This 100,000-acre forest in southeast Asia is a mecca for tree biodiversity research. A 125-acre plot can host up to 300 species of trees. "Normally one species will win out over the other species, but not in this forest," says Gary Hartshorn at the World Forestry Center.

Scientists have for 25 years flocked to this lowland forest to find out why. Britain's Royal Society, a scientific academy, built housing, dining and lab facilities for scientists who want to stay long-term. It doesn't hurt that it's also a beautiful place to visit. "The trees are clean and cathedral-like," says Hartshorn. "And there's lots of wildlife, like elephants."