FIU Magazine - Spring 2000

It is an ecosystem where temperatures are always high and rainfall exceeds 70 to 100 inches per year. Tropical rainforests contain more than half of the world's species, although they cover only 7 percent of the earth's land surface. Given the biological richness of the tropical rainforests, only a minority of plant and animal species have been described and named. For millions of years, complex interrelationships between the rainforest's inhabitants have shaped their evolution.

It is the coldest of all biomes. The tundra looks like frozen-over prairie land most of the year. Found only in the most extreme northern and southern latitudes, temperatures often reach -50 degrees F in the winter. Only the top layer of the soil is able to thaw out during the brief summers; deeper layers of soil remain frozen throughout the year, a condition known as permafrost. Trees cannot grow in this harsh climate, only low-growing plant life and wildflowers.

No two ecosystems would seem to have so little in common. Quite often, though, there's more than what meets the eye.

Steven Oberbauer

For Steven Oberbauer, FIU professor of Biological Sciences and director of the Tropical Biology Program, the tundra and the tropical rainforests provide valuable clues for changes affecting the entire planet. For more than 20 years, Oberbauer has conducted extensive research in the Alaska tundra and the Costa Rican rainforest, and to this day he continues to divide his time between FIU and trips to these remote locales.

While much of his research has been in botany, his interest goes far beyond the plants. He analyzes their impact on the ecosystem and, in turn, the ecosystem's impact on the atmosphere. This global perspective focuses on an invisible element in these divergent ecosystems - carbon dioxide - and its potential impact on global warming. A large portion of the earth's carbon is trapped beneath tundra in the form of peat and other plant life that hasn't entirely decomposed. Tropical rainforests are known to play a vital role in the exchange of gases between the biosphere and atmosphere.

"We know the carbon dioxide concentration in the atmosphere is increasing," Oberbauer said recently, a few weeks before leaving on a trip to Alaska. "That's the purported cause of global warming.

The walk-up tower built in the middle of old-growth tropical forest near La Selva, Costa Rica.

"There's no question that the carbon dioxide concentration has gone up and there's no question that it directly affects plants. The increase in carbon dioxide affects plant photosynthesis. Plants use carbon dioxide - that's what they take out the air for photosynthesis to make sugars. So we're basically fertilizing all the plants in the world with the increased levels of carbon dioxide in the atmosphere. So their photosynthetic rates are higher than they used to be before the carbon dioxide increase started happening."

Like most scientists, Oberbauer's research interests evolved over the years as the result of his studies and work with university professors. His interest in biology, however, dated back to his early years growing up in the "back country" near San Diego. As early as fourth grade, he knew he wanted to become a scientist/biologist, and his favorite pastimes included bird watching and gardening. He credits his older brother, Tom, with stimulating his interest in botany. Today, Tom is a botanist and planner for San Diego County.

After completing his B.S. in biology at San Diego State University in 1976, one of his professors offered him a job that would take him to a region of future research. He soon found himself in Fairbanks, Alaska, conducting research in plant ecophysiology.

A research assistant at the field station at La Selva, Costa Rica.

"Ecophysiology used to focus on how individual plants would work," Oberbauer explained. "For instance, how does this plant live in this environment? Now the whole field has changed to more of: How does that plant working in that environment affect the whole ecosystem process? Ecophysiologists began addressing even bigger questions that addressed big global issues."

Wood samples from trees in the Costa Rican rainforest that are measured for levels of carbon dioxide.

Oberbauer returned to San Diego State for his master's degree in biology, continued working in Alaska and was subsequently admitted to Duke University's doctoral program in botany, one of the best in the country. When he arrived at the Durham, North Carolina campus in 1979, Boyd Strain, his academic advisor, made him an offer he couldn't refuse.

"Strain said, `What do you think about going to the tropics? I said, `Sure, why not?'" Oberbauer recalled.

Strain conducted pioneering research on the way in which higher carbon dioxide levels were affecting plants. Another member of the department, Don Stone, was the director of the Organization for Tropical Studies (OTS). The OTS is a consortium of universities and research institutions from the United States, Latin America and Australia dedicated to education and research on the tropics and their natural resources. At the time, Stone was trying to encourage faculty and students to conduct more research at field stations in Costa Rica maintained by OTS.

"So I went to Duke and my first semester there I went on an OTS course at their La Selva Biological Station, a 4,000-acre site located northeast of San Jose," Oberbauer related. "I spent the whole semester in Costa Rica. It was wonderful. Even though I was doing ecophysiology, I was very interested in identifying plants and plant taxonomy. In Alaska you could show me any plant, and I would know what it was. In Costa Rica you can find 200 species of trees in a very small area, and there are 2,000 species of plants in the small area where I work. It was a fabulous experience."

A field station plot on plant growth in the Alaskan tundra.

Stone noted how conditions at La Selva were "pretty primitive" and the contributions Oberbauer made to advance research at the site.

"With the advent of the work that Steve did, he helped establish the field of ecophysiology at La Selva," Stone said. "He was part of tremendous change at that field station and in tropical work in general. Today, La Selva is one of top two field stations in the world. I think of Steve as being a pioneer in the tropics. FIU has also come from nowhere to having a national presence in tropical research." While in Costa Rica in 1982, he met Maureen Donnelly, a woman studying poison dart frogs. Three years later, they would become husband and wife. Today, Maureen is also an associate professor of Biological Sciences at FIU.

A research assistant at a field station in the Alaskan tundra.

"We carried out a long-distance romance until 1992, when she came to Miami from New York," he said. After receiving his doctorate in 1983, Oberbauer returned to Costa Rica for a post-doctoral project on drought tolerance of tropical trees. Next, he embarked on a project with the station directors at La Selva, David and Deborah Clark.

"We wanted to start a project together," Oberbauer said. "They worked on rats for their Ph.Ds. They were tired of dealing with blood and dead animals and things that bite you. So they embarked on what they hoped to be this long-term study of how trees grow. How fast they grow, which ones survive, which ones die, what kind of conditions do they like, what kind of conditions do they die in. They were demographers studying population processes. But they said, `You know, to really understand why these plants are dying in these conditions, we need a physiologist to work on these.' So we teamed up and started writing grants together."

After completing his post-doc in 1984, Oberbauer returned to San Diego State as a research associate and also traveled to Alaska to work on projects funded by the U.S. Department of Energy (DOE). The federal agency was interested in learning how oil development on the North Slope could damage the ecosystem. In 1988, he accepted his position at FIU.

Today, Oberbauer is engaged in two major research projects thousands of miles apart: the Carbono Project, at La Selva, Costa Rica, and another at the Alaskan North Slope near Toolik Lake.

The Carbono Project was conceived in 1992 and funded in 1996 by the Department of Energy as part of the AmeriFlux and FluxNet networks, U.S. and worldwide networks of sites monitoring the carbon balance of ecosystems. Additional funding has been provided by the National Science Foundation.

Plant samples from the simulated longer growing season studies in Alaska.

The initial component of the project was born when Oberbauer and his La Selva colleagues began to study the factors that help or hinder tree growth. The Clarks had found that there were large annual variations in tree growth occurring at the forest level, and they wanted to discover which specific climactic conditions (light, wind, humidity and temperature) were associated with these swings.

The second component of the project is to study the factors affecting the productivity of tropical rainforests and their contribution to the carbon balance of the atmosphere. Undisturbed tropical forests have long been thought to be in carbon balance with the atmosphere; that is, they take up as much carbon dioxide as they release. Recent studies in Brazil, however, suggest that undisturbed tropical forests there may be taking up carbon. On the other hand, studies of the composition of the atmosphere suggest that tropical forests may be releasing carbon during some years, a finding possibly associated with periods of drought.

In order to measure the exchange of carbon dioxide, they built a 132-foot high walk-up tower in the middle of old-growth tropical forest where sensitive micrometeorological measurements determine the exchange of carbon dioxide and water of the surrounding forest with the atmosphere.

"The logistical challenges of setting up the project have been formidable, but the results coming in are well worth the headaches," Oberbauer said. "The main question in the most simplistic sense is: Are tropical forests helping, hurting or neutral with regard to this carbon dioxide increase in the atmosphere and climate warming. What it looks like so far is that this forest (at La Selva) is actually taking carbon dioxide out the atmosphere, net, and storing some. So then you ask, where is that carbon dioxide going? Well, some is going into the wood in the trees, some is going into the wood that has fallen to the ground and some is going into the soil."

The project has been a magnet for related studies, with more than 10 investigators from five universities undertaking or proposing collaborative research. These studies involve scientists from FIU, University of Missouri-St. Louis, University of Florida and University of Göttingen in Germany. Oberbauer hopes to keep the project operating for at least another six years and is confident that DOE will provide the funding to make it possible.

"One of the reasons DOE is interested in this is they're subject to pressures from lobbyists from fuel companies," he explained. "There's a certain amount of pressure to show that the North American continent is actually a sink for carbon, that we're taking up carbon. And there are quite a number of studies that suggest this is true, even though we are also the largest users of fossil fuels (which add carbon to the atmosphere). So they set up this network to do this, and they would like this network to go at least 10 years - not only to find out where we are now, but to see how these forests are going to respond to the increasing temperatures we're seeing."

Since 1995, some 4,000 miles north of Miami in the Alaskan tundra, Oberbauer has been studying how plants would respond to a longer growing season prompted by global warming - and how that might affect the ecosystem. Climate models suggest that the higher latitudes and the poles will experience more global warming than temperate or tropical areas.

To simulate a longer growing season (which ordinarily starts late May-early June), Oberbauer removes snow from small plots of land and heats the soil in some of them. Then he compares the growth between the experimental samples and those that grow under normal conditions. He has found that the experimental plants that start growing earlier in the season finish growing earlier; they can't take advantage of the longer growing season. "In terms of the net ecosystem affect, it's basically balancing out in terms of how much carbon is exchanging," Oberbauer noted. "It's not changing the system dramatically in terms of the net balance of carbon dioxide based on the extended growing season."

A great deal of carbon is also locked beneath the tundra in the form of peat. For years, the arctic tundra was thought to be a carbon "sink" that stores more carbon dioxide than plants release. Due to global warming, however, this peat would decompose and enter the atmosphere - which would make global warming even worse.

"The tundra is already changing from being a sink and helping the carbon dioxide problem to being a source and making it worse," Oberbauer commented.

"People are now becoming quite convinced that the climate is warming, and it's probably due to carbon dioxide that we've released in the atmosphere. According to physics, if you put more carbon dioxide in the atmosphere, the atmosphere has to get warmer - by physical principles that has to happen. There are other variables. We're dumping all this other stuff in the atmosphere that is reflecting light. But, ultimately, with the higher carbon dioxide there's going to be warming."