Correlation between ozone exposure and visible foliar injury in ponderosa and Jeffrey pines

Ozone exposure was related to ozone-induced visible foliar injury in ponderosa and Jeffrey pines growing on the western slopes of the Sierra Nevada Mountains of California. Measurements of ozone exposure, chlorotic mottle and fascicle retention were collected during the years 1992–1994 for 11 sites located throughout the Sierra Nevada. From these data, summer season (1 June–15 October) hourly ozone concentrations were used to calculate various ozone exposure indices. Injury scores based on fascicle retention, chlorotic mottle and an index containing both were correlated with exposure. It is shown that the combined injury index correlates with exposure better than either single variable index. For the relatively low levels of injury measured, exposure indices which included 14 h of daylight exposure (06:00–19:59) or full-day exposure consistently correlated better with injury than did exposure indices in which only 7 h (09:00–15:59) exposures were included. Conversely, the W95 index and the 7 h indices were less well correlated with injury.