The circle of trees, as seen from the outside. The white pipe seen near the top delivers either normal air, one, or both of the experimental gasses to the trees. (Photo by Bob Kelleher)
In northern Wisconsin, they’re finding that gasses such as carbon dioxide and ozone will change the makeup of what survives in a future forest. An open air experiment called the Aspen FACE project has been testing trees in elevated levels of ozone and carbon dioxide for ten years. But they don’t know whether the forest can change as quickly as the climate does. The GLRC’s Bob Kelleher has more:
Transcript
In northern Wisconsin, they’re finding that gasses such as carbon dioxide and ozone will
change the makeup of what survives in a future forest. An open air experiment called the
Aspen FACE project has been testing trees in elevated levels of ozone and carbon dioxide
for ten years. But they don’t know whether the forest can change as quickly as the
climate does. The GLRC’s Bob Kelleher reports:
We’re standing inside a circle of trees: paper birch, aspen, and sugar maples, maybe 15
feet high. And they’re surrounded by a ring of large white pipes spraying the trees with
gasses – that’s the high pitched noise.
Among 12 different circles of trees, some get carbon dioxide, or ozone, or a
combination. These are the very gasses believed responsible for changing the climate –
they hold in the earth’s warmth, forcing surface temperatures higher.
Dave Karnosky, with Michigan Technological University, heads the Aspen FACE project,
near Rhinelander, Wisconsin. Karnosky’s trying to predict how these gasses will affect
the northern forest:
“Those species, with aspen and aspen mixed with birch and maple make up a huge
portion of our northern forests, and there was a lot of interest by industry as well as to
what’s going to happen in the future as these greenhouse gasses continue to build up in
the atmosphere.”
Even ten years ago, when this project started, it was clear that carbon dioxide and ozone
levels were on the increase.
Ozone is destructive. It’s bad for people and for plants. Carbon dioxide, on the other
hand, is what we exhale, and what green plants need to grow. Both gasses have been on
the increase, largely due to burning fossil fuels such as in coal-fired power plants and in
cars and trucks. Karnosky says he knew aspen were quite responsive to both CO2 and
ozone:
“We weren’t sure much about the interaction, but we were sure interested in what would
happen with that, because those two pollutants are both increasing at about the same rate
in the atmosphere.”
The Aspen FACE project has shown that most trees grow well when exposed to carbon
dioxide, and most do poorly in ozone. With the gasses combined, bad effects tend to
offset the good ones, but results vary greatly between the different kinds of trees, and
even within a single species of trees, like aspen.
Karnosky has found there’s a tremendous range of genetic variation even among the
relatively few trees they’ve tested. That variation makes clear predictions difficult:
“It’s very tough to make a single prediction for species or individuals within species,
there’s so much genetic variation. So that’s been one of the, I think, kind of the highlights
from what I see in terms of a bit of a surprise for us.”
That genetic variation could be the forest’s salvation. Karnosky thinks that if some
aspens, for example, die off from ozone, maybe others will do okay, and fill the forest
back in. Sugar maples, which seem more tolerant of ozone, could replace some aspen
and birch. Then, the mix of trees in the forest would change, but the forest would
survive.
But, there could be problems if the air changes the forest too quickly. Neil Nelson is a
plant physiologist with the US Forest Service. Nelson says the region’s paper and pulp
industries rely heavily on aspen trees. He’s uncertain how quickly the forest, and forest
industry, can respond if aspen begins to die off – and how long it might take for other
trees to grow in.
“One of my colleagues has said, you know, the key issue may be whether things change
too fast for our society and economy to adjust to, and I think that’s an open question.
There seems to be great plasticity, and we aren’t quite there in terms of predicting from a
forest management standpoint what these results mean.”
It takes time to grow trees, maybe too much time if the climate suddenly shifts. The
Aspen FACE project has already provided regulators preliminary data on ozone. It could
become the basis for future pollution law. But, even ten years into the Aspen Face
project, there’s still a lot more data to harvest among the aspen and hardwoods.
For The GLRC, I’m Bob Kelleher.
