Peat swamp forests of Borneo PART 1: Hydrology and biodiversity

Sabangau peat swamp forest, Central Kalimantan. Photo by SThornton.

It was previously thought that the peat swamp forest was devoid of much biodiversity and was therefore of less interest to biologists, but through recent years researchers have found that this habitat is actually rich in species. In Part 1 I will introduce you to this unique habitat; it’s hydrology and its importance for carbon storage, as well as it’s special flora and fauna. The parts following will discuss the local people who depend on these forests, and the management of these forests with regards to the past, present and future.

Peat swamp forests (PSFs) represent about 12% of the land area in Southeast Asia, which equals more than 27 million hectares, of which 83% is found in Indonesia¹. In Indonesia; Sumatra, Kalimantan (Indonesian Borneo) and Papua contain most of the peatlands.

The island of Borneo is shared by three countries; Malaysia, Indonesia and Brunei. Indonesian Borneo is split into the provinces of East, West, North, Central and South Kalimantan. Once, forests covered the majority of the island of Borneo. In recent decades the provinces of Indonesia and Malaysia have witnessed a dramatic increase in palm oil production which has unfortunately led to devastation of one of the world’s oldest rainforests, especially the PSFs. The biggest area of this classification of forest left is found in the Sabangau catchment in the south of Central Kalimantan.

Map of Borneo from Wikimedia Commons.

Hydrology and Carbon Sequestration

PSFs are tropical forests in which waterlogged soils (soils which are very saturated with water) hinder decomposition of natural organic materials (such as fallen leaves from trees) – leading to the gradual formation of peat. Tropical peat soils of PSFs account for 20% of global peat soil carbon and 2% of global soil carbon². They are extremely important in carbon sequestration and Indonesian PSFs store a massive 35 Pg of carbon³. Due to their large capacity for underground carbon sequestration and storage, they have great potential in the global climate change crisis⁴.

Hydrology (or, how the water acts in the area) is an important factor influencing the carbon balance in tropical PSFs as seasonal variation in soil and air temperature is less than in temperate and boreal peatlands². During the wet season the PSF is often inundated; slowing down aerobic decomposition and thereby favouring the formation of peat. During the dry season the water level falls and there is an increase in the oxic peat profile (i.e. the amount of peat exposed to the air), leading to CO2-releasing decomposition².

Water level decrease can be due to climatic variability or the drainage of peatlands (which is done for palm oil or timber plantations to lower the water table, or in logging operations where canals are built in the landscape to transport timber out of the area). Eventually, a lower water level can cause decreased peat accumulation and eventual collapse of the peat structure, furthermore causing the PSF to shift from a net carbon sink (i.e. absorbs carbon from the atmosphere) to a net carbon source². Damming sources of peatland drainage is one action that is being taken, and where absent is vitally required to slow down peat degradation.

Flora and Fauna

 PSFs are rich in endemic and endangered flora and fauna⁴, and these have become easier to study with an improvement of access to remote PSFs. Recent studies have suggested that they harbour greater biodiversity than first thought⁵. The peatland forests of Southeast Asia are of vital importance for the survival of several charismatic megafauna:

• Orangutans (Sumatran and Bornean, Pongo spp.)

• Sumatran Tiger (Panthera tigris sumatrae)

Sumatran tiger, photo by Trisha M Shears

• Sumatran Rhinoceros (Dicerorhinus sumatrensis)

Sumatran rhino, photo by International Rhino Foundation

• Storm’s Stork (Ciconia stormi)

Storm’s stork

• False Gharial (Tomistoma schlegelii)

False gharial, photo by SThornton

There are three main PSF sub-types present; the mixed-swamp forest at the perimeter of the peat dome which exhibits relative species diversity, the low-pole forest near the centre of the area which is species poor, and lastly the tall-interior forest at the watershed of the dome which is species-rich⁸. The majority of the orang-utan population is supported by the mixed-swamp forest⁹.

Biodiversity research has been going on since 1993 in the Sabangau forest (southern Central Kalimantan), and has identified it as home to the largest population of wild orang-utans (Pongo pygmaeus wurmbii)³.  PSFs are favoured by orang-utans because of their more regular and larger fruit crops, compared to neighbouring dipterocarp forests⁴.

PSFs in Borneo also provide habitat for eight other primate species, including the Southern Bornean Gibbon (Hylobates agilis albibarbis) and Red Langur (Presbytis rubicund). For the gibbons, the Sabangau catchment also represents one of the largest remaining continuous populations worldwide⁶, and is therefore a vital area for the conservation of these primates.

It has been found that 45% of mammals and 33% of birds recorded in PSFs have an IUCN Red List status of near threatened, vulnerable or endangered¹⁰. They are home to endangered felids (i.e. from the cat family) such as the flat-headed cat (Prionailurus planiceps), Sunda clouded leopard (Neofelis diardi), and marbled cats (Pardofelis marmorata). The conditions of PSFs are also thought to favour evolution of specialized fish species, and each patch of peat swamp could contain its own endemic species¹⁰.

PSFs also support a great variety of plant and tree species, many which are also facing threats of extinction¹⁰ .While these may be less charismatic than apes or large mammals; they are vital for the conservation of these forests and their biodiversity.

Tropical PSFs have greater floral diversity than any other peatland in the world¹⁰. Due to the specific hydrology and structure of the peat, trees have to adapt to fluctuating water levels and unstable grounds – with pneumatophores, stilt roots and buttresses¹⁰(see photos below; stilt roots can provide structural support for the trees to deal with unstable soil; buttress roots can help with the same issue of unstable soil by helping to stop the uprooting of large trees; pneumatophores are “breathing roots” which, as might be evident, help in getting oxygen into the root to supply the roots which are under the swamp water). PSFs require all of these adaptations at the same time, making them unique to other tropical forests¹⁰.

Pneumatophore, photo from Wikimedia Commons

Stilt roots, photo by Cesar Paes Barreto

Buttress root, photo by Marco Schmidt

What makes PSFs additionally distinctive, is that as the peat characteristics determines the tree species found (depending on the depth of the peat, water level etc.), there is no single peat swamp forest vegetation type; each PSF will differ from another with regards to vegetation and ecology¹⁰. It is a continuous and distinct change in forest structure and tree species composition; from riverine forest, to mixed swamp forest, to low pole forest to tall interior forest⁸. This highlights the need for protection of multiple sites to protect the full range of this ecosystem.

Concluding remarks

The survival of these forests is not only important due to their endemic and endangered species, but also due to their role as large carbon sinks. There are few intact PSFs remaining, and even these and those under an official protected status are still affected by illegal logging and encroachment¹. Nearly 45% of remaining PSFs have been severely affected by large-scale developments, deforestation and illegal logging, with another 45% negatively affected by selective logging and draining¹. Several millions of hectare have been lost, are are lost, to fires with rage across drained peatlands every year. Without an improvement in the protection of these forests, the PSF’s and the endangered species which inhabit them will increasingly be threatened with extinction.

Keep an eye out for the following Part 2, where we will be introducing the local inhabitants who depend on these forests.

Sabangau forest, photo by SThornton

Related articles

• The Orangutan Tropical Peatland Project (outrop.com)
• The cost of an orangutan’s forest (worldagroforestry.org)
• Demand Malaysian Government Reduce Logging (forcechange.com)
• Why Indonesia cannot stop the fires and haze (isaacloo.wordpress.com)

References

1. Wetlands International (online) (2012) Tropical peat swamp forests. Accessed online: http://www.wetlands.org/?TabId=2739

2. Hirano T, Jauhiainen J, Inoue T, and Takahashi H (2009) Controls on the Carbon Balance of Tropical Peatlands. Ecosystems 12:873-887. Accessed online: http://www.springerlink.com.ezproxy.webfeat.lib.ed.ac.uk/content/50217652v55x2364/fulltext.pdf

3. Wich S., Riswan, Jenson, J., Refisch, J., and Nellemann, C. (2011) Orangutans and the Economics of Sustainable Forest Management in Sumatra. UNEP/GRASP/PanEco/YEL/ICRAF/GRID-Arendal. Accessed online: http://www.orangutanreport.un-grasp.org/media/orangutan_report_eng.pdf

4. Cattau M (2010) Using the Ecosystem Service Value of Habitat Areas for Wildlife Conservation: Implication of Carbon-rich Peatswamp Forests for the Bornean Orang-utan, Pongo pygmaeus. Masters Project, Duke University. Accessed online: http://www.outrop.com/uploads/7/2/4/9/7249041/cattau_megane_mastersproject.pdf

5. Buckley C, Nekaris KAI, Husson SJ (2006) Survey of Hylobates agilis albibarbis in a logged peat-swamp forest: Sabagau catchment, Central Kalimantan. Primates 47: 327-335. Accessed online: http://www.springerlink.com.ezproxy.webfeat.lib.ed.ac.uk/content/f064220n28237q4k/fulltext.pdf

6. Cheyne SM, Thompson, CJH, Phillips AC, Hill RMC, and Limin SH (2008) Density and population estimates of gibbons (Hylobates albibaris) in the Sabangau catchment, Central Kalimantan, Indonesia. Primates 49:50-56. Accessed online: http://www.springerlink.com.ezproxy.webfeat.lib.ed.ac.uk/content/c257551727539871/fulltext.pdf

7. Orang Utan Republik Foundation (OURF) (2012) Rainforest Ecology. Orang Utan Republik Foundation. Accessed online: http://ourf.org/become-aware/biodiversity/rainforest-ecology

8. Page SR, Rieley JO, Shotyk OW and Weiss D (1999) Interdependence of Peat and Vegetation in a Tropical Peat Swamp Forest. Philosophical Transactions: Biological Sciences 354(1391)1885-1897. Accessed online: http://www.jstor.org.ezproxy.webfeat.lib.ed.ac.uk/stable/57054?seq=12

9. Morrogh-Bernard HC, Morf NV, Chivers DJ and Krutzen M (2011) Dispersal Patterns of Orang-utans (Pongo spp.) in a Bornean Peat-swamp Forest. Int J Primatol 32:362-376. Accessed online: http://www.springerlink.com.ezproxy.webfeat.lib.ed.ac.uk/content/37k24k821718g82w/fulltext.pdf

10. Posa MRC, Wijedasa LS and Corlett RT (2011) Biodiversity and Conservation of Tropical Peat Swamp Forests. BioScience 61(1): 49-57. Accessed online: http://ehis.ebscohost.com.ezproxy.webfeat.lib.ed.ac.uk/ehost/detail?vid=4&hid=20&sid=bcc5d19f-6e35-4a54-bf89-69c0bd08918c%40sessionmgr11&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=afh&AN=57643526