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Biologic Markers of Air-PoDution
Stress and Damage in Forests
INTRODUCTION
The effects of air pollution on forests have long been the object of study and
public concern. For example, smelters in Copper Hill, Tennessee, in Sudbury, Ontario,
and in Palmerton, Pennsylvania (reviewed by Kozlowski, 1985) have devastated forests
over large areas. In contrast, the effects of New York City's air pollution on the
growth of corticolous lichen populations on Long Island (Brodo, 1966) have been subtle:
the changes documented were so obscure that even an experienced botanist observing a
segment of the gradient might overlook the changes and dismiss the differences as being
well within the normal range of variation. Similarly, patchiness in the distribution,
vigor, reproductive success, and other attributes of trees in forests often is accepted
as normal. But the extent of normal variation is not well known, so understanding normal
variability has taken on new importance with the accumulation of evidence of declines
over the last 25 years in the vitality of many forests in the United States and in Europe
(e.g., Johnson and Siccama, 1983; Andersson, 1984; Schutt and Cowling, 1985; McLaughlin
et al., 1987; Sheffield and Cost, 1987; Woodman and Cowling, 1987; Pitelka and Raynal,
1989).
Even if forests are distant from sources of pollutants, ambient concentrations
of airborne chemicals can be sufficient to produce visible injury, alter biochemical and
physiologic processes that control metabolism and carbon allocation, reduce resistance
to disease, reduce resistance to abiotic stress, and lead to the death of individual
trees (Berry and Riperton, 1963; Linzon, 1966; Dochinger, 1968; Cobb and Stark, 1970;
Miller and McBride, 1975; Cowling, 1985; Kozlowski, 1985; McBride et al., 1985;
McLaughlin, 1985~. However, the cause-and-effect relationships in such examples often
are difficult to discern.
The pollutants most often suspected in cases of forest stress and damage are
combinations of sulfuric acid and sulfur oxides, nitric acid and nitrogen oxides, and
ozone. As research progresses, the list might grow to include an array of other organic
and inorganic substances. The effects of a wide variety of stresses on trees and forests
often are similar, and it remains to be seen whether a particular set of symptoms can be
s
Representative terms from entire chapter:
nitrogen oxides
