EVALUATION OF OZONE INJURY ON FOLIAGE OF BLACK-CHERRY (PRUNUS-SEROTINA) AND TALL MILKWEED (ASCLEPIAS-EXALTATA) IN GREAT-SMOKY MOUNTAINS NATIONAL-PARK

The incidence and severity of visible foliar ozone injury on black che rry (Prunus serotina) seedlings and saplings and tall milkweed (Asclep ias exaltata) plants in Great Smoky Mountains National Park (GRSM) wer e determined by surveys along selected trails conducted during late su mmer 1992. The incidence (% injured plants) of ozone injury on black c herry was 47% and the percent injured leaves/injured plant and average leaf area injured were 43 and 6%, respectively. Maximum severity (avg . leaf area of the most severely injured leaf) was 12%. Black cherry s eedlings and saplings exhibiting ozone injury were taller than non-inj ured plants. When insect feeding was present, it occurred 96% of the t ime on plants with ozone injury. Significantly more injury (p=0.007) o n black cherry (% injured leaves/injured black cherry) occurred in the NW section of GRSM compared with the other Park sections. Regression analyses showed no relationships in ozone injury with respect to aspec t, slope or elevation. Tall milkweed was evaluated twice during August for ozone injury. The incidence (% injured plants) of ozone injury wa s 74 and 79% for the first and second survey, respectively. The percen tage of injured leaves per plant from the first to second survey was 6 3 to 79%, respectively. Tall milkweeds showing ozone injury were talle r than the non-injured plants, The percentage of insect-damaged plants was 50% among plants without ozone injury and 60% among ozone-injured plants. Noninjured tall milkweed had fewer flowers and/or pods than t he injured plants. Mean leaf area injured increased over time, and mea n maximum leaf area injured increased from 8 to 11% during the same pe riod. Regression analyses showed no differences in ozone injury regard ing aspect, slope or elevation. Our findings indicate that ozone injur y is widespread throughout the Park on sensitive vegetation. (C) 1997 Elsevier Science Ltd.