Empirical evidence of growth decline related to visible ozone injury

Abstract

Differences in radial growth at breast height of yellow-poplar ( Liriodendron tulipifera L.) and black cherry ( Prunus serotina Ehrh.) were tested between individual trees with a history of visible foliar ozone injury and those not expressing foliar injury to ozone at three sites in Great Smoky Mountains National Park, USA. No significant differences in growth for black cherry were found although there was a 12% reduction in radial growth over 5 yrs (1990–1994) ( p-level 0.4) and 8% over 10 yrs (1985–1994) ( p-level 0.6). There was a significant difference in radial growth for yellow-poplar of 43% over 5 yrs ( p-level 0.001) and 30% over 10 yrs ( p-level 0.005). Even though the trees of both species were selected to balance the diameter distribution of each species between the two groups at each site, it was still possible that the differences were due to some other factors than sensitivity to ozone exposure. Therefore, a series of multiple linear regressions were used to identify the most explanatory model based on principal components derived from the following independent variables: Diameter at breast height, total height, height to the live crown, percent slope, and a number of competition indices based on the diameter and distance to competitors. These regressions were then tested for different intercepts and slopes between the sensitive and nonsensitive trees. Once again, no significant differences occurred for black cherry ( p-levels of 0.4 and 0.7 for five-year and ten-year radial growth, respectively) and some differences for yellow-poplar ( p-levels of 0.04 and 0.1 for five-year and ten-year radial growth, respectively). Although the conclusions did not change, the importance of proper balancing of the diameter distribution and accounting for the effects of uncontrollable independent variables are discussed.