Trabuco Creek - Climate and Biology

Climate and Biology

The climate of the Trabuco Creek watershed is almost entirely semi-arid. Scrubland and chaparral make up most of the vegetation in the hilly and sometimes mountainous Trabuco Creek basin. 16 different vegetation "bands", or zones, have been identified in the San Juan Creek watershed as a whole, and most of these also exist in the Trabuco Creek watershed. These range from riparian to chaparral, coastal sage scrub and rocky outcroppings where little to no vegetation grows. In the undeveloped Plano Trabuco, there are grasslands, and most of the lower Trabuco Creek Valley is urbanized.

Riparian zones, consisting of small to medium-sized trees and a variety of other streambank flora, line Trabuco Creek, Tijeras Canyon Creek, and the upper tributaries including Live Oak Canyon, Falls Canyon and Holy Jim Canyon. These riparian habitats are now only found in the upper watershed. Oso Creek is heavily developed, and has little to no riparian vegetation. Lower Trabuco Creek still supports some riparian zones, but they have decreased in health because of the introduction of urban and agricultural runoff.

Aside from the large mammals including mountain lions, coyotes, and bobcats (the last California grizzly bear in the Santa Ana Mountains was shot near Trabuco Canyon) the creek was once a productive habitat for steelhead trout. Its upper portions, which include numerous gravel beds and bars, stream pools, and cascades, are suitable habitat for the anadromous fish, which still exist as rainbow trout in upper Trabuco Creek. Because of extensive modifications—affecting the stability and water quality of the creek—steelhead no longer migrate to the upper reaches of the Trabuco Creek watershed. Conversely, steelhead were sighted in 2003 and 2005 along the creek. A project was proposed in 2005 to build a fish ladder into a concrete drop structure in Trabuco Creek that blocks steelhead passage. $1.2 million was allocated by the California State Wildlife Conservation Board in 2005 to fund the project, but it has not been begun.