The flora of this ecoregion also includes tree species such as gray or foothill pine (Pinus sabiniana), scrub oak (Quercus dumosa), California buckeye (Aesculus californica), the rare Gowen cypress (Cupressus goveniana), the rare Monterey cypress (Cupressus macrocarpa), and a wealth of endemic plant species, including the extremely rare San Gabriel Mountain liveforever (Dudleya densiflora), Catalina mahogany (Cercocarpus traskiae), and the threatened most beautiful jewel-flower (Streptanthus albidus ssp.

Chaparral, like most Mediterranean shrublands, is highly fire resilient and historically burned with high-severity, stand replacing events every 30 to 100 years.

[4][5] Today, frequent accidental ignitions can convert chaparral from a native shrubland to nonnative annual grassland and drastically reduce species diversity, especially under global-change-type drought.

[citation needed] The region has been heavily affected by grazing, logging, dams, and water diversions, intensive agriculture and urbanization, as well as competition by numerous introduced or exotic plant and animal species.

Some unique plant communities, like southern California's Coastal Sage Scrub, have been nearly eradicated by agriculture and urbanization.