The geographic distribution of Bornean orang-utans and its overlap with existing land-use categories (protected areas, logging and plantation concessions) is a necessary foundation to prioritize conservation planning. Based on an extensive orang-utan survey dataset and a number of environmental variables, we modelled an orang-utan distribution map. The modelled orang-utan distribution map covers 155,106 km2 (21% of Borneo's landmass) and reveals four distinct distribution areas. The most important environmental predictors are annual rainfall and land cover. The overlap of the orang-utan distribution with land-use categories reveals that only 22% of the distribution lies in protected areas, but that 29% lies in natural forest concessions. A further 19% and 6% occurs in largely undeveloped oil palm and tree plantation concessions, respectively. The remaining 24% of the orang-utan distribution range occurs outside of protected areas and outside of concessions. An estimated 49% of the orang-utan distribution will be lost if all forest outside of protected areas and logging concessions is lost. To avoid this potential decline plantation development in orang-utan habitats must be halted because it infringes on national laws of species protection. Further growth of the plantation sector should be achieved through increasing yields in existing plantations and expansion of new plantations into areas that have already been deforested. To reach this goal a large scale island-wide land-use masterplan is needed that clarifies which possible land uses and managements are allowed in the landscape and provides new standardized strategic conservation policies. Such a process should make much better use of non-market values of ecosystem services of forests such as water provision, flood control, carbon sequestration, and sources of livelihood for rural communities. Presently land use planning is more driven by vested interests and direct and immediate economic gains, rather than by approaches that take into consideration social equity and environmental sustainability.

New surveys provide higher estimate of Sumatran orangutans than previously, but future scenarios indicate decline continues.

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To conserve species it is essential to understand which factors determine their distribution and density. Here we focus on the critically endangered Sumatran orang-utan and examine factors that influence the distribution and density in the Batang Toru area, the southernmost area where wild orangutans occur on Sumatra. We contrast a scenario in which orang-utan distribution is mainly determined by ecological, and topographic variables with a model that includes hunting and human impact. We show that orang-utan distribution and density are best explained by hunting pressure and elevation. These results indicate that an assessment of anthropogenic factors that might influence density such as hunting needs to be included in surveys that aim to predict orang-utan distribution and density. As anthropogenic impact becomes higher with increasing human population density and increased forest access in most areas where orang-utans occur the consequence is that orang-utan conservation will have to be achieved in an environment modified by humans. In such areas the potential for a range of conflicts such as hunting that lead to human-caused mortality for orang-utans will remain a constant threat and need to be mitigated. To conserve species it is essential to understand which factors determine their distribution 27 and density. Here we focus on the critically endangered Sumatran orang-utan and 28 examine factors that influence the distribution and density in the Batang Toru area, the 29 southernmost area where wild orang-utans occur on Sumatra. We contrast a scenario in 30 which orang-utan distribution is mainly determined by ecological, and topographic 31 variables with a model that includes hunting and human impact. We show that orang-utan 32 distribution and density are best explained by hunting pressure and elevation. These 33 results indicate that an assessment of anthropogenic factors that might influence density 34 such as hunting needs to be included in surveys that aim to predict orang-utan distribution 35 and density. As anthropogenic impact becomes higher with increasing human population 36 density and increased forest access in most areas where orang-utans occur the 37 consequence is that orang-utan conservation will have to be achieved in an environment 38 modified by humans. In such areas the potential for a range of conflicts such as hunting 39 that lead to human-caused mortality for orang-utans will remain a constant threat and 40 need to be mitigated. 41 42

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