Transcript The study of native shrub species advancing into grassland.

Follow the Leader:
The study of native shrub species advancing into grassland.
Samantha Lough1; Dr. Chrys Rodrigue4; Jade Dean4; Nancy Ko2; Dr. Paul Laris4; Koang KC Chea1; Trina Ming1; Darrell Patterson5; Randy Peterson3; Brian Nagy4; Kyra Engelberg4
Geosciences Diversity Enhancement Program, California State University Long Beach
1: Lakewood High School, 2: Los Alamitos High School, 3: Wilson High School, 4: California State University Long Beach, 5: Long Beach Polytechnic High School
Abstract
Methods
Our study consists of research done within the La Jolla Valley. The purpose was to
examine whether or not certain native shrub species led the way in advancing
into the grassland. Transects were lain across stable boundaries as well as
recovering boundaries. Along the transect plant species were identified together
with their percent cover. The collection of species data was then analyzed for
patterns and specific differences. It has been found that six native shrub species
are pioneer species that aid CSS by leading the way into the annual grassland to
potentially create a suitable environment for other native shrubs. These species
include Artemesia californica, Eriogonum fasciculatum, Baccharis pilularis, Mimulus
auirantaicus, Nassella pulchra, and Melica imperfecta.
Field work: Transects were picked based on a map produced by Kyra Engleberg. The transects were placed
at an area that included a definite boundary between CSS and the annual grasslands. The transect tape
began in the transition zone and was laid out 25 meters into the CSS and then 25 meters into the grassland
(Fig. 5). At every five meters along the tape, a 1 x 1 meter quadrat was used. The quadrat was utilized to
identify (Fig. 6 and 7) and quantify (in percent cover) plant species along the transect (Fig. 3). Because of
overlapping canopies, percent cover sometimes ended up over a hundred percent. Unidentifiable species
were described with much detail and a sample was collected to be identified later. At the transition zone, five
meter, and ten meter marks in grassland as well as in CSS, soil samples were taken from the upper level and
the lower levels using a soil auger (Fig. 4). In addition to the soil samples, at the same meter marks, a soil
penetrometer was used to take three soil compaction readings within the quadrat (Fig. 6).
Lab work: In the lab, all the data collected from the field was entered into a database, with fields for the
transect location, the soil compaction readings, and the plant species and percent cover. This database was
then linked in a GIS to additional spatial data, including maps of topography and disturbance. This data set
was further analyzed for patterns, then compiled into separate spreadsheets. Using Chi Square analysis, the
data was evaluated for significant differences.
Introduction
Photo credit to Jade Dean
Southern California is one of the world’s many biodiversity hotspots. A biodiversity
hotspot is a habitat with a significant amount of biodiversity that is threatened by
destruction. Covering a predominant portion of this hotspot is California Sage
Scrub (CSS). This environment houses the California Gnatcatcher, an endangered
bird species that lives only in CSS. CSS is threatened by two major variables,
persistent development of housing and other structures plus the invasion of exotic
grasses that were introduced in the late 18th century.
Currently there is only 10-15 % of the original CSS habitat, with much of the
remaining CSS degraded within State Parks and conservation areas. Postdisturbance, studies have shown that CSS recovers at a slower rate than annual
grasslands. One hypothesis is that CSS thrives on areas with steeper slopes in
coarse, rocky soil whereas the grasses prefer a flat slope with a finer soil texture.
Clements (1934) discusses that the landscape used to be covered solely by
native grasslands but, Wells (1962) argues that the annual grasslands invaded
land previously dominated by CSS.
Another hypothesis concerns land disturbance, including fires, overgrazing, and
mechanical disturbance. Keeley (1984) suggests that due to too frequent fires,
the CSS is unable to recover. Freudenberger (1987) believes it to be a
combination of the frequent fires, but also overgrazing of the land. Others have
mentioned mechanical disturbance as a factor, but it is usually discussed in the
context of overgrazing.
The purpose of this study was to determine the different factors that may
influence as well as limit the advancement of CSS into the areas controlled by
grasslands. In order to accomplish this, focus was placed on mapping and
comparing the changes in the boundaries between CSS and grassland during
the time period of the 1980s-2000s. We also examined whether or not certain
shrub species led the way in advancing into the grasslands. Westman (1981)
studied the factors that affect the development of mono-specific species stands.
Stylinski and Allen (1999), who studied intensively disturbed areas, found that only
two CSS species were able to successfully colonize areas dominated by nonnative grasses. These are Eriogonum fasciculatum and Baccharis sarothroides.
Some Native California Plants
Scientific Name
Common Name
Figure 3
Figure 6
Figure 5
Figure 4
Results
Native Shrub Species in the Grassland
Table 1 depicts the native shrub species that were
found thriving within the grassland. The number of
quadrats containing native shrubs that appear to
be advancing into the grassland and at which
meter along the transect they were found.
Name
Number of Shrubs
Meter Location
Salvia leucophylla
2
30m, 35m
Baccharis pilularis
1
35m
Isocoma menziesii
2
30m, 50m
Hazardia squarrosa
1
45m
Eriogonum fasciculatum
4
35m, 40m, 45m, 50m
Table 1
Average % of Native Species
Study Sites
100
Average Percent
80
Chart 1 shows the average percent cover of the
native plant species within the CSS, the transition
zone, and the grassland. It also breaks up the
percent cover between the transects with stable
boundaries and recovering boundaries.
60
CSS
Transition
40
Grassland
20
0
Recovery
Stable
Boundaries
Chart 1
Recovery vs. Stable: Leading Native Species
Artemesia
californica
Figure 2
Figure 1
Eriogonum Baccharis
Mimulus
fasciculatum pilularis aurantiacus
Nassella
Melica
pulchra imperfecta
Other
Recovery
31
13
6
10
13
8
39
Stable
7
3
0
2
4
0
35
Chi Square
Probability
0.00010
0.01242
0.01431
0.02092
0.02905
0.00468
Difference
> 0.05
Table 2
Within Table 2, the species in the CSS, proven
to be leading the advancement into the
grasslands are shown. It is broken down to
recovering and stable transects, with the
quadrat counts for each leading species and
the sum of the remaining species as well as
their chi square values.
Artemesia californica
Baccharis pilularis
Encelia californica
Eriogonum fasciculatum
Hazardia squarrosa
Isocoma menziesii
Melica imperfecta
Mimulus auirantaicus
Nassella pulchra
Salvia leucophyila
Salvia mellifera
CA Sagebrush
Coyote Bush
CA Bush sunflower
CA Buckwheat
Sawtooth Goldenbrush
Coast Goldenbrush
Onion Grass
Sticky Monkey flower
Purple Needlegrass
Purple Sage
Black Sage
Figure 7: CSS
Figure 6: CA
Buckwheat
Photo credit to Jade Dean
Discussion
This study found that certain native shrub species are leading the advancement
of CSS into grasslands. A chi square analysis has proven that Artemesia
californica, Eriogonum fasciculatum, Baccharis pilularis, Mimulus auirantaicus,
Nassella pulchra, and Melica imperfecta all have chi square values less than
0.05, which indicates that they are disproportionately more common in the
recovery versus stable boundaries. This significant difference proves that these
six native species may be considered pioneer species (Table 2).
Patterson’s and Ming’s research explored various edaphic factors that have
been proposed as influences on CSS and grassland dominance. Their work has
shown that neither carbon to nitrogen ratios nor grain size affects CSS in any
way. Chea’s research evaluated elevation, slope, and aspect and found that
only elevation and aspect were significant in differentiating stable from
recovering CSS boundaries.
Westman (1981a) discusses possible allelopathic effects emitted from the shrubs
or the dominance of herb species as factors of species distribution. Westman
(1981b) explains other factors that influence the distribution of certain Salvia
species, and their development as mono-specific stands.
Our study results support Wells’ (1962) theory that annual grasses invaded CSS.
They counter Keeley’s (1984) and Freudenberger et al’s (1987) notion that
frequent disturbances prevents CSS recovery. In our study area grazing ended
45 years ago and there has been but a single fire in 1993 during the study
period. They also confirm the findings of Sylinski and Allen that CSS is slow to
recover in some cases and that only a few species can invade areas
dominated by exotic grasses.
Conclusion
This project found that specific native shrub species are more capable of
establishing in grassland territory. The following appear to be pioneer species,
Artemesia californica, Eriogonum fasciculatum, Baccharis pilularis, Mimulus
auirantaicus, Nassella pulchra, and Melica imperfecta. We conclude that future
restoration projects should prioritize the species that have demonstrated the
ability to establish in grasslands, such as those in Table 1. Restorationists should
avoid using species that have not demonstrated the ability to colonize in
grasslands regardless of whether they are found in the proximity to the
restoration site. Future research should focus on whether these other species
can establish once the pioneer species are in place.
Acknowledgements
I would like to thank the National Science Foundation [award #0703798] for funding
GDEP at CSULB. I would also like to thank Dr. Chrys Rodrigue, Dr. Paul Laris, and Sr.
Randolpho Peterson for providing guidance throughout the entire research process,
Brian Nagy for answering any and all technical questions, and Koang Chea, Jade
Dean, Nancy Ko, Trina Ming, and Darrell Patterson for help with collecting all the
data out in the field as well as always being there for support and entertainment.
References
Chea, K. 2010. Does Slope and Aspect Affect California Sage Scrub Recovery? GDEP Research Symposium (CSULB).
Clements, F. 1934. The Relict Method in Dynamic Ecology. Journal of Ecology 22, 1: 39-68
Freudenberger, D.O.; Fish, B.E.; Keeley, J.E. 1987. Distribution and stability of grasslands in the Los Angeles Basin. Bull.
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Keeley, J. Postfire Recovery of California Coastal Sage Scrub. American Midland Naturalist 111, 1: 105-117.
Ming, T. 2010. Does Size Matter?. GDEP Research Symposium (CSULB).
Patterson, D. 2010. Is Carbon and Nitrogen the Reason in Season?. GDEP Research Symposium (CSULB).
Wells, P. 1962. Vegetation in Relation to Geological Substratum and Fire in the San Luis Obispo Quadrangle, California.
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