How Orangutans Cope With Fragmented Forests

Bornean orangutans in human-disturbed forests search for areas with denser and taller trees, making such patches of forest crucial for conservation.

AsianScientist (July 31, 2017) – Bornean orangutans living in forests impacted by human commerce seek areas of denser canopy enclosure, taller trees and sections with trees of uniform height, according to research from published in the Proceedings of the National Academy of Sciences.

Bornean orangutans are critically endangered, and despite intense conservation efforts, their numbers continue to decline. Additional habitat management strategies that account for their presence in forests affected by logging and other human activity are needed to ensure the species’ survival.

To determine which human-impacted forest areas are most-crucial to preventing orangutan extinction, a team of researchers led by Professor Greg Asner at the Carnegie Institution for Science used light detection and ranging (LiDAR) to forest structure in the Lower Kinabatangan region of Sabah, Malaysia, on the island of Borneo.

In addition to the LiDAR data, which uses reflected laser light to image vegetation in 3D, the study also used three years of highly detailed field observations of orangutans by researchers at Universiti Malaysia Sabah.

“Our combination of field and airborne data on orangutans and their habitat was key to understanding how they move through and use disturbed forests in Borneo,” said first author Dr. Andrew Davies, a postdoc at the Carnegie Institution for Science. “Similar approaches will be needed to determine the minimum habitat requirements of other endangered species in human-modified landscapes.”

They found that orangutans preferentially selected certain canopy attributes within forests that had been disturbed or fragmented by human activity. This means that some human-impacted forest segments are more important than others for orangutan conservation.

Because of their size, organutans require strong branches to move laterally through the forest canopy. They can descend and cross large canopy gaps on the ground, but this wastes energy and exposes them to predators. This could explain their observed preference for enclosed canopy, tall trees, and areas with uniform tree height in the human-disturbed forests studied by the team.

The researchers had anticipated that areas with a great deal of vertical complexity would be preferentially selected to assist the orangutans with climbing up and down trees. But this proved not to be the case, as lateral movement appeared to be a greater need for the orangutans.

“Considering that most of the critically endangered orangutan’s habitat is disturbed by human activities, understanding the habitat elements required to ensure orangutan survival in degraded forests is key for their long-term survival,” added Dr. Marc Ancrenaz of HUTAN/Borneo Futures, a core project partner.

The results of this orangutan study contribute to a larger Bornean biodiversity mapping mission co-led by Carnegie and the South East Asia Rainforest Research Partnership. The research group, along with government and NGO partners in Sabah, are in the process of generating a portfolio of ecological maps, ranging from forest carbon stocks to plant and animal biodiversity. The forthcoming maps have been hailed as key input to an upcoming decision by the Sabah Forestry Department about what area should next be designated as protected.

“This orangutan study is another critical piece of information we are assembling to support the Sabah government to determine where to save the most species in this super-biodiverse region of the world,” Asner added.

The article can be found at: Davies et al. (2017) Canopy Structure Drives Orangutan Habitat Selection in Disturbed Bornean Forests.


Source: Carnegie Institute of Science; Photo: Marc Ancrenaz.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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