Kerangas forest, also known as heath forest, typically grows in transitional lowland zones between peat-swamp and hilly dipterocarp forest.
Heath forest is generally found on quartz sand and podzol soil, which has low nutrient levels and a low pH. The distribution of heath forests in Indonesia spans across the islands of Sumatra, Belitung, Singkep and Borneo. However, this kind of forest mainly occurs in Kalimantan (Indonesian Borneo).
Heath forests contain a diverse variety of trees , including dipterocarp species (Katagiri, 1991). However, most trees that grow in heath forest are relatively small, with thick leaves, which helps them to survive in nutrient-poor and acidic conditions.
Based on The Consortium for Revision (HCV Toolkit for Indonesia, 2009), heath forest is considered High Conservation Value Forest (HCVF). Many threatened species can be found in these forests, including Critically Endangered Bornean orangutans and Endangered white-bearded gibbons.
The Rungan Landscape: a Unique Heath Forest in Central Borneo
Rungan’s unique natural landscape is flanked by the Rungan and Kahayan rivers, which form the lifeblood of local indigenous Dayak communities. Rungan is a mosaic forest, featuring dryland and swamp habitats on sandy soils, collectively known as heath forest.
There are two distinct subtypes of heath forest in the Rungan Landscape, distinguished by their sandy soils and tree composition. The first is black sand heath forest,usually found close to the riverside. The second is white sand heath forest, which tends to grow at higher elevations (Maimunah, et al., 2019).
Although Rungan is among the largest relatively intact lowland forests remaining in Borneo, it does not contain the substantial below-ground carbon stocks of the island’s peat-swamp forests, nor the huge trees associated with Borneo’s Heartlands, and has thus been something of a conservation afterthought.
Heath Forest Biodiversity
Heath forest is often regarded as having low levels of biodiversity, so seldom registers as a priority habitat for conservation. However, in their natural state, heath forests can have higher levels of biodiversity—both fauna and flora—than any other lowland forests in Borneo.
The Rungan Landscape is a critical habitat for orangutans and other threatened species. With an area of more than 130,000 hectares, Rungan is home to an estimated ~2,000 individual orangutans (PHVA, 2016).
Beside orangutans, eight other primate species are can be found in the Rungan Landscape. These include the Bornean white-bearded gibbon, proboscis-monkey, red langur, grey langur, Sunda pig-tailed macaque, long-tailed macaque, slow loris, and the western tarsier.
Additionally, our long-term monitoring programme has uncovered the presence of five species of wild cat in Rungan: the rare Borneo bay cat, clouded leopard, leopard cat, flat-headed cat, and the marbled cat. This makes Rungan the only known site in Central Kalimantan inhabited by all of the island’s five cats species, further highlighting its conservation importance.
See also: The Hidden Paradise of Kerangas
Collaborative Conservation Efforts in Rungan’s Heath Forest
As a mixed-use landscape, subject to multiple stakeholders, Rungan’s heath forest presents a unique conservation challenge. BNF takes a collaborative, multi-stakeholder approach that aims to build partnership opportunities for co-management to maintain forest cover. Ultimately, our main objective is to connect all remaining forest areas across the landscape and avoid further fragmentation.
BNF supports social forestry programmes in promoting communities management rights over their ancestral forests, as well as engaging partners in the private sector to protect any High Conservation Value Forest (HCVF) areas within their concessions. We are also working to strengthen Forest Management Units as an extension of the government’s bid to manage forests at the site-level. Finally, a crucial element of our work in the Rungan Landscape is empowering communities through alternative livelihoods training, including backyard permaculture initiatives and fish ponds.
Written by Desi Natalia, Communications Manager