Study Finds Sharp Rise in Ozone Damage to Yosemite Pine Trees

The number of pine trees in Yosemite park damaged by ozone has increased fivefold in the last five years, according to a new study.

The report says 29.7% of Yosemite’s pines show mottling caused by damage from ozone, a colorless, odorless gas produced by auto and industrial emissions. A similar study in 1985 found 5.7% of the trees had suffered damage then, the National Park Service reported.

Officials at Yosemite, which celebrated its 100th birthday as a national park Oct. 1, said they need to study the 1990 findings before they can comment on ways to alleviate the problem.

A decade-old master plan for the park in the central Sierra Nevada calls for abolishing vehicle traffic by tourists into Yosemite Valley, their prime destination.

No timetable has been announced to force tourists to switch to trams or buses and leave their cars above Yosemite Valley. National Park Service Director James Ridenour has promised that park maintenance facilities will be moved out of the valley, perhaps starting in the 1992 fiscal year.

Ozone damage is widespread in the park, according to the 1990 study that Dan M. Duriscoe of Three Rivers, Calif., prepared for the Park Service.

“Based on the results of this study, no area in the yellow pine zone can be said to be free of ozone pollution,” Duriscoe wrote.

“Jeffrey and ponderosa pine with visible ozone injury had poorer needle retention than uninjured trees,” he said. “Of the 1,650 trees sampled, three were found with obvious severe ozone stress--very thin crowns and chlorotic mottle on the current year’s needles. If ozone concentrations continue at their present level or increase, these (trees) will die or will continue to exist in a state of decline.”

The effects of ozone in the Sierra Nevada were discovered in the 1970s at Sequoia National Park, 100 miles south of Yosemite and less than 150 miles north of Los Angeles. The Park Service has commissioned research to determine if ozone affects giant sequoias as it does pine trees.

Diane Ewell, Sequoia’s air quality specialist, said officials may start a system to warn visitors when the park’s ozone is high, much like the smog stage alerts in the Los Angeles Basin.