was used to assess the distribution of Aquilaria species in Indonesia, indicating population concentrations in Sumatra and eastern Kalimantan. Analysis of NFI data indicated that population densities are relatively low, with values generally <1.2 individuals ha−1; mean values recorded in field surveys were <0.6 individuals ha−1. Analysis of probability distributions emphasized the rarity of Aquilaria species, with a probability of encountering one or more individuals of Aquilaria in 1 ha being less than 0.2 in field assessments. Calculation of Morisitaʹs index of dispersion indicated that the species are generally clumped, with Ip typically <0.6. Analysis of stand structure suggested continuous recruitment in some areas, but a general absence of larger individuals. Given current deforestation rates, these data suggest that all Aquilaria species in Indonesia classify as Vulnerable according to the IUCN Red List criteria.