The Rimba Raya Biodiversity Reserve REDD Project

Compositionally, freshwater swamps share many species incommon with lowland dipterocarp forest, but in general they arefar less species-­‐rich (though exceptionally diverse examples havebeen documented). The most abundant tree species in thisvegetation type are members of the following genera: Alstonia,Campnosperma, Dyera, Koompassia, Litsea, Neesia, Saraca andSyzygium.The distribution of freshwater swamps in the Project Area hasnot been mapped for Rimba Raya, reflecting the limitations ofremote sensing in capturing the fine-­‐scale pattern of its naturaldistribution. The vegetation type no doubt occurs in closeassociation with rivers, and future efforts to conduct ground-­basedvegetation mapping will assist with mapping this type.ii. Peat swamp. Peat swamp is the dominant forest type inthe Project Area, with compositional and structural variationdepending on peat depth and hydrology. Peat swamp is widelydistributed throughout northern, western and southern Borneoin coastal and lowland areas. However, forested peat swampshave declined markedly in extent over the past several decadesdue to wild fires and conversion to non-­‐forest uses, includingsmall scale and industrial oil palm estates (Wikramanayake et al.2002). In Indonesia, a small proportion of remaining peatlandecosystems has formal protected status. A Presidential Decreeissued in 1990 declared all peat lands > 300 cm deep as protectedareas unsuitable for development, yet this is rarely enforced.According to maps produced by Wetlands International(Wayunto et al. 2004), peat depth in the project area ranges from50-­‐100cm, but maps of peat depth based on RePPProT landsystems (RePPProT 1989) show deeper peat layers ranging from50-­‐200 cm in the MDW land system covering ca. 60% of theProject Area (see Annex 1). Field surveys of Rimba Raya showthat peat depths exceed 400-­‐600 cm in project area peatlands,which dominate major drainages of the Seruyan River. Much ofthese peat areas remain in forest cover that varies in level ofdegradation from lightly disturbed to heavily degraded by fireand logging. The largest peat swamp forest block in Rimba Rayacovers the center third of the Project Area is contiguous withextensive forests in the adjacent national park.Dominant species of conservation concern in peat swamps, andwhich are confirmed or very likely present in the Project Area,include the endangered dipterocarps Shorea teysmanniana, S.uliginosa and S. platycarpa; the protected species Gonystylusbancanus (CITES Annex II); and Dyera costulata, which is alsoprotected by the Government of Indonesia and severelyoverharvested throughout its range.iii. Lowland mixed dipterocarp forest. Lowland mixeddipterocarp forest is the richest and tallest stature lowland foresttype on Borneo, with canopy height ranging from 35-­‐50 m,emergent trees to > 60 m, and aboveground biomass valuesranging from ca. 300-­‐600 Mg (metric tons) per ha, which is onaverage 60% higher than that of the Amazon (Slik et al. 2009;Paoli et al. 2008). The floristic composition of mixed dipterocarpforest, which occurs on mineral soils, differs from all forms ofswamp forest described above, though many genera are sharedin common.Lowland mixed dipterocarp forest occurs in parts of the greaterTPNP landscape (Susilo 1997), intergrading with kerangas foreston sandy soils and peat swamp forest in low-­‐lying drainages. Thisforest type is prevalent where mineral soils occur on the north-­easternside of Tanjung Puting, bordering Rimba Raya. This high14