Introduction
While California is recognized as a biodiversity hotspot, many of the
vegetation formations here have experienced massive losses to agricultural and
urban, suburban, and exurban development, air pollution, and anthropogenic
climate change. These include the focus of this paper: California sage
scrub. Slide 2
California sage scrub or CSS is a distinctive complex of shrubs, subshrubs,
and herbaceous plants, generally forming a rather open scrub, dominated by
shrubs and subshrubs about half a meter to 2 meters in height. It contrasts
visually with chaparral scrub, not only in terms of density and height, but in
color, especially during summer months. CSS plants are often greyish or a
beige, tan, or taupe color. This brownish appearance results from facultative
summer deciduousness. Here are a few images of CSS Slide 3
Slide
4 Slide 5
CSS occurs in a few subtypes depending on coastal or interior locations,
extending from the Bay Area down into Baja. Slide 6
The entire complex has seen very substantial territorial losses, Slide 7
declining by half since the 1930s (Talluto and Suding 2008) and estimated to
occupy only about 10-33% of its original extent (Westman 1981; Allen et al.
2000). Human pressures effecting this loss include early ranching and grazing
activities, plowing and cultivation, residential development, alterations in
fire regimes, and soil nitrogen deposition due to air pollution. Slide 8
Very commonly, patches of CSS will be type-converted to exotic annual-
dominated grassland, itself subject to further invasions by very aggressive
tall forbs. Slide 9
Once type-converted, exotic annual grassland is very persistent and
successfully resists re-encroachment by CSS species or native perennial grass
species (Vann-Foster 2015).
This reduction in area has cost several
animal species critical habitat, putting several on endangered and threatened
species lists. Slide 10
These include the California gnatcatcher (Polioptila californica), Slide
11 the coastal cactus wren (Campylorhynchus brunneicapillus), Slide
12 Stephen's kangaroo mouse (Dipodomys stephensi), Slide
13 Belding's orange-throated whiptail lizard (Aspidoscelis hyperythra
beldingii), and many others.
Realization of the habitat function of CSS has spurred efforts to identify and
protect intact CSS and to restore sites. Restoration projects have generally
been disappointing, with the planted CSS overwhelmed with exotic grasses and
forbs and dying off (Cox and Allen 2008; Antcliffe 2009). As Allen et al.
(2000) put it, "CSS . is becoming one of the most intractable vegetation types
to restore."
Slide
14 Work at CSULB has uncovered a few heartening exceptions to the general
gloom surrounding CSS restoration efforts. In 2006, Scott Eckardt utilized
decades of air photos and remote sensing imagery to plot the decline of CSS in
Calabasas. He documented the decline of CSS there but also unexpectedly
identified small sections in his study site where CSS had actually expanded on
its own. Slide
15 These small areas of recovering CSS have since been spotted in several
other areas in Southern California, as seen in this image of Charmlee Park in
Malibu. Note the area on the north side of the CSS patch that expands
aggressively while nearby to the south the patch holds stable throughout the
timeline.
The idea that CSS could self-restore became the focus of several projects.
Slide
16 The Geoscience Diversity Enhancement Project (NSF Award # 0703798)
there organized research one summer to identify differences between
long-stable boundaries between CSS and grasslands and boundaries where CSS was
recovering, this in the Serrano and La Jolla valleys of the westernmost Santa
Monicas. These data were collected on behalf of Kyra Engelberg, who selected
the sites using air photos and remote sensing imagery to classify boundaries
as stable or recovering. Her thesis (2011) linked the different boundaries to
disturbance histories. Stable boundaries were more often associated with
sites having a history of plowing, while areas having a grazing history were
likelier to host recovering boundaries. Her work and one of the GDEP projects
(Lough et al. 2010) found differences in plant communities between
recovering and stable boundaries.
Slide
17 My graduate seminar in 2012 returned to La Jolla Valley to collect
more transects and quadrats and test hypotheses about other contrasts between
stable and recovering boundaries, including facilitating species, hard rock
geology, soil classifications, slope and aspect, herbivory, and mycorrhizal
communities (Rodrigue et al. 2013). Several classes in the Department of
Geography and the Environmental Science and Policy Program have since
continued to collect transect and quadrat data at several sites throughout
Southern California.
Data and Methods
I have assembled the seven years of data into a common database.
Slide
18 The database so far includes 1,093 transect sampling points from 49
transects, with 56 species identified. Of these 1,093 sampling points, 496
are from recovering boundaries and 597 are from stable boundaries. Sites
include La Jolla Valley, Serrano Valley (both in Pt. Mugu State Park in the
westernmost Santa Monicas), Charmlee Park (Malibu), Stoney Point Park
(Chatsworth), Sepulveda Dam (San Fernando Valley), Palos Verdes Peninsula, and
Bolsa Chica Wetlands in Huntington Beach.
Slide
19 There may be shortcomings: The data were collected by teams of students, so
there may be errors in identification. There are different types of sampling
systems used, and there were different goals in getting students into the
field.
Slide
20 The sites in the western Santa Monica Mountains have been the ones
most explicitly concerned with the stable/recovering boundary divergence,so,
for this case study, I extracted these three sites: La Jolla Valley, Serrano
Valley, and Charmlee Park. This yielded 201 identifications from recovering
boundaries and 126 from stable boundaries. Gamma diversity for this cluster
was 26; alpha diversity for La Jolla Valley was 20, for Serrano Valley it was
12, and for Charmlee Park it was 9.
Slide
21 The species richness, however, is not produced by an even relative
abundance of species. There are, rather, 9 CSS shrub, subshrub, or bunchgrass
species that are quite common (with more than 13 individuals counted in each),
all 9 found in La Jolla Valley, 5 in Serrano Valley, and 6 in Charmlee Park.
The Shannon Equitability index is highest for La Jolla Valley at 0.83,
declining to 0.78 for Serrano Valley, and to 0.64 for Charmlee Park.
Slide
22 Here are the 9 dominant species. Given that these are less subject to
small sample effects, I used these 9 to analyze differences in the native
plant community in the 5 following contexts:
Slide
23
-
community behind the recovering boundary or ecotone
-
community behind the stable boundary
-
individual CSS species in the transition area, up to 25 m out from recovering
boundaries
-
individual CSS species in the transition area, up to 25 m out from stable
boundaries
-
CSS individuals found isolated in the middle of grassland (these were not
transected but individually hunted and GPSed)
Results
Slide
24 The first comparison was of the frequencies with which each of the 9
species occurred behind recovering and stable boundaries and the distribution
of frequencies among all native species found behind the two boundary types.
Three species significantly favored recovering CSS boundary zones:
Baccharis pilularis,
Artemisia californica, and Eriogononum
fasciculatum. Another 3 occurred significantly more frequently behind
stable boundaries:
Salvia mellifera,
Eriogonum cinereum, and
Malosma laurina. The remaining 3 show no significant bias:
Stipa
pulchra,
Salvia leucophylla, and
Mimulus aurantiacus. So,
each boundary type has a triad of species that markedly favor it.
Slide
25 The second comparison examined those CSS species encountered on just
those transects that were placed half in CSS and half in grassland (25 m out
from the boundary in either direction). In front of the recovering boundary,
34 CSS individuals of 9 species were encountered, of which 27 were of 4 of
the dominant species: Baccharis pilularis, Eriogonum cinereum,
Artemisia californica, and Stipa pulchra. In front of the
stable boundary, there were only 12 individuals of 6 species found among the 7
transects. Of these 12, only 4 were of the dominant species: 1 Artemisia
californica and 3 Stipa pulchra. Baccharis pilularis is
significantly more prevalent in the grasslands in front of recovering
boundaries and is, in fact, absent from the grassland in front of stable
boundaries, as is Eriogonum cinereum . There is no preference in the
case of Stipa pulchra or Artemisia californica. So, the
grassland in front of recovering boundaries shows a number of juveniles trying
to establish themselves, and these are dominated by Baccharis pilularis
and Eriogonum cinereum.
Slide
26 The third comparison focusses on the CSS individuals found out in the
middle of grassland far from CSS communities. Thirty-three native plant
individuals were censused, identified, and GPSed, belonging to 6 species. Of
these, 14 or 42% were Baccharis pilularis and an additional 12 or 36%
were Artemisia californica. These 2 species, belonging to the 9
dominant species in the western Santa Monica Mountains, make up nearly 80% of
the vanguard species making a go of it out in the grassland environment.
Slide
27
This slide represents the relative abundances of each of the 9 species in each
of the 5 contexts.
Discussion
These results have implications to improve active restoration efforts. The
CSULB group has established that, while CSS is dwindling throughout Southern
California in the face of development and type-conversion, it has shown an
ability to self-restore in at least a few places. It is apparent that
beachheads of CSS juveniles are getting well out into the grasslands far from
CSS patches.
Slide
28 This is not a random process: There are definite vanguard species
out in the grassland, species that lead out from expanding boundaries, and
species that are disproportionately represented in the CSS communities behind
the recovering boundaries. Slide
29 The alpha diversity of the communities behind recovering and stable
boundaries is identical at 17, but the recovering communities show more
dominance among their 17 species than the stable communities do with their 17
(Shannon's Equitability index is 0.71 for the community behind recovering
boundaries, which indicates greater primacy among fewer species than seen in
the communities behind the stable boundaries, which have an index of 0.86).
Moving out into the near grassland, the areas in front of the recovering
boundaries has an alpha diversity of 9, while those in front of the stable
boundaries have only 6. The areas in front of recovering boundaries show the
same tendency toward primacy, with a score of 0.84, compared with the more
even distribution of species seen in the 0.91 score for the areas in front of
stable boundaries. Out in the grassland itself, the process of winnowing
continues, with an alpha diversity of 6 but a Shannon Equitability score of
0.74.
What this suggests is that there are a few CSS species that can tolerate the
conditions out in the grasslands. These are the vanguard species: Baccharis
pilularis at 42% and Artemisia californica at 36%. Moving in from the edges
of the grassland, Baccharis pilularis dominates the grassland near the
recovering boundaries at 32%, but now joined by Eriogonum cinereum at 24% and,
in minor roles, Artemisia californica with 12% and Stipa pulchra with 12%.
Back in the CSS behind recovering lines, Artemisia californica rises to
dominance at 40%, while Baccharis pilularis subsides to 12% and Stipa pulchra
at 8%, while Eriogonum californica, Salvia leucophylla, and Mimulus
aurantiacus, become noticeable between 6 and 8%. While the CSS community
behind stable boundaries may reflect a kind of "ailing" CSS unable to get out
and mix it up with the exotic annual grassland, another way of looking at it
is that the flora back there may represent "old growth" CSS. In that spirit,
its mix of species shares 3 dominant species with the community behind
recovering boundaries Salvia leucophylla, Mimulus aurantiacus, and Stipa
pulchra, but it disproportionately includes some different species: Eriogonum
cinereum and Salvia mellifera and Malosma laurina, both the latter of which
are also often seen in chaparral communities. Meanwhile, this community is
conspicuous for the absence of the vanguard species, Baccharis pilularis and
Artemisia californica, as though their job in recovery is done and they
eventually fade away.
A recent CSULB thesis is apposite here. Sean Brennan (2015, 2013) tested the
idea that Baccharis pilularis is a nursemaid species, facilitating the
establishment of other CSS species. He found that young Baccharis
pilularis plants easily get into grassland through wind dispersal and
establish themselves. Their initial growth habit is dense and upright at
first, with only grass around them. They are exploited as cover by rabbits,
who make quick forays from them to forage in grass and then bolt back into
them to avoid predation. As the plants age, however, their growth habit
becomes more recumbent and open with much deadwood in the center. This stage
is characterized by a number of other CSS seedlings and many Stipa
pulchra bunchgrasses establishing under and around them, but these do not
include juvenile Baccharis pilularis. After 30 - 50 years, the
Baccharis pilularis individuals die out, leaving a diverse community of
maturing CSS where they once stood. This phenomenon, in fact, is regarded as
undesirable in conservancies trying to salvage the very few instances of
native California grassland, especially in Northern California where
Baccharis pilularis is regarded as a pest (Vann-Foster 2015). Brennan's
findings, however, do offer evidence that Baccharis pilularis also acts
as nursemaid to native California grasses, at least for Stipa pulchra.
Given certain parallels with Artemisia californica - ability to
establish in grassland, growth habit and change with age, it is possible that
it, too, may be a nursemaid species.
Conclusions and Recommendations
Slide
30 For conservancies trying to conserve their shoestring budgets and
volunteer labor, these findings suggest a few recommendations. First and most
hearteningly, there is a possibility of passive, unattended self-restoration
by CSS in certain circumstancpes. Figuring out what those circumstances are
could identify areas where conservancy labor is not needed, freeing it up for
more challenging situations requiring active restoration.
Second, the CSULB group has tried to evaluate geological (Nesbit and Winslow
2013), soil nitrogen (Patterson et al. 2010), and slope steepness (Chea
et al. 2010) with recovering and stable boundaries, with no significant
differences in underlying geology, soil nitrogen levels, or slope. One of
our studies found no significant difference between the boundary types and
soild grain size (Ming et al. 2010), though another did (Engelberg
2013). There is some evidence that CSS may restore more efficiently downhill
("the gravity theory")(Santana et al. 2013; Laris 2013), though slope
steepness was dismissed in another study using a different methodology (Chea
et al. 2010). Native animal herbivory may produce sharp boundaries with
nearly bare transition zones, which are more common in stable than recovering
boundaries (Vaughan et al. 2013). We have not found that too-frequent
fire or a history of intense grazing will prevent CSS self-restoration or
recovery after disturbance (Engelberg 2011; Eckardt 2006; Ko et al.
2010; Dean et al. 2009). What we have found, however, is that
mechanical disturbance of soil, as in plowing, is a show-stopper (Laris 2013;
Engelberg 2011; Fenderson et al.2009). Areas plowed, even once, are
persistently dominated by exotic annuals. Those grazed or burned, even four
times in one decade, come back. A promising line of work, followed by Mills
and Ducoing Chaho (2013) is the idea that mechanical disturbance may work its
persistent effects through disruption of subsurface mycorrhizæ.
Third, an important implication is that conservancies might want to
stop using soil scraping or plowing to suppress the exotic seed bank: That is,
ironically, the one thing that might ensure a poor outcome for an active
restoration project! So, rather than preparing a site for active restoration
by plowing or scraping it, this to reduce the weed seed bed, perhaps they
could experiment with planting CSS species that have shown the ability to
survive in grassland, notably Baccharis pilularis and, probably,
Artemisia californica. These plants may provide encouragement for
certain fauna to venture out to exploit grasses, such as brush rabbits
(Silvilagus bachmani) and black-tailed jackrabbits (Lepus
californica).
Any groups of surviving Baccharis pilularis or Artemisia californica could be
augmented with a wider palette of CSS species in a few years' time, such as
Eriogonum cinereum and Stipa pulchra. If the small patches of CSS species
persist and coalesce, other species could be added in, selected from the
species typical of the area behind a recovering boundary: Eriogonum
fasciculatum, Salvia leucophylla, and Mimulus aurantiacus.
When this is established and when the original Artemisia californica
and Baccharis pilularis pioneers are dying off, a wider palette could
be added in, including Salvia mellifera and Malosma laurina.
Basically, rather than try to restore with soil preparation and planting of a
wide palette, conservancies could try imitating the gradient of species going
from the grassland vanguard through the species just in front of the
recovering boundary to the mix of species found behind the recovering boundary
and ultimately including the species found behind the stable boundaries.
Scraping a site and planting most of the CSS species in an active restoration
site often fails as exotics overwhelm the restoration site. Trying to copy
natural processes of post-disturbance succession here, notably the post-fire
succession of fire-follower annual forbs, then perennial subshrubs, and then
the larger shrubs may not work with CSS, either, since exotic annuals will
swamp the native forbs, too. What is worth a try is a kind of space-time
substitution or faux succession: starting with the shrubs and
subshrubs that can establish in grasslands, moving on to include more species
that venture into the edges of the grassland in front of self-recovering
boundaries, and then adding a fuller palette of CSS species seen behind the
self-recovering boundaries.
For the CSULB group, we will continue augmenting this database, having
students explore the themes of restoring and stable boundaries in other study
sites. As the database grows, we will acquire the statistical power to
evaluate distance from the boundary as a driver of species mix. We've become
interested in the vanguard species and will census for them more
systematically and in a wider set of field sites. The database will
eventually be made public.
Last but not least would be an experimental approach, working with a local
conservancy to devise test plots in which the graduated approach suggested
here could be tested and contrasted with other restoration efforts. This
would move this from an inductive approach to a fully experimental, deductive
approach and enable outcomes assessment for future active restoration
projects.
References
Allen, Edith B.; Eliason, Scott A.; Marquez, Viviane J.; Schultz, Gillian P.;
Storms, Nancy K.; Stylinski, Cathlyn Davis; Zink, Thomas A.; and Allen,
Michael F. 2000. What are the limits to restoration of coastal sage scrub in
Southern California? In
2nd Interface between Ecology and Land Development
in California, ed. Jon E. Keeley, Melanie Baer-Keeley, and C.J.
Fotheringham.
U.S. Geological Survey Open-File Report 00-62: 253-262.
Article available at
http://www.faculty.ucr.edu/~eallen/allenetal_2000.html
(full anthology available as a 118 meg PDF at
http://pubs.usgs.gov/of/2000/of00-062/of00-062.pdf).
Antcliffe, Samantha L. 2009. Native Plant Restoration Following the
Eradication of Invasive Tamarisk in the Tijuana Estuary, California.
Thesis, Department of Geography, California State University, Long Beach.
Brennan, Sean. 2015. The Long Term Consequences of Coyote Brush Invasion
in a Type-Converted Landscapeof Southern California. Thesis, Department
of Geography, California State University, Long Beach.
________. 2013. Coastal sage scrub and the successional influence of coyote
brush. Presentation to Symposium on California Sage Scrub, Southern
California Academy of Sciences, Long Beach, CA. Available from: https://home.csulb.edu/~rodrigue/SCAS/
Chea, Koang KC; Nagy, Brian; Rodrigue, Chrys; Lough, Samantha; Ming, Trina;
Patterson, Darrell; Ko, Nancy; Dean, Jade; Engelberg, Kyra; Peterson, Randy;
and Laris, Paul. 2010. Do slope, aspect, and elevation affect California sage
scrub recovery? Presentation to the Geoscience Diversity Enhancement Project
Symposium, Long Beach, CA. Available at http://web.csulb.edu/depts/geography/gdep/2010/biogeography/posters/Chea.ppt
Cox, Robert D., and Allen, Edith B. 2008. Stability of exotic annual grasses
following restoration efforts in southern California coastal sage scrub.
Journal of Applied Ecology 45, 2: 495-504.
doi: 10.1111/j.1365-2664.2007.01437.x.
Dean, Jade; Fenderson, Karryssa; Roun, Marylynn; Zamora, Victoria; Cardoza,
Daniel; Hazel, Jason; Nagy, Brian; Laris, Paul, and Rodrigue, Chrys. 2009.
How does disturbance type and frequency affect coastal sage scrub recovery?
Presentation to the Geoscience Diversity Enhancement Project Symposium, Long
Beach, CA. Available from http://web.csulb.edu/depts/geography/gdep/symposium.html
Eckardt, Scott W. 2006. Assessment of Wildfire Frequency and Coastal Sage
Scrub Vegetation Dynamics in the Santa Monica Mountains of Southern
California. Thesis, Department of Geography, California State University,
Long Beach.
Engelberg, Kyra. 2011. Anthropogenic Disturbance Regimes and Coastal Sage
Scrub Recovery: Comparing the Long-Term Impacts of Grazing and Cultivation in
Southern California. Thesis, Department of Geography, California State
University, Long Beach.
________. 2013. Characterizing biophysical differences between shifting and
fixed css-grassland boundaries. Reclamation of ground cover from exotic
grassland. Presentation to Symposium on California Sage Scrub, Southern
California Academy of Sciences, Long Beach, CA. Available from: https://home.csulb.edu/~rodrigue/SCAS/
Fenderson, Karryssa; Zamora, Victoria; Roun, Marylynn; Dean, Jade; Cardoza,
Dan; Manack, Jason; Hazel, Jason; Rodrigue, Christine M.; and Laris, Paul.
2009. The effect of mechanical disturbance on soil compaction and soil
texture in coastal sage scrub. Presentation to the Geoscience Diversity
Enhancement Project Symposium, Long Beach, CA. Available from http://web.csulb.edu/depts/geography/gdep/symposium.html
Ko, Nancy; Dean, Jade; Nagy, Brian; Laris, Paul; Engelberg, Kyra; Lough,
Samantha; Ming, Trina; Chea, Koang KC; Patterson, Darrell; Peterson, Randy;
and Rodrigue, Chrys. 2010. A historical analysis: Influence of grazing on
coastal sage scrub recovery. Presentation to the Geoscience Diversity
Enhancement Program Symposium, Long Beach, CA. Available at http://web.csulb.edu/depts/geography/gdep/2010/biogeography/posters/Ko.ppt
Laris, Paul. 2013. Passive restoration of California sage scrub? What
historical ecology can tell us. Presentation to Symposium on California Sage
Scrub, Southern California Academy of Sciences, Long Beach, CA. Available
from: https://home.csulb.edu/~rodrigue/SCAS/
Lough, Samantha; Rodrigue, Chrys; Dean, Jade; Ko, Nancy; Laris, Paul; Chea,
Koang KC; Ming, Trina; Patterson, Darrell; Peterson, Randy; Nagy, Brian; and
Engelberg, Kyra. 2010. Following the leader: The study of native shrub
species advancing into grassland. Presentation to the Geoscience Diversity
Enhancement Program Symposium, Long Beach, CA. Available at http://web.csulb.edu/depts/geography/gdep/2010/biogeography/posters/Lough.ppt
Mills, Mystyn, and Ducoing Chaho, Paola. 2013. Is there fungus among us?
Presence and absence of mycorrhizæ fungus in California sage scrub.
Presentation to Symposium on California Sage Scrub, Southern California
Academy of Sciences, Long Beach, CA. Available from: https://home.csulb.edu/~rodrigue/SCAS/
Ming, Trina; Patterson, Darrell; Stuehler, Conni; Lough, Samantha; Ko, Nancy;
Chea, Koang KC; Nagy, Brian; Rodrigue, Chrys; and Laris Paul. 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.
Presentation to the Geoscience Diversity Enhancement Program Symposium, Long
Beach, CA. Available at http://web.csulb.edu/depts/geography/gdep/2010/biogeography/posters/Ming.ppt
Nesbit, Paul, and Winslow, Scott. 2013. Geology, substrate, and native
vegetation recovery in La Jolla Valley: A pilot study. Reclamation of ground
cover from exotic grassland. Presentation to Symposium on California Sage
Scrub, Southern California Academy of Sciences, Long Beach, CA. Available
from: https://home.csulb.edu/~rodrigue/SCAS/
Patterson, Darrell; Ming, Trina; Paterson, Randy; Stuehler, Conni; Lambert,
Nolan; Chea, Koang KC; Lough, Samantha; Ko, Nancy; Dean, Jade; Nagy, Brian;
Engelberg, Kyra; Laris, Paul; and Rodrigue, Chrys. 2010. Is carbon and
nitrogen the reason in season? Presentation to the Geoscience Diversity
Enhancement Project Symposium, Long Beach, CA. Available at http://web.csulb.edu/depts/geography/gdep/2010/biogeography/posters/Patterson.ppt
Riordan, Erin C., and Rundel, Philip W. 2009. Modelling the distribution of a
threatened habitat: The California sage scrub. Journal of
Biogeography 36: 2176-2188. doi: 10.1111/j.1365-2699.2009.0215.x
Rodrigue, Christine M.; Laris, Paul; Avelar-Portillo, Lourdes Johanna;
Brennan, Sean; Diminutto, Joseph; Mills, Mystyn; Nesbit, Paul; Santana, Abel;
Tabag, Carin; Vaughan, Chelsea; and Winslow, Scott. 2013. Reclamation of
California sage scrub: Reclamation of ground cover from exotic grassland.
Presentation to Symposium on California Sage Scrub, Southern California
Academy of Sciences, Long Beach, CA. Available from: https://home.csulb.edu/~rodrigue/SCAS/
Santana, Abel; Avelar-Portillo, Lourdes Johanna; and Diminutto, Joseph. 2013.
Challenging gravitational theory in CSS seed dispersal: A spatial study of La
Jolla Valley, CA plant boundaries. Presentation to the CSULB College of
Liberal Arts Student Research Showcase, Long Beach, CA. Available from https://home.csulb.edu/~rodrigue/SCAS/
Talluto, Matt V.; Suding, Katherine Nash; and Bowler, Peter A. 2006. Factors
affecting understory establishment in coastal sage restoration.
Madroño 53, 1: 55-59.
Vann-Foster, Rachel. 2015. Native California grasslands-- La Jolla Valley,
Malibu: Species change and recovery rates overtime. Presentation to the
Association of Pacific Coast Geographers, Palm Springs, CA (24 October).
Vaughan,Chelsea; Tabag, Carin; and Brennan, Sean. 2013. Effects of herbivory
on coastal sage scrub recovery in the La Jolla Valley of Point Mugu State
Park. Presentation to Symposium on California Sage Scrub, Southern California
Academy of Sciences, Long Beach, CA. Available from: https://home.csulb.edu/~rodrigue/SCAS/
Westman, Walter E. 1981. Diversity relations and succession in Californian
coastal sage scrub. Ecology 62, 1: 170-184. doi: 10.2307/1936680