Two mathematical models (TASS and PT AEDA2) were applied to the study of long-term interactions of air pollution stress and forest growth and yield. TASS was previously developed to examine the dynamics and yield of Douglas-fIr, and PTAEDA2 was previously developed to examine individual tree growth and stand development in loblolly pine plantations.

Differential levels of pollution stress were incorporated into TASS through the reduction of the input variables photosynthetic efficiency and average needle retention. Reductions of photosynthetic efficiency included 0, 7.5, and 15 percent, while average needle retention was reduced 0 and 1 year. These reductions were distributed evenly over each of the five most current years' needles. Percentage volume reductions of 0, 17.3, 4.4, 23.1, 16.0, and 32.4 were obtained as results from six TASS scenarios. Given these percentage volume reductions, several levels of crown ratio reduction (0, 5, 10, 12, 15, and 22 percent) were applied to PTAEDA2 in order to determine the crown ratio reductions necessary to cause the same percentage volume reductions obtained from TASS. Results indicate that crown ratio reductions of 0, 5, 10, 12, 15, and 22 caused total volume reductions of 0, 6.3, 14.9, 18.7, 22.6, and 33.3 percent. These results are not intended to be final quantitative answers to the question of possible volume reductions due to air pollution impacts. However, they do offer insights to the possible effects of air pollution stress on forests.