Page 144 - Environment: The Science Behind the Stories

in CO than today’s (equal to what is
2
expected for the year 2050). Sen- Control
sors monitor wind conditions, and
computers control for the influence
of wind by adjusting CO releases,
2
keeping ambient concentrations stable CO 2
within each plot.
The pipes at the Aspen plots
also release tropospheric ozone (O , a Ozone Clone E
3
major pollutant in urban smog; p. 483), Clone D
and researchers study how this gas CO Clone C
and CO affect plant growth, leaf and + 2 Clone B
2
root conditions, soil carbon content, Ozone Clone A
and much more. Pipes at some plots
release normal air, serving as controls 0 1 2 3 4 5 6 7 8
for the treatment plots. Estimated volume of growth
3
Researchers using the Aspen (1000 cm )
FACE facility have been asking Figure 2 data from five clones of aspens show that during the
whether forest trees will seques- study period, trees supplied with carbon dioxide grew more than
ter more carbon as CO levels rise, did the control trees, whereas those supplied with ozone grew
2
whether this will change as trees grow, less. Trees supplied with both gases did not grow differently from
how CO interacts with ozone, and the controls. Source: Isebrands, J.G., et al., 2001. Growth responses of
2
how these gases affect trees’ interac- Populus tremuloides clones to interacting elevated carbon dioxide and tropo-
tions with insects and diseases. They spheric ozone. Environmental Pollution 115 (3): 359–371, Fig. 2.
have learned a number of things so far,
including:
a variety of negative impacts on trees cease funding. The DOE advised sci-
and forests. Thus, the old expectation entists to cut the trees down and dig
• Insects and diseases that attack that more CO makes for happier plants
aspen and birch trees increase as appears to be an oversimplification. up the soil to analyze carbon content.
2
atmospheric levels of ozone and Indeed, research from other FACE sites This analysis would provide urgently
CO rise. needed data on carbon sequestra-
2
• High CO concentrations delay as- is showing that increased growth from tion, the DOE said, and then millions
2
enhanced CO is often temporary and
pen leaf aging, which makes some that growth rates later flatten out or of dollars could be shifted toward a
2
aspens vulnerable to frost damage decline. Recent work on crop plants new and improved generation of FACE
in winter. experiments.
• Elevated CO levels increase pho- has even shown that high CO makes The trees at the Aspen site were
2
2
some crops less nutritious.
tosynthesis and tree growth—but Obtaining solid answers to ques- harvested for analysis in 2009, and
moderate levels of ozone offset tions like these often takes years or researchers are now regrowing forest
this increased growth (Figure 2). decades, and FACE experiments are on the site with funding from the United CHAPTER 5 • Envi R onm E n TA l S y STE m S A nd E C o S y STE m E C ology
Because many modelers have not designed to monitor plots for the long States Forest Service. The knowledge
taken ozone into account when term as the plants mature. Some FACE gains from this project, and other FACE
estimating how much carbon trees sites have been operating for 20 years sites in which growth is ongoing, have
can sequester, the Aspen FACE and are beginning to produce data that been substantial. Data from the Aspen
data suggest that their models may could not be gathered in any other way. FACE project alone has generated
overestimate the amount of CO that Thus, researchers were shocked more than 180 peer-reviewed scientific
2
trees will pull out of the air. articles and is helping scientists today
in 2008 when the U.S. Department of better predict how forest ecosystems
Together, such results indicate that Energy (DOE), which funds Aspen and will respond to the atmosphere of
rising carbon dioxide levels could have other major sites, announced it would tomorrow.

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