Conservation importance of native coastal sage scrub and non-native grassland habitat patches in urban/suburban Los Angeles County, California, USA

Background/Question/Methods: The coastal sage scrub (CSS) ecosystem, native to low elevation areas in Southern California, is listed as endangered (85-98% lost) by the USGS. Estimates indicate that stands of CSS are reduced to less than 10% of their original distribution, largely due to both urbanization and colonization of non-native species. For example, many native CSS habitat fragments have been converted to non-native grasslands following disturbances.  As such, studies must focus on all three common low elevation habitat types (CSS, non-native grassland, and urban/suburban) if we are to make informed decisions regarding the preservation of biodiversity and ecosystem function in this region. Here we report on two projects that examined differences in carbon storage and arthropod communities among habitat types. Using empirical data and modeling techniques we examined the amount of carbon stored in the four major terrestrial carbon storage components: aboveground biomass, belowground biomass, soil, and litter in each habitat type. We used pitfall trap sampling to examine differences in the arthropod communities among habitat types. Both studies were conducted in and adjacent to the Robert J. Bernard Field Station which hosts both CSS and non-native grassland habitats and is surrounded by urban/suburban habitat.

Results/Conclusions: More carbon was stored in the CSS (6.31 kg C m^-2) than in the grassland habitat (3.06 kg C m^-2). Our measurements show that CSS stores comparable amounts of carbon to that recorded in urban forests (national average: 7.69 kg C m^-2; Los Angeles County average: 4.59 kg C m^-2). Arthropod communities differed among all three habitat types with the largest compositional differences observed between the suburban habitat and both the CSS and non-native grassland habitats. While species richness did not differ among CSS and non-native grassland habitat types, both had significantly higher numbers of species than in the suburban habitat. In addition, while non-native arthropod species were recorded in both CSS and grassland habitats, the frequency of detection was much lower than the suburban habitat. Our results highlight that: (1) the native CSS habitat stores significant amounts of carbon, and (2) preservation of non-urban/suburban Southern California open space is essential to maintain arthropod biodiversity within the Southern California urban/suburban matrix.