Reintroduced Sumatran orangutans (Pongo abelii): using major food tree species as indicators of habitat suitability.

Reintroducing orangutans (Pongo spp.) into the wild requires a suitable, secure habitat. To identify acceptable areas for their reintroduction and define priority conservation sites, we analysed the tree species composition in the Bukit Tigapuluh ecosystem in Jambi, Sumatra. We used this information to determine the distribution patterns of those species that represent an essential part of the diet of reintroduced orangutans. Important orangutan food tree species showed significant differences in composition, frequency and abundance among topographic forest types and recovered selectively logged and unlogged forests. Riparian forests and recovered selectively logged areas offered a vegetation composition and forest structure most suitable for the reintroduction of orangutans and showed numerous important tree species that serve as indicator species, i.e. species growing predominantly or exclusively in a specific forest type.