SBR- Content.pmd - INBO

State of the Basin Report - 2003(Tectona grandis). Deciduous dipterocarp forest is the other major deciduous forest type. It is themost widespread forest type in mainland Southeast Asia, occurring mainly in areas with 1,000-1,500 mm annual rainfall and 5-7 months drought. All six deciduous members of the Dipterocarpaceaeoccur in this formation, which occurs in Thailand, Lao PDR, Cambodia and Viet Nam. Fourdipterocarp species, Shorea siamensis, S. obtusa, Dipterocarpus obtusifolius and D. tuberculatusgenerally comprise the dominant species.Under heavy human pressure, the lowland areas of deciduous dipterocarp forest may be convertedto open savannah woodland. Under the influence of fire in particular, a few of the hardier treespecies remain and other fire-adapted species, together with thorny shrubs and grasses, becomemore abundant. Such formations occur in parts of the Korat Plateau, northern Cambodia and drierareas in southern Viet Nam.Freshwater swamp forests are rich in biodiversity andare nutrient rich spawning grounds for fishFreshwater swamp forests occur in areas ofseasonal inundation associated with coastaldelta areas and inland wetlands. There areextensive areas associated with the Tonle SapGreat Lake. They are floristically andstructurally distinctive from freshwaterswamp forests elsewhere in the world. Thedominant tree species is Combretumtrifoliatum, which is generally low in statureand loses its leaves during inundation in thewet season.Lower montane forests normally occurabove 800-1,000 m altitude in northernThailand and Lao PDR, and at lowerelevations of 600-700 m in northern VietNam. They occur in regions with annual rainfall above 2,000 mm, and a mean temperature in thecoldest month of below 15°C. This forest type is floristically distinct from the lowland forest, withfamilies like the Dipterocarpaceae absent and families such as the Fagaceae, Magnoliaceae andLauraceae being well represented. Epiphytes are also common in this forest type, including much ofthe orchid diversity of the region.Montane conifer forests are common on drier montane sites with less than 2,000 mm annual rainfallat elevations of 800-1500 m. Two dominant conifer species, Pinus kesiya and Keeteleria evelyniana,are particularly widespread. The former through northern Thailand and into Lao PDR and VietNam, and the latter restricted to Lao PDR and Viet Nam. The Annamite Range in Viet Nam containsa rich assemblage of conifer species.2. Vertebrate faunaThe vertebrate fauna of the Mekong Basin is difficult to quantify, partly because most inventorieshave been conducted on a country basis, partly because the inventories are clearly incomplete, andpartly because the taxonomic studies on which such inventories depend are incomplete. MRC 1997provided some estimates of the biota of the four lower basin countries that included 830 mammalspecies, 2,800 bird species, 1,500 fish species, 250 amphibians and 650 reptiles. However, theseestimates should be treated as indicative only.30