The distribution and density of Tapanuli orangutans (Pongo tapanuliensis) at potential corridor locations between forest fragments in Batang Toru, North Sumatra, Indonesia

Abstract

Abstract. Nasution A, Perwitasari-Farajallah D, Utami-Atmoko SS. 2020. The distribution and density of Tapanuli orangutans (Pongo tapanuliensis) at potential corridor locations between forest fragments in Batang Toru, North Sumatra, Indonesia. Biodiversitas 21: 5382-5388. The newly discovered Tapanuli orangutan (Pongo tapanuliensis) is in danger of being lost in a few decades due to their small population number in fragmented forest of Batang Toru. The major threats faced by this critically endangered ape, including: hunting, habitat loss, and fragmentation due to large infrastructure development and other developments in the key corridor area. The establishment of corridor and buffer zone is one such effort to maintain their population and bring them from the brink of extinction. Data on the population and distribution are needed to assess and provide baseline information for investigating the habitat condition of potential corridors and buffer zones. This study aimed to analyze population and distribution of Tapanui orangutan (Pongo tapanuliensis) in buffer zone and potential corridor of Batang Toru. Our study provides an initial dataset prior to the development of the hydrodam, which is important to understand the future post-development impact. The study was carried out in disturbed (Hutaimbaru and Bulu Mario) and undisturbed forest (Sitandiang and Hopong) of Batang Toru from June 2015 until February 2016. Orangutan nest, fig (Ficus spp.), and trees bearing fruit were recorded using a line transect method. This research showed that population and distribution of orangutan were influenced by forest conditions, threat level, and fruit availability. There were fewer nests per km2 in disturbed forest than in undisturbed forest, resulting in an orangutan density estimation to be 0.24 ind/km2, 0.14 ind/ km2 (Hutaimbaru and Bulu Mario) and 0.74 ind/km2, 0.36 ind/km2 (Sitandiang and Hopong). Number of nest in transects was influenced by the availability of fig class I and class II, but not fruit tree. The APL forest of Sitandiang is key area to connect the three populations of Tapanuli orangutan: east Batang Toru, west Batang Toru, and Sibualbuali. Furthermore, orangutan’s nests were encountered both in protected and non-protected forest, thus protection of such areas, especially areas including primary forest that harbor orangutan is essential for their long term survival. The conservation measures and action Tapanuli orangutan is alarming, thus we recommend all remaining habitat should be officially and strictly protected and collaboration work with multi-stakeholder is essential to establish the corridor as well as the strategic management plan of Tapanuli orangutan.

Population Status of Tapanuli Orangutan (Pongo tapanuliensis) within the Renewable Energy Development and its Management Implications

“…However, those studies were used a different method which led to a different result from previous orangutan density study for Tapanuli orangutan. Our finding supports previous study in which orangutan density was increased at the time of less disturbances from the construction activities considering low threats (Wich et al, 2012;Nasution et al, 2020).…”

“…The distribution of Tapanuli orangutan was focused in undisturbed forest (Wich et al, 2012), and other populations could be found in the disturbed forest (Nasution et al, 2020;Kuswanda et al, 2020). Aligned with those findings, Rahman et al (2019) calculated the suitability habitat for Tapanuli orangutan, which protected area was potentially suitable for orangutans i.e.…”

“…Specifically, Nasution et al (2018) conducted a study in the east block and focused on the Sibual-buali reserve area in 2015 and estimated the population density to be 0.4 ind/Km 2 . Recently, Nasution et al (2020) published a new update on Tapanuli orangutan density focusing on east block population. They found the ranges to be from 0.14 -0.74 ind/Km 2 depending on geographical elevation and land status.…”

“…As the distribution of Tapanuli orangutan was separated into two different and more significant populations i.e. west and east blocks (Wich et al, 2019), and the population within the east block was scattered into some small populations (Nasution et al, 2020;Kuswanda et al, 2020). The local government has initiated the creation of corridors to connect the orangutan populations known as Sibual-buali corridor and Sipirok corridor to connect the west and east population, and a corridor to connect Sibual-buali and Sipirok populations.…”

“…Although, the implementation might be challenged, the collaboration could be conducted with local communities and government. The previous findings on orangutan distribution outside the protected area shall be considered (Nasution et al, 2020;Kuswanda et al, 2020).…”