Redwood Reader

RHINELANDER, Wis. - Inside what conspiracy buffs might guess is a communications center for UFOs, scientists instead are asking a very down to earth question. What are we doing to our trees?
About 60 researchers from seven countries are trying to find the answer In northern Wisconsin, studying the impacts that elevated carbon dioxide And ozone pollution have on aspen, birch and maple trees. Scientists are probing the soil for bugs and nutrients, electronically monitoring how individual leaves and tree trunks "breathe," checking how much water roots take up and conducting a dozen other major experiments. So many scientists come here that they must be careful not to bump into each other's work. It's called FACE -- Free Air Carbon Enrichment -- and the effort is revealing human impacts on forests never before documented.
In an abandoned farm field northwest of Rhinelander, researchers have Built 12 giant rings of PVC pipe around meticulously planted experimental forests. Each open-air ring, 100 feet in diameter with pipes 30 feet high, contains 650 aspen, maple and birch trees planted in 1997. For the past seven growing seasons, some of the trees have been getting a dose of carbon dioxide equivalent to the level all forests are expected to see later this century. Carbon dioxide, or CO2, is the primary pollution created when coal, oil and gas are burned.
Some of the trees also are getting a daily blast of ozone, another fossil fuel pollutant. Ozone, O3, is the kind of pollution once associated with big city smog. Now, it's spreading across the globe to inundate rural areas as well. It's the only large-scale experiment in the world measuring the effects Of carbon and ozone on trees. "We're trying to be a window into the future of what our forests will look like under the elevated carbon dioxide and ozone levels that we'll see a few years from now," said David Karnosky, director of the FACE project and a Michigan Technological University scientist.
MORE CARBON, MORE OZONE
That carbon levels are way up isn't in question. Background carbon dioxide levels in our air were stable at about 280 parts per million for 100,000 years, according to data published by NASA. But during the past 100 years,
that's increased to 360 parts per million and continues to rise at least 1.5 parts per million each year. Carbon levels are expected to hit 560 parts per million by the end of this century.
Ozone also is increasing rapidly, from about 10 parts per billion 100 years ago to more than 40 parts per billion today and higher than 80 parts per billion in urban areas during smoggy days. That's more than enough to cause
major damage to trees, the FACE experiment is showing.
What those levels of ozone and carbon dioxide, called greenhouse gases, might do to global climate in coming decades is the subject of heated debate. A majority of scientists say they probably will create a warmer world. But the researchers in Rhinelander don't have a dog in that fight.
"Our experiment has nothing to do with global warming. Whether or not global warming is happening, the amount of carbon and ozone is increasing. That's not in dispute," Karnosky said. "We want to know the impact on trees, not on the weather."
THE DANGER OF OZONE
The findings are drawing interest on many fronts. High doses of carbon dioxide make trees grow fast. That's exactly what most scientists thought would happen, since carbon dioxide is the most basic element trees need to survive. Trees inside of the carbon-only rings are noticeably thicker, leafier and much taller than those in nearby rings exposed only to natural air.
Ozone's impact is even more stark, but in the negative. Many trees near the ozone-spewing pipes already have died. Those farther inside the rings are stunted and prone to diseases.
Trees exposed to elevated levels of both carbon and ozone grow about normally. The combined effects of increased carbon and ozone appear to cancel each other out, although scientists aren't sure why. Broader, long-term impacts of the experiment still are developing along With the trees inside the rings.
"What does this mean on a landscape level, over a long period? The answers to the most intriguing questions are still out there a few years away," Karnosky said while examining an aspen branch inside one of the rings.
While carbon-enhanced trees are bigger and grow faster, for example, the entire ecosystem around them appears to be thrown off-kilter. The same thing is happening around trees that get both carbon and ozone.
"Ozone at relatively moderate levels, not even high levels, negates the productive effects of elevated CO2," said Kevin Percy, a scientist with the Canadian Forest Service participating in the FACE project. "We're talking
levels that we already see in southern Wisconsin right now, and levels that are expected to affect 50 percent of all forests globally in a few years." Mark Kubiske, a research plant physiologist for the U.S. Forest Service and a FACE researcher, said ozone pollution probably already has cut forest productivity in the Northland. One research paper estimates aspen productivity has been cut 30 percent.
"Ozone is the most severe pollutant we have in the Lakes states. We like to think of our air up here as clean. And it is, relatively," Kubiske said. "But, already, three or four days each month, we're seeing ozone plumes that
reach (the Northland) at levels enough to cause harm to plants and trees."
CHANGING ECOSYSTEMS
Scientists also are finding abnormalities in the soil when trees are exposed to higher ozone and carbon. Leaves die earlier each year, and root systems are smaller, probably making the trees more susceptible to drought
Inside the high carbon rings, forest tent caterpillars increase in Numbers during their outbreaks. Leaf rust and aphids increase along with carbon and ozone, and wood-boring insects do more damage. But each type of tree reacts a little differently. "There is a pretty big range of variation," Karnosky said, noting one variation of aspen is doing better under higher ozone levels, probably because its competition is dying off.
When carbon and ozone are increased, even forest composition -- the Types of trees that make up a forest -- may be changing. Birch trees tolerate more ozone than aspen. If birch come to dominate over aspen, as the experiment seems to indicate might happen, there could be major changes in the type of trees available for paper and board mills and for wildlife in our forests. Grouse, deer and moose thrive off young aspen, for example, but not as much off birch. "We could have a substantive change in forest dynamics in just a fewyears," Percy said. "Birch might be the winner in the northern forest of 2050."
The future of our forests is a critical issue for the Northland – for quality of life, the timber harvest industry and tourism. Dense forests define the Northland, provide habitat for its wildlife, filter water for streams and lakes, and provide a living for many residents. Any efforts to deal with carbon and ozone pollution worldwide, or a lack of effort, will affect trees here at home. A similar experiment in Illinoisis looking at the pollutants' impact on crops. "To the public in the Lake states, this is pretty important stuff," Kubiske said. The increasing levels of carbon dioxide and ozone pollution "have the potential to affect just about everyone's lives up here. You're talking about altering entire forest ecosystems and possibly agriculture systems. People should pay attention."
CARBON SINK CLOGGED?
It's not just local impacts of a changing forest, however, but what value our trees might have in helping to solve the global climate change problem. Scientists want to know how trees react to carbon and ozone to test a theory
that northern forests may act as a carbon "sink" that will help diminish the global carbon problem.
The increase in carbon, from burning fossil fuels that release carbon, is being blamed by many scientists for raising global temperatures enough to affect our climate. All that carbon dioxide is keeping heat in like a greenhouse, the theory goes. It's already credited with melting polar ice fields and glaciers, making plants bloom earlier each spring and lakes freeze later each fall.
The carbon sink theory is that trees will absorb much of the excess carbon now being spewed by power plants, cars and factories from Connecticut to Chile to China. In some countries, tree planting efforts already have
Begun to act as carbon "credits" so nations can meet global agreements to reduce carbon.
But the Rhinelander scientists are exposing a pesky fly in the carbon sink theory. When exposed to elevated levels of carbon and ozone in the atmosphere, trees are taking in and storing less carbon in their trunks and in the nearby soil. Some of the young trees may even be giving off more carbon than they absorb, contributing to the problem rather than helping it. Increased exposure to the pollutants is causing increased respiration of carbon.
"The potential of forests to have major impacts at reducing carbon dioxide in the atmosphere isn't what some
people predicted," Percy said. "When you add in ozone to the equation, in many trees, respiration of CO2 goes
up."
The results could have a staggering impact on international carbon reduction efforts as political discussions continue on how to solve a growing global pollution problem. And if trees can't take more carbon in, experts
Trying to solve the carbon problem will have to look elsewhere -- probably at cutting carbon emissions instead.
"The results, hopefully, will speak for themselves," said Neil Nelson, U.S. Forest Service liaison to the FACE experiment. Kubiske agreed, noting he hopes policy-makers are listening. "There's a lot we still need to tease out as we go forward," he said. "But the preliminary results indicate that forests may not be as important for carbon storage as was hoped. That's going to get a lot of attention in the next few years all over the world."

Reference
Rebbeck, J., Scherzer, A.J. and Loats, K.V. 2004. Foliar physiology of yellow-poplar (Liriodendron tulipifera L.) exposed to O3 and elevated CO2 over five seasons. Trees 18: 253-263.
Background
The authors note that studies of the combined effects of elevated ozone (O3) and carbon dioxide (CO2) on long-lived woody plants have been conducted before, but that "few have reported results for more than two or three seasons," and that few such studies of trees have been done "during their development from seedlings to saplings or mature trees." Consequently, their five-year study - which does both of these things - is rather unique.
What was done
Rebbeck et al. grew yellow poplar (Liriodendron tulipifera L.) seedlings for five years within open-top chambers in a field plantation at the Northeastern Research Station's Forestry Sciences Laboratory at Delaware, Ohio, USA, exposing them continuously from mid-May through mid-October of each year to either (1) charcoal-filtered (CF) air to remove ambient O3, (2) ambient O3, (3) 1.5 times ambient O3, and (4) 1.5 times ambient O3 plus 350 ppm CO2 above ambient CO2, (target concentration of 700 ppm CO2), while they periodically measured a number of plant parameters and processes. Throughout the study, the trees were never fertilized, and they received no supplemental water beyond some given in the first season.
What was learned
Averaged over the study's five growing seasons, the midseason net photosynthetic rate of upper canopy foliage at saturating light intensities declined by 10% when the trees were grown in ambient O3-air and by 14% when they were grown in elevated O3-air, when compared to the trees that were grown in the charcoal-filtered air, while seasonal net photosynthesis of foliage grown in the combination of elevated O3 and elevated CO2 was 57-80% higher than it was in the trees exposed to elevated O3 alone. There was also no evidence of any photosynthetic down regulation in the trees exposed to the combination of elevated O3 and CO2, with some of the highest rates being observed during the final growing season.
What it means
In the words of the authors, "the results of this five-season field study suggest that elevated CO2 may ameliorate the negative effects of increased tropospheric O3 on yellow-poplar." Indeed, their results suggest that a nominally doubled atmospheric CO2 concentration more than compensates for the deleterious effects of a 50% increase in ambient O3 levels … and by several times over.


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