A Historical Analysis: Influence of Grazing on Coastal Sage Scrub RecoveryNancy Ko1, Jade Dean3, Brian Nagy3, Dr. Paul Laris3, Kyra Engelberg3, Samantha Lough2, Trina Ming2, Koung KC Chea2, Darrell Patterson4,

Randy Peterson5, Dr. Chrys Rodrigue3

Geoscience Diversity Enhancement Program (GDEP), California State University of Long Beach 1Los Alamitos High, 2Lakewood High, 3CSULB, 4Poly High, 5Wilson High

Abstract

Introduction

References

Conclusion

Acknowledgements

MethodsResults

Special thanks to: GDEP at Cal State Long Beach for giving me the opportunity to conduct research, the National Science Foundation Award #0703798 for funding GDEP Track 2, Dr. Rodrigue and Dr. Laris for their leadership, Brian Nagy for his much valued technical genius, Wilson High School teacher Randolpho Peterson for his manly presence, Jade Dean for her loving guidance, and my colleagues Samantha Lough, Trina Ming, Kacey Chea, and Darelle Patterson for their help and support.

Field Methods:A total of nine transects were done in La Jolla Valley. Each transect consisted of fifty meters, with twenty-five meters for the CSS region and another twenty-five meters for the grass region. Data was collected first in the transition zone, which is located between the CSS and the grasses, then the CSS, and finally the grasses. A quadrat was taken every five meters starting with zero meters; therefore, eleven quadrats were taken per transect. Quadrat 1 was taken on the far CSS end of the transect, with Quadrat 11 ending on the end of the Grass end. For each transect, the aspect, slope, topography, and microtopography were recorded. For each quadrat, the percentage of plant species and bare soil were recorded. Additionally, for Quadrats 4~8, soil compaction and soil samples were taken.

Transect Locations in La Jolla Valley

DiscussionFigure 1

The California Floristic Province, a global biodiversity hotspot, is home to the California Sage Scrub (CSS) a native California plant community crucial to California’s biodiversity and home to the endangered California Gnatcatcher. With increasing development and invasion of exotic annual grasses, however, native plants and animals are further threatened. While much recovery work and research are underway, not all CSS show recovery. Some areas still remain as nonnative grasses.One hypothesis is that CSS recovers only on areas originally occupied by shrubs. As noted by Clement (1934), areas currently occupied by nonnative grasses were once covered by native perennials suggesting that CSS never existed there. Wells (1962) disagrees and argues that invasive grasses cover previous CSS sites, which raises the question, what prevents CSS recovery? This has prompted some to question whether disturbance influences CSS recovery.Keeley (2002) concluded that too frequent fires prevent CSS recovery while Freudenberger (1987) hypothesized that a combination of grazing and fire are prevalent factors for determining CSS regrowth or stagnancy. Davis (1994), on the other hand, hypothesized that mechanical disturbances such as plowing significantly inhibited CSS recovery. In spite of the emphasis on disturbance, little research has examined the rate of advancement of CSS in areas where grazing and mechanical disturbances have ended and fire frequency is low. The purpose of this study was to determine the factors that support or limit CSS advancement into grassland. We hypothesized grazing was the main factor which limited CSS recovery. Satellite imagery from La Jolla Valley in Coastal Southern California dating from 1947, 1970, 1984, and 2000 were used to compare and contrast CSS-grass boundary changes over time.

Site land use history: The ranchland was grazed and mechanically disturbed to remove shrub cover in the period prior to 1940 (Hobbs 1980). The ranch was then grazed without much mechanical disturbance from 1947 until 1965. After 1965, grazing ended and the land was sold and eventually obtained by the park service. During this time, there was no grazing but there were signs of shrub clearance in few areas. Fires burned the area in 1952, 1973, and 1993.

Study Area: The area of study was located in La Jolla Valley, Ventura County, Coastal Southern California.

Figure 2

Figure 3 Figure 4

Figure 6: 1947 Black and white image of study area

Figure 9: 2000 Color image of study area

Figure 5

Photo Credit: Jade Dean

CSS includes Purple Sage, Artemesia, Ashy-leaf Buckwheat, CA Buckwheat, etc.

The endangered CA Gnatcatcher is one of many species that need CSS to survive.

Measuring tape is used to mark the transects.

Photo Credit: Jade Dean

Photo Credit: California’s Own Native Landscape Design Photo Credit: birdforum.net

1m x 1m quadrats are placed every 5m to record percentage of various plant species and bare soil.

Lough, S. 2010. Follow the Leader: The Study of Native Grass Species Advancing into Grassland. GDEP Research Symposium (CSULB).Ming, T. J. 2010. Does Size Matter: An Extensive Study on Different Soil Textures Within the Coastal Foothills and Its Effect on the Distribution of Grass and Shrub Species. GDEP Research Symposium (CSULB).Patterson, D. 2010. Is Carbon and Nitrogen the Reason in Season? GDEP Research Symposium (CSULB).Freudenberger, D.O.; Fish, B.E.; Keeley, J.E. 1987. Distribution and stability of grasslands in the Los Angeles Basin. Bull. Southern California Acad. Sci 86, 1: 13 – 26Keeley, J. 1984. Postfire Recovery of California Coastal Sage Scrub. American Midland Naturalist 111, 1: 105-117.Hobbs, E. 1986. Characterizing the boundary between California annual grassland and coastal sage scrub with different profiles.Vegetatio 62, 2:115-126 Wells, P. 1962. Vegetation in Relation to Geological Substratum and Fire in the San Luis Obispo Quadrangle, California. Ecological Monographs 32, 1 :79-103

CSS Gain and Loss

CSS Loss

CSS Gain

Restorationists are spending much time and resources to restore degraded CSS lands. Understanding the factors that cause CSS loss and prevent its recovery is critical for understanding fundamental ecology of this endangered habitat (Keeley 1993). Our study finds that CSS is advancing into grassland at a rate of approximately 2ht/yr during the period 1947-2000. We also found that the rate of recovery during the early grazing period was close to the average recovery rate to the entire period (1.9ht/yr). We conclude that grazing does not prevent CSS recovery, and that researchers should explore other causes such as long term effects of intensive mechanical disturbance. Observations of neighboring Serrano Valley indicate that disking and plowing were widespread during the early 1900s. Future research should examine whether these disturbed areas do or do not recover.

Results are shown in the above four maps and Table 1. As seen from the results, there are both CSS loss and gain for every time span. There was more CSS gain than CSS loss for every time period. While every rate of CSS gain/year were different, the second time span (1970-1980) showed more CSS gain than any other period. Overall, the rate of CSS recovery slowed over the 53 years, despite the absence of grazing.

Our results find CSS recovery rates varied between 1.6 and 2.5 ht/yr. Somewhat surprisingly, the recovery rate during the early grazing period (1947-1970) was greater than the recovery rate 15 years after release from grazing (1983-2000). This suggests that grazing is not as strong a force in suppression of CSS recovery as others have argued. Our analysis also shows that grazing had little effect on CSS loss as loss during this period was the smallest. Not surprisingly, the period immediately following the release from grazing (1970-1983) had the highest rate of recovery in spite of the fact that the area was burned in 1973. We suspect that this rapid recovery rate occurred on areas where grazing had held CSS recovery in check. We also suspect that the reason the recovery area dropped after 1983 was that additional factors other than grazing prevent CSS recovery. Davis(1983) and Stylinsky (1999) and Dean (2009) all found that severe mechanical disturbance can prevent CSS recovery for periods over 50 years. Our observation of the recovery patterns suggest that some areas recovered far more rapidly than others. We hypothesize that the long term effect of intense mechanical disturbance may be a reason for lack of recovery in some areas of our study. Hobbs, who studied the same area in 1980, found similar results. She documented an average recovery rate of 2.4 ht/yr from 1965-1980. Hobbs did not examine the recovery rate during grazing. Several authors included Hobbs have suggested that grazing can reduce CSS coverage. Our results, however, did not find this. Many studies have been conducted to determine the factors behind CSS recovery. Possible factors include fire, nitrogen amounts in soil, soil characteristics, grazing, and mechanical disturbance. Keeley (2002) showed that more than one fire every decade prevents CSS recovery. In our study areas, the fire frequency was low, about one fire every 15 years. Patterson’s research (2010) indicates that nitrogen plays no significant role in CSS regrowth or stagnancy, and Ming’s research (2010) shows that grain size of the soil does not impact CSS recovery.  

1 2 3

4Maps showing CSS growth and loss between: 1: 1947-1970 2: 1970-1980 3:1980-2000 4: 1947-2000

Table 1

Lab Methods: We conducted a land cover change analysis for three periods, 1947-1970, 1970-1983 and 1983-2000 using a series of historic aerial photographs and satellite images. The periods reflect different land use eras. Each period was also disturbed by a single fire. Using ArcMap, the boundaries of the CSS and grass were drawn for each historical photo, encircling areas dominated by grass (Fig 10). We then calculated the loss and growth of CSS for each period, and mapped the areas of change using a GIS.

Figure 10Digitized polygons surrounding grassland from 1947-2000. Islands of CSS and sparse shrubland were included as grass.

Many possible factors have been attributed to Coastal Sage Scrub (CSS) recovery, stability, and loss. In our study, we wanted to focus on the changing boundaries between CSS and grassland. To study the effects of disturbance, transects were laid in stable and recovering boundaries, and vegetation coverage was recorded. Shifts in boundaries could be the result of heavy grazing or mechanical disturbance and could have potential effects on the native vegetation in La Jolla Valley. In order to study this phenomenon over time, historical aerial photographs from 1947-2000 were obtained from Ventura County. Using a GIS, we calculated the amount of CSS loss and growth over 53 years. The rates of recovery decreased over time, with the highest being the period. right after grazing ended. We came to the conclusion that grazing was not as strong of a suppressive force on CSS as other studies have suggested.

All units are in square meters.

Figure 8: 1983 Color image of study area

Figure 7: 1970 Color image of study area