We acknowledge Robin Foster as the lead field scientist setting up the Barro Colorado 50-ha plot, whose botanical expertise was essential over the first three censuses and whose guidance was essential for all of us still working in the plot. The censuses have been made possible through support of the U.S. National Science Foundation (awards 8206992, 8906869, 9405933, 9909947, 0948585 to S.P. Hubbell), the John D. and Catherine D. McArthur Foundation, and the Smithsonian Tropical Research Institute. We also thank the dozens of field assistants and botanists who have measured and mapped the trees over the past 35 years. This research was also supported by research grant #7738 from the Natural Sciences and Engineering Research Council of Canada (NSERC) to P. Legendre. （awards 8206992, 8906869, 9405933, 9909947, 0948585 to S.P. Hubbell）