Do Slope, Aspect, and Elevation Affect California Sage Scrub Recovery?

1. Do Slope, Aspect, and Elevation Affect California Sage Scrub Recovery? (1)Koang KC Chea, (5)Brian Nagy, (5)Dr. Chrys Rodrigue, (1)Samantha Lough, (1)Trina Ming, (2)Darrell Patterson, (3)Nancy Ko, (5)Jade Dean, (5)Kyra Engelberg (4) Randy Peterson, (5)Dr. Paul Laris, Geosciences Diversity Enhancement Program, California State University of Long Beach (1)Lakewood High School, (2)Long Beach Polytechnic High School, (3)Los Alamitos High School, (4) Wilson High School, (4)California State University of Long Beach Abstract Field Methods Lab Methods Discussion There seems to be less Coastal Sage Scrub (CSS) in the present day than in the past when plowing by farmers were not yet introduced. Annual invasive grasses grow really fast and can survive in harsher conditions than CSS does. Azimuth and slope maps provide a better understanding of where the CSS is recovering and where the grasses are invading the CSS. Map analysis can elucidate whether slope, aspect, and elevation play a role in recovery. Others have noted that aspect has some influence on CSS and grassland location, but our study is one of the first to demonstrate its importance to shrub advancement. We suspect that CSS is recovering in areas it inhabited before the invasive annual grasses. In many areas we have CSS that is recovering along boundaries even with invasive annual grass species. The so-called “gravity theory,” by Randy Peterson and Paul Laris, may also play a role. Observations in the field and in the imagery suggest that CSS advances primarily downslope because heavier CSS seeds are falling downhill. This is why there are more CSS growing at the downhill foot of the boundary lines. • First, we hiked up the La Jolla valley to do our field research between the CSS and the invasive grass species. • The transects were across transition zones 25m into CSS, at the midpoint (the transition zone), and 25m into grasslands. • GPS units were used to mark waypoints along the transects. • A 1x1 meter quadrat used to measure the coverage of individual plant species inside the quadrat square. • The clinometer device was used to indicate the degrees of slope of the transects. • The soil penetrometer was used to indicate the compaction of the soil. There were 3 readings of the soil penetrometer at every transect. • 1 sample of soil was taken from each of 5 quadrats at 2 depths (<10 cm and 10-20 cm) • 2 soil samples in the grass were taken along with 2 in the CSS, and 1 in the transition zone by using a soil augur to extract soil from both depths • The slope and aspect maps were created to see whether the slope orientation with the sun or the steepness of the slope of our transects was important to CSS recovery or stability. • In the computer lab, ArcGIS software was used to input data from the GPS units. • In the GIS software, arc catalog was used to make shape files to indicate the transect lines. • Once we had the transect layers opened, each transect was divided in half, and color-coded as CSS (black) or grassland (white). • Arc catalog was used to add a slope layer to help readers know the elevation of the transect points. • Arc catalog was used again to add the aspect layer to indicate which slopes were facing the sun. Bright red marls the south-facing slopes where the surface faces the sun. Bright green is for slopes that face north. • The following were used o compute zonal statistics -Select Spatial Analyst -Zonal statistics (this define the zones) -Zone data set – GPS transects -Zone field – Key field (this select and compute each half transects) -Open the attribute table for the AOI layer and look for low standard deviation for consistency in the aspect layer. Introduction The California gnatcatcher is one of the most elegant and powerful birds in the world and is now an endangered species. The gnatcatcher prefers California (Coastal) Sage Scrub (CSS) to nest and feed. CSS is an endangered habitat due to coastal development in addition to fires, mechanical disturbances, invasive annual grasses, and overgrazing. Currently there is only 10 – 15% of the CSS area remaining from its original amount. In some cases CSS plants are slowly recovering but in others they are slowly degrading because of the invasion of annual grasses. There are two arguments why CSS is not recovering. The first is CSS never occupied some areas currently covered by annual grasses (Clement 1984). Second is that frequent disturbances prevent the recovery of CSS. To back up the first argument, study shows that topography and soil textures limit where CSS could grow. CSS is found mostly at steeply sloped areas with rocky soil. The annual grasses are found mostly at the flat base of the slopes that consist of deeper finer soils. According to Wells (1962), the disturbance regime also limits where CSS could sprout their seedlings. Wells argued that fires, invasive annual grasses, mechanical disturbances etc… are making it impossible for the CSS to recover. One part of the first argument hypothesizes that CSSrecovers along surfaces that are facing the sun. Related to the second argument, one hypothesis is that frequent fire along with plowing by farmers and cattle ranchers is preventing the CSS from recovering (Freudenberger 1987). Farmers purposefully removed the CSS to have more land for their farm and cattle. Most studies have not investigated the influence of these factors on both stable and recovering CSS boundaries. Few studies have examined the influence of topography on the CSS/grassland boundary. Determining whether topography, specifically aspect, slope, and elevation, influences or limits CSS advancement into grasslands is the main focus of this research. We did this by mapping the changes in CSS/grass boundaries between 1980s – 2000s and overlaying them in a GIS on maps of the slope and aspect and topography. Conclusion Results The study supported my hypothesis because we found that areas that are facing the sun (aspects) are likelier to experience CSS recovery. Related to the “gravity theory,” elevation also correlates with this phenomenon. Finally we found that steepness of slopes has no effects on CSS recovery. We can improve our study methods in the future by having more transects to increase sample size and a larger quadrat in order for us to improve the match between larger shrubs’ size and the scale of the quadrat frame. Figures 1-6 summarize the results. Elevation and aspect are significant to the CSS recovery according to the study at the 0.05 level. But the steepness does not affect CSS recovery. These facts are derived from numerous transects we did in the La Jolla Valley. Figure 2 – The slope map of La Jolla Valley. ndicating that our transects were mostly at low elevation level where the invasive grasses and CSS were intermixed Figure 1 - The map of La Jolla Valley with transects. Acknowledgements I would like to thank: The National Science Foundation Award #0703798 for funding GDEP and California State University of California at Long Beach for allowing the program to be possible. I would also like to thank my colleagues , (1)Samantha Lough, (1)Trina Ming, (2)Darrell Patterson, (3)Nancy Ko, (4)Jade Dean, (4)Dr. Chrys Rodrigue, (4)Dr. Paul Laris, (4) Randy Peterson, (4)Brian Nagy, (4)Kyra Engleberg. Where the helpful people are from: (1)Lakewood High School, (2)Long Beach Polytechnic High School, (3)Los Alamitos High School, (4)California State University of Long Beach. And last but not least I would like to thank Geosciences Diversity Enhancement Program, at California State University of Long Beach for this helpful internship. Figure 3 – The aspect map of La Jolla Valley. The red color indicates that the surface is facing South (hot) . The green shows the surface is facing North (cool). Figure 4 – Azimuth and elevations are significantly different for recovering and stable boundaries. Slope is not. Figure 6 – This is a pixel sized image of (CMR LJ T097, CSS, Stable) transect. Each square represents the number of pixel that the transect is in. References _Freudenberger, D; Fish, B; Keelye, J. 1987. Distribution and stability of grasslands in the Los Angeles Basin. Bull. Southern California Acad. Sci. 86, 1: 13 – 26. _Bell, D; Muller, C. 1973. Dominance of California Annual Grasslands by Brassica Nigra. American Midland Naturalist 90, 2: 277 – 299. _Fleming, J; Diffendorfer, J; Zedler, P. 2009. The Relative Importance of Disturbance and Exotic-Plant Abundance in California Coastal Sage Scrub. Ecological Applications. 19, 8: 2210 – 2227. Figure 5 - The recovering boundaries are much likelier to be found on hot slopes than on cool slopes. There is less than 0.001 chance that this is a random pattern.