SBR- Content.pmd - INBO

4 - Biota of the Mekong BasinBiota of the 4Mekong BasinThe Mekong Basin occurs at the junction between several different biogeographical zones. Thenorthern end of the tropical Malayan Peninsula meets the southeastern extension of the Himalayasand the southern edge of the northern temperate region of China. This results in a great variety ofecosystem types and the presence of a wide range of species, 1 although the actual species richness isprobably lower overall than in the extremely biodiverse tropical forests of southern peninsularMalaysia and Indonesia. 2 The Mekong Basin constitutes a significant component of the Indo-Burmabiodiversity hotspot, considered by Myers and co-authors 3 to be one of the eight major hotspots forbiodiversity worldwide. This section will briefly outline knowledge of the biota, with an emphasison the components associated with the river system.1. VegetationRundell 4 employed an ecological system of forest classification, dividing the forest first into montaneand lowland types, and then by rainfall and tree assemblages.The wet evergreen forests of mainland Southeast Asia are structurally similar to the better knownIndo-Malaysian forest formations which occur south of about 6° North latitude, but they are lessfloristically rich. They share many genera with the more southern forests, but are distinct at thespecies level. Within the basin, this forest type occurs in the Cardamom and Elephant Mountains inCambodia, and the Annamite Range in Viet Nam.Semi-evergreen or dry evergreen forestoccurs in regions where mean annualrainfall is generally between 1,200 mm and2,000 mm, and the dry season is 3-6months. Characteristically, they containmixed deciduous stands and/or deciduousdipterocarps. They are widespread acrossnorthern and central Thailand, extendingthrough Lao PDR and Cambodia.Mixed evergreen forest, Phnom Tbeng,Preah Vihear, CambodiaMixed deciduous forest or monsoon forestextends from Burma through northernThailand and Lao PDR, and is oftencharacterised by the presence of teak29