Scientists debate the role of pollution in killing trees how it works in conjunction with onslaughts of insects, disease, or climate changes. Most agree, however, that airborne pollutants play a significant role. Trees are dying in West Germany's Black Forest. These and other pollutants may damage the needles' cell membranes, allowing nutrients to escape. They may also acidify the soil, destroying organisms necessary to the nutrient cycle, as well as injuring the trees' fine root systems.
Weakened trees become more vulnerable to drought, frost, fungi, and insects.
Tests so far have found no simple cures. In other areas dirty air is held even more culpable. Man-made monuments that have endured for thousands of years are now being rapidly eaten away. In the American West spectacular vistas are fading behind an aerosol haze. Ozone resulting from automobile emissions annually reduces crop yields significantly, sometimes by as much as 20 percent of the soybean harvest.