Trends of ozone damage to conifer forests in the western United States, Particulary southern California : Air Pollution and Forest Decline. 14th International Meeting for Specialists in Air Pollution Effects on Forest Ecosystems

1989

9 Abb., 1 Tab., 15 Lit. Ang., En, Zfsg. En

Unselbständiges Werk

9091

200034644

At present there is certain evidence of ozone damage to mixed conifer forests in California, including the Siera Nevada and the southern California mountains. The evidence for ozone damage to forests in the Pacific northwest and the Rocky Mountain areas is either incomplete or not available. In California, the forest regions subject to chronic ozone exposure are typically mountain areas inland from coastal cities. Chronic ozone injury to ponderosa pine (Pinus ponderosa) and companion species was first identifield in the San Bernardino Mountains of southern California in the early 1950's. Ponderosa pines in forest plots located along a gradient of decreasing ozone dose have been observed for change in crown condition and accumulated increase in stem cross-section area during three intervals between 1974 and 1988. During this time, ozone concentrations declined from the mid-1960's to the mid-1970's and have remained fairly stable for the last 10 years. Crown condition as measured by an oxidant injury index has improved between 1974 and 1988 at 9 of 11 plots studied.Incremental increases of stem cross-sectional area were not related to average oxidant injury score in plot-to-plot comparisons where site, climate, and stand condition differences were complex. The oxidant injury scores of trees in a single plot were only weakly related to incremental changes in stem growth. The establishment and mortality of new seedlings was influenced by both predipitation and ozone concentrations. Establishment was highest and morthality the lowest during the moist 1978 to 1983 period. Mortality was highest dduring the drier 1974 to 1977 period when ozone concentrations were the highest. These results show that ponderosa pine was u useful indicator of improved ozone air quality during the 1974 to 1988 period.