RELATIONSHIPS OF OZONE EXPOSURE TO PINE INJURY IN THE SIERRA-NEVADA AND SAN-BERNARDINO MOUNTAINS OF CALIFORNIA, USA

Hourly ambient ozone exposure data and crown injury measurements were gathered in the Sierra Nevada and San Bernardino Mountains of Californ ia to develop relationships between the Ozone Injury Index (OII), the Forest Pest Management Index (FPM), chlorotic mottle, fascicle retenti on (OII index components) and cumulative ambient ozone indices for Pin us ponderosa Dougl. ex Laws and Pinus jeffreyi Grev. and Balf. Eleven sites located in the mixed conifer forest near ambient ozone monitorin g sites were evaluated annually for 4 years. Four other sites in the S an Bernardino Mountains were evaluated for 1 year. Analyses showed OII to be functionally equivalent ( r(2) = 0.96) to the FPM, and to depen d only on fascicle retention and chlorotic mottle (R-2 = 0.95) of the fourth whorl (or if four whorls are not present at the site, then the last whorl present for the majority of trees). Significant association s were found between OII and 4-year 24-h. summer SUMO, SUM06, W126 and HRS80 ozone indices. Three sites had higher levels of cumulative chlo rotic mottle for individual whorls and larger numbers of trees with vi sible crown injury than other sites with similar cumulative ambient oz one levels. Including an indicator variable to discriminate between th ese two groups of sites increased R-2 and decreased root mean square ( RMSE) for all indices, especially SUMO (R-2 = 0.93, RMSE reduced by 46 %). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.