USC Dana and David Dornsife College of Letters, Arts & Sciences

By Will Getz

The Deer Valley trail, recently completed by USC ENST faculty and students[i] provides great insight into the Mediterranean climate and chaparral biome that characterizes southern California. Dry and warm with low precipitation, this climate still supports a variety of grasses, plants and tree species.[ii] Located a few hundred meters from the Wrigley Center, Deer Valley serves as part of the greater watershed that terminates into the Marine Protected Area (MPA) of Fisherman’s Cove. This course’s weekly fieldwork has been dedicated to analyzing soils along the Deer Valley trail and their possible role in the larger watershed dynamic as well as the other environmental issues associated with them.

The surface soil quality along the trail seems fairly uniform up the valley supporting large populations of the native Coastal Sage, Coastal Prickly Pear Cactus, and Toyon bush, and other scrub. However, the climate has brought on the prolific invasive Mediterranean Fennel, which has outcompeted native scrub. Fennel removal is one of the new projects of the Wrigley Center, and this class has aided in that effort. The prolific and virulent Fennel are persistent and can survive in a wide variety of soils and variable climate conditions. Controlling the already prevalent Fennel is a challenging task, and is the subject of future work by the ENST program. About a half kilometer into the trail there is a section of soil, which has undergone great degradation where the organic layer and topsoil were removed for road development and subsequently eroded via water and wind. This area is a site of restoration, with the goal to regenerate the top layers of soil and seed native scrub. Preventing large-scale loss of soil quantity and quality such as occurred in is important to maintain health of the watershed.

In our elementary survey of the surface layer soils on the trail (most likely the O and A Horizons), we sampled ten different sites and took one sample at the beachfront adjacent to Fisherman’s cove to analyze particle size and soil porosity as well as pH. Due to material and time constraints, we were only able to analyze six of the samples collected. Presently, the soil texture analyses have not yielded any conclusive results. However, from the raw pH data collected, one interesting trend that emerged was an increasing basicity of soils moving down the watershed from the top of the trail towards the trail entrance at Little Fisherman’s Cove road. The pH of the soil at the top of the trail is 6.0. This value gradually increased moving up the trail to the trail entrance where the pH value is 7.0-7.5. The pH of the soil at the beachfront was measured to be 6.5. In viewing a soil survey of Catalina conducted by the US Department of Agriculture, most soils at comparable altitudes with similar vegetation had pH within the neutral pH range observed 6.0-7.0.[iii] According to the survey, most surface soils on Catalina are slightly acidic, with some being more acidic such as Dewpoint having a pH of 5.5 and Luff a pH of 5.3 at the time of the survey in 2008.

It is premature to make any conclusions from this rough survey of the soils. We certainly did not perform a comprehensive survey of the trail given a number of details: The sample size was not large enough and we did not collect enough replicates of soil samples to reanalyze in order to remove probability that observed results were due to error or random chance. We also only analyzed soils that were in relative proximity to the trail, and not those of a significant distance from the trail path. However, these interesting preliminary results are motivation for extensive future study. The variation of pH we observed was not drastic, moving from slightly acidic to slightly alkaline down the trail. If this trend is accurate, it may reveal that soils near the bottom of the trail have a better buffering capacity or have greater interaction with basic minerals, which can affect what flora are capable of growing which can change watershed dynamic. These initial tests hold great promise for future soil surveys of the Deer Valley trail looking into how the soils might play a role in the watershed function and proliferation of invasive species.

About the Author: Will Getz is a junior working toward dual degrees, a BS in Chemistry, and a BA in East Asian Languages in Cultures with a minor in Environmental Studies in the USC Dana and David Dornsife School of Letters, Arts, and Sciences.

[i] Hoops, R. (2011, July 15). A Trail-Blazing Summer Internship USC Dana and David Dornsife College of Letters, Arts and Sciences. Retrieved August 7, 2012, from http://dornsife.usc.edu/news/stories/980/a-trail-blazing-summer-internship/

[ii] Regional Climate Center. (2012, June 30). SANTA CATALINA WB AIRPO, CALIFORNIA – Climate Summary . Western Regional Climate Center. Retrieved August 9, 2012, from http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca7910

[iii] United States Department of Agriculture. (2008). Soil Survey of Santa Catalina Island, California (Part of the Soil Survey Area of the Channel Islands (CA688)) Washington, DC: Natural Resources Conservation Service. Retrieved August 7, 2012, from http://soils.usda.gov/survey/online_surveys/california/catalina/Catalina_CA.pdf