Concern about deforestation and its effects on the wildlife of Sumatra started long before the modern industrial age. The Gunung Leuser National Park was originally created as a wildlife reserve in 1934 and after many changes to its borders, was established as a national park in 1980. Together with the Bukit Barisan Seletan and Kerinci Seblat National Parks the GLNP forms the UNESCO World Heritage Site, Tropical Rainforest Heritage of Sumatra (TRHS).
Following a huge increase in government sanctioned logging during the 1980’s and 90’s it was recognised that degradation of the land within the National Park made it no longer large enough to maintain its biodiversity and the Leuser ecosystem was established in 1995.
Located in the Bukit Barisan Mountains the landscape of the GLNP is predominantly montane forest surrounded by lowland tropical forest. 40% of the park, mainly in the northern part, is steep and over 1,500 m, but in the lower southern half, 12% of the park is below 600 m. Its exceptional range of biodiversity is possible because of the wide ranges of altitude, from sea level to over 3000 m and the variety of forest types and ecosystems. The GLNP includes areas of sub-alpine forest, scrub and shrub thickets, peat and mangrove swamps, lakes and rivers. It has the most diverse range of habitats of the TRHS sites.
With its wide range of habitats, the Leuser Ecosystem is home to the majority of species that might be found in this area. Although ecological studies have been made of some of the larger mammals, such as the Sumatran subspecies of tiger, elephant, rhinoceros and orangutan, very little is known about the populations of other mammals, particularly smaller species such as bats, tree shrews, squirrels, and rats. The reptiles, amphibians, insects and arachnids are equally under investigated as is plant diversity.
Tigers need large areas of forest with minimal disturbance that include wildlife corridors to connect breeding populations. They are threatened by habitat loss due to expansion of palm oil and paper pulp plantations which also reduces their prey, reduction of population viability as a result of forest fragmentation, human-tiger conflict through encroachment of their territory and poaching for fur and body parts for traditional Chinese medicine. Satellite imagery of the GLNP area shows significant illegal forest clearance for palm oil outside licensed concessions, often in protected areas, further increasing fragmentation.
Encouragingly, in areas where there are effective anti-poaching patrols numbers are increasing, and tiger cubs have been recorded by camera traps. Maintaining forest integrity is critical for the long term survival of tigers.
The subspecies Dicerorhinus sumatrensis sumatrensis is mainly found in Sumatra, where there are 170 to 230 individuals, with about 60 to 80 animals in the GLNP. Rhinoceros are solitary creatures who only come together to breed. Ranging over a large territory from sea level to over 2,500 m, they breed readily but are dependent on water supplies. Access to mud wallows is essential for thermo-regulation and the eradication of skin parasites.
The two principal threats to rhinoceros are poaching and reduced population viability. Thanks to anti-poaching patrols by Rhino Protection Units (RPU) operating in the National Parks, the population decline has slowed. Camera traps have recorded images of a Sumatran rhino mother and calf in the GLNP, showing the existence of a breeding population. Continued protection, combined with consolidating small, fragmented populations into larger ones, will provide the best chance for the survival of the species.
An island survey of Sumatra in 1985 revealed 44 separate elephant herds across all eight mainland provinces, estimating a population of 2,800 – 4,800. By 2008, as a result of deforestation, elephants had become locally extinct in 23 of the previously identified ranges. This decline has continued unrecorded and further research is urgently needed. Although they are protected under Indonesian law, the majority of their preferred lowland habitat and migratory paths are not in protected areas and are likely to be converted for agricultural purposes.
Although they can occur up to 1,500m above sea level, most orangutans are found in lowland forests in river valleys or floodplains. These are unprotected areas, outside the GLNP within the wider Leuser Ecosystem. Since the negotiation of a peace deal in Aceh province in 2005 which allows the local government more autonomy, there has been an increase in applications to open up logging concessions and palm oil estates in orangutan habitat, as there has been a dramatic increase in demand for timber and other natural resources for reconstruction after the December 2004 tsunami.
Another threat is the 400km extension of the Ladia Galaska road network, part of the Aceh Spatial Plan, which if approved by the government would connect the east and west coasts of Aceh, severing the ecosystem in nine places. This will fragment the forest forcing orangutans to come down to the ground to reach other forest areas making them vulnerable to poaching and predation. The plan is supported by Aceh’s president despite conservationists’ claims that it is in breach of Acehnese law. Satellite evidence from previous road building in the park shows that access facilitates illegal logging, settlement and poaching which all pose significant threats to the integrity of the forest.
According to UNESCO the Leuser Ecosystem is the largest and most significant forest remnant remaining in Sumatra.
Indonesia has made many commitments to environmental conservation, but they conflict with its Masterplan for the Acceleration and Expansion of Economic Development (known as MP3EI). Where these objectives conflict, the government is generally failing to protect forests and peatland. The devolution of power to provincial authorities is also an issue, as they are responsible for concession permits and the development of spatial and land-use plans for their territories.