Article from the Star Tribune – Published July 27, 2002

by Tom Meersman

A Natural Choice

Chris Clark, a University of Minnesota researcher working with a dozen undergraduates in the fields recently, was swatting deerflies as he clipped and removed long, narrow strips of foliage from small plots in a grasslands experiment.

The students, some wearing bandanas over their noses and mouths, loaded the greenery into marked bins and took them to a cargo van. In a lab that afternoon, they sorted every plant by species and bagged them for future weighing to determine growth rates.

“You really get to appreciate the process of research when you’re out here,” Clark said. “It’s not easy, but in the end you get a lot of good results out of it.”

Most of the students had not been born when the first group of researchers mapped the plots 21 years ago. Since then, different groups have gathered data every year, comparing areas treated with extra nitrogen with those that have been left alone.

The experiment is one of more than 160 during the past two decades at the Cedar Creek Natural History Area, 5,400 acres owned by the University of Minnesota near East Bethel, about 30 miles north of the Twin Cities.

Cedar Creek is one of the few spots where North America’s three major ecosystems overlap. It has inspired scientists for decades and will celebrate its 60th anniversary in a few weeks. Although largely unknown to the public, it has become one of the country’s premier centers for long-term ecological research.

“Cedar Creek ought to be better known,” said Paul Ehrlich, president of the Center for Conservation Biology at Stanford University in California. “It has made Minnesota famous among people interested in ecology, and classic work is being done there.”

Ideal Research Site

Cedar Creek was founded by several citizens and scientists who realized as early as the 1930s that it was an ideal research site because of its location at the juncture of the continent’s three great biological systems:

* the northern conifer forest
* the eastern deciduous forest
* and the western tallgrass prairies.

The site includes a cedar bog where Raymond Lindeman, one of the pioneers of modern ecology, developed his theories in the 1940s. Another area contains a rare example of oak-savanna, agrasslands system interspersed with oak trees that once dominated much of southern Minnesota.

Scientists have burned the savanna two out of every three years since the mid-1960s, mimicking what occurred naturally. An adjacent oak-savanna parcel hasn’t been burned to learn which species of trees and shrubs will take over if fire is suppressed over time.

Scientists at Cedar Creek also invented electronic telemetry technology in the 1960s, which allows animal behavior to be studied by using radio tracking devices.

Since 1982, Cedar Creek has been designated by the National Science Foundation as one of about two dozen sites in the Long-Term Ecological Research network. About 50 experiments are underway at Cedar Creek, supported by $1.5 million annually in grants from federal agencies and private foundations.

The grasslands experiment was devised by David Tilman, a University of Minnesota ecology professor and the director of Cedar Creek. It involves 400 plots on four fields and is intended to mimic what will happen as nitrogen accumulates in the environment from fertilizers and the burning of fossil fuels.

Tilman said the results show that more nitrogen leads to less plant diversity. He and others have documented a 30 percent decline in plants, mainly rare species, over 20 years.

He said the experiment has continued under an evolving team of scientists who build on one another’s work, ask new questions and formulate new experiments at Cedar Creek.

“These are attempts to understand how ecosystems are put together and why they function the way they do,” Tilman said. “And beyond that, what happens when they’re perturbed as the climate changes, when nitrogen is deposited, when fire frequency changes.”

Other Experiments

The experiments are not limited to plants; they have expanded to include the importance of insects, fungi in the soil and other factors. More than 4,000 insects have been identified at Cedar Creek and cataloged on computers, making it one of the most intensely studied grasslands systems on Earth.

In another experiment, 342 more mini-plots were planted with up to 16 species of grasses and plants to study whether those with more diversity grow more robust, and to learn how species compete and coexist. A more recent experiment on some plots is testing which ones are vulnerable to weeds and other invasive species. The more diverse plots, Tilman said, have been shown to be more productive and less likely to be taken over by non-native species.

Another study is even more ambitious. Hundreds of plots with varying numbers of plants and grasses are divided into six groups and surrounded by 8-foot plastic pipes with holes in them. In three of the groups, carbon dioxide is pumped through the pipes to mimic conditions in 2050, when carbon dioxide levels in the atmosphere are expected to be much higher than they are today.

Tilman calls it a “time machine” experiment that is studying the effects of fertilizing the earth with carbon dioxide. It is also testing the effects of nitrogen added to some plots with varied numbers of plants.

“I don’t know of any other experiment in the world that is actually looking at three major aspects of global change, and doing so with enough replicates where you can separate the effects and look at the interactions,” Tilman said.

Long-term outdoor study, with emphasis on quantifying how nature will behave, is relatively new in ecology, Ehrlich said. Traditional experiments have tended to be short-term fieldwork or laboratory “growth chamber” research, he said — both of limited value in determining whether the results were valid over time in the natural world.

“Cedar Creek and Tilman have filled a very important niche in ecology,” Ehrlich said, by developing the methods to study nature over longer time spans and by assembling multidisciplinary teams of researchers.

Tilman said that understanding how ecological systems function and what they provide in terms of clean water and air will be even more important in the future. Traditional farming, transportation and energy use are changing the way nitrogen, carbon and water cycle on the planet, he said. Humans are also inadvertently moving species around the world.

“I’m hoping that the work we’re doing will provide useful information,” Tilman said. “We need to go from a place where decisions are made inadvertently to a world where we know more about what we’re doing, where we look at the costs and benefits, and we try to make a rational choice among those.”

— Tom Meersman is at meersman@startribune.com