Kalimantan (Indonesia) rainforests

• Category: Forest Biomes.
• Geographic Location: Southeast Asia.
• Summary: These extremely valuable rainforest habitats are spread across much of the world’s third-largest island, Borneo.

Kalimantan is the Indonesian state that takes up the southern two-thirds of the great island of Borneo. Two basic types of rainforest here combine for one of the oldest intact rainforest ecosystems on Earth: the Borneo montane rainforests and the Borneo lowland rainforests. The Kalimantan Rainforests biome spreads across some 155,000 square miles (400,000 square kilometers), with the Equator running directly through the center.

Geography and Climate

Borneo is the third-largest island in the world. It is located in the middle of the great Australasian archipelago, and its territory is split between three nations; Indonesia controls the greatest extent, followed by Malaysia and Brunei. Kalimantan, which serves as the Indonesian name for the entire island of Borneo, is also an administrative name for its four provinces here, which together comprise 210,000 square miles (543,000 square kilometers).

This land includes coastal mangroves, broad alluvial plains dotted with peat swamp forests, a generally hilly interior, and central mountain ranges that in some cases, such as the Muller and Schwaner Mountains, climb as high as the tallest peak of Mount Raya—7,474 feet (2,278 meters)—but generally rise to the level of 3,940–5,580 feet (1,200–1,700 meters). Among these ranges are the Kayan Mentarang, Apokayan, Meratus, and Sambeliung. The land tends to be very well watered, with networks of small streams and extensive wetlands. Major rivers fan out from the interior; these include the Kahayan, Barito, Mahakam, Kapuas, Katingan, and Rajang.

The climate of the biome is humid tropical, or wet equatorial; moist year round but with a somewhat drier season from July to October and the rainy season extending through much of the other eight months. Rainfall occurs in the range of 110–134 inches (280–340 centimeters) annually. Temperatures are consistently warm and vary little throughout the year, generally staying within the range of 73–88 degrees F (23–31 degrees C).

Biodiversity

The Kalimantan lowland rainforests are replete with dipterocarp tree species, those with twin-winged fruiting seeds. An open canopy is one result of the plant diversity here; it is also quite tall. The forest is quite dense and tends to be dark below the canopy, with intertwined lianas (vine plants), mosses, ferns, and hardwood trees. Bornean ironwood, renowned for its hardness, is a prized species for the timber industry. Sadly, they grow quite slowly, meaning that logged stands may not see a re-growth of ironwood for many decades. Nestled into hollows between tree roots and among the twisting lianas are pitcher plants, many species of which feature spiky traps for flies and other insects.

Animals that spend much of their lives high in the canopy here include flying lizards; Kuhl’s gliding gecko, a very well-camouflaged species; Prevost’s squirrel, a striking, inky black one; Colugo lemur; harlequin flying frog; and Wallace’s flying frog, which does spend time on the forest floor, mainly to lay eggs in ponds and pools. Moving across the forest floor, as well as the higher levels, are such endangered fauna as the proboscis monkey and the orangutan—easily the most iconic animal of Kalimantan.

Montane rainforests in Kalimantan, generally those occurring above 3,000 feet (900 meters), are populated by myrtle and laurel species, as well as oaks that would be considered stunted if found at lower elevations. In the understory, ferns and rhododendrons dominate, except at the highest altitudes where heathers are more in evidence. Pitcher plants are also common on the forest floor in these higher-altitude forests.

Kalimantan montane rainforests support an amazing abundance and diversity of species. Of orchids, the biome is estimated to host more than 2,500 species, with perhaps one-third of these endemic (found nowhere else).

Bats and rodents boast the highest number of individual species among mammals here. Larger and medium-sized mammals include the Borneo elephant, sun bear, Sunda clouded leopard, bearded pig, Sambar deer, red muntjac, banteng, banded palm civet, short-tailed mongoose, yellow-throated marten, Malaya badger, and smooth-coated otter. Birds include the mountain blackeye and pygmy white-eye—both endemic genera—mountain serpent eagle, long-tailed parrots, and a wide range of hornbills.

Threats and Conservation

Logging, coal and mineral mining, and petrochemical extraction and processing are among the heavy industries that have increasingly plagued the ecosystems of Kalimantan since the mid-20th century. The spread of human population in from the coasts, and outward from inland industrial centers—combined with road-building, illegal logging, and periodic uncontrolled land-clearance fires—have resulted in increasing deforestation, which threatens both habitats’ degradation and fragmentation.

Kalimantan holds the greatest expanse of tropical rainforests in Indonesia, and the thick jungles and myriad insects have tended to discourage large-scale agriculture. However, in 1983, large swaths of Kalimantan’s tropical rainforests were destroyed by wildfire, causing heavy damage to the ecosystem. Then, in 1996, the government sponsored a program to convert peat swamp forest to rice paddies, through massive excavations that backfired by draining the areas—and making them far more fire-vulnerable. Indonesia established a program to explore restoring peatland ecosystems in 2018. Fire as a clearing tool in agriculture continues to cut away at rainforest, but logging and mining are far more aggressive than the planting of rice, tobacco, sweet potatoes, and sugarcane. In the 2010s, extensive deforestation occurred in southern Borneo to establish oil palm plantations to meet global demand for palm oil.

Climate change effects, combined with more frequent El Nino oceanic and atmospheric events, are projected to heavily impact the Kalimantan Rainforests biome. Higher water temperatures in the Indian Ocean are predicted to combine with El Nino events to reduce rainfall over Borneo—even potentially to drought levels, effectively making annual dry seasons much drier. While wet seasons may see heavier rain as climate change sets in, the soils in most of Kalimantan are not likely to store enough water to overcome the dry-season precipitation deficits, according to some researchers. Also troubling, rainforests often hold carbon, so the destruction of the forests results in large carbon emissions, further exacerbating climate change.

Rainforest tree species are not known for their drought-resistance; therefore, the impact could well accelerate itself, as insects, disease, and invasive species work to decimate the native rainforest habitat—and undercut its contribution to slowing global warming by virtue of eroding its large carbon-absorption capacity. The increasing incidence of fire events, coupled with more pronounced habitat fragmentation, will also work against rainforest sustainability here.

Kalimantan administrators have partnered with the World Wildlife Fund (WWF) to help maintain the region’s rich biodiversity by implementing new protected areas or adding on to existing ones. Among the WWF’s focal animal groups for habitat preservation priority are primates and the bird family Bucerotidae, known as hornbills. Management policies aimed at protecting their habitats will reinforce managing the protected areas, as well as surrounding landscapes, as integrated systems. Freshwater swamps are under-represented among the protected areas, as are peat swamp forests.

Indonesia has established a network of parks and reserves that buttress efforts to protect the rainforests and related biomes here. Located in the Central Kalimantan province is the Tanjung Puting National Park, which serves as the oldest conservation site of Kalimantan’s flora and fauna. In the Gunung Palung National Park, close to Mount Raya, there are a great number of rare and beautiful flora and fauna, including perhaps more than a dozen species of Rafflesia, the celebrated, if carrion-scented, giant parasitic flower that makes its home upon various vines. Rafflesia grow to 3 feet (1 meter) across or more, and can weigh 22 pounds (10 kilograms). Other preserves in Kalimantan include the Danau Sentarum; Baka Bukit Raya; Kutai; and Kayan Mentarang National Parks.

Bibliography

Guhardja, Edi, Mansur Fatawi, Maman Sutisna, and Tokunori Mori, eds. Rainforest Ecosystems of East Kalimantan: El Nino, Drought, Fire and Human Impacts. New York: Springer, 2000.

Jong, Hans Nicholas. "Palm Oil Plantations, Coal Mines Linked to Deadly Indonesia Flood." Mongabay, 20 Jan. 2021, news.mongabay.com/2021/01/palm-oil-plantations-coal-mines-deforestation-indonesia-south-kalimantan-flood/. Accessed 19 Nov. 2024.

Kieft, Johan, and Leona Liu. "Deforestation in Borneo Is Slowing, but Regulation Remains Key." United Nations Environment Program, 18 Feb. 2019, www.unep.org/news-and-stories/story/deforestation-borneo-slowing-regulation-remains-key. Accessed 19 Nov. 2024.

Kumagai, Tomo’omi, and Amilcare Porporato. “Drought-Induced Mortality of a Bornean Tropical Rainforest Amplified by Climate Change.” Journal of Geophysical Research 117, no. 1 (2012).

Laurance, William F., and Carlos A. Peres, eds. Emerging Threats to Tropical Forests. Chicago: University of Chicago Press, 2006.

World Wide Fund for Nature (WWF). “Conservation in Borneo.” 2012. . Accessed 19 Nov. 2024.