Sungai Lesan Protected Forest
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Summary
- Northeast Bornean orangutans (Pongo pygmaeus morio) are present in Sungai Lesan Protected Forest.
- The orangutan population size is unknown.
- The orangutan population trend is decreasing.
- The site has a total size of 102.4 km².
- The main reported threats are illegal logging, deforestation for palm oil plantations, illegal mining activities, and human–wildlife conflicts.
- Conservation efforts have primarily centered on rehabilitating natural habitats, orangutans release site and community awareness raising.
- Since 2013, the site has held a protected area status.
Site characteristics
Sungai Lesan Protected Forest', ranging from 40 to 430 meters above sea level, represents one of the remaining well-preserved lowland forests in Berau Regency. Around 85% of the area consists of healthy, previously logged forest dominated by Dipterocarpaceae species. It serves as a vital habitat for Northeast Bornean orangutans and plays a crucial role in maintaining regional water balance. As a catchment area for the Pesan and Leja Rivers—tributaries of the Lesan River—any degradation to this ecosystem may worsen downstream watershed conditions, particularly by increasing sedimentation in the Kelay River, which flows into Tanjung Redeb.(Hutan Lindung Sungai Lesan 2025).
Table 1. Basic site information for Sungai Lesan Protected Forest
| Species | Pongo pygmaeus morio |
| Area | 102.4 km² |
| Coordinates | Lat: 1.60693 , Lon: 117.12662 |
| Type of site | Protected area (Protection Forest) |
| Habitat types | Subtropical/tropical moist lowland forest |
| Type of governance | Governance by government |
Types of sites Governance types Habitat types
Ape status
Table 2. Ape population estimates reported for Sungai Lesan Protected Forest
| Species | Year | Occurrence | Encounter or vistation rate (nests/km; ind/day) | Density estimate [ind./ km²] (95% CI) | Abundance estimate (95% CI) | Survey area | Sampling method | Analytical framework | Source | Comments | A.P.E.S. database ID |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Pongo pygmaeus morio |
Sampling methods Analytical frameworks
Threats
Table 3. Threats to apes reported for Sungai Lesan Protected Forest
| Category | Specific threats | Threat level | Description | Year of threat |
|---|---|---|---|---|
| 2 Agriculture & aquaculture | 2.1 Annual & perennial non-timber crops | High (more than 70% of population affected) | Deforestation due to palm oil expansion (Fund Forests 2025). | Ongoing (2025) |
| 3 Energy production & mining | 3.2 Mining & quarrying | Present (unknown severity) | Illegal gold mining, was reported (Fund Forests 2025). | Ongoing (2025) |
| 5 Biological resource use | 5.1.5 Persecution/human wildlife conflict | Present (unknown severity) | Human-wildlife conflict is reported as notable issue, with orangutans and other primates frequently entering nearby farms in search of food (Fund Forests 2025). | Ongoing (2025) |
| 5 Biological resource use | 5.3 Logging & wood harvesting | High (more than 70% of population affected) | Illegal logging activities are reported present (Antara News 2018, Fund Forests 2025). | 2018-Ongoing (2025) |
Conservation activities
Table 4. Conservation activities reported for Sungai Lesan Protected Forest
| Category | Specific activity | Description | Implementing organization(s) | Year of activity |
|---|---|---|---|---|
| 5 Protection & restoration | 5.2 Legally protect ape habitat | Sungai Lesan Protected Forest has held protected status since 2013 (Sherman et al. 2022). | 2013-Ongoing (2026) | |
| 5 Protection & restoration | 5.6 Habitat restoration | Habitat management activities were reported to be present (Sherman et al. 2022). | Ongoing (2022) | |
| 6 Species management | 6.7 Translocate (capture & release) wild apes from human impacted sites to natural habitat elsewhere | Sungai Lesan Protected Forest has been designated as both a protected area and a release site for orangutans (Sherman et al. 2022). In October 2021, “Chiko,” an adult male habituated to humans in the PT Kaltim Prima Coal concession, was relocated to Sungai Lesan Protected Forest. Authorities confirmed the forest’s capacity to support him, noting suitable wilderness habitat and low orangutan density (PT Kaltim Prima Coal 2021). | PT Kaltim Prima Coal (KPC) | 2021-Ongoing (2022) |
| 4 Education & awareness | Other | Community outreach and capacity building (Sherman et al. 2022). | Ongoing (2022) |
Challenges
Enablers
Research activities
Research activities have been reported in Sungai Lesan Protected Forest, the details remain unknown (Sherman et al. 2022).
Documented behaviours
Exposure to climate change impacts
External links
References
Antara News. (2018, February 8). Deforestation threatens orangutan population. https://en.antaranews.com/news/114548/deforestation-threatens-orangutan-population
Fund Forests. (2025). Lesan River Forest. https://www.fundforests.org/lesan-river-forest
Hutan Lindung Sungai Lesan. (2025). Hutan Lindung Sungailesan (HLSL) 11. Blogspot. https://hutanlindungsungailesan.blogspot.com/p/hutan-lindung-sungailesanhlsl-11.html
PT Kaltim Prima Coal. (2021, November 10). Chiko has occupied his new home in the Sungai Lesan. https://www.kpc.co.id/2021/11/10/chiko-has-occupied-his-new-home-in-the-sungai-lesan/
Sherman, J., Voigt, M., Ancrenaz, M., Wich, S. A., Qomariah, I. N., Lyman, E., …, & Meijaard, E. (2022). Orangutan killing and trade in Indonesia: Wildlife crime, enforcement, and deterrence patterns. Biological Conservation, 276, 109744. doi:10.1016/j.biocon.2022.109744
Page created by: Aime Mizero Date: 2025-06-02