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Sumatran montane rain forests



Gunung Leuser National Park, Indonesia (Photograph by Herman Rijksen)
Gunung Leuser National Park, Indonesia (Photograph by Herman Rijksen)

The Sumatra Montane Rain Forests are home to a wide variety of species and are one of the most outstanding examples of montane rain forests west of Wallace's Line. The Sumatran montane rain forests are home to both Amorphophallus titanum, which grows on a stalk that measures more than 2 meters (m) tall, and the parasitic Rafflesia arnoldii, which produces the largest flower in the world (up to 1 m wide). Sumatra's montane forests are also home to some of the most endangered species in the Indo-Pacific region. The Sumatran rhinoceros, tiger, and Sumatran rabbit all inhabit these forests.

Location and General Description

This ecoregion represents the montane forests (>1,000 m) along the Barisan Mountain Range of Sumatra. The geologic history of Sumatra provides insights into the origins and amount of Sumatra's biodiversity. About 150 million years ago Borneo, Sumatra, and western Sulawesi split off from the Gondwanaland and drifted north. About 70 million years ago India slammed into the Asian landmass, forming the Himalayas, and an associated thrust formed Sumatra's Barisan Mountains, which run the length of Sumatra. As the Barisan Range buckled upward, it formed a deep water channel to the west of Sumatra. Today, to the east of the Barisan Range, low hills and plains exist as a result of tectonic and volcanic events. Continued mountain building, volcanic activity, and sedimentation in the lowland have occurred over the past 25 million years. Podzolic soils associated with altosols or litosols are the predominant soils found in this ecoregion. Large limestone areas occur in northern Sumatra, and they are associated with brown podzolic and renzina soils.

Based on the Köppen climate zone system, Sumatra falls in the tropical wet climate zone. The montane rain forests of the Barisan Range receive more rainfall on their western slopes than their eastern slopes, which are in a rainshadow. However, most of Sumatra experiences less than three consecutive months of dry weather (less than 100 mm rainfall/month), and rainfall in the montane rain forests averages more than 2,500 millimeters (mm) per year.

Sumatra's montane rain forests can be separated into three major forest zones: lower montane forest, upper montane forest, and sub-alpine forest. Temperature and cloud level are the major factors determining these forest zones. The lower montane zone forests are similar to lowland rain forests but begin to get smaller. The canopy height typically is no more than 35 m high. Emergents may extend to 45 m, but buttresses are rare. Lianas usually are absent, and epiphytes such as orchid begin to increase in abundance. The upper montane zone sharply changes from lowland rain forests. The canopy becomes even and rarely exceeds 20 m. Emergents may extend to 25 m, but buttresses usually are absent. Trees rarely have compound leaves or lianas. Orchids and other epiphytes such as moss, lichen, and liverworts are very common. Beyond this forest lies the sub-alpine forest, a complex of grass, heath, and bog areas. Small, stunted trees may reach 10 m high, orchids become very rare, but moss, lichen, and liverworts are very abundant.

The montane flora of Sumatra originates from two sources: local sources (autochthonous) and areas that have a center of origin outside of Sumatra (allochthonous). The local source can be divided into two categories: species that are characteristic of lowland rain forest, such as Dipterocarpaceae, Bombacaceae, and the genus Ficus (figs), and those that have a large global latitudinal distribution such as pines, Cruciferae (e.g., mustard), Theaceae (e.g., tea), and tree ferns. The allochthonous flora belong to genera whose species are found only in cold climates, not near equatorial rain forests. These species in the tropics are never found below 1,000 m and usually dominate the sub-alpine flora. Genera include Rhododendron, the pretty herbs Gentiana, and grass Deschampsia. Most of these species dispersed from Asia or Australia during cooler glacial periods when the Sunda region was a single landmass. Forest zones were all 350-400 m lower than their present height, providing numerous stepping stones.

The characteristic vegetation in lower montane forests changes from Dipterocarpaceae, the dominant lowland family, to Fagaceae (oaks) and Lauraceae (laurels). Lithocarpus, Quercus, and Castanea are common genera in the Fagaceae family, and Cinnamomum burmansea, Persea americana, and Litsea spp. are common Lauraceae species. Other families common to the lower montane region include Cunoniaceae, Monimiaceae, Magnoliaceae, and Hamamelidaceae. Tree ferns in the genus Cyathea are also common in the lower montane forests. The upper montane forest is characterized by conifers (pines and related trees), particularly by the Ericaceae (Rhododendron, Vaccinium) and Myrtaceae (Eucalyptus, Melaleuca) families. Dacrycarpus imbricatus and Leptospermum flavescens are also abundant in these forests, which because of their smaller stature are called elfin forests. Lichens are common to the drier parts of this zone, whereas mosses and liverworts are common in the moister parts of this zone that coincide with where clouds form and are commonly called cloud or moss forests. The sub-alpine zone is characterized by smaller specimens of the montane forest. There is also an increased abundance of grasses (Agrostis and Festuca), rushes and sedges (Juncus, Carex, Scirpus, and Cyperus), and small, colorful herbs.

Five of the sixteen species of the parasitic Rafflesia plant are found in Sumatra and have been recorded as high as 1,800 m on Mount Lembuh, Aceh. Rafflesia arnoldii, which produces the largest flower in the world, is found in this ecoregion. Its large brown-orange and white flowers can reach 1 m in diameter. Rafflesia have no leaves, instead deriving all their energy from the tissues of its host, the ground vine Tetrastigma. Large buds emerge from the vine and have five large, flowery petals surrounding spikes, which smell like rotting meat and attract pollinating insects.

Biodiversity Features

Sumatra's montane forests contain far higher levels of mammal and bird endemism than the lowland forests, in part because of their longer periods of isolation and distinctive forest types. Seven mammal and eight bird species are endemic (Table 1, Table 2), whereas the Sumatran Lowland Rain Forests have only one mammal and one endemic bird species. The mammal species includes Thomas's leaf-monkey (Presbytis thomasi), one of Sumatra's four leaf-monkeys, Sumatran rabbit (Nesolagus netscheri), and Sumatran shrew-mouse (Mus crociduroides). This ecoregion also contains two near-endemic mammal species and twenty-one near-endemic bird species.

Table 1. Endemic and Near-Endemic Mammal Species.




Crocidura baluensis


Presbytis thomasi*


Hylopetes winstoni*


Mus crociduroides*


Rattus korinchi*


Rattus hoogerwerfi


Maxomys hylomyoides*


Maxomys inflatus*


Nesolagus netscheri*

An asterisk signifies that the species' range is limited to this ecoregion.

Table 2. Endemic and Near-Endemic Bird Species.


Common Name



Red-billed partridge

Arborophila rubrirostris*


Sumatran pheasant

Lophura hoogerwerfi*


Salvadori's pheasant

Lophura inornata*


Bronze-tailed peacock-pheasant

Polyplectron chalcurum


Green-spectacled pigeon

Treron oxyura


Pink-headed fruit-dove

Ptilinopus porphyreus


Sumatran ground-cuckoo

Carpococcyx viridis*


Rajah scops-owl

Otus brookii


Waterfall swift

Hydrochous gigas


Blue-tailed trogon

Harpactes reinwardtii


Schneider's pitta

Pitta schneideri*


Black-crowned pitta

Pitta venusta


Sumatran drongo

Dicrurus sumatranus*


Sunda minivet

Pericrocotus miniatus


Blue-masked leafbird

Chloropsis venusta


Shiny whistling-thrush

Myiophonus melanurus


Rufous-vented niltava

Niltava sumatrana


Sunda robin

Cinclidium diana


Sumatran cochoa

Cochoa beccarii*


Cream-striped bulbul

Pycnonotus leucogrammicus


Spot-necked bulbul

Pycnonotus tympanistrigus


Sunda bulbul

Hypsipetes virescens


Black-capped white-eye

Zosterops atricapillus


Sunda warbler

Seicercus grammiceps


Sunda laughingthrush

Garrulax palliatus


Vanderbilt's babbler

Malacocincla vanderbilti*


Rusty-breasted wren-babbler

Napothera rufipectus


Marbled wren-babbler

Napothera marmorata


Mountain serin

Serinus estherae

An asterisk signifies that the species' range is limited to this ecoregion.
Rafflesia species, Sumatra, Indonesia (Photograph by Iris van Dijk)
Rafflesia species, Sumatra, Indonesia (Photograph by Iris van Dijk)

This ecoregion overlaps with a portion of the Sumatra and peninsular Malaysia Endemic Bird Area (EBA). Thirty-five restricted-range bird species are found in this ecoregion and include two threatened species that are also endemic to this ecoregion: the Sumatran cochoa (Cochoa beccarii) and Sumatran ground-cuckoo (Carpococcyx viridis).

Another distinctive feature of Sumatra's fauna is that it can be split into two regions, one to the north of Lake Toba and the other to the south. Lake Toba formed 75,000 years ago as part of a volcanic eruption that had a devastating impact on Sumatra. Seventeen bird species are found only north of Lake Toba, and ten are found only to the south. The white-handed gibbon (Hylobates lar) occurs only north of Lake Toba, and the dark-handed gibbon (Hylobates agilis) is found to the south. The tarsier (Tarsius bancansus), banded leaf-monkey (Presbytis melalophus), and endangered Malayan tapir (Tapirus indicus) are all found to the south of Lake Toba. The Malayan tapir is the largest of the four living tapir species and the only Old World representative. The Sumatran population of the Malayan tapir is close to extinction, with no more than fifty animals left in the wild, mostly in the lowland forests.

The Sumatran tiger (Panthera tigris),Indonesia's largest terrestrial predator, lives in lowland and montane rain forest, as well as freshwater swamp forests throughout Sumatra. There are an estimated 500 Sumatran tigers remaining in Sumatra, with approximately 100 found in Gunung Leuser National Park in northern Sumatra. There are three Level I Tiger Conservation Units (TCUs) in Sumatra that overlap this ecoregion. The two-horned Sumatran rhinoceros (Didermocerus sumatrensis) once ranged through much of southeast Asia. Today the entire population numbers about 500 individuals scattered in several populations in Sumatra, Borneo, and peninsular Malaysia. Another distinctive species of Sumatra's montane forests is the serow (Capricornis sumatraensis). The serow lives from 200 m to the vegetated summits of Sumatra's highest peaks. It can also be found on forested limestone hills.

Several other mammal species are found in this ecoregion, including numerous primate species such as several leaf-monkeys, siamang (Hylobates syndactylus), the region's largest gibbon, wild dog (Cuon alpinus), sun bear (Ursus malayanus), and clouded leopard (Pardofelis nebulosa).

Current Status

Despite Sumatra's dense human population, this montane ecoregion contains several large blocks of intact forest, stretching along the Barisan Mountain Range, running the length of the island. Numerous protected areas are scattered along the range and cover 40 percent of the ecoregion's area (Table 3). The large Gunung Leuser National Park extends into the northern part of the ecoregion. In the middle, the Kerinci-Seblat National Park-the largest reserve in Sumatra-protects the watersheds of two of Sumatra's most important rivers: the Musi and Batang Hari. To the south, Bukit Barisan Selatan, another of Sumatra's large reserves, also extends into this ecoregion, covering more than 2,000 square kilometers (km2).

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

Protected Area

Area (km2)

IUCN Category

Lingga Isaq



Gunung Leuser



Dolok Sembelin



Dolok Surungan



Dolok Sipirok



Malampah Alahan Panjang



Lembah Harau






Gunung Sago/Malintang/Karas



Gunung Singgalang



Gunung Merapi



Kerinci Seblat



Punguk Bingin



Bukit Dingin/Gunung Dempo



Bukit Hitam



Bukit Balal



Bukit Raja Mandara



Gumai Pasemah



Isau-Isau Pasemah



Gunung Patah/Bepagut/Muara Duakisim



Bukit Balai Rejang



Bukit Barisan Selatan



Bukit Nantiogan Hulu/Nanti Komerung Hulu



Gunung Raya






Gunung Betung





Types and Severity of Threats

At the current rate of deforestation, Sumatra's remaining lowland rain forest will be completely gone within the next ten years unless drastic actions are taken to halt the rampant logging. Given this ominous prediction, the only remaining natural forests in Sumatra will be the hill and montane forests of this ecoregion. This ecoregion is extremely fragile and sensitive to disturbance, especially in the upper montane and sub-alpine zones. They probably will be targeted for intense logging activities, especially in light of the rampant illegal logging currently taking place throughout Indonesia. From 1985 to 1997, 15,000 km2 of montane forest was destroyed, more than 1,000 km2/year. Since 1997 this annual rate of forest loss has increased gradually, and after the fall of the Suharto government and economic collapse of 1998, even the large protected areas such as Gunung Leuser, Kerinci Seblat, and Bukit Barisan Selatan national parks are threatened by encroachment and poaching.

One example of illegal logging inside Indonesia's protected areas is the unabated illegal logging that has occurred in and around the biologically valuable Gunung Leuser National Park since April 1999. The destruction includes prime habitat for the orangutan, siamang, and white-handed gibbon. In Gunung Kerinci Seblat National Park, Indonesia's first fully gazetted national park, illegal logging is increasing, and more than 400 families are staking claims along the road bordering the park. Kerinci-Seblat National Park is an important site for one of the last remaining populations of the Sumatran rhinoceros and Sumatran rabbit, as well as siamang and agile gibbon.

Poaching is another threat to the great diversity of life in these forests. From 1990 to 1996 the number of Sumatran rhinoceros in Kerinci-Seblat National Park fell from 300 to about 30.

Justification of Ecoregion Delineation

We recognized six ecoregions on Sumatra. MacKinnon placed all the biomes in Sumatra within two subunits (21a and 21b), with the subunit division based on a faunal break to the south of Lake Toba. We used the 1,000-m contour from a Department of Environmental Management (DEM) to delineate the montane forests along the Bukit Barisan-Gunung Leuser Mountain Range as the Sumatran Montane Rain Forests. However, these montane forests include extensive forest areas over limestone. Whitmore shows small, scattered patches of limestone forests in his vegetation map of Malesia. The FAO map shows no limestone. Much of the uncertainty probably arises because these limestone substrates do not show extensive outcropping. Based on recommendations by Tony Whitten, we treated these limestone forests as a distinct habitat type within the more broadly distributed montane moist forests rather than placing them in a separate ecoregion.

MacKinnon's biounit 21 largely corresponds to Udvardy's Sumatra biogeographic province. However, Udvardy did not include the Nicobar Islands. Eight ecoregions overlap Udvardy's Sumatra biogeographic province: Sumatran Lowland Rain Forests, Sumatran Montane Rain Forests, Mentawai Islands Rain Forests, Sumatran Peat Swamp Forests, Sumatran Freshwater Swamp Forests, Sundaland Heath Forests, Sumatran Tropical Pine Forests, and Sunda Shelf Mangroves.

Additional Information on this Ecoregion

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.



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