XVI International Botanical Congess

Tropical forests of Amazonia and Southeast Asia have the highest tree a-diversity in the world, yet global diversity maps show the highest peaks in species richness in southern Central America and the Andes. Here I examine ß-diversity in Panama to see how total richness can be so high while a-diversity is middling. From the perspective of conservation, ß-diversity may be even more important than a-diversity, because it speaks directly to geographic issues about where and how many natural areas should be protected. Moreover, ß-diversity has much to say about the forces that organize community composition. I will start with the 50 ha plot in Panama to describe how tree species composition changes with distance at a local scale. Then, I describe network of small plots in Panama designed to test how distance, geology, and climate affect forest composition. Species composition changes abruptly, and the same species are seldom dominant at more than one site. Geology, elevation, and climate divide the flora into three major elements, but there is substantial variation in tree species composition that cannot be explained easily by environment. The only way of prediction tree species at a site with any reasonable accuracy is by examining an immediately adjacent site.