Influence of forest structure on Sumatran orangutan ecology in a recovering lowland dipterocarp forest

Authors: Abernethy, J., Nowak, M., Korstjens, A.H., Hill, R.A., Consiglio, R.A., Slater, H.D. and Wich, S.A.!programme/c6xf

Start date: 29 June 2016

Orangutan nests are widely used for estimating their population numbers and densities, and also enable research into their habitat preference and ability to cope with change. Given that orangutans spend significant proportions of their lives at nests, the quality of nest sites must have implications upon an individual’s survival and fitness. Sikundur, an area of lowland dipterocarp forest in the Gunung Leuser National Park, presents an opportunity to investigate orangutan numbers and preferences across a gradient of human influence, from primary rainforest, to natural recovered and recent human-led reforestation. Expected results are a bias towards areas with less disturbance and human activity and the selection of taller, older trees better able to provide safe nesting sites. Through vegetation and nest line transects, in-depth forest structure data has been collected using a mix of traditional methods along with canopy hemispherical photography and ground based LiDAR, to more accurately quantify forest structure. Preliminary results show a clear bias for taller trees (t1307=4.76, p=<0.0001) and a predilection for certain species, with 8 of the 27 genera recorded containing 52% of all nests. Canopy hemispherical photography will help quantify the quality of the forest and how gaps and canopy contiguity affect orangutan habitat preference. Further data will be collected this year from the primary and reforestation sites, supplemented with ground based LiDAR along with point cloud data from drone flights. A developed density surface model will use forest structure factors alongside nest data to predict areas of greater orangutan densities and conservation significance.

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