The Bornean orangutan (Pongo pygmaeus) in a vanishing peatswamp forest: Increasing habitat connectivity in the former Mega Rice Project, Indonesia

Background/Question/Methods

I conducted a spatially explicit analysis of a fragmented peatswamp forest area in Indonesia that explores whether the conservation targets of ape preservation and carbon storage can be mutually satisfied through land management strategies. As peatswamp forests become increasingly fragmented due to logging, development of agricultural plantations, and fires, the peat soil emits CO₂ as it degrades. Furthermore, the species that depend upon these forests, notably the endangered Bornean orangutan (Pongo pygmaeus), are dwindling. The patchy peatswamp forest fragments that compose a failed agricultural project, known as the Mega Rice Project (MRP) in Central Kalimantan, Indonesia are all reported to contain orangutans. However, no comprehensive survey for orangutans has ever been conducted. I carried out a survey of the density and population size of the orangutans in a portion of the MRP, by surveying 26.3 km of line transects for orangutan sleeping nests and identifying remaining forest fragments by conducting a supervised classification of Landsat 7 TM imagery. Then, I analyzed habitat connectivity and proposed corridors through degraded areas between six priority patches using least-cost path methods. The corridors included areas of high carbon value and of high habitat suitability identified using maximum entropy methods.

Results/Conclusions

I found that the area of the remaining peat-swamp forest totaled 66,906 hectares, only 53,687 hectares of which forms patches larger than 350 hectares, the minimum required to support an orangutan individual. I estimate the average regional population density of orangutans as 2.52 individuals / km², and the total population of orangutans in Block C of the MRP as 2,161 individuals, only 1,146 of which were located in forest fragments with a population size large enough to be considered viable in terms of long-term demographic and genetic stability. The proposed corridors would increase the viable population size to 1,788 individuals. This project demonstrates that there is still a substantial population inhabiting the area, but highlights the need to restore connectivity between these patches and prevent agricultural development, logging, and fires from destroying and further fragmenting the remaining forest patches. This project also demonstrates how the incentive of carbon financing can make possible wildlife protection strategies, and how spatial planning can be used to maximize biodiversity and ecosystem service benefits on the landscape.