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David Tilman, Regents Professor of Ecology

David Tilman, Regents Professor of Ecology, uses biodiversity research to see the future of Earth's ecosystems.

Icon in ecology

Discoveries at Cedar Creek propel U researcher to prominence

By Peggy Rinard

Published on June 10, 2005

If David Tilman were a prairie plant, he might be Andropogon gerardi, the native prairie grass known as Big Bluestem. Like Big Bluestem, Tilman uses resources with exquisite efficiency, says Clarence Lehman, associate director of Cedar Creek Natural History Area, where Tilman conducts research that has made him one of the world's foremost ecologists. But while Big Bluestem dines on nitrogen, Tilman thrives on time. "Dave is one of the most focused people I know," Lehman says. "If he finds he has three minutes to spare before a seminar begins, he'll pop back into his office to write another sentence for the paper he's working on. That's one reason he gets so much done." And Tilman, who has one foot in research and one in environmental advocacy these days, has a lot to do. Resource competition has been a key theme of Tilman's research since he published a doctoral study on the subject in Science in 1976. Since then, his use of mathematical models to better understand ecosystem dynamics has helped shape the field of ecology, making it a much more quantitative and predictive science, according to an article published in Proceedings of the National Academy of Sciences in 2004 to recognize Tilman's membership in that august body. So it's not surprising that he keeps an eye on the clock and puts his own resources to good use.

Hidden Treasure

Big Bluestem is one of hundreds of plant species in Tilman's biodiversity research plots at Cedar Creek. By varying combinations of species and nutrients in each of the plots, Tilman explores the role of biodiversity in ecosystems. The 20-year-old project is funded by the National Science Foundation as part of a national network of Long-Term Ecology Research projects. And it has elevated Tilman and Cedar Creek to international prominence. Although Cedar Creek is a hidden treasure within Minnesota, its name and Tilman's research are well known by ecologists around the world. Located just 30 miles north of the Twin Cities, Cedar Creek makes an ideal living laboratory for ecology research because of its biodiversity. Most of North America's primary ecosystems--western prairies, northern coniferous forests, and eastern deciduous forests--are represented within its 5,400 acres. The Minnesota Academy of Science acquired Cedar Creek and transferred ownership to the University in the early 1940s. Shortly afterward, graduate student Raymond Lindeman, who is credited with coining the term "ecosystem," established the modern theory of ecosystem ecology based on his research at Cedar Creek. Tilman arrived on the scene and created his biodiversity plots, which resemble a patchwork quilt of prairie plants, in the early 1980s. The long-term nature of the research is what makes it valuable, he says. "Cedar Creek is a time machine that shows what could happen in 50 or 75 years if we remain on the same course and continue increasing the amount of nitrogen and carbon dioxide in the environment."

Strength in Biodiversity

Tilman stunned the international ecology community during the mid-1990s with a series of groundbreaking articles, published in Science and Nature, showing that biodiversity strengthens ecosystems and species, and that nitrogen fertilizers decrease biodiversity and ecosystem function. His most well-known article, published in 1994 in Nature, rejected a long-held belief that diversity destabilizes individual species and thus, presumably, entire ecosystems. The discoveries made him the most cited ecologist for more than a decade and led to a Pew Fellowship, a MacArthur Award, and membership in the National Academy of Sciences, among other honors. His discoveries also compelled Tilman to share his news and concerns with a broader audience. A few years ago, he started Issues in Ecology, a publication for educators and policymakers. Each edition takes on a major issue related to human impact on the environment. Other efforts range from public lectures to Congressional testimony to international conference presentations. About a year ago, Tilman began working with Stephen Polasky, professor of applied economics and ecology, to calculate the full costs of energy and agricultural practices and to place an economic value on the services that ecosystems provide. Polasky focuses on economic strategies to encourage people to preserve the environment. "The economics of nature and the economics of society are amazingly similar," Tilman says. The economic analogy is important, he believes, because consumers make economic choices that often harm the environment without realizing the long-term costs. And ecosystems provide a valuable service to consumers by filtering at least some pollutants out of the air and water. "By placing a monetary value on nature's services, we can determine if environmental policies will cost us money or save money," he says. "Then we can make decisions that have the best long-term benefits for society." One of his primary concerns is the impact of agriculture on the environment. "People don't realize that agriculture takes an even greater toll on the environment than energy," he says, citing the double impact of eliminating ecosystems to plant crops and then using nitrogen fertilizers, which leach into water supplies and reduce biodiversity elsewhere. With the global population projected to increase from six billion to nine billion over the next 50 years, the problem could get much worse, he says.

Public Education

While Tilman is committed to advocacy, he is concerned about the amount of time it keeps him away from his research at Cedar Creek. So he has a plan to bring public education to him. It's part of a larger effort to expand Cedar Creek's very modest research and education facilities to accommodate the growing number of students and faculty who study and work there, and the growing importance of the work. The new center will include an auditorium and meeting rooms to hold educational programs for teachers, legislators, journalists, park naturalists, and others who can help get his message out to the public. He and others at Cedar Creek have raised more than $1 million of the $4 million needed and hope to break ground within the next year. Perhaps this will give him a little more quality time with Big Bluestem and friends at Cedar Creek. "There's a lot more to learn about biodiversity," he says. "Why are there so many species? And how do they co-exist? These are questions that have intrigued biologists since Darwin. Without knowing the answers, we can't really understand how ecosystems are affected when species are lost, and how humans will ultimately be affected by diminished ecosystems."

This article originally appeared in BIO, spring 2005, the magazine of the College of Biological Sciences.