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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
Field Methods
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.
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
CSS recovers 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.
Lab Methods
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
•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
•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.
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.
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,”
Figures 1-6 summarize the results. Elevation and aspect are significant to the CSS
elevation also correlates with this phenomenon. Finally we
recovery according to the study at the 0.05 level. But the steepness does not affect CSS
found that steepness of slopes has no effects on CSS
recovery. These facts are derived from numerous transects we did in the La Jolla Valley.
We can improve our study methods in the future by
Figure 2 – The slope having more transects to increase sample size and a larger
quadrat in order for us to improve the match between
map of La Jolla
Figure 1 Valley. ndicating
The map of
larger shrubs’ size and the scale of the quadrat frame.
GPS Transects
GPS Transects
0.1 - 3.0
3.1 - 6.0
6.1 - 8.0
La Jolla
Valley with
8.1 - 10.0
10.1 - 12.0
12.1 - 15.0
15.1 - 20.0
20.1 - 25.0
25.1 - 30.0
30.1 - 40.0
40.1 - 45.0
45.1 - 55.0
55.1 - 70.0
70.1 - 75.0
75.1 - 80.0
GPS Transects
GPS Transects
0 100200300400500
Figure 3 – The
aspect map of
La Jolla Valley.
The red color
that the surface
is facing South
(hot) . The
green shows the
surface is facing
North (cool).
Figure 6 – This
is a pixel sized
image of (CMR
LJ T097, CSS,
transect. Each
represents the
number of
pixel that the
transect is in.
that our
transects were
mostly at low
elevation level
where the invasive
and CSS were
Figure 4 – Azimuth and elevations are significantly different for
recovering and stable boundaries. Slope is not.
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
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.
_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.