Ecoregional Assessment of Biological Diversity in East Kalimantan

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East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems C. Peat Swamp Forest Description In East Kalimantan, Peat Swamp Forests are most abundant in the lakes area of the middle Mahakam Basin and around the marine alluvial plains of the Kayan River. MacKinnon et al. (1996; Table 3.1) reports that the extent of this forest type in East Kalimantan has shrunk from an original area of 749,000 ha. to 594,000 ha. in 1996. Our LandSat analysis shows an areal extent of just over 303,000 hectares as of 2001 – indicating perhaps an even swifter decline of this endangered habitat type. Peat Swamps are typically large rain-fed swamps throughout Kalimantan that occur behind the coastal mangrove swamps along the coast and in poorly-drained depressions at higher altitudes. The soil of these swamps has more than 65% organic matter content, which is commonly around 50cm deep but can be as much as 20 meters deep. The surface is a solid fibrous material forming a crust over the semi-liquid interior. It is extremely deficient in nutrients and has a high acidity (pH ≤ 4). Peat Swamps are drained by ‘blackwater rivers’, as is the case with the Heath Forests. Most peat swamps are zonal in nature with several concentric rings, starting with tall forest with an outer uneven canopy (See Figure2.C.1 – adapted from MacKinnon, 1996), then inner zones of trees of diminishing height- with a reduction in species richness of plants towards the center of the swamp. These forests share many of the tree species found in adjacent lowland evergreen dipterocarp forests. There are conspicuous parallels in structure and physiognomy between the more central parts of the Peat Swamp Forests and the Heath Forests (Whitmore 1984). 11
East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems Fig.2.C.1. Schematic aerial diagram of river delta and typical component forest types Ocean A A Ocean Dry land B B R A = Mangrove Forest c B = Mixed Mangrove/Nypa c c = Freshwater Swamp d d e d = Peat Swamp e = Lowland Rainforest R = River Dry land The largest patches of Peat Swamp Forest in East Kalimantan are in the middle Mahakam Basin. In that area, Unna Chokkalingam (pers. com.) considers that fragmentation of the Peat Swamp Forest probably began seriously about 20 years ago. But unlike some other Peat Swamps in Kalimantan (Mackinnon et al. 1996) those in the Mahakam Basin are not generally rain-fed swamps; instead they receive water from surrounding rivers and watercourses. As such, the Mahakam peat swamp forests were probably all integrated as well as connected to the small fingers of swamp forest that follow the rivers inland for some distances. Land conversion and burning has most likely created the existing fragmentation. Unna Chokkalingam (pers. com.) considers that much of the Mahakam Peat Swamp Forest was in reasonably good condition before the last El Nino event of 1997-1998. Prior to that time, roughly 30-40 % had only been burned once, during the earlier El Nino in 1983-1984. The fires in 1997-1998 burnt all but a small area in the center of the large northeast patch (Belayan) and a few other scattered small fragments. These unburned fragments probably comprised less than 5% of the remaining Peat Swamp Forest. Interestingly, Unna Chokkalingam (pers. com.) considers that the patches of Peat Swamp Forest burnt only in the period 1997-1998 are regenerating very well and, if not burnt again, would probably recover well. This is an area that could represent as much as 50-60% of the remaining Peat Swamp Forest. Unfortunately, areas that have been burnt twice, or that are located along the edges of the rivers and waterways, do not regenerate well and probably will not be given a chance to recover. No species of mammal or bird is restricted to the Peat Swamp Forests, although many occur in this forest type, including the Bornean Gibbon, Orangutan and most other species of diurnal primates. Long–tailed Macaques (Macaca fascicularis) and Silver langurs (Presbytis cristata) are more abundant in Peat Swamp Forest than in other lowland forest types (see references listed in MacKinnon et al. 1996) and the Peat Swamps are a key habitat for the 12
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Ecoregional Assessment of Biological Diversity in East Kalimantan

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