My second field methods trip from last semester was to Portuguese Bend in Palos Verdes. This one was somewhat better in terms of temperature and travel. Plus it is a place I have been before and is in fact a popular hiking spot. There are even horse trails. Best of all though is the view of the ocean!
Our mission for this trip was to examine and identify the types of vegetation, in particular coastal sage scrub. You can read my group’s process and findings below.
Note: The following information is from a group report written by myself and two teammates.
Mediterranean-climate regions of California support smaller stature semi-deciduous sage scrubs that are periodically burned by high-intensity fires. These crown fires kill all aboveground biomass over broad portions of the landscape and initiate a successional sequence leading to community recovery within a few decades (Jon E. Keeley 2005). The California coastal sage scrub (CSS) community spans the western coast from central California to Baja Mexico. Approximately 85-90% of this vegetation has been lost through a variety of anthropogenic factors during the past century (Robert S. Taylor 2005). Coastal sage scrub has declined in land area and shrub density, and is being replaced by Mediterranean annual grasses (Dezzani 1998) (Edith B. Allen 1998). Post-fire succession in these Mediterranean-climate shrublands is driven largely by residual species present at the time of fire; however, competitive displacement plays a strong role in successional change. Shrub recovery is negatively correlated with cover of annuals (Jon E. Keeley 2005)
Coastal sage scrub recycles carbon, filters water, and replenishes oxygen. Coastal sage scrub provides habitat for several threatened species including the California gnatcatcher (Polioptila californica) and the Palos Verdes blue butterfly (Glaucopsyche lygdamus palosverdesensis) (C.M. Rodrigue 2013) as well as supporting more than 200 endemic plant species. Throughout the years invasive species have not only posed a threat to the coastal sage scrub but also the species that depend upon it. With the fragmentation that initially began due to agriculture and heavy grazing, species have lost valuable habitat. Human activities in Southern California have led to the introduction of invasive and exotic plant species, which have increased the potential for fires not consistent with previous natural fire cycles (R. Vann-Foster 2014). Today coastal sage scrub is in a period of rapid decline.
Two hypotheses were presented. The first was “Following a very intense fire, Coastal Sage Scrub will be slow to recover and non-native invasive grasses will colonize the burned site”. The second was “Adjacent to the Lemonade Berry Area is a grassy plot that was disked or plowed decades ago. Our goal is to determine the density of shrubs on the plot and compare it with the density on the intensely burned Lemonade Berry plot”.
For approximately 4,000 years the Native American Tongva tribe occupied Palos Verdes. Portuguese Bend is named for explorer Juan Cabrillo who first stepped foot on Tongva land in 1542. In the late 1800’s Japanese immigrants began to farm the area (City of Palos Verdes, 2012). In his memoir, explorer Captain Juan Bautista de Anza repeatedly curses the esthetics of the landscape (DesertUSA.com and Digital West Media, Inc., 2014). This has been a commonly held opinion of native California vegetation for centuries, resulting in the removal of both coastal sage scrub and marshlands (R. Vann-Foster 2014). From the turn of the century through the 1920’s, agriculture and grazing continued to take a toll on the region’s ecosystem and coastal sage scrub population, and while this destructive process was slow to initiate, the effects can be seen today. “Decades of fire suppression in chaparral have allowed the accumulation of senescent vegetation, creating conditions for catastrophic hot fires that kill dormant seed beds and plants that are usually resistant to low-intensity fires” (David Olson, 2014). In 1914 Frank Vanderlip, Sr. purchased what is known today as Palos Verdes Estates with the intention of creating an exclusive community for the wealthy. This development cleared a large portion of the native coastal sage scrub habitat and marked the beginning of the man-made erosion of the coastal sage scrub population in the region.
In an effort to protect coastal sage scrub habitats, the Palos Verdes Peninsula Land Conservancy, PVPLC, was founded in 1988 and has successfully preserved 1,600 acres of open space. Some of the methods utilized by PVPLC include seeding and planting native species along with weeding out invasive species (Palos Verdes Peninsula Land Conservancy, 2012). In order to effectively focus on restoration, there must be an understanding on the causes preventing the natural return of the coastal sage scrub. Active restoration is required in such instances where natural processes are not returning the land to the desired vegetation cover or reaching management goals (Allen, 1999). The Portuguese Bend Reserve is located between the Forrestal and Upper Filiorum Reserves in Palos Verdes and covers 399 acres On August 28, 2009 a fire burned through much of the reserve, spanning approximately 188 acres.
To answer hypothesis one, our group started in a non-disked section of Lemonade Berry. One-meter quadrants were used and sections were chosen every five meters using a linear method with a transecting tape. The group chose the starting location, so it was from the edge of the clearing moving uphill 93 degrees southwest along a 28-degree west-facing slope. The stems of the plants were also measured by eyeballing them to assess the effect of fire on the plants. Quadrants were sampled until the percentage of a species was repeated, totaling seven quadrants for our group. Percentage of plant species was estimated by sight.
For hypothesis two, our group used two different sampling techniques in the disked section, which was bare and burned in a fire. For the first technique, one-meter quadrants were used. The starting point was selected by Professor Laris, as the fourth shrub uphill along the Rim Trail, and subsequent points were chosen every four meters by random by spinning a pencil and going in the direction it pointed. We went uphill 220 degrees southwest along a 10-degree slope. The number of quadrants sampled was decided by Professor Laris and set at nine. Percentage of plant species was estimated by sight.
The second technique within the disked area utilized a two-meter quadrant. Dr. Laris set the number of samples to be collected at five and threw a rock in a random direction to select the groups starting point. Subsequent points were selected using the random direction pencil method and spaced apart by four meters. Percentage of plant species and soil cover was estimated by sight and agreed upon by the group.
The non-disked site of the Lemonade Berry plot had the greatest percent bare soil present of our three sample areas. As reflected in Table 1, bare soil represented on average 20.71% of the seven samples taken at this area. At this site the percentage of bare soil increased steadily through the first two sample sites and dropped off completely. It increased again for another two sample sites until it disappeared again at the top of the slope.
The next two sample areas were in the disked area adjacent to the Lemonade Berry plot. Mainly other annuals dominated this disked area. Table 2 shows the average species coverage at this site using a one-meter quadrant. Other annuals (shown in red) dominate almost all of the nine samples taken. The bare soil at this site had a total average of 15.56% ground coverage spanning the nine samples.
The final sample site in the disked area used a two-meter quadrant. This method gave us the least soil coverage of the three sites. Still mainly dominated by other annuals, as shown in Table 2, the two meter quadrant showed only a 9% total bare soil coverage spanning the seven samples taken at this site.
It is important to note a few biases in our results. While recording the data within the quadrants at all three sample sites, we estimated the ground coverage. No tools were used to analyze exact coverage, thus making our data slightly compromised. Another bias is our unfamiliarity with the species in the area. We have minimal experience with the plants present, so it is possible we misidentified them.
The first sample site in the non-disked area was next to a clearing, which may have created additional bias in our results. However, we do not think this clearing was necessarily detrimental to our results. Assessing the area with the naked eye, Lemonade Berry was the dominant species with minimal bare soil. Regardless of the clearing present, our results are representative of the entire area; so we are able accept this method as adequate.
An additional bias in the disked area (sample sites two and three) was the introduction of rodent burrows and deer scat. The natural presence of animal activity may have potentially impacted our data. We recorded the number or burrows and they are graphed in our tables as coverage, but they could have been accounted for bare soil, which would have increased the bare soil average. Again, this would not have significantly changed the data overall for the area.
Hypothesis one seeks to determine if Coastal Sage Scrub will recover slowly and non-native invasive species will colonize the area. At the Lemonade Berry site (sample site one) the absence of CSS leads us to believe that an intense fire does affect its recovery in the area. However, we cannot fully reject this hypothesis because the area is dominated by Lemonade Berry, which is native to California. Our bare soil coverage, 20.71%, has the lowest average amongst the collective data for the class, which averaged 31.05% for soil coverage. Our coverage of other annuals in this area was 7.86, while the group average was 8.59%. Based on this data, we can conclude that invasive species do not dominate the area.
The goal of hypothesis two is to compare the density of shrubs on the intensely burned Lemonade Berry plot with disked plot adjacent to it. We can partially accept this hypothesis based on our data. Immediately we can determine shrubs are more dense in the disked area because the average soil coverage in this area is less than that in the Lemonade Berry area. The one-meter quadrant method showed a representation of 20.71% bare soil within the Lemonade Berry plot; the remaining area was species density. Using the same one-meter quadrant in the disked field, 15.56% was bare soil with the remaining area being species density (dense?). Using the two-meter quadrant method in the same adjacent disked area represented 9% bare soil coverage. Using soil coverage to determine plant density, we can conclude that all areas are plant dense, however the disked area has more density.
The data our group gathered is overall a good representation of the area studied, despite the aforementioned biases stated. Using the one-meter quadrant, we were able to efficiently take more samples and be more accurate with our estimations due to the smaller size. The two-meter quadrant was very difficult to transport and place, making the accuracy of distance and data collected harder. Because we had a larger area with the two-meter quadrant, we had greater potential for estimation error.
The behavior of the species is important to monitor because of the recent decline of California Sage Scrub and the introduction of non-native invasive species in the area. With the absence of CSS, frequent fires occur, which threaten the plant and animal inhabitants, as well as the human population in the surrounding area. Conservation efforts are being taken to replenish the native Coastal Sage Scrub. Our data represents how species react to the human and natural disturbances bestowed on the landscape.