Putting orang-utan population trends into perspective

Is it true that “the orang-utan could be virtually extinct within five years”, as reported by [1] in a recent issue of Current Biology? The dire conservation status of this ape warrants a sense of urgency [2], but we would like to present a more balanced view and highlight the emergence of some positive trends. Illegal logging, forest conversion and associated fires occur in most Indonesian national parks containing orangutan populations [3]. But on both Borneo and Sumatra about 75% of all orangutans occur outside national parks [3,4]. To predict the future of the two orangutan species (Pongo spp.), forest loss trends in these areas must be considered. Using World Conservation Monitoring Centre data, we estimate that, in 1990, there was 174,627 km2 of orangutan habitat on Borneo, of which 130,919 km2 remained in 2004 (based on Landsat TM imagery 2004/2005). This indicates a mean annual reduction of 3,122 km2, which, if continued, will lead to extinction of the Bornean orangutan just before 2050, if habitat loss were the only factor considered. Different data sources and methodologies produce different forest loss estimates. Rather than quibble over numbers we point to hopeful trends. Our forest cover monitoring indicates that by 2005, the rate of loss of orangutan habitat in East Kalimantan Province had declined to less than 0.6% per year, from 2% per year between 1996 and 2002 [5]. The main reason for this decline was the development of forest management programs, including protected areas, co-managed by local communities and local government, and the improvement of timber concession management (our unpublished data). On Borneo, orangutans appear to cope relatively well with timber extraction, and there well managed timber concessions are compatible with orangutan conservation [6–8]. In addition, field surveys of illegal logging, another major threat to orangutan habitat, indicate that the Indonesian Government has since 2005 managed to reduce this in East and West Kalimantan. In most Sumatran orangutan habitat, forest loss was around 1–1.5% per year between 1985 and 2001 (adapted from total forest loss data in [6]), but in recent years this has slowed down to about 0.4%/year (based on SPOT imagery analysis: M. Griffiths, pers. comm.) in the Leuser Ecosystem where 76% of the Sumatran orangutans occur [5]. Through recent political changes, management responsibility for the Leuser Ecosystem has been ceded to the provincial government of Nanggroe Aceh Darussalam (although the legality of this remains disputed). The Aceh government recently announced a temporary moratorium on logging in the province. Meanwhile, the Leuser management team has successfully implemented long-term operations in the Leuser Ecosystem to stop illegal logging, conversion and encroachment. Pressure on the forests remains, but we consider these developments as hopeful signs. We do not want to play down the decline of orangutan habitat and the loss of orangutans through hunting, pet trade, and possibly disease [3,8]. The present positive developments are tentative and could still revert to situations like those that caused vast orangutan loss in the 1990s. The state of the Sumatran orangutan is critical with 7,000– 7,500 animals surviving in a much fragmented forest landscape [3]. Compared to the Bornean orangutan, the Sumatran species appears to cope less well with logging [3,4]. Some 40,000–50,000 Bornean orangutans remain, but these are distributed over almost 50 geographically isolated subpopulations [3,4]. The conversion of lowland forest for oil palm and other plantation crops is a serious threat to orangutans. For the survival of many orangutan populations it is crucial that these plantations are only established on deforested and heavily degraded lands and that fire is not used in land preparation. In summary, a critical view is needed of the factors that threaten orangutan survival, as well as current orangutan conservation efforts [4,9]. But we want to ensure that the criticism is constructive and realistic.