The Rimba Raya Biodiversity Reserve REDD Project

ground area, which marks the division of the Kumai and Seruyanwatersheds, represents the southernmost extent of low foothillsthat descend from the northern interior of the province down tothe Java Sea. In the Project Area, lowland mixed dipterocarpforest is restricted to the far northwest and is contiguous withsimilar forest in northeastern Tanjung Puting.iv. Kerangas forest. Kerangas forest, sometimes referred toas heath forest, is a distinctive Sundaland forest type developingon nutrient-­‐poor, often waterlogged sandy soils. Kerangas isextremely variable in structure and composition depending onsoil and climatic conditions, with tall kerangas producing amaximum canopy height of 35-­‐40 m, and severely stuntedkerangas reaching a canopy of less than 5 m. All forms share incommon a surface organic layer (10 to over 100 cm); apredominance of trees with small, thick, nutrient-­‐poor leaves; tallnarrow crowns; and a relatively uniform canopy with few if anyemergent trees (except in examples of tall kerangas).Kerangas supports lower plant and animal diversity than lowlandforests on well-­‐drained soils, but harbors a large number ofendemic plants, especially understory and epiphytic woody orherbaceous species. Common woody plants include Vacciniumlauriflorum, Rhodomyrtus tomentosus, Tristianopsis whiteana,Gymnostoma nobile, Shorea retusa, Hopea kerangasensis, Hopeadryobalanoides, Swintonia glauca, Combretocarpus rotundatus,Cratoxylum glaucum, and a rich assemblage of species in thegenus Syzygium.Many plant species have specialized adaptations to the lownutrient conditions typical of kerangas, including the epiphyticmyrmecophytes (ant plants) Myrmecodia and Hydnophytum, thecarnivorous pitcher plants (Nepenthes), sundews (Drosera), andbladderworts (Utricularia), and understory and epiphytic orchidsincluding the protected black orchid (Coelogyne pandurata). Incomparison to other forest types on Borneo, kerangas forestscontain a relatively high density of plants of Australasian origin,including the families Myrtaceae and Casuarinaceae, andgymnosperms of the southern hemisphere, including Agathis,Podocarpus and Dacrydium.Kerangas vegetation occurs in the northern and southern parts ofthe Project Area, on sandy terraces, which intergrade with peatswamps and also with mixed dipterocarp forest on mineral soilsin the northwest. Most of these kerangas areas have beenburned and tall forest has been replaced by sparse scrubvegetation on open sand.v. Marshy swamp. A dominant and widespread vegetationtype throughout the Project Area is marshy swamp. Theseperiodically inundated grasslands with no forest cover arevariously represented on Ministry of Forestry and othergovernment maps as open swamp, seasonal lake, andunproductive wetlands.In the Project Area, marshy swamp occurs in three major blocks:one in association with flood plains of the Seruyan River,extending from the southeastern boundary of Rimba Rayanorthward up to and beyond Muara Dua village; and the othertwo along the major drainages to the Seruyan along the Sigintungand Baung Rivers. Along these interior rivers, marshy swamps arecontiguous with intact peat swamp forest. The extent to whichthe current distribution of these open swamps is natural,manmade, or a combination of both is not well understood.vi. Disturbance classes. The Project Zone has experienced avariety of disturbance histories, ranging from low intensity15