Leuser Ecosystem
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Summary
- Sumatran orangutans (Pongo abelii) are present in the Leuser Ecosystem.
- It has been estimated that 13,846 (CI: 11,561-16,805) individuals occur in the site.
- The orangutan population trend is decreasing.
- The site has a total size of 2.6 million ha.
- Key threats to orangutans are deforestation, construction of roads and planned construction of hydroelectric power plants, poaching, and capturing of young orangutans for the illegal pet trade.
- Several NGOs are involved in the implementation of conservation interventions; for example, the Human-Orangutan Conflict Response Unit rescues and relocates orangutans trapped by humans.
Site characteristics
The site is located in the provinces of Aceh and North Sumatra, at the northernmost tip of Sumatra, Indonesia. The area is extremely rich in biodiversity; more than 200 mammal species, 580 bird species, and an estimated 10,000 plant species, including 17 endemic genera, can be found at the Leuser Ecosystem. Within Leuser, the coastal peat swamp forests of Tripa, Kluet, and Trumon-Singkil harbour the highest densities of orangutans. In addition to Sumatran orangutans, the Leuser Ecosystem is also home to the last remaining viable populations of Sumatran tigers, Sumatran rhinoceros, and Sumatran elephants (Sumatran Orangutan Conservation Programme). The Leuser Ecosystem is designated as a National Strategic Area for its environmental function. This designation does not exclude non-forest uses, but stresses the importance of sustainable management (Singleton et al. 2018). The Gunung Leuser National Park is found within the Leuser Ecosystem, which is also designated a Man and Biosphere Reserve, and is part of the Tropical Rainforest Heritage of Sumatra World Heritage Cluster Site by UNESCO (Singleton et al. 2018). The park supports only 25.3% of Sumatra’s Orangutans. Also within the Leuser Ecosystem, is the 1,025 km² Singkil Swamps Wildlife Reserve (Singleton et al. 2018).
Table 1. Basic site information for Leuser Ecosystem
| Species | Pongo abelii |
| Area | 26000 km² |
| Coordinates | 3.630896, 97.378969 |
| Type of site | Conservation area (National Strategic Area) |
| Governance type | Governance by government |
| Habitat type | Subtropical/tropical dry forest, plantations, subtropical/tropical heavily degraded former forest |
Ape status
The peat-swamp forests of the Leuser Ecosystem hold the highest Sumatran orangutan densities (Wich et al. 2016). The species is predicted to decline across a variety of land-use scenarios; as many as 4,500 individuals could vanish by 2030 (Wich et al. 2016).
Table 2. Ape population estimates in Leuser Ecosystem
| Species | Year | Occurrence | Encounter or visitation 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 abelii | 1999-2013 | Present | 0.73 | 13846 (11561-16805) | Leuser Ecosystem | Line transects | Wich et al. 2016 |
Threats
Key threats to orangutans at the Leuser Ecosystem include habitat destruction, habitat fragmentation, hunting, and the illegal pet trade (SOCP). New roads are continuously being cut through the habitat. In addition to habitat encroachment, palm oil concessions, and new hydro electric schemes and geothermal energy plants are proposed in critical areas (SOCP). As a by-product of land-conversion and increased proximity to humans, orangutans are sometimes killed due to human-wildlife conflict situations, for example, when orangutans raid farmlands (Singleton et al. 2018).
Table 3. Threats to apes in Leuser Ecosystem
| Category | Specific threats | Threat level | Description | Year of threat |
|---|---|---|---|---|
| 1. Residential & commercial development | Unknown | |||
| 2. Agriculture & aquaculture | Unknown | |||
| 3. Energy production & mining | 3.3 Renewable energy | Low | Proposed construction of several new hydroelectric power plants leading to habitat loss (Wich pers. comm. 2020; SOCP). | Ongoing (2020) |
| 4. Transportation & service corridors | 4.1 Roads & railroads | Medium | The construction of roads is causing forest loss and forest fragmentation (Wich et al. 2016). | Ongoing (2016) |
| 5. Biological resource use | 5.1.5 Persecution/human wildlife conflict | Low | Poaching/persecution. Orangutans are captured or killed when they leave the forest and enter agricultural land or areas that have been recently deforested (Wich et al 2016; Singleton et al. 2018). | 2016-Ongoing (2018) |
| 5. Biological resource use | 5.1.4 Capture for the live animal trade | Present (unknown severity) | Capturing young orangutans for illegal pet trade (SOCP). | Ongoing (2023) |
| 5. Biological resource use | 5.3 Logging & wood harvesting | Medium | Deforestation as a result of land-cover changes (Wich et al. 2016). | Ongoing (2016) |
| 6. Human intrusion & disturbance | Unknown | |||
| 7. Natural system modifications | Unknown | |||
| 8. Invasive & other problematic species, genes, diseases | Unknown | |||
| 9. Pollution | Unknown | |||
| 10. Geological Events | Absent | |||
| 11. Climate change & severe weather | Unknown | |||
| 12. Other options | Absent |
Conservation activities
A number of NGOs are active in the implementation of conservation activities, including the Sumatran Orangutan Conservation Programme (SOCP), the Orangutan Information Center (OIC), the Leuser International Foundation (LIF), and HAkA.
Table 4. Conservation activities in Leuser Ecosystem
| Category | Specific activity | Description | Implementing organization | Year of activity |
|---|---|---|---|---|
| 1. Development impact mitigation | Not reported | |||
| 2. Counter-wildlife crime | Not reported | |||
| 3. Species health | Not reported | |||
| 4. Education & awareness | Not reported | |||
| 5. Protection & restoration | Not reported | |||
| 6. Species management | 6.7 Translocate (capture & release) wild apes from human impacted sites to natural habitat elsewhere | The Human-Orangutan Conflict Response Unit rescue, relocate, and confiscate orangutans in human-orangutan conflict situations (OIC). | Ongoing (2023) | |
| 7. Economic & other incentives | Not reported | |||
| 8. Permanent presence | Not reported |
Conservation implementation challenges and enablers
Table 5. Challenges reported for Leuser Ecosystem
| Category | Challenge | Source | Year(s) |
|---|---|---|---|
| 1. Site management | 1.2 Need for improved coordination | Wich pers. comm. 2020 | |
| 2. Resources & capacity | Not reported | ||
| 3. Engaged community | Not reported | ||
| 4. Institutional support | 4.1 Lack of law enforcement | Singleton et al. 2018 | |
| 4. Institutional support | 4.3 Lack of protected area status | Singleton et al. 2018 | |
| 5. Ecological context | Not reported | ||
| 6. Safety & stability | Not reported |
Table 6. Enablers reported for Leuser Ecosystem
| Category | Enabler | Source | Year(s) |
|---|---|---|---|
| 1. Site management | Not reported | ||
| 2. Resources & capacity | Not reported | ||
| 3. Engaged community | Not reported | ||
| 4. Institutional support | Not reported | ||
| 5. Ecological context | Not reported | ||
| 6. Safety & stability | Not reported |
Research activities
Documented behaviours
Table 7. Ape behaviors reported for Leuser Ecosystem
| Behavior | Source |
|---|---|
| Not reported |
External links
References
Singleton, I., Wich , S.A., Nowak, M., Usher, G. & Utami-Atmoko, S.S. 2017. Pongo abelii (errata version published in 2018). The IUCN Red List of Threatened Species 2017: e.T121097935A123797627. http://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T121097935A115575085.en
Page completed by: Serge Wich & A.P.E.S. Wiki team Date: 30/12/2020