Oxidant Exposure and Effects on Pines in Forests in the Mexico City and Los Angeles, California, Air Basins

Abstract

Forests south and southwest of Mexico City and east of Los Angeles, California, share several similarities, including: the location of mixed conifer forests downwind of large urban “smog” source areas, some of the highest seasonal and yearround tropospheric ozone exposures in the world, foliar and canopy injury symptoms typical of severe ozone exposure, and a prominent pine component afflicted with decline and tree death. These similarities eventually led to joint studies using similar research methods, in which differences in climate and seasonal occurrence of elevated ozone concentrations became apparent. The smaller contrast between the summer and winter temperatures of the Mexico City region may eventually help researchers predict how forests in California might respond to ozone under suggested trends of a warming climate. In this chapter, the early studies of air pollution symptoms exhibited by vegetation indigenous to the forests surrounding the Valley of Mexico will be reviewed along with more recent joint Mexican—US studies which further define the problem.