San Diego’s ecology reflects the diversity of Southern California’s landscapes. Coastal sage scrub dominates the west, while chaparral covers the eastern hills, both consisting mainly of drought-resistant shrubs. The city’s rugged topography and proximity to the ocean create a range of habitats, including tidal marshes, river valleys, and urban canyons. These ecosystems are fire-prone, and wildfire frequency increased in the 20th century, particularly at the interface between urban development and wildlands.

San Diego preserves much of its natural heritage through extensive protected areas, including Torrey Pines State Natural Reserve, Los Peñasquitos Canyon Preserve, and Mission Trails Regional Park. Torrey Pines and its adjacent coastal strip are one of only two locations worldwide where the rare Torrey Pine (Pinus torreyana) grows naturally. Many urban canyons, such as Switzer Canyon, Tecolote Canyon Natural Park, and Marian Bear Memorial Park, serve as additional protected habitats, benefiting wildlife and offering recreational opportunities.

The region is exceptionally biodiverse, hosting numerous endangered plant and animal species. Its position on the Pacific Flyway makes it a premier birding destination, with 492 recorded bird species, the highest count of any U.S. region. San Diego consistently ranks among the “birdiest” areas in the country during the annual Christmas Bird Count.

However, the city and surrounding backcountry are vulnerable to wildfires, which have periodically devastated the region. The Cedar Fire of 2003 burned 280,000 acres, destroyed more than 2,200 homes, and killed 15 people, while the 2007 wildfires severely impacted communities such as Rancho Bernardo, Rancho Santa Fe, and Ramona. These events highlight the delicate balance between urban growth and natural preservation in San Diego.