Southern California’s montane forests are unique and fundamental to the region.
Montane forests (forests >5,000 ft elevation) are restricted to "sky islands" of mountain habitat found in the Peninsular and Transverse Ranges of Southern California, with most of the montane forest area found in the San Jacinto, San Bernardino, and San Gabriel Mountains and extending to smaller areas on mountains further north and south. As in the Sierra Nevada, southern California montane forests are dominated by a mix of conifers (mostly pines, firs, and incense cedar) and hardwood (mostly oak) species.
Map depicting extent of hardwood (light green) and coniferous forest (dark green) in southern California in relation to National Forest boundaries.
Montane forests protect the upper watersheds of all of the region's major rivers and provide important ecosystem services, including carbon sequestration, soil conservation, erosion and sedimentation reduction, plant and wildlife habitat and migration corridors, shading and cooling of surface waters, recreational opportunities, and aesthetic and spiritual connections. These watersheds also provide about 40% of the water used for human, agricultural, and industrial purposes in Southern California.
These forests are under threat from a suite of rapidly intensifying stressors and disturbances, including many that have strong climate connections.
The region is characterized by high habitat diversity, strong ecological and climatic gradients, and a suite of active processes such as wildfires, earthquakes, mountain uplift, floods, and debris flows. In addition, the region supports a large and growing human population (25 million people, nearly 8% of the US total) which poses a threat to one of the country’s most biodiverse regions, affecting plants and animal populations, their habitats, and the ecosystem services they provide. Sensitive, threatened, and endangered state and federal species number in the hundreds. Specific threats include the most rapid climate warming in the US; one of the most variable precipitation regimes in the US; persistent, long-term droughts; the highest ozone pollution levels in the nation; increasingly large and severe wildfires; massive levels of habitat loss due to urban and suburban expansion; and an expanding list of damaging invasive species.
& Severe Wildfires
Since the turn of the century, the status of montane forests in southern California has markedly declined. Climate warming has accelerated; ozone pollution has continued to exceed national standards; two major drought periods and associated bark beetle outbreaks have killed tens-of-millions of trees; large and severe wildfires have burned large areas of forest; and new invasive species are posing new threats (e.g. the Gold-Spotted Oak Borer).