Amazonia represents the quintessence of biodiversity the richest ecosystem on earth. Yet a study by Smithsonian scientists, published this week in the journal Science, shows that differences in species composition of tropical forests are greater over distance in Panama than in Amazonia. The finding also challenges recent models proposed to explain forest species composition.

The research team, led by Richard Condit of the Smithsonian Tropical Research Institutes Center for Tropical Forest Science, compared data from single-hectare (2.47 acre) tropical forest plots near the Panama Canal with plots of the same size in the Yasuni National Park of Ecuador and in Perus Manu Biosphere Reserve. After identifying, tagging and measuring more than 50,000 individual trees with stems of ten centimeters or more in diameter in all three forests, they observed that a wide swath of the western Amazon has a forest in which the species change very little over distances of more than 1000 kilometers. The tree species counts in any one locale are high, but each locale turns out to be much like the others in terms of species composition.

In contrast, forests on the Isthmus of Panama change dramatically in tree species composition from one site to the next. Forests just 50 kilometers apart in Panama are less alike than forests 1,400 kilometers apart in the western Amazon. As a result of such high landscape variation, parts of Panama have as many or even more tree species than parts of Amazonia. Ecologists have a technical term for landscape variation in forest types: beta-diversity, Condit explained. Beta-diversity is high when forests change a lot over short distances as in Panama but low when forests are similar over long distances as in Ecuador and Peru. The unique aspect of this research by the Smithsonian team, including colleagues from France, the United States and South America, was a precise mathematical prediction of beta-diversity that helped
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Contact: Richard Condit
condit@ctfs.si.edu
202-786-2094 8045
Smithsonian Tropical Research Institute
24-Jan-2002

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