National Park Service

State of the Park Reports

State of the Park Report for Cabrillo National Monument

Resource Brief – Coastal Sage Scrub

Old Point Loma Lighthouse
Old Point Loma Lighthouse at Cabrillo National Monument

Coastal Sage Scrub (CSS) is a community of low-growing shrub species located along the immediate southern coast of California and northern Baja Mexico (Barbour et al. 2007). The CSS community is part of the broader Mediterranean-climate ecosystem, which is globally rare (covering approximately 2% of the Earth's land surface) yet accounts for nearly 15% of the total vascular plant flora (Rundel 2004). Favorable climate and environment has led to a vast majority of the potential habitat having been developed and is now highly degraded. Within California, it is estimated that no more than 15% of the original distribution of CSS is still intact and what lands do remain are highly fragmented and sensitive to disturbance (Westman 1981, Minnich and Dezzani 1998, Taylor 2004). With so little habitat remaining for the typically narrow-ranged species of CSS, the potential for local, and even global, extinction for this habitat type exists (Westman 1981).

Cabrillo National Monument (CABR) protects some of the highest quality CSS remaining in San Diego County and the greater southern California area. Many of the most common CSS species are well-represented at CABR, as are many exceptional and sensitive species. Eleven of the species found within the park are listed as sensitive by the California Native Plant Society Rare Plant Program (CNPS 2012). CABR and the Point Loma peninsula are located at the transition between the coastal sage scrub community of southwestern California and the maritime succulent scrub characteristic of northwestern Baja California (Barbour et al. 2007). This unique geographical setting is the driving force behind the unique assemblage of vegetation, which is not found anywhere else in the United States.

Under the management of NPS, the vegetation of CABR is afforded some of the greatest protection possible. However, external forces pose powerful threats to the stability and integrity of native plant communities within CABR. While past land use, urban development and habitat fragmentation has despoiled much of the surrounding landscape (Soule et al. 1992), CABR native landscapes have escaped such degradation. Bounded by development, military infrastructure and water, CABR is an isolated island of natural habitat. It is the effect of this isolation that presents the greatest threat to the CSS community at CABR. The residential and military development serves as a source of non-native species introductions, while at the same time limiting the ability of native species to disperse, restricting the flow of genetic material into and out of the park.

Ecological processes, which are critical to maintaining a healthy native landscape, have also been disrupted. Fire, while never frequent at CABR, has been completely excluded by the military development (NPS 2006). The absence of fire is a potential long-term threat to at least one unique community component, Ceanothus verrucosus, which requires fire to germinate (Keeley 1975, Lawson et al. 2010). At the same time, many other unique elements of the flora, especially succulents, are fire intolerant and may have developed to their current extent because of fire exclusion. Most of the larger mammals (bobcats, foxes, etc.) have been extirpated from the park, and lack of habitat continuity is the most likely culprit. Seven species of reptiles have also been lost in recent years for unknown reasons (Atkinson et al. 2003).

The natural resource staff at CABR is committed to improving the quality of CSS habitat in CABR. An annual, statistically robust monitoring program will begin in 2012 to provide park managers with reliable status and trend data for both common and uncommon native plant species (Tiszler et al. 2012). Furthermore, a commitment to be free of invasive species by 2016 will improve habitat quality, particularly for less common, low-lying annuals, by opening up space for native CSS species to re-establish.

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