The Effect of Mechanical Disturbance on Soil Compaction and Soil Texture in Coastal Sage Scrub Karryssa Fenderson (Wilson High); Victoria Zamora (Polytechnic High); Marylynn (Wilson High); Jade Dean (LBCC); Dan Cardoza (CSULB); Jason Manack (Polytechnic High); Jason Hazel (Polytechnic High); Christine M. Rodrigue (CSULB); and Dr. Paul Laris (CSULB) Geoscience Diversity Enhancement Program (GDEP), California State University of Long Beach In 1784, the Spanish granted the first three land concessions in California, one being Rancho San Pedro, to Juan José Sepulveda (OAC 2009). Cattle and sheep ranchers of the 1920s and, later, farmers dominated the landscape, resulting in the plowing of certain areas throughout the Peninsula. In the early to mid twentieth century, Japanese farmers farmed the southern slopes with such crops as beans and tomatoes, and farmers of the northern slopes cultivated barley (Ranchos Palos Verdes 2009). As a result, landscapes became barren from overgrazing, and the plowing of native species established the annual grasses and other exotics. Traditional thought assumed that the weight of the plowing machines and cattle would result in an increased soil compaction (Brejda 1997). This study analyzed the differences in soil resistance between sites of intact coastal sage scrub and those dominated by exotic species on disturbed land. Introduction Methods Field Work: In a variety of sites on Palos Verdes Peninsula (Fig. 1), Three Sisters (Fig. 2), and White Point (Fig. 3), 3 m by 3 m quadrats were assembled. These sites included: largely intact coastal sage scrub (CSS), restored CSS, lemonade-berry dominated CSS, old fields that had been plowed between the 1920s and 1940s, and areas that had been more recently brush cut. The Durham Geo Pocket penetrometer was used to measure the soil resistance in 30 separate readings, with 3 readings taken in each of 10 spots in the quadrats. Lab Work: The compiled data from the field were then tested for significant differences among the five classes of quadrats as a group, using ANOVA. This was followed by t-tests of all possible pairs of vegetation types. Probability values on these tests that fell below 0.05 determined if there was a significant difference. Results ANOVA produced a significant difference among the penetrometer readings of the five quadrat types, meaning the chances that particular differences among them were random sampling error, was less than 5% (figure below). Follow-up t-tests also showed that there were significant differences among most pairs of quadrat types, shown in bold. Conclusions The associations among mechanical disturbance, such as grazing and disking, and soil compaction are not as straightforward as literature led us to expect. Other factors must be important on the Palos Verdes Peninsula, such as the underlying geology, geochemistry, and topography differences that can exist among the soil types these factors can create. Analysis of soil texture (Fig. 6) suggests that it may be an important factor affecting with vegetation, disturbance history, and compaction. The vegetation communities we see in the Palos Verdes Peninsula today may reflect the land’s potential for agriculture. Farmers may have avoided the more compacted and/or rockysoils of CSS. An opening for the introduction of exotic species, such as Brassica nigra (black mustard) and Foeniculum vulgare (fennel) may have been created when the farmers selected softer and deeper soils for their fields. It is possible that the breaking up of the soil by plowing it for agriculture destroyed shrub roots of CSS, and thereby allowed annual grasses and other exotics to invade. The low soil compaction readings of restored CSS in comparison with intact CSS may have been a result of the areas having been used for agriculture because of their softer soils and then later restored. Our study of the effects of the compaction did not directly reveal the reasons for those results, but requires additional research and analysis. Suggested work could focus on the effects of plant communities on a landscape over time, and the effects of the geology of the landscape on its soil conditions. Further work is needed to isolate each possible factor and its effects. Because the native cover of the peninsula has been significantly decreased due to disturbance, the understanding of the differences in soil compaction may be important for future knowledge to sustain native species. Discussion Soil penetrometer readings tests among the five classes of quadrats creates puzzling results (Fig. 4 and 5). CSS Intact and Recent Brush Cut quadrats proved to be most similar by the highest soil compaction (kg/sq. cm) means obtained; CSS Restored and Old Field also showed similarities by having the lowest compaction readings. Lemonade berry was an intermediate between the two extremes. Our expectation was that the two categories of heavily disturbed vegetation (Old Field and Recent Brush Cut) would share higher penetrometer readings due to compaction associated with such disturbance (Brejda 1997). We expected CSS quadrats to share lower penetrometer readings. We attempted to investigate other characteristics of the soil to clarify these results by returning to the field to collect soil samples from 15 sites: Our original 10 sites in Portuguese Bend, and an additional 5 from Three Sisters and Filiorum to the east of PB. Using the British Rural Development Service (BDRS 2006) method, we identified the textures of the 15 samples brought back to the lab (Figure 6). Although the samples were too small to analyze statistically, the CSS quadrat samples do seem to cluster on well- drained loamy soil types and exotic-dominated quadrats on heavy clayey soils. Zamora et al. (2009) supported these results with a grain size analysis on 6 soil samples taken from the original 10 sites. References Brejda, John J Soil Changes following 18 Years of protection from Grazing in Arizona Chaparral. The Southwestern Naturalist. 42, 4: British Rural Development Service (BRDS) Soil texture. Technical Advice Note 52. Online Archive of California (OAC) Rancho San Pedro Reference Collection, Ranchos Palos Verdes: The Birth of a City."The City of Ranchos Palos Verdes The City of Ranchos Palos Verdes. 31 Jul Zamora, Victoria; et al Disturbia: The real dirt on the Palos Verdes Peninsula. GDEP Symposium. Acknowledgements A special thanks to Geoscience Diversity Enhancement Program at Cal State University of Long Beach for funding this experience through the National Science Foundation Award # I would like to thank Dr. Christine M. Rodrigue and Dr. Paul Laris for their direction and, the assistance from graduate student Daniel Cardoza and high school science teachers Jason Manack and Jason Hazel, in the field and the lab. Thank you to Ann Dalkey at the Palos Verdes Land Conservancy, as well as Friends of the Colorado Lagoon and the Bolsa Chica Land Conservancy. Furthermore, the peer support and assistance of Victoria Zamora, Jade Dean, and Marylynn Roun were very much appreciated. CSS Intact CSS Restored Lemonade Berry Old Field Recent Brush Cut CSS Intact CSS Restored Lemonade Berry Old Field Recent Brush Cut ANOVA F=24.86 Dfb=4.00 Dfw= Prob=< Key *Significant relationships are bolded Quadrats Map Key CSS Intact CSS Restored Lemonade Berry Old Field Recent Brush Cut Restored Prairie Old Entrance Mustard (Unplowed) graph courtesy of Dr. Christine M. Rodrigue 5