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Computer Modeling of Trees Under Stress
| Article
# : |
17192 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
12 / 1990 |
3,008 Words |
| Author
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Robert Kohut
Robert Kohut is associate plant pathologist in the
environmental biology program at the Boyce Thompson Institute
for Plant Research at Cornell University in Ithaca, New York. |
A tree in the forest is an enduring fixture from a human time perspective. Yet we know that tress grow and live and die according to their own unique characteristics. In the last 30 years, numerous reports have noted an apparent decrease in the vigor and growth of some tree species, especially some exposed to such anthropogenic environmental stresses as elevated ozone levels and acidic rain. From red spruce in the high Appalachian Mountains, to loblolly pine in the southern forests, and to ponderosa pine in California, patterns of decline have been observed. Scientists have faced serious challenges in trying to substantiate the precise causes and nature of these declines.
Trees are such long-lived organisms that they express cumulative, long-term impacts from environmental stresses whose effects in any single year may be too subtle to detect. While environmental stresses may initially cause changes in the growth, physiology, or nutrition of individual trees, eventually the changes in individual trees appear as noticeable changes in the forest. The long life span of trees and the relative stability of tree-dominated ecosystems are in part the result of control and feedback mechanisms that enable trees to limit the short-term harmful consequences of environmental perturbations. These mechanisms ameliorate the climatic, edaphic (soil and water), and biological stresses on each species of tree. Given the present exposure of forest trees to elevated ozone levels and acidic rain, an important question is whether or not these protective mechanisms can operate effectively against these pollutants. (Paradoxically, while ozone in the upper atmosphere serves as a valuable protective shield against penetration by ultraviolet radiation, at ground level, ozone may be harmful to vegetation.)
Ozone and acidic rain are the focus of attention among those who study forest health because (1) these two pollutants are widespread in the areas in which forests are declining, (2) the onset of the declines appears to be associated with increases in ozone and acidic rain, and (3) it has been well substantiated that ozone is poisonous to plants. Other air pollutants, such as sulfur dioxide and oxides of nitrogen, do not occur in high enough concentrations in the areas affected to be considered potential agents of stress.
Rational for research
Past studies have been too limited in their focus, disciplinary scope, and duration to acquire the data needed for developing a mathematical computer model to answer questions about the long-term effect of air
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