It's the intensity of summer temperature and the extent of annual rainfall that determines species distribution. Using his working ecological model as a foundation, Westman created a new model that simulates the influence of the forecasted climate changes in the 21st century. Plants in the model are subjected to increased precipitation and temperatures, increased ozone levels, and varied fire frequencies. Westman and Malauson are the first scientists to examine the combined effect of climate change, heightened air pollution, and altered fire frequency on vegetation. Altered air pollution would result from the change in the incidence of inversions, plus increased summer temperatures which would lead to more rapid photo-catalytic conversion of hydrocarbons and nitrogen oxide into ozone.
Ozone is the main component of smog, and is strongly damaging to coastal sage.
With this complex of variables in its digital memory, the model is able to simulate how the plant community changes under various scenarios over a two century span. Different climate conditions and different fire frequencies interact and can produce radical changes in the coastal sage scrub community. Many scientists believe that climate change would result in extinctions, but the model makes a substantial case for this prognosis. Currently, controlled burns of scrub lands are done about every 12 years in the Los Angeles area. Following wildfire on coastal sage scrub, mudslides, which envelop and crush homes, cars, and anything in their path, often occur.