DIVERSITY OF AN EARLY SUCCESSIONAL PLANT COMMUNITY AS INFLUENCED BY OZONE

An early successional plant community was exposed to various ozone con centrations for two growing seasons (1994-1995) in open-top chambers i n Auburn, Alabama, USA. The ozone treatments were: AA, ambient air (op en plots); CF, carbon-filtered air (c. 0.5 x ambient air), 1 x, non-fi ltered air, and 2 x, twice ambient air. Vegetative canopy cover exhibi ted a pattern of accumulation in the spring, with maximum canopy cover attained in summer, then senescence of foliage in the autumn 1994. Th is pattern was not observed in 1995 as a result of a drought during th e spring and summer. Varying ozone exposures caused shifts in the comp etitive interactions between plants, thereby altering community struct ure. Higher canopy cover, vertical canopy density (layers of foliage), species richness, diversity, and evenness existed in the CF treatment s than in the other treatments. In addition, winged sumac (Rhus copall ina L.) became a major component of the CF treatments only during 1995 . Surprisingly, blackberry (Rubus cuneifolius Pursh.), a species consi dered ozone-sensitive, based on visible injury, dominated canopy cover within the 2 x treatments, 41 and 33% of total canopy cover in 1994 a nd 1995, respectively. From these results it is concluded that plant c ommunities existing in areas where lower ozone concentrations are prev alent might be more complex and diverse than those existing in areas w ith higher ozone concentrations.