Leuser Ecosystem

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Summary

Forest view in Leuser Ecosystem © Perry van Duijnhoven

• 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 relocate orangutans trapped by humans.

Site characteristics

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  Sumatran orangutan © Perry van Duijnhoven
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  Female orangutan © Perry van Duijnhoven
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  Flanged male Sumatran orangutan © Perry van Duijnhoven

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

Area	2.6 million ha
Coordinates	3.630896 N, 97.378969 E
Designation	National Strategic Area
Habitat types	Subtropical/tropical dry forest, plantations, subtropical/tropical heavily degraded former forest

IUCN habitat categories Site designations

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	Abundance estimate (95% CI)	Density estimate [ind./ km²] (95% CI)	Encounter rate (nests/km)	Area	Method	Source	Comments	A.P.E.S. database ID
Pongo abelii	1999-2013	13,846 (11,561-16,805)	0.73		Leuser Ecosystem	Line transects (Distance)	Wich et al. 2016

Threats

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  Deforestation for small scale agiriculture © Perry van Duijnhoven
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  Draining canals in peat swamp © Perry van Duijnhoven
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  Small-scale logging © Perry van Duijnhoven

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	Quantified severity	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 Hunting & collecting terrestrial animals	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).	Ongoing (2018)
	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	12.1 Other threat	Present, but threat severity is unknown		Capturing young orangutans for illegal pet trade (SOCP).	Ongoing

IUCN Threats list

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	Year of activity
1. Residential & commercial development	1.2. Relocate primates to non-residential areas	The Human-Orangutan Conflict Response Unit rescue, relocate, and confiscate orangutans in human-orangutan conflict situations (OIC).	Ongoing
2. Agriculture & aquaculture	Not reported
3. Energy production & mining	Not reported
4. Transportation & service corridors	Not reported
5. Biological resource use	Not reported
6. Human intrusion & disturbance	Not reported
7. Natural system modifications	Not reported
8. Invasive & other problematic species, genes, diseases	Not reported
9. Pollution	Not reported
10. Education & Awareness	Not reported
11. Habitat Protection	Not reported
12. Species Management	Not reported
13. Livelihood; Economic & Other Incentives	Not reported

Conservation activities list (Junker et al. 2017)

Challenges

Table 5. Challenges reported for Leuser Ecosystem

Challenge	Source
Lack of law enforcement	Singleton et al. 2018
Lack of national protection	Singleton et al. 2018
Lack of management	Wich pers. comm. 2020

Research activities

Documented behaviours

Table 6. Ape behaviors reported for Leuser Ecosystem

Behavior	Source
Not reported

External links

Leuser International Foundation
HAkA
OIC
SOCP

Relevant datasets

A.P.E.S Portal

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