land clearance for agriculture. Tey fragment the forests into ever smaller patches, and hence the species, such as orangutans, that live within them into smaller and smaller populations that may no longer be large enough to survive in the long term.
Remote sensing and computer modelling of road developments in North Sumatra and Aceh reinforce these observations, since they confirm that roads lead to large increases in forest loss, with accompanying reductions in orangutan numbers (Gaveau et al. 2009). Many planned roads threaten the forests where orangu- tans occur, including both peat swamp forests and inland forests on mineral soils (Map 9). Often such roads are crossing pro- tected areas such as the Gunung Leuser National Park.
Agricultural expansion Te lowland forest areas, where most Sumatran orangutans are found, also represent by far the most suitable land for agricultur- al development, especially for plantation crops such as cacao, oil palm and rubber. Of these, the rapid expansion of oil palm plan- tations in recent years probably represents the greatest single agricultural threat to orangutan survival in the region because of its rapid expansion (Dros 2003; Koh and Wilcove 2007; Murdi- yarso et al. 2010). Te establishment of many of these planta- tions has resulted in significant losses in orangutan habitat, since they have been created by converting forests instead of making use of already deforested areas, such as existing agricultural or low current use value land (Map 10).