In summary, the forests of the West contain more than half the nation's reserve of softwood (USDA 1982). Old-growth trees that are already in a natural decline of growth rate and younger trees suffering severe competition from companion trees are sensitive to additional stress agents, such as air pollution. From the viewpoint of commercial forestry practice it is essential t harvest old-growth stands while trees with large volumes of wood are still alive. It is much less attractive to attempt only the salvage of dead and dying trees. On the other hand, market demand cannot handle a wholesale sell-off of older timber just to shift from management of old stands to the management of young ones. The management of young stands requires considerable thinning, which in turn could result in an excess of certain timber products derived from small-diameter trees. In addition, these old-growth forests represent an inheritance that provides other amenity values, such as recreation and a high- quality watershed, for many generations to come. Older trees already under stress from other biotic and abiotic agents have a poorer capacity to survive additional stress. It therefore becomes even more important to avoid the degradation of air quality in older stands.
