City v. Forest

Most Americans still think of urban blight in terms of immediate effects: filth, smoke and noise that all can see, smell and hear. But dirty cities affect far more than the people in them; they also poison the distant countryside--as Los Angeles is now doing to the San Bernardino National Forest, which is fully 80 miles away.

Swept east by wind, the city's smog is killing the forest's majestic ponderosa pines at the rate of 3% a year. Incense cedar and white fir have also suffered. In all, the smog has caused moderate to severe damage in 60% of the forest's 160,000 acres of pines. Last week loggers began cutting down dead trees in the hardest hit 1,000 acres.

U.S. Forest Service officials first began to notice a peculiar yellowing of needles on on the the San Bernardino trees in the 1950s. Not until the early 1960s was the cause of the disease traced to smog. "Photosynthesis is inhibited almost immediately," says Paul Miller, a plant pathologist with the Forest Service at Riverside. In controlled experiments, smog concentrations of as little as .15 ppm. caused a 20% inhibition of photosynthesis within 60 days. The reality is grimmer. On hot summer days, the smog level in the San Bernardino forest can reach .5 ppm. The average is .20 to .25 -- enough to reduce photosynthesis by 66% . In turn, this impedes the flow of protective pitch with in the tree, allowing pests to attack its trunk with near impunity.

Present plans call for selling diseased ponderosas to lumber companies and replacing them with nearly 70,000 giant Sequoia and sugar pine trees, which are thought to be more resistant to smog. Meantime, the smog rolls on, doubtless affecting the forest in other ways that are not yet known.

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