Editor's Note: The challenge of proving the effects of air pollution on vegetation has been awkward and frustrating at best, the more awkward as venal interests have pressed ever more insistently for proof of specific causes and evidence that the damage is worth correction.

Walter Westman has addressed this challenge in the coastal region of southern California where the effects of one of the world's most insidious problems with air pollution have been accumulating for decades. He has used an extraordinary combination of techniques including field studies along well-defined gradients of pollution and chamber studies under controlled conditions. The field studies were supplemented with remotely sensed imagery.

The conclusions are classical, powerful, persuasive…and about as specific and definitive as they come: a trend toward impoverishment involves systematic reduction in the vigor of indigenous plants, an increase in the abundance of exotic annuals, an increase in the frequency of fire, and, on slopes, increased erosion including landslides. In parallel with the changes in the structure and successional patterns of the vegetation, Westman shows a series of biochemical changes in plants that include increases in the concentration of nitrogen in tissues after ozone exposure, an increase in the ash content with increasing pollution, and shifts in the chlorophyll content. Here, in an apparently hardy, drought-resistant vegetation, the patterns of impoverishment become conspicuous when sought systematically and follow patterns similar to those found in other vegetations around the world.