1. Abundance and distribution of invasive understory species at Redwood Regional Park with
proximity to roads
Oakland, CA
Beverly Perez
May 18th, 2015
San Jose State University
Senior Seminar
Spring 2015
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Abstract:
This study focuses on the abundance and distribution of native and invasive understory species
with proximity to roads in Redwood Regional Park in Oakland, California. Abundance of
invasive species was predicted to be higher near road, and abundance of native species to be
higher far from road. Distribution of native species was predicted to be higher more than three
kilometers from road, and distribution of invasive species to be higher less than two kilometers
from road. Samples were taken with a 1.8 ft. by 1.8 ft. quadrant and data was later analyzed
using a non-parametric test of Kruskal-Wallis, and a regression analysis. Results lead to rejecting
all of the null hypotheses. Roads clearly have a strong influence on the distribution and
abundance of species. For clearer results, all species surveyed should be identified, and an area
that is not between two roads should be surveyed.
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Table of Contents:
Introduction and literature review: .……………………………………………………………...4
Research Objectives: .……………………………………………………………………………6
Methods:...………………………………………………………………………………………..6
Study System: .………………………………………………………………………………...6
Study design: .…………………………………………………………………………………6
Data Collection Procedures: .………………………………………………………………….7
Analytic Methods: .……………………………………………………………………………8
Results: …………………………………………………………………………………………..8
Discussion: ...………………………………………………………..……………………….....11
Conclusion: ...…………………………………………………………………………………..12
Recommendations: …………………………………………………………………………..…12
References cited: …………………………………………………………………………..…...14
Appendix A: ……………………………………………………………………………………16
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Introduction and literature review:
Redwood forests have been under the influence of human activity since California’s 1849
gold rush, when redwood logging initiated (Save the Redwoods League 2015). During this
period, more than eighty percent of old growth was logged, which has left less than five percent
leading to dramatic disturbances and changes within the forests (Save the Redwoods League
2015). Redwood forests tend to have high ecological diversity with very detailed and intricate
vegetation webs, but can be disrupted dramatically due to human influences such as roads
(Keyes and Teraoka 2014). Human interaction largely impacts the health of redwood forests,
causing the trees and other plant life to stress and die, even more so if they are located along the
edge of highways or near areas that have high human impacts (Jones). It is essential that the
health of redwood forests is closely monitored to develop restoration plans. Evaluating the health
and diversity of redwood forests can be done through analyzing the type, abundance, and
distribution of understory species within the area. Categorizing the amount of native vegetation
versus amounts of non-native vegetation can help with developing a plan for restoration, as well
as what areas to target (Keyes and Teraoka 2014).
During the 19th century redwood harvesting was heavily taking place by companies such
as Pacific Lumber who had great incentives to harvest old growth forests precisely because those
trees no longer matured (DeAngelo 1998). Effects of timber harvesting are prolonged in the
ecological structure of a forest, and studies have shown that canopy cover, basal area, and
species abundance in redwood forests continue to be affected even a hundred years after
harvesting has taken place (Russell 2009). Plant diversity and structure can be affected up to 150
meters into the forest due to human activities causing the plants to stress (Russell and Jones
2002) and change the composition of species (Chen et al. 1992). Plant species composition has
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been analyzed in redwood forests in Mendocino and Santa Cruz County. If plant species
composition is greatly altered by simply being located in areas that have been harvested, it is
probably the same situation for the areas located near roads, which are highly susceptible to
disturbance. Finding out abundance and distribution of understory species within Redwood
Regional Park can help with management practices in the city of Oakland.
In second growth forests, or highly disturbed areas within Mendocino and Santa Cruz
Counties, non-native species were more commonly found than in old growth forests, or
undisturbed areas (Russell 2009). One of the limitations for this study is the lack of knowledge
of species composition within the park prior to human disturbance (Ashton et al. 2005). In order
to be able to fully understand how much redwood forests have been truly disturbed by human
activity, information regarding redwood development before the eighteenth century is required
(Lorimer et al. 2009).
Studies have shown that the amount of stress on species caused by roads is high and
negative. The negative effects roads have on species abundance and distribution greatly
outweigh the positive effects (Fahrig and Rytwinksi 2009). Redwood Regional Park is a
recreational park, and recreation activities and roads both have the tendency to negatively affect
the dynamics of habitats by causing stress to the species within the area (Astudillo et al. 2014).
The influences roads have on biodiversity are usually not well documented, if documented at all
(Astudillo et al. 2014). A study done in Cajas National Park in Ecuador explains that the overall
abundance of species did not differ with proximity to roads; however, averages indicated that
bird abundance was higher far away from roads (Astudillo et al. 2014).
Another study done in the lower Florida Keys, analyzing the abundance of the invasive
fire ant with proximity to roads also indicated that roads have high influence on species
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abundance (Forys et al. 2002). Samples closest to roads had higher probability of containing fire
ants; however, fire ants were equally found in all of the different habitats (Forys et al. 2002). A
study done on Mount Norikura, Japan also indicated that roads changed the composition of plant
species (Takahasi and Miyajima 2010). The size of roads does not affect abundance of invasive
species, but there is a clear pattern that presence of roads greatly alters species distribution and
abundance (Mckinney 2002).
Research Objectives:
The general idea of this study is to find the percentage of plant species diversity within Redwood
Regional Park and their proximity to roads.
H1. Invasive species abundance is higher near the road.
H2. Native species abundance is higher far away from the road.
H3: Invasive species distribution is higher >2 meters from road.
H4. Native species distribution is higher <3 meters from road.
Methods:
Study System:
Data collection took place in Redwood Regional Park in Oakland, California.
The park is located about two miles off Skyline Boulevard. Understory species were
surveyed near and far away from main road to determine the influence roads have on
species abundance.
Study design:
In order to determine species diversity, thirty-eight samples were collected in
total. Nineteen locations were randomly selected along the edge of the road (Ashton et al.
2005), and randomization was conducted by generating a random number of footsteps to
take alongside road. Another nineteen locations were randomly selected far away from
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the road, and randomization also took place by generating a list of random number of
footsteps.
Data Collection Procedures:
A 1.8 x 1.8 ft. quadrant made out of PVC pipes and wire was used to calculate the
percentage of species within the area. The quadrant has a total of sixteen squares, where
each square totals approximately six percent. The data sheet following this description is
what was used on the field to collect the data. Unknown species were categorized as
“Species A,” “Species B,” “Species C,” and so forth.
Native Invasive
Quadrant# Proximity
to road
% % % % % % Total
Native
Total
Invasive
Table 1: Data sheet
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Analytic Methods:
The data collected was skewed, and the parametric test resulted less than |2|. An attempt
to transform the data was made but was still not normal; therefore, a non-parametric test was
conducted. Kruskal-Wallis test was conducted to figure out the abundance of species with
proximity to the road and then transformed into box plots. A regression test was conducted to
analyze the distribution of native and invasive understory species. The Kruskal-Wallis test for
abundance of invasive plants yielded a significant p-value of 0.004, and the Kruskal-Wallis test
for abundance of native plants yielded a significant p-value of 0.007. The regression analysis for
invasive species distribution yielded a significant p-value of 0.007, and the regression analysis
for native species distribution resulted in a p-value of 0.002.
Results:
A total of 38 quadrants were surveyed, where nineteen were near the road and nineteen
away from road (Appendix A). Abundance of invasive species was significantly greater near the
road, where p=0.004 (Fig. 1). Abundance of native understory species was significantly greater
far from the road, but had a few outlying native plants near the road and p= 0.007 (Fig. 2).
Native plants were oddly distributed throughout the park, with a gap between two and three
kilometers (Appendix A). Distribution of native understory species with proximity to road was
significantly higher away from road, F (11,020) = 8.28, p=0.007 and R2 = 0.187 (Fig. 3).
Distribution of invasive species was significantly greater near the road, F (1, 025) = 11.42, p=
0.002, and R2= 0.241 (Fig. 4). At the beginning of the trails near the road, large amounts of
Forget me not, Periwinkle, and Poison Oak were seen, all invasive, but decreased farther from
the road. On the other hand, Trillium, Fat Solomon Seal, and Miners Lettuce, all native, were
only seen on trails away from road. Seeing the distribution of species began to indicate that
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roads have great influence on the distribution and abundance of species. There was an
observation that the native plants found near the road were Wild Strawberry and California
Blackberry, both water loving plants. There is a stream that runs next to the road, which explains
why Wild Strawberry and California Blackberry are present near the road.
Figure 1. Abundance of invasive species with proximity to road.
far near
PROX$
0
50
100
150
TOTAL_NATIVE
Figure 2. Abundance of native plant species with proximity to road obtained through quadrant
sampling.
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Figure 3. Distribution of native understory species from zero to five kilometers from road,
and p= 0.007, R2=0.187, and SE=3.50.
Figure 4. Distribution of invasive understory species from zero to five kilometers from road, p= 0.002,
R2= 0.241, and SE= 0.910.
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Discussion:
The statistical results indicate that roads clearly have an effect on species distribution and
abundance. Invasive species had a much smaller margin and abundance farther away from the
road, and also due to less human and car activity. Native species abundance was greater farther
away from the road, but had a few outliers near the road. The native plants found near the road
were Wild Strawberry and California Blackberry, both plants are water loving and are usually
found near streams. There is a stream that runs alongside the road, which can mean that the
outlying native species can be due to the stream that is adjacent to the road. Distribution of
invasive plants was higher less than two kilometers from the road, which can be due to high
amounts of car, horse, dog, and human activity.
On the other hand, distribution of native plants was spread throughout the five kilometers
surveyed, but native distribution was much higher away from the road. The native species found
near the road could be the Wild Strawberry and California Blackberry that are next to the stream,
adjacent to the road. The higher amounts of native plants away from the road can be due to less
human and car activity in the trails further away from the road. Most of the human activity was
seen closer to the road, and only a few people were seen hiking the trails that were farther from
the road and deeper into the park, however, a study done in 77 areas within United States parks
indicated that that the amount of human activity did not influence the abundance of invasive
plant species (McKinney 2002). Higher amounts of invasive plants near the road can also be due
to open canopy leading to increasing access to sunlight (Takahashi and Miyajima 2010).
There is a gap within the park that was not surveyed, which can be altering the results
because there is information missing. In addition, the area in the park that was surveyed was
located in the middle of two roads, which put a limitation on how far into the park plots could be
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surveyed. In order to get a much clearer idea of the influence roads has on plant distribution and
abundance, another area that is not in the middle of two roads should be surveyed. There is also
the issue that not all plant species that were surveyed were identified. This was due to lack of
time and resources. If all plants were identified, it would yield clearer and more specific results.
Even though there were several limitations and issues with the study, results indicate that
the null hypotheses are all rejected. As the studies conducted in Japan, Ecuador, and Florida
analyzing bird, ant, and plant distribution with their proximity to roads indicated that roads
indeed influence species abundance and distribution, this study too confirms that roads alter
species composition.
Conclusion:
It is clear that the City of Oakland has good management practices since this study found
that native plants are abundant throughout the park with high amounts farther from the road, and
non-natives high only near the roar, however, there could be an extra effort to remove the non-
native species or reduce the activities allowed on the park. For example, dogs and horses are
allowed in the park, and there is an area with barbeque pits for parties. If activities are lessened
to only hiking this would reduce the amount of stressors and influences on plant abundance and
distribution.
Recommendations:
This study indicated that abundance of native plant species is greater farther from the
road, and non-native plant abundance is higher from the road. The study also indicated that
native plant distribution is spread through the park near and far away from road, and non-native
plants are only found near the road; however, not all plants surveyed were identified due to lack
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of resources. If all plants were identified, results would give a clearer idea of native and non-
native plant distribution and abundance.
In addition, plants were only surveyed from zero to 1.56 kilometers, and from 3.21
kilometers to 4.76 kilometers. There is a gap from 1.56 kilometers to 3.21 kilometers that was
not surveyed. In order to give a clearer understanding of plant distribution throughout the entire
park, this gap would have to be surveyed. There is also the issue that Redwood Regional Park is
small, and there is a back road. This back road makes it difficult to find an area that is
completely far away from a road, because the farther I got from the main road, the closer I got to
the backroad. Another park within Oakland could be surveyed to see the impact of roads on plant
abundance and distribution.
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Farwig N. 2014. The impact of roads on the avifauna of páramo grasslands in cajas national
park, Ecuador. Stud Neotrop Fauna Environ 49(3):204-12.
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Forys EA, Allen CR, Wojcik DP. 2002. Influence of the proximity and amount of human
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McKinney ML. 2002. Influence of settlement time, human population, park shape and age,
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forests in the coastal redwood region. Forest Ecology & Management 257(5):1427-33.
Russell W and Jones C 2002. The effects of timber harvesting on the structure and
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Save the Redwoods League [Internet]. c2015.[cited 2015 Feb 5]. Available from: http:// ww
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