Biodiversity

Air pollution can effect biodiversity. For example, prolonged exposure of the vegetation in the San Bernardino

Mountains in southern California to photochemical oxidants has shifted the vegetation dominance from ozone-sensitive pines to ozone-tolerant oaks and deciduous shrubs (Barker and Tingey 1992). The fundamental influencing factors include the pollutant's environmental partitioning, exposure pattern, and toxicity and the sensitivity of the affected species. Biodiversity impacts occur on local, regional, and global scales. Local plume effects reduce vegetation cover, diversity, and ecosystem stability. Regional impacts occur via exposure to photochemical ox-

FIG. 5.1.11 Areas where air pollution affects forest trees and agricultural crops. (Reprinted, with permission, from J.J. Mackenzie and M.T. El-Ashry, 1989, Tree and crop injury: A summary of the evidence, chap. 1 in Air pollution's toll on forests and crops, edited by J.J. Mackenzie and M.T. El-Ashry, New Haven, Conn.: Yale University Press.)

FIG. 5.1.11 Areas where air pollution affects forest trees and agricultural crops. (Reprinted, with permission, from J.J. Mackenzie and M.T. El-Ashry, 1989, Tree and crop injury: A summary of the evidence, chap. 1 in Air pollution's toll on forests and crops, edited by J.J. Mackenzie and M.T. El-Ashry, New Haven, Conn.: Yale University Press.)

idants, wet or dry acid or metal deposition, and the longrange transport of toxic chemicals.

Air pollution effects on biodiversity are difficult to document. Unlike habitat destruction, which results in a pronounced and rapid environmental change, the effects of air pollution on biota are usually subtle and elusive because of their interactions with natural stressors. Years can be required before the ecological changes or damage within ecosystems become evident due to continuous or episodic exposure to toxic airborne contaminants or global climate changes (Barker and Tingey 1992).

A number of domestic animals are subject to air pollutant effects. The most frequently cited example is the effects of fluoride on cattle. Other air pollutants also affect animals, including ammonia, carbon monoxide, dust, hydrogen sulfide, sulfur dioxide, and nitrogen oxides.

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