A computer simulation model (FINICS) was used to project the interactive effects of CO2-induced climate change on a drought-deciduous shrubland. FINICS simulates the competitive relations of five dominant shrub species of Californian coastal sage scrub, based on their aboveground growth and reproductive behavior. The model was used to simulate the separate and combined effects of altered precipitation, temperature, ambient ozone levels, and fuel loads and fire intensity, on species composition. Both growth chamber and field data were used to parameterize the model. Projections show that changes attributed to climate variation alone were markedly accentuated when the indirect effects of climate change on fire intensity and ozone pollution were considered. Model results emphasized that change in community composition will result from shifting competitive abilities of individual species under the changed environmental conditions. While neither all of the secondary effects of climate change nor all possible species were included in the model, the projections suggest that inclusion of secondary interactions and species competition will be important in predicting vegetation change realistically.