Foliar response of ozone-sensitive hardwood tree species from 1991 to 1993 in the Shenandoah national Park, Virginia

Abstract

During the late summers of 1991, 1992, and 1993, the occurrence and severity of foliar symptoms on ozone-sensitive eastern hardwood species (black cherry (Prunusserotina Ehrh.), yellow-poplar (Liriodendrontulipifera L.), and white ash (Fraxinusamericana L.)) in the Shenandoah National Park, Va., and relationships between the observed symptoms and cumulative ambient ozone exposures were determined. Three plots containing 30 trees of each species were established adjacent to air quality monitoring stations located at three different elevations. The symptom response of black cherry was most clearly correlated with ozone exposure. The best-fit regression model describing the relationship between cumulative ozone exposures and foliar injury was quadratic (y = a + bx2 + e); the most significant relationships were foliar injury versus the cumulative ozone concentrations of ≥60 ppb and the cumulative ozone concentrations weighted by a sigmoidal function. These observations suggest that higher ozone exposures are more important to foliar symptom development, but cumulatively all exposures contribute to the effect. In 1992, the progression of symptom development on 10 black cherry trees at each site was observed and related to cumulative ozone; there was an exponential increase of foliar injury with cumulative ozone throughout the summer. In 1993, eight subplots of five black cherry saplings were established, and ozone-induced symptom incidence and severity was compared with those on overstory trees at associated trend plots. There was no significant difference in symptom expression between overstory and sapling trees; therefore, Park Service personnel can use the more accessible saplings instead of overstory trees to monitor ozone symptoms in the Park.