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Plotting the Future: Why Biodiversity Matters in an Age of Global Warming

by Jennifer Amie

Thirty-five miles north of the Twin Cities, in the outdoor "laboratory" of Cedar Creek Natural History Area, the forces that shape our global environmental future are played out in six circular plots of prairie plants. Within each 20-meter plot, 16 species are cultivated, including big and little bluestem, lupine, quack grass, milkweed, goldenrod and prairie clover. They're common plants serving an uncommon purpose. These microcosms are providing critical insight into one of the most urgent environmental issues of our day: global climate change.

We're using prairies as a model system to understand what's happening to the planet," says Professor Peter Reich, holder of the F.B. Hubachek, Sr. Chair in Forestry in the University's College of Natural Resources and lead researcher of the project, dubbed "BioCON."

"Our climate is changing," says Reich, "and with that, the world will change. What we're trying to understand is whether the change will happen in a way that's sustainable for humans and the environment."

The rate of global climate change depends, in large part, on plants. Plants take carbon dioxide from the atmosphere to fuel the process of photosynthesis, which, in turn, produces oxygen. In an unaltered system, this exchange of carbon dioxide and oxygen is in balance. Over the past century, however, humans have tipped the scales. Pollution caused by burning fossil fuels is increasing the levels of carbon dioxide (and other "greenhouse gases") in the atmosphere, where they trap heat from the sun, causing the earth's temperature to rise.

"The amount of carbon dioxide in the atmosphere has risen from 280 parts per million in the pre-industrial age to 368 parts per million today, " says Reich. Some experts predict that carbon dioxide levels will reach 550 parts per million by the year 2050.

Today, two thirds of the excess carbon dioxide is absorbed by the oceans and by plants and soils. By acting like a sponge soaking up excess carbon dioxide from the atmosphere, plants are, to some extent, mitigating the damaging effects of pollution. But Reich and other scientists are concerned that one day this "sponge" will become saturated—and unable to absorb any more carbon dioxide. The BioCON experiment is designed to determine whether this saturation effect will occur, and whether two factors—biodiversity and soil nutrients—affect the ability of plants to absorb excess carbon dioxide.

"What we don't want," says Reich, "is for the greenhouse effect to create major changes that are too fast for us to adapt to. If the polar ice caps melt and all the coastal areas of the world are flooded, that creates a huge environmental, economic, and social impact."

To date, the models used by scientists to predict the rate and effects of global climate change do not take into account the possibility of saturation or the factors that might contribute to it. "One problem is that we haven't been able to prove that saturation will occur," says Reich. The BioCON experiment, and its results, will help scientists better understand the real rate of global climate change and how it is affected by plant ecosystems.

The BioCON researchers are looking closely at how soil nutrition affects plants' ability to absorb carbon dioxide from the atmosphere. Half of the prairie plots at Cedar Creek are receiving added nitrogen, a nutrient essential for plant growth. These well-fertilized soils can absorb more carbon dioxide—for a while. But over time, the saturation effect occurs. "Year by year, their ability to absorb carbon is going down," says Reich.

Significantly, the project also simulates the environmental conditions of future global warming by adding increased amounts of carbon dioxide to three of the six large, circular prairie plots. Applying carefully measured quantities of a gas in an outdoor environment is no small task, and at Cedar Creek it's accomplished by an ingenious system of upright pipes that ring the prairie plots like large, white fence posts. BioCON is one of only a handful of experiments in the world to use this technology.

Reich and his colleagues are testing how biodiversity—the number and kinds of species—affects the plants' ability to absorb the atmosphere's excess carbon dioxide. At Cedar Creek, the biodiversity of the prairie plots is varied. Each of the six plots is subdivided into 61 sections of land. Some sections have 16 species of plants, while others have nine, four, or just one.

"What we're finding," says Reich, "is that the more diverse plots take up and store more carbon." Reich and his colleagues discovered that when they increased carbon dioxide concentration in the atmosphere, the sections of land containing all 16 species of plants absorbed 22 percent more carbon dioxide than sections with 16 species that received no additional carbon dioxide. In other words, the more diverse plots are absorbing a good portion of the extra carbon dioxide. In comparison, the less diverse plots absorb a much smaller fraction of the extra carbon dioxide. Sections planted with just one type of plant absorb only seven percent of the added carbon dioxide.

"That's important," says Reich, "because it suggests that we need to worry about unintended consequences of biodiversity loss around the world."

Globally, urbanization, agriculture, deforestation, and other practices combine to dramatically reduce the number of species living on the planet. Says Reich: "Around the world, we manage the vegetation in our ecosystems. In Europe, for example, 99 percent of the vegetation is human-determined. We are simplifying ecosystems, and we're losing diversity."

Reich's experiment is one dramatic example of why maintaining biodiversity is important to all life on the planet. The miniature prairies of Cedar Creek warn that disruption of the earth's ecological balance will have serious repercussions. "The lesson here," says Reich, "is that we shouldn't play with matches around gasoline without knowing whether the lid is on the gasoline can. We're looking at effects that are global in nature and long-term—yet as a society, we fail to take a long-term view. We need to figure out whether our lack of planning will have adverse consequences. We need to look toward the future and think carefully about how we manage our resources."

Peter Reich's research is featured in the Bell Museum exhibit "Biodiversity 911: Saving Life on Earth."