Vietnam's secret life: naturalists exploring the country's mountains and forests are finding that the keys to its extraordinary biodiversity may lie deep in the past

A long Vietnam's border with Laos runs the Truong Son range, known to the Laotians as Saiphou Louang and to much of the rest of the world as the Annamites. But the mountains are becoming known--to conservation biologists as well as to everyone else concerned with preserving the world's species--as a region of exceptional biodiversity. In the early 1990s investigators began visiting Vietnam's natural areas in greater numbers than at any time since the beginning of what is known to the people of the region as the Second Indochina War. And the investigators--ecologists, evolutionary biologists, and specialists in a broad spectrum of life-forms--soon confirmed what the local peoples had long known: an astounding array of organisms dwell in the country. For many biologists to this day, entering Vietnam is like entering uncharted territory, an area of vast biological abundance, where new species, it seems, can turn up virtually anywhere you look.

Biologists exploring the Truong Son have discovered--or, importantly, rediscovered--three previously unrecognized species of muntjac, or barking deer; one species of pig; and one species of rabbit [see illustrations of the latter two animals on page 53]. Those findings alone are remarkable; after hundreds of years of systematic biology, who would have thought that large or medium-size mammals would remain to be described? And that list doesn't even include the saola, the sole member of Pseudoryx, a genus entirely new to the cattle family. Weighing in at about 220 pounds, the saola is the largest land-dwelling mammal introduced to science since the kouprey, or gray ox, was described in 1937. (That animal ranged through northern Cambodia and adjacent areas of Thailand, Laos, and Vietnam, but may now be extinct.)

But Vietnam promises more to biologists than just the windfall that is the Truong Son range. Ever since the mid-nineteenth century, up until the beginning of the Second World War, forays by Vietnamese and visiting naturalists had sketched a spotty but telling portrait of the country's biodiversity. More recently, since peace came to Vietnam, further hints of biological abundance have come from collaborations between Vietnamese and foreign investigators.

But only in the past ten years have biologists understood that the newly recognized charismatic megafauna are only the tip of an iceberg of heretofore unknown species that live in the Truong Son as well as in other, primarily montane, areas of Vietnam. Among the organisms new to science (though, again, not to natives of the area) are three species of birds, nineteen species of amphibians, sixteen species of reptiles, and, just since the year 2000, at least twenty-nine species offish and 516 species of invertebrates. And--perhaps just as intriguing--many of the species native to Vietnam do not occur anywhere else: a phenomenon known as endemism.

The ferment of scientific activity in Vietnam in the past decade is a result of several historical developments: the restoration of political stability after decades of war; the recent opening of strategic border areas to scientists; and the reopening of the country to foreign scientific collaborators, such as our group from New York's American Museum of Natural History. Of course, Vietnam's turbulent political history can only explain why so many discoveries are emerging just now. History and politics (aside from the destruction they wreak) have little to say about the country's biodiversity--particularly about why so much of that biodiversity is endemic to it.

The real roots of the region's biodiversity lie in the dynamic interplay over time of geographic, geological, and climatic forces. The heaving of mountains, the shifting courses of rivers, and the expansion and contraction of seas and forests have successively isolated and reunited populations of plants and animals. As new habitats arise and old ones shift, existing organisms can disperse, adapt, or die. Those three options have largely created the unusually complex mosaic of life that exists in the region today.

Mountains and hills wrinkle the vast majority of Vietnam's 127,000 square miles. Major mountain blocks include the highlands in the northeast, the Hoang Lien Son in the northwest (the southeastern-most extension of the Himalaya), and the Truong Son along the border with Laos. A range of forest habitats, each adapted to a different amount of yearly rainfall, blanket the slopes of these mountains.

The seasonality of the rainfall is, in part, a consequence of the monsoon circulation pattern, the dominant climatic feature of southern and eastern Asia for at least the past seven million years. In the winter, strong northeast monsoon winds blow, as air flows from cold, high-pressure areas in Asia along the eastern edge of the Tibetan Plateau toward a hot, low-pressure zone over Australia--a process that brings cold, dry winds to Vietnam. In the summer, air masses move in from the opposite direction, from Australia and the Indian Ocean; passing over Vietnam the air releases moisture picked up along the way, hence the country's summer rains. Those dynamic circulation patterns interact with the terrain and the surrounding ocean to expose Vietnam to widely varying amounts of rainfall.