Underdogs in the understory: Study suggests nature favors rarer trees

A study of seven tropical forests around the world has revealed that nature encourages biodiversity by favoring the growth of less common trees. The landmark study, conducted by 33 ecologists from 12 countries and published in the Jan. 27 issue of the journal Science, conclusively demonstrates that diversity matters and has ecological importance to tropical forests. Helene Muller-Landau, an assistant professor of ecology in the University of Minnesota's College of Biological Sciences, is a co-author of the study, which supports previous research by her colleague David Tilman, a Regents Professor of Ecology, into the causes and value of biodiversity.

"This research has the surprising finding that biodiversity in tropical rain forests and Minnesota prairies arises from the same kinds of underlying processes. It brings us a step closer to understanding the causes of the world's amazing biodiversity," Tilman said.

Muller-Landau contributed quantitative skills for analyzing and interpreting the data.

"After all the effort that went into the analyses, it was neat to see that results from such different forests were so similar," Muller-Landau said.

The study was conducted on seven undisturbed forest plots, or "tropical forest observatories," maintained and studied by research institutions in Borneo, India, Malaysia, Panama, Puerto Rico and Thailand, under the coordination of the Center for Tropical Forest Science of the Smithsonian Tropical Research Institute, based in Panama. Christopher Wills, professor of biology at the University of California, San Diego, was the lead author.

The forest plots are themselves diverse. They range from dense and species-rich wet rain forest to drier and more open forest that is often swept by fires. Even so, all the forests show the same pattern of increasing local diversity as trees age.

The authors say rare trees may have an advantage because they are less vulnerable to animals, fungi, and microorganisms that prey on common trees and because they don't have the same resource needs as common trees.

Trees in "monoculture" forests, where all individuals are the same species, are very susceptible to predators and diseases, and also compete with each other for the same resources.

The new study raises questions about whether other ecosystems, from temperate forests to coral reefs, also select for biodiversity.

(Photos of Muller-Landau and a tropical forest are available on request.)

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