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Biogeography & Species Diversity

Overview

Current efforts to measure, conserve and protect global biodiversity require us to develop and test a number of research and conservation strategies in the field. This analytical and data-based approach to conservation demands carefully constructed in-country studies to assess species diversity, distributions, and endemism in threatened ecosystems. The extent to which these species and habitats are adequately protected by current conservation measures must also be assessed.

The CBC's multi-taxa surveys of flora and fauna were designed to create core research collections to be used for phylogenetic and biogeographic analyses and conservation and management decisions. The study sites and focal taxa were carefully chosen to provide a diverse sample of Vietnam's threatened biogeographical areas, ecosystems and species to meet these goals. The relationship between these areas and Vietnam's current network of protected areas, and their potential value as additions to the system, were incorporated into the site selection process.

These research efforts will help form the basis of key impending natural resource and management decisions and will significantly affect Vietnam's future capacity to study and conserve its rich and endangered biodiversity.

For descriptive overviews of the study areas visited during the 1998-2001 biotic inventory studies, please visit the Research Sites.

 

Biogeography and Species Diversity

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Situated along the southeastern margin of the Indochinese Peninsula, Vietnam covers approximately 329,500 square kilometers from a latitude of 23° N to 8° 30' N. It is bordered to the north by China, to the west by Laos and Cambodia, and along its eastern coast by Tonkin Bay and the South China Sea.

Vietnam's north-south orientation of more than 1650km incorporates biogeographic regions ranging from the northern Chinese-Himalayan Paelearctic zone in the foothills of the Himalayas, through the Central Annamite region, to the southern Indo-Malayan Tropical zone. It spans two major delta regions: the Red and Black Rivers in the north and the Mekong River in the south. To the east of the Red River, the limestone ranges of northeastern Vietnam show strong affinities to the flora and fauna of southern China. Along the western border, the Truong Son (Annamite) Mountain Range in central Vietnam forms an important barrier between Vietnam's moist uplands and the drier monsoon ranges of Laos. Stretching from Lao PDR to the South China Sea at approximately 11° N, the slopes and passes traverse the transition zone between the subtropical north and the tropical south.

This unique combination of a strong north-south axis, ecology, geology and climate contributes to Vietnam's complex assemblage of biogeographic zones, divergent habitat types, and endemic areas.

Origins of Vietnam's Biota
The rising of the Himalayas over the last 10 million years effectively cut off the exchange of species between the northern Palearctic and the southern Indo-Malayan realms. This barrier, reinforced by increased climatic cooling after the Miocene, isolated the Indo-Malayan region and created conditions for subsequent species divergence. Recent relatively stable equatorial conditions, combined with dynamic geological changes, allowed isolated populations to diverge further, contributing to the enormous species richness and high levels of endemism that now characterize Southeast Asia.

Within Vietnam, important topographical and geological features are thought to have contributed to these patterns of species diversity, distribution and endemism. The Red and Black Rivers' gorges and deltas in the north, and the east-west extension of the Truong Son Range in north-central Vietnam, are considered barriers contributing to the isolation of northern and southern floral and faunal elements. The Truong Son Mountains in central Vietnam along the Laos border are hypothesized to have provided stable refugia for forest-dwelling species during climatic fluctuations associated with the Pleistocene glaciations. This montane fauna has apparently diverged from ancestral forms in the Annamites and northern highlands. Divergent weather patterns across this range - drier and more seasonal to the west in Lao PDR, wetter and more stable along the east in Vietnam - have also contributed to these patterns of endemism, species diversity and distribution.

The currently sampled biota of Vietnam reflects a divergence between northern elements with strong Sino-Himalayan affinities and southern elements with Indo-Malayan ones. These distribution patterns are coupled with a transition zone in Central Vietnam reflecting an admixture of northern and southern influences as well as high rates of locally-centered endemism and historical patterns of species divergence. Disjunct primate distributions between North and South and the recent discovery of new bird and large mammal species in Central Vietnam (see below) both indicate support for this interpretative framework of Vietnamese biodiversity patterns.

In addition to its direct conservation goals, this multi-taxa survey focused on the Truong Son Range and its transition with the Central Highlands to the south, and on comparative surveys along a North-South transect to gather data testing the hypothesis that these barriers structure patterns of species diversity and endemism.

Current Biodiversity Research
Past and recent research into Vietnamese biodiversity indicates a species-rich biota and accompanying high levels of endemism:

Flora: Vietnam is estimated to have 12,000 vascular plant species (out of 15,000 in Vietnam, Laos and Cambodia, combined), of which approximately 7,000 have been identified. This represents approximately 3.2% of world diversity. In the north an estimated one-third of the flora is endemic, and the country-wide figure is 40%. The most comprehensive account of forest type diversity in Vietnam shows particularly high levels of endemism in the Hoang Lien Son Range, the Da Lat Plateau, and in the northern highlands (Rothe, 1947). Vegetation types include lowland and montane evergreen forests, deciduous Dipterocarp forests, limestone karst forests, littoral forests, and peatswamp and mangrove forests.

Fauna: Faunal endemism in Vietnam is the highest in the Indochinese region (MacKinnon & MacKinnon, 1986). Vietnam is known to have at least 160 species of mammals, 723 of birds, 180 of reptiles, 80 amphibians, and over 2,000 species of fish. In Asia, Vietnam ranks highest in fish species richness per unit area, although this figure is based only on data from freshwater fish in the Lower Mekong region. New discoveries are continuing: in the last ten years three new large mammal species, and two new bird species have been discovered in the Truong Son, along with one hare, five fish species and a tortoise species. This spectacular yield of new species descriptions from this region suggests it is a region of both high endemism and undersampled biodiversity.

The current survey and secession of field sites is thus designed to conduct inventories on each of these vertebrate groups, as well as on invertebrates and plants, within regions most likely to have high rates of species diversity and endemism.

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