1. 1
The Strawberry Canyon Research Plot and Investigation of the
Factors Influencing Invasive Versus Native Woody Plant
Establishment
Rich Pauloo1,3
, Paul Fine1,2,4
, Sarah Williams1
, Nga Le1
, Ka Thao1
, Kelsey Killorian1
, Katherine He1
,
Audrey Ragsac1
1. Department of Integrative Biology, University of California, Berkeley, 1005 Valley Life Sciences
Building 3140, Berkeley, California 94720-3140
2. University and Jepson Herbaria, University of California, Berkeley, California 94720-2465
3. E-mail: richpauloo@gmail.com
4. E-mail: paulfine@berkeley.edu
ABSTRACT
The Strawberry Canyon Research Plot (SCRP) is a newly established plot in
Berkeley, CA described in this paper. SCRP bounds an area of 0.16 ha, measuring 30 m
east and 50 m south from the northwest corner located at 37°52'20.30"N,
122°14'24.35"W and is located in Strawberry Canyon on land owned and maintained by
the University of California for research and recreational purposes. SCRP is the first
research plot of its kind in Berkeley. In SCRP, 17,225 woody stems were censused,
representing 16 genera and 17 species. Of these individuals, 5,736 were identified as
invasive, non-native plants, accounting for 33.3% of the total individuals. The understory
is dominated by invasive Rubus discolor and native Toxicodendron diversilobum, and the
canopy, by native Quercus agrifolia and Umbellularia californica. Quercus agrifolia
made up nearly 70% of the plot’s total basal area, yet had a seedling to mature tree ratio
of 1:3—the lowest value of every tree represented. Conversely, invasive Prunus
cerasifera, took up less than 2% of the plot’s total basal area, yet had a seedling to mature
tree ratio of 26:1. No statistically significant relationship was found between light
availability and invasive species establishment, distance from the creek and invasive
species establishment, or basal area and invasive species establishment, suggesting that
invasive species establishment in SCRP is controlled by factors other than light, water
availability, and basal area.
INTRODUCTION
A. Invasive species alter ecosystems.
Major economic and environmental problems can result from the introduction of
invasive species to native ecosystems. In California alone, the latest Jepson Manual lists
more than 2,000 introduced plants out of the nearly 8,000 vascular plants native or
naturalized to the state. By altering nutrient cycling, community dynamics, fire regimes
and suppressing the seedling establishment of native plants, invasive plant species have
homogenizing effects on plant communities, leading to shifts in endemic plant and

2. 2
animal species composition. Altered ecosystems are more susceptible to fragmentation,
damage, and variance, all of which put natural resources at risk (Gordon, 1998).
A recent study by the University of Florida elucidates the mechanisms by which
invasive species swiftly and dramatically alter landscapes (Gordon, 1998). The study
characterizes “invasive” species by their:
(1) effective reproductive and dispersal mechanisms;
(2) competitive ability superior to that of natives in the original or modified
system;
(3) few to no herbivores or pathogens, especially in herbivore-controlled
communities;
(4) ability to occupy a ‘‘vacant niche’’; and
(5) capability of altering the site by either significantly changing resource
availability or disturbance regimes or both.
Invading alien species in the United States cause major environmental damages
and losses totaling almost $120 billion per annum (Pimental, 2007).
A lack of immediate response to invasive species will have permanent and
widespread repercussions in recreation, biodiversity, historic preservation and wildlife
management. Our experiment in Strawberry Creek Canyon has generated a baseline
quantitative species list to document the abundance of native and invasive plant species,
and enables the observation and quantitative measurement in ecological change in an
invasive-plant-impacted ecosystem over time.
B. What factors promote invasive species success and why?
As land managers work to minimize the impact of invasive species and limit their
spread in California ecosystems, an important question remains: what factors promote the
establishment of invasive plants? The factors promoting invasive species establishment
have been addressed in academic literature but are not well understood in SCRP’s study
system. The knowledge of such factors will equip local land managers to respond to
invasive plant establishment, prepare preventative measures, and effectively organize and
protect valuable natural resources. Understanding the distribution and abundance of
established invasive plant communities requires taking a closer look at the history of
invasive plants and human settlements.
Most invasive plants in California were either purposely or inadvertently
introduced by European settlers (Novak, Mack, 2001). Accordingly, many invasive
species are associated with human-modified landscapes such as agricultural and grazing
lands. These ecosystems harbor little in the way of native plant competition and usually
offer high light availability, which places them at risk for invasive plant establishment
and ecosystem alteration (Yates, Levia, Williams, 2004). Furthermore, a smaller number
of intentionally introduced species in California were originally confined to personal
landscaped property, but a subset of these plants are adapted to tolerate shade in their
native ranges and have since proliferated in non-agricultural landscapes. One example is
Prunus cerasifera, a highly common invasive plum tree found in Strawberry Canyon.
Some studies suggest that invasive plants may be experiencing ecological release
in their introduced range because they have escaped their specialist enemies, and can live
in a wider variety of habitats in their introduced range than in their native range (Denslow
et al. 2004).

3. 3
Plant physiology and life history are two factors that can influence the relative
success of a native or an invasive species in an ecosystem. Plants become shade tolerant
by adapting to their environment through their leaf structure or root allocation (Kleunen
et. al., 2011). Disturbances such as fire, fire suppression, trail-making, and human traffic
make forests more susceptible to invasion by non-native species such as Hedera helix
(English Ivy), Rubus discolor (Himalayan Blackberry), and Mahonia sp. (Oregon grape).
These species can survive most natural stresses but grow relatively slowly. Many ivy and
vine-like species, including Hedera helix and Rubus discolor, are shade tolerant, quickly
proliferate, and are very invasive (Gray, 2005). They can spread quickly and outcompete
the native vegetation, as in the case of Strawberry Creek Canyon, a shady oak and laurel
forest with an understory dominated by dense mats of Hedera helix and Rubus discolor.
Invasive and non-invasive species alike may have the ability to change their
phenotypes to adapt to their environment (Kleunen et. al., 2011). This adaptive plasticity
allows plants to thrive in a greater range of environments than their normal range and
thus increases a plant’s chance of becoming invasive (Kleunen et. al., 2011). For
example, a recent study found that although the invasive species had higher shoot-root
ratios and longer leaf-blades under both shaded and non-shaded environments, there was
no difference in the shade-induced responses between the invasive species and native
species (Kleunen et. al., 2011).
Fire can also facilitate the expansion of non-native invasive species, and in other
cases, fire can be used to select against invasive species and pathogens (Davis, Borchert
2006). Fire occurs naturally in many ecosystems, and was the most widely used tool for
ecosystem management by the indigenous peoples of California (Anderson, 2006).
Modern fire suppression has led to widespread changes in many plant communities,
including those of the central coast, and possibly in Strawberry Creek Canyon (Davis,
Borchert, 2006).
C. What makes a good invasive plant biology study system in California woodland
communities?
The Strawberry Creek Canyon Natural History Area in Berkeley, California serves
as an excellent study system for Californian invasive plant biology for three reasons: 1) it
hosts many species representative of the mixed evergreen woodlands found throughout
Coastal California; 2) it hosts a variety of common invasive plants; and 3) its disturbance
history in the past several hundred years, which includes burning, grazing, logging, and
damming and modification of the watercourses, is characteristic of many California
ecosystems.
Drivers of biodiversity change in terrestrial ecosystems arranged in order of highest
to lowest impact are: land-use change, climate change, nitrogen deposition, biotic
exchange, and elevated carbon dioxide concentration (Sala et. al. 2000). Being situated
in a ecosystem that has experienced sweeping land-use changes, SCRP is likely to
experience biodiversity change faster than other terrestrial ecosystems in California, and
should reflect the influence of all biodiversity change drivers acting on the region.
D. How can we study invasive plants at the community level?
Permanent plots allow the possibility to quantify patterns of invasive plants and
their association with biotic and abiotic factors including interactions with other plants,

4. 4
light availability, and soil moisture, to name a few. Permanent plots establish the
framework to re-census, and monitor ecological processes that occur over large time
scales, such as tree phenology, pollination, tree mortality and replacement. To date, there
have been no permanent plots established in Strawberry Canyon. However, two
permanent plots in California have been established in recent years, one at UC Santa
Cruz and one in Yosemite National Park. Both are a part of the Center for Tropical
Forest Science’s international forest ecology plot network. These plots have been used to
test a variety of questions about California forest ecosystems and make comparisons to
other sites to learn about the structure and diversity of forests worldwide.
A research plot provides a hands-on, outdoor, educational laboratory for students
and classrooms studying ecology. Once a plot is successfully established, it provides a
baseline data set from which existing studies can be expanded into long-term studies, and
newer studies benefit from previously collected data.
An example of a successful plot is the UC Santa Cruz Forest Ecology Research
Plot (FERP) established in 2007. It is a 6 hectare plot in the campus Natural Reserve
which serves as an outdoor laboratory for student research and ecological monitoring
(Gilbert et. al., 2010). It contextualizes classroom studies in a pertinent and accessible
location. FERP uses standard measurements congruent with the Center for Tropical
Forest Science’s (CTFS) methodology which allows for comparisons to be made between
FERP and other plots in the CTFS network worldwide. CTFS facilitates a global
network of plots which monitor the effects of climate change, guide sustainable forest
management, increase scientific understanding of forest ecosystems, and build capacity
for forest science. The CTFS monitors the growth and survival of approximately 6
million trees and 10,000 species. Within the CTFS global network, FERP is the only plot
in a Mediterranean ecosystem and thus an important resource for ecosystem and land
managers in Mediterranean biomes. SCRP adds to the data collected at FERP by acting
as a second reference point, which is useful for indicating the regionality of biodiversity
drivers, and creating a unique baseline data set for Berkeley’s understudied Strawberry
Canyon, a gem of the UC Natural Reserve.
METHODS
A. Location
SCRP is located in the hills of Strawberry Canyon behind Berkeley on land
owned and maintained by the University of California for research and recreational
purposes. SCRP is located off of the main trail and is rarely visited by hikers. The
canopy of the site is dominated by Quercus agrifolia and Umbellularia californica and
the understory is dominated by Toxicodendron diversilobum and Rubus discolor.
The plot bounds an area of 0.16 ha, measuring 30 m east and 50 m south from the
northwest corner located at 37°52'20.30"N, 122°14'24.35"W. It is oriented to magnetic
north. Strawberry Creek flows along the north side of the plot. The plot is encompassed
by the main trail, which winds around its north, east, and south sides. A small social trail
about 1 ft. in width runs through the plot from east to west. The plot is situated on a hill

5. 5
which slopes upwards from the creek, running north to south. The slope increases from
15° near the creek, to 40° at the southern border.
Figure 1. Location of SCRP in the hills behind Berkeley. The plot’s .16ha area is contiguous, and forms a
0.15 ha rectangle with a 0.01 ha protrusion on its east border. The plot is in close proximity to Centennial
Road, Memorial Stadium, Lawrence Berkeley labs, the UC Botanical Gardens, and the Hayward Fault.
A plot of 0.16ha is sufficient to yield a representative species list of the micro-
ecosystem bounded by the creek, and its establishment and census is a feasible goal for a
group of 7 students in one semester. It does not capture the entire vegetative diversity of
the Strawberry Creek Watershed. Along Strawberry Creek but not within SCRP, Sequoia
sempervirens, Pinus radiata, Heteromeles arbutifolia, and other woody species can be
found.

6. 6
SCRP was created to provide baseline data for the understudied and valuable
ecosystem and recreational area of Strawberry Creek. In addition, the plot was an
attempt to answer questions regarding invasive species growth specific to this ecosystem.
Lastly, it will continue to serve as an accessible outdoor laboratory and field sampling
site for University students in the natural sciences, providing opportunities to ask
research questions and draw from a previous dataset.
B. Sampling
All woody stems in the plot with DBH > 1-cm were measured at 1.3-m high, in
accordance with the standards set forward by the Center for Tropical Forest Science, and
utilized by a neighboring Mediterranean plot in Santa Cruz, FERP (Gilbert et al., 2010).
Center for Tropical Forest Science methodology was used to ensure that comparisons
could be made between our plot and FERP, and other plots worldwide (Losos, 2004).
“Shrubs” were defined as all woody plants with DBH <1-cm, and “trees” were defined as
all woody plants with DBH ≥1-cm.
Each sub-plot was divided into 10, 1-m x 10-m belts running east-west.
Replicating this method in all 16 sub-plots generated 160 belts of varying distance from
the creek, ranging from 0-m to 50-m. Proceeding through each sub-plot, belt by belt, all
woody stems and woody seedlings with DBH < 1-cm were also surveyed. A census of
all ferns was also taken.
To establish the plot, a compass was used to orient sub-plots to magnetic north
and to one another, a 50-m transect tape was used to measure 10-m borders, and all-
purpose twine was used to delineate the borders. Flagging tape was used to mark 1-m
segments along the twine in order to orient trees within the plot and facilitate surveys by
belt. Once 10-m x 10-m borders were established for a sub-plot, transects tapes were
used to divide the plot into belts, which were then systematically surveyed for vegetation.
10-m DBH tapes were used to record DBH of woody stems > 1-cm at 1.3-m high, and
metal tags were assigned to each of these stems to facilitate future relocation. All notes
were recorded in a field notebook.
C. Species Identification
Species were identified by morphology with dichotomous keys and assistance
from the UC Berkeley Jepson Herbarium. Representative species from all woody
stemmed species and some herbaceous species were identified, collected, and pressed.
The taxonomic nomenclature used was congruent with the University of California
Jepson Museum interchange for California floristics.
D. Climate
Under the Köppen-Geiger climate classification, the plot falls within a "dry-
summer subtropical" climate (classified as Csa and Csb), commonly referred to as
"Mediterranean" (Peel, et al. 2007). According to the Köppen-Geiger climate
classification, the warmest average temperature of "C" zones is above 10 °C (50 °F)
(Peel, et al. 2007). The average coldest temperatures range from 18 °C (64 °F) and −3 °C
(26.6 °F) (Peel, et al. 2007). Overall, Mediterranean climates are characterized by dry
summers, wet winters, and temperatures that rarely drop below freezing (Peel, et al.
2007).

7. 7
E. Soils and Geology
According to the Strawberry Creek Management Plan, SCRP soil is a Maymen-
Los Gatos complex, a dominant soil type in the watershed comprising 23% of the total
soil types (Charbonneau, 1987). The composition of this soil is 50% Maymen soils, 35%
Los Gatos soils, and the final 15% derive from small areas of Millsholom silt loan and
some rock outcrop (Charbonneau, 1987). Bedrock depth ranges from 10-40 inches
(Charbonneau, 1987). Maymen-Los Gatos soil is excessively drained soil with rapid to
very rapid runoff potential and high to very high risk of erosion (Charbonneau, 1987).
This soil is found on slopes ranging from 30-75% (Charbonneau, 1987). The pH of this
soil complex ranges from 4.5-7.3, or strongly acidic to neutral (Charbonneau, 1987).
Maymen-Los Gatos complex is formed in material that weathered from sedimentary rock
and is underlain predominately by sandstone and shale (Charbonneau, 1987). The
Hayward fault runs along the western border of SCRP (Watson, 1997).
F. Site History
Figure 2. Strawberry Canyon in 1870 (photo courtesy of U.C. Berkeley).
Prior to Western arrival and influence, the canyon was inhabited by Native
Americans who used the creek during the summer, and managed the land by the
extensive use of controlled burns to clear the underbrush, facilitate acorn gathering, and
promote the growth of seed-bearing annuals (Anderson, 2006). Strawberry Canyon has
seen a dramatic shift in land use since the arrival of the Spanish and other settlers in the
late 1700s (Keeley, 2002). The vegetation observed in the canyon today is the result of
more than 300 years of fire suppression, introduced species, and the introduction and then
removal of grazing. Prior to the late 1700s, the landscape would have appeared to be an
open oak woodland and grassland filled with perennial bunch grasses and herbaceous
flowering plants (Keeley, 2002). Much of the tree cover would have been limited to the

8. 8
stream channels, which is much different from what we see today (Keeley, 2002). In the
1860s, waterworks were also constructed in Strawberry Canyon to supply water to farms
and speculators. Irrigation paved the way for ranchers to settle the land, and though they
did not burn the landscape, they maintained a grassland-type system by introducing
heavy cattle grazing, which continued in the hills until the 1930s (Allen, 1935).
Surprisingly, little research has investigated the logging history of the hills, but it is
known that a robust timber trade significantly depleted the tree cover of the upper creeks
as East Bay populations grew and the demand for lumber increased.
Much of the industrial use of the creek and upper watershed/canyon area occurred
during the establishment of the UC Berkeley campus and the surrounding township in the
late 1800s and early 1900s. The construction of the University, the Lawrence Berkeley
Laboratory facilities, the UC Botanical Garden, homes, and fire trails all mark a shift in
canyon land use away from timber production and water diversion. Due to the intensive
clearing of the landscape in the early 1900s, flooding was and continued to be a
significant problem in the watershed until the 1970s. The soil of the canyon areas,
particularly on the north-facing slopes, also lends itself to high runoff and erosion due to
its high impermeability.
According to the 1987 Strawberry Creek Management Plan, the major vegetation
type on moist valley bottoms and in deeper soils—generally north and east facing
slopes—consisted of oak-bay woodlands and eucalyptus stands, primarily comprised of
Umbellularia californica, Aesculus californica, Quercus agrifolia, Acer macrophyllum,
Pinus radiata, Arbutus menziesii, and Eucalyptus spp (Charbonneau, R. B., 1987). The
understory predominantly consists of Toxicodendron diversilobum, Rubus discolor,
Corylus cornuta, Sambucus spp., Symphoricarpos spp., and numerous other shrub and
herbaceous species (Charbonneau, R. B., 1987). Today, most of the research and work
on Strawberry Creek Canyon concerns the creek in the campus proper, creek runoff
through culverts and diverted waterways, and managing stream flow through the UC
Botanical Garden. The Strawberry Creek Restoration Project is dedicated to restoring
natural areas within the campus by removing invasive ivy species and Rubus discolor and
re-planting native forbs and trees. Many areas of the creek are campus-owned, thus
extant flora are under the jurisdiction of campus landscapers, and cannot be modified by
student groups without special permission.
RESULTS
A. Species Composition
A total of 17,225 individuals of woody plants were censused, of which 17,039
were identified as shrubs (DBH < 1-cm), and 186 were identified as trees (≥1-cm). The
total population represented 16 genera and 17 species. The canopy was dominated by
Quercus agrifolia and Umbellularia californica, together composing 98.2% of the total
basal area. Toxicodendron diversilobum and Rubus discolor dominated the understory
representing, 49.8% and 29.7% of individuals, respectively. No other species constituted
more than 10% of the total number of individuals.

9. 9
Of the 17,225 individuals, 5,736 were invasive and 11,489 were native.
Therefore, 33.3% of individuals in the census were non-native, invasive woody plants. In
order of abundance, the invasive species were: Rubus discolor, Prunus cerasifera, Hetera
helix, and Ilex aquifolium.
Of the trees, Umbellularia californica was the most abundant at 55.9% of total
trees, and made up 26.1% of the basal area of the plot. This is followed by Quercus
agrifolia at 20.9% of all trees and Prunus cerasifera. at 11.8% of all trees, Quercus
agrifolia made up an overwhelming 72.1% of the basal area of all stems with a DBH ≥1-
cm. Prunus cerasifera and Ilex aquifolium were the only non-native invasive trees, and
they made up 12.4% of the trees.
B. Regeneration: Seedling to Mature Tree Ratios
Within the plot, invasive tree species accounted for less than 2% of the total basal
area, but 33.3% of all individuals, and more than 63% of the seedlings found.
Table 1. Plot basal area per species.
Genus_ Basal % Basal Average # seedlings # Mature
species Area (cm2
) Area* DBH (cm) Trees
Acer_mac 0.02 0.30 12.6 3 2
Cory_cor .002 0.03 1.99 33 8
Frang_ca .002 0.03 1.81 50 9
Ilex_sp* 0.01 0.10 10.1 0 1
Prun_cer* 0.11 1.37 8.14 567 22
Querc_ag 6.03 72.1 60.5 12 39
Umbel_ca 2.18 26.1 16.3 238 104
* invasive species
Acer_mac = Acer macrophylum; Cory_cor = Corylus cornuta; Frang_ca = Frangula californica;
Ilex sp. = Ilex sp.; Prun_cer = Prunus cerasifera; Querc_ag = Quercus agrifolia; Umbel_ca =
Umbellularia californica
While Umbellularia california accounted for more than half of the mature trees
present, it only contributed about 25% of the plot’s total basal area. Twice as many
seedlings than mature trees of U. california were observed.
Conversely, Quercus agrifolia made up nearly 70% of the plot’s total basal area,
yet only constituted about 20% of the total trees with DBH > 1-cm present. Consistently,
the average DBH of Q. agrifolia was substantially larger than all other trees. The
seedling to mature tree ratio for Q. agrifolia was 1:3—the lowest value of every tree
represented.
Interestingly, Prunus cerasifera, the only large woody invasive, took up less than
2% of the plot’s total basal area with 22 trees. P. cerasifera seedlings outnumbered
mature P. cerasifera trees 26:1, and constituted far more seedlings than any other species.

10. 10
Figure 3. Comparison of number of seedlings and mature trees for each tree species.
Acer_mac=Acer Macrophylum; Corylus_cor=Corylus cornuta; Frang_ca=Frangula californica;
Quercus_ag=Quercus agrifolia; Umbel_ca=Umbellularia californica; Prunus_cer=Prunus cerasifera
C. Factors Promoting Invasive Species Establishment
Light
Using a fisheye lens, canopy photos were taken from the center of each plot at a
height of 6 ft. from the ground. These photos were analyzed for their light transmittance
by ImageJ, a Java-based image processing program developed at the National Institutes
of Health (Schneider, 2012).
Table 2. Light transmittance in SCRP, sub-plots A0-D3. All numbers for Direct, Diffuse, and Total Light
Transmittance are reported as percentages.
Type of Light Transmittance
Plot Direct Diffuse Total
A0 25.59 19.82 22.71
B0 15.90 15.11 15.51
C0 12.46 15.39 13.92
D0 17.50 16.73 17.12
E0 9.86 13.10 11.48
A1 21.91 18.92 20.41
B1 16.27 15.06 15.66
C1 19.96 16.27 18.11
D1 14.54 14.94 14.74
E1 13.83 12.88 13.36
A2 9.40 16.07 12.74
B2 19.50 18.74 19.12
C2 20.27 14.29 17.28
D2 12.15 18.41 15.28
E2 21.13 17.95 19.54
D3 18.78 17.84 18.31
Average Light 16.82 16.35 16.58
Transmittance

11. 11
Using light transmittance data obtained from fisheye photos and processed with
ImageJ, no significant relationship between light availability and invasive species
composition was found.
Figure 4. Number of invasive species within each plot as function of light transmittance.
Water
The number of invasive species per belt were plotted against their distance from
the creek, in meters. No significant relationship between distance from the creek and
invasive species establishment was observed.
Figure 5. Number of invasive species within each belt as function of distance from the creek.

12. 12
Basal Area
Furthermore, no relationship between basal area and invasive species density was
observed in the plot. This finding is likely due to the homogeneity of the invasive species
throughout the plot.
Fig. 6. The number of invasive species individuals as a function of basal area.
DISCUSSION
Here we describe a new 0.16 ha plot in Strawberry Canyon where every woody stem has
been censused. The following questions were asked:
1. Are invasive plant species regenerating faster than native plant species? What are
the regeneration rates of different woody plants in the Strawberry Creek Canyon
watershed, measured by their saplings?
2. What are the relative abundances of woody plant species in Strawberry Creek
Canyon, and what factors control invasive plant establishment?
We formed the following hypotheses:
1. We suspect that invasive plant species are regenerating faster than native plant
species, and expect to find more invasive saplings than native saplings.
2. We expect that increased light availability promotes invasive species
establishment, that areas closer to the creek are less prone to invasive species
establishment, and that high basal area in a plot will predict higher rates of
invasive species establishment.

13. 13
A. Species Composition
The 17,225 individuals of woody plants identified within SCRP predominately
reflect Toxicodendron diversilobum and Rubus discolor, which co-dominate the
understory with a combined 79.5% of individuals. The basal area of the plot tells a
different story, reflecting a co-dominant canopy of Quercus agrifolia and Umbellularia
californica, together composing 98.2% of the total basal area. Overall, 16 genera and 17
species of flora were accounted for.
Of the 17,225 individuals, 5,736 were invasive and 11,489 were native, meaning
33.3% of individuals in the census were non-native woody plants. No invasive, non-
native species was sufficiently tall enough to reach the canopy, but Rubus discolor easily
dominated the understory, homogenizing it into a bramble of thorns. Without knowledge
of what the understory vegetation density and composition looked like before the
invasion of Rubus d. is unclear if what changes have occured in the plant and animal
ecology of Strawberry Canyon, post-invasion.
Future studies might investigate the plant ecology of a non-invaded representative
of SCRP, possibly further up Strawberry Canyon, away from the influence of the city of
Berkeley, hikers, and the UC Botanical Garden. With a non-invaded site to make
comparisons to, a future study will provide a snapshot of what SCRP might have looked
like before the introduction of invasive species, elucidating the effects of the invasion on
native plants and animals, and offering a roadmap to restoration.
B. Regeneration: Seedling to Mature Tree Ratios
The finding that invasive Prunus c. (an introduced cherry tree) had 26 times more
seedlings than mature trees was very interesting, and suggests that the establishment
success of this plant is tied to its ability to disperse seeds more effectively than the native
plants represented in SCRP. All of the Prunus c. seedlings were found near mature
Prunus c. trees, suggesting they fell from the trees, although seed dispersal by animal is
also possible. When compared to native plants that dominate the canopy of SCRP, such
as Quercus agrifolia and Umbellularia California, Prunus c. seems more reproductively
fit than native trees adapted to Strawberry Canyon. The mature Prunus c. plants in SCRP
ranged from 1-cm DBH to 14.5-cm DBH, suggesting a mixed distribution of sexually
mature trees. If the number of 567 Prunus c. seedlings found is representative of an
average year, the 22 mature Prunus c. suggest a very low seedling survival rate.
An interesting follow-up question to be addressed in the next census would
examine the success of Prunus c. seedlings. In other words, how many seedlings actually
mature into trees? Answering this question will enable predictions to be made as to the
rate of Prunus c. establishment in SCRP, and contribute to the knowledge available on
Prunus c. establishment in Mediterranean, low-light, riparian, oak woodlands. Moreover,
oak regeneration rates for this ecosystem were very low. Oak trees have historic and
cultural significance, and play a role in ecosystems as habitat and sustenance for
amphibians, birds, and small mammals (Block et al., 1994). Their dense root networks
also provide erosion control, guarding canyons that subject to floods. Given the historic,
cultural, and biological significance of oak trees, an understanding of how they
regenerate in invaded areas is of particular interest to land managers and conservationists.

14. 14
C. Factors Promoting Invasive Species Establishment
Light
It was hypothesized that invasive plants might be correlated with elevated light
availability because light availability is associated with gaps in the canopy and
disturbance, which might promote invasive plant establishment, and some invasive plants
are associated with high light environments (Yates, Levia, Williams, 2004). Gaps in the
canopy are commonly found along constructed trails which also present opportunities for
seed dispersal by people and animals.
There are two explanations for the observed lack of relationship between invasive
plant abundance and light transmittance. First, total light transmittance in all plots ranged
from 11.48% - 22.71%, yielding a range of 11.23%. It may be that light has some effect
on invasive plant establishment, but the range of light transmittance in SCRP was not
wide enough to capture the influence of this factor. Without a wider range of light to
account for, a significant relationship between light and invasive species establishment
within SCRP cannot be ruled out entirely. Second, the major invasive species in the plot,
Rubus discolor and Prunus cerasifera, are both shade-tolerant—their presence is not
constrained by light—and they seem to occur equally in all sub-plots with a light
transmittance ≤ 23%. What remains to be seen is if the density of Rubus discolor and
Prunus cerasifera differs in sub-plots of light transmittance much greater than 23%.
While light transmittance is mostly homogenous throughout SCRP, it might on
the verge of change. Some oaks in the SCRP were noted as old and dying, and as those
trees fall, they will open space in the canopy, letting more light through and possibly
influencing invasive species establishment in the understory. In fact, no measurements of
down and decaying logs were taken, but a few downed Quercus agrifolia were noted
within the plot. Another interesting study might test for the presence of Phytopthora
ramorum or other Phytopthora species known to cause Sudden Oak Death. To this date,
no cases of Phytopthora have been documented in Strawberry Canyon, and if found,
would have dire implications for local land managers.
Water
It was hypothesized that invasive species density would decrease as distance from
the creek increased, because water availability may promote dispersal of native plant
seeds adapted to the riparian environment, and because the availability of water near the
creek might support more biodiversity and consequently a lower density of invasive
species.
Distance from the creek ranged from 1 to 50 meters, and it is possible that
groundwater is nearly homogenous up to 50 meters from the creek. Soil measurements
of water availability would have been a stronger indicator of water availability than
distance from the creek, and future studies might take this measurement.
Basal Area
Basal area presumably was associated with higher invasive species establishment,
because oaks obviously constitute a majority of the basal area in SCRP and it is known
that Fagaceae are associated with “nutrient pools,” owing to the rich microbiome and
leaf litter beneath the trees (Dahlgren et al., 2003). Possibly because invasive species and

15. 15
native species compete equally well for resources, there was no observed significant
relationship between basal area and invasive species establishment. What remains
unknown is how the invasive species in SCRP interact with other native flora found in
Strawberry Canyon, not found in the plot, such as Sequoia sempervirens, Pinus radiata,
and Heteromeles arbutifolia.
D. Summary
The Strawberry Canyon Research Plot (SCRP) in Berkeley, CA is the second plot
of its kind in a Mediterranean climate, after the Forest Ecology Research Plot (FERP) in
Santa Cruz, CA. SCRP addresses issues of invasive species establishment, and
documents a heavily invaded ecosystem representative of larger parts of the Strawberry
Creek watershed. The measurements taken at SCRP can be compared to other plots that
are a part of the Center for Tropical Forest Science’s international forest research plot
network. Within the CTFS network and on a global scale, FERP is currently the only
Mediterranean ecosystem plot. SCRP would be the second, and is thus an important
resource for ecosystem and land managers in Mediterranean biomes. Data collected at
SCRP will augment data from FERP in addition to creating a baseline data set in
Berkeley’s valuable and understudied Strawberry Canyon.
SCRP establishes the framework to monitor ecological processes that occur over
large time scales such as tree phenology, pollination, tree mortality and replacement. It
also provides a hands-on, outdoor, educational laboratory for students and classrooms
studying ecology, complete with a baseline data sets from which existing studies can be
expanded into as long-term studies, and newer studies benefit from past data.
The data gathered at SCRP points to four trends: 1) invasive Prunus cerasifera
seedlings establish in far greater number than native woody plants, although it remains to
be seen how successful these Prunus are in surviving to maturity; 2) there is no
significant relationship between invasive species establishment and light transmittance;
3) there is no significant relationship between invasive species establishment and distance
from the creek; 4) there is no significant relationship between invasive species
establishment and basal area. Future studies should: 1) establish plots further up
Strawberry Canyon for comparative study, investigating the extent of ecological change
in Mediterranean riparian oak woodlands following invasion of Rubus discolor and
Prunus cerasifera; 2) seek to expand SCRP’s area and methodology to further illuminate
possible relationships between water and light not addressed by this study, via soil
moisture tests and new plot areas with higher light transmission.
Acknowledgments
We would like to thank Paul Fine for direction and support, Ben Carter for data
management tips, Kim Kersh and the Jepson Herbarium for aiding in the preparation of
samples, Kevin Koy and the Geospatial Innovation Facility, Michelle Koo of the
Museum of Vertebrate Zoology for help with GIS, and the UC Reserve System for
allowing us to establish SCRP in Strawberry Canyon.

16. 16
References
Allen, RH. 1935. The Spanish Land Grant System as an Influence in the Agricultural
Development of California. Agricultural History, Vol. 9, No. 3. pp.127-142.
Anderson, M.K. 2006. The Use of Fire by Native Americans in California. Fire in
California’s Ecosystems, University of California Press. (417-430).
Aranda I, Arrieta S, Lorenzo D, Sanchez-Gomez D, Tena D, Pardos A, Valladares F.
2005. Shade Tolerance, Photoinhibition sensitivity and phenotypic plasticity of Ilex
Aquifolium in Continental Mediterranean Sites. Tree Physiology. 1041-1052.
Block, et al. 1994. Assessing Wildlife-Habitat-Relationships Models: A Case Study with
Oak Woodlands. Wild. Soc. Bull. 22: 549-561.
Capian, Joshua; Yeakley, Alan. 2006. Rubus Armeniacus (Himalayan blackberry)
Occurrence and Growth in Relation to Soil and Light Conditions in Western Oregon.
Environmental Sciences and Resources Program, Portland State University. 9-17.
California Invasive Plant Council. 2006. California Invasive Plant Inventory. Cal-IPC
Publication 2006-02. Berkeley, CA, US.
Callaway, R.M. 1992. Morphological and physiological responses of three California oak
species to shade. International Journal of Plant Sciences, 153(3), 434-441.
Charbonneau, R. B. 1987. Strawberry Creek Management Plan. Professional Report
prepared for the Office of Environmental Health and Safety, University of California
Berkeley, CA, US.
Charbonneau, R. 2000. Strawberry Creek, The Making of an Urban Creek, and Restoring
the Creek. Strawberry Creek Management Plan. Professional Report prepared for the
Office of Environmental Health and Safety, University of California Berkeley, CA,
US.
Cockrell, R.A. 1976. Trees of the Berkeley Campus, October 1976. Professional Report
Prepared for UC Berkeley. Berkeley, CA, US.
Colwell, Robert K. EstimateS: Statistical Estimation of Species Richness and Shared
Species from Samples. Computer software. EstimateS. Vers. 8.2. Department of
Ecology & Evolutionary Biology, University of Connecticut, 20 July 2009. Web. 25
Apr. 2012. <http://viceroy.eeb.uconn.edu/estimates>.
Dahlgren RA, Horwath WR, Tate KW, Camping, TJ. 2003. Blue oak enhance soil
quality in California oak woodlands. California Agriculture, Volume 57, Number 2:
42-47.
Davidson, J.M., Wickland, A.C., Patterson, H.A., Falk, K.R., and Rizzo, D.M. 2005.
Transmission of Phytophthora ramorum in mixed-evergreen forest in California.
Phytopathology, 95(5), 587-596.
Davis, F.W. and Borchert M.I. 2006. Central Coast Bioregion. Fire in California’s
Ecosystems (321-349). Ewing, NJ, USA: University of California Press.
Denslow, Julie S.; DeWalt, Saara J.; Ickes, Kalan. 2004. Natural-Enemy Release
Facilitates Habitat Expansion of the Invasive Tropical Shrub Clidemia Hirta. Ecology.
471-483.
Dunning C E, Paine T D, Redak R A. 2002. Insect-oak interactions with coast live oak
(Quercus agrifolia) and Engelmann oak (Q. engelmannii) at the acorn and seedling
stage. Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California’s
Changing Landscape, 22–25: Pages 205–218 October 2001, San Diego CA.

17. 17
Gilbert, Gregory S., Elizabeth Howard, Bárbara Ayala-Orozco, Martha Bonilla-Moheno,
Justin Cummings, Suzanne Langridge, Ingrid M. Parker, Jae Pasari, Daniella
Schweizer, and Sarah Swope. 2010. Beyond the Tropics: Forest Structure in a
Temperate Forest Mapped Plot. Journal of Vegetation Science 21.2: 388-405.
Gordon, Doria. 1998. Effects of Invasive, Non-Indigenous Plant Species on Ecosystem
Processes: Lessons from Florida. Ecological Applications 8: 975–989.
Gray, Andrew. 2005. Eight Nonnative Plants in Western Oregon Forests: Associations
with Environment and Management. Environmental monitoring and Assessment 100:
109-127
Howe, H. and Smallwood, J. 1982. Ecology of Seed Dispersal. Annual Review of
Ecology and Systematics 13: 201-228.
Huston, Michael. 2004. Management strategies for plant invasions: manipulating
productivity, disturbance, and competition. Diversity and Distributions. Vol 10, 174.
Keeley, Jon. 2002. Native American Impacts on Fire Regimes of the California coastal
ranges. Journal of Biogeography, 29: 303-320.
Losos, E.C. & Leigh Jr., E.G. (eds.) 2004. Tropical forest diversity and dynamism.
Findings from a large-scale plot network. University of Chiacgo Press, IL., US.
Magurran, Anne E. 1988. Ecological Diversity and Its Measurement. Princeton, NJ:
Princeton UP.
Novak, Stephen and Mack, Richard. 2001. Tracing Plant Introduction and Spread:
Genetic Evidence from Bromus tectorum (Chetgrass). Bioscience, Vol. 51 No. 2: 114
Pimental, David. 2007. Environmental and Economic Costs of Vertebrate Species
Invasions into the United States. 2007 College of Agriculture Cornell University.
Managing Vertebrate Invasive Species. Paper 38.
Peel, M. C. and Finlayson, B. L. and McMahon, T. A. 2007. Updated world map of the
Köppen–Geiger climate classification. Hydrol. Earth Syst. Sci. 11: 1633–1644.
Rizzo, D. M., Garbelotto, M., Davidson, J. M., Slaughter, G. W., and Koike, S. T. 2002.
Phytophthora ramorum as the cause of extensive mortality of Quercus spp. and
Lithocarpus densiflorus in California. Plant Disease, 86, 205-214.
Sala OE, et. al. 2000. Global biodiversity scenarios for the year 2100. Science. Volume
287 (5459):1770-4
Schneider CA, Rasband WS, Eliceiri KW. 2012. NIH Image to ImageJ: 25 years of
image analysis. Nat Methods 9 (7): 671–675.
Swiecki T.J., Bernhardt E.A., Arnold R.A. 1990. Impacts of diseases and arthropods on
California’s rangeland oaks. A report to the California Department of Forestry and
Fire Protection, Forest and Rangeland Resources Assessment Program (FRRAP),
Sacramento, (CA). Contract 8CA74545.
Tyler C.M., Mahall B.E., Davis F.W., Hall M. 2002. Factors limiting recruitment in
valley and coast live oak. Pages 565–572 in Proceedings of the Fifth Symposium on
Oak Woodlands: Oaks in California’s Changing Landscape, 22–25 October 2001, San
Diego (CA).
Tyler, C.M., Kuhn, B., and Davis, F.W. 2006. Demography and recruitment limitations
of three oak species in California. The Quarterly Review of Biology, 81(2), 127-152.
Van Kleunen Mark; Schlaepfer Daniel R.; Glaettli Melanie; et al. 2011. Preadapted for

18. 18
invasiveness: do species traits or their plastic response to shading differ between
invasive and non-invasive plant species in their native range. Journal of
Biogeography. Vol 38, 1294-1304.
Watson, J. 1997. The branches of the San Andreas fault system in central California.
United States Geologic Survey.
Yates, Emily, Levia Jr., Delphis, Williams, Carol. 2004. Recruitment of three non-native
invasive plants into a fragmented forest in southern Illinois. Forest Ecology and
Management Volume 190, Issues 2-3: 119-130.