Soil Ecology and Research Group
last update March 18, 2004
FOR INVASIVE SPECIES CONTROL AND
NATIVE HABITAT ENHANCEMENT
SUBASE ICE PLANT AND ACACIA ERADICATION
AT NAVAL BASE POINT LOMA
The primary goals of the Invasive Species Control and Habitat Enhancement project included the removal of exotic plant species from a five-acre portion of land located adjacent to the Fort Rosecrans National Cemetery at Naval Base Point Loma and native habitat restoration at a separate site known as the "U-Shaped Gully "site. While removal of exotic species was the only work done on the site adjacent to Fort Rosecrans National Cemetery, the main focus of the U-shaped gully project has been to restore a disturbed section of southern maritime chaparral and create potential habitat for native plants to flourish. The focus of the first seven months of the project was the removal of invasive plant species threatening native flora in the U-Shaped Gully and the creation of potential habitat for native coastal sage scrub. Different treatments were implemented on-site to determine the most effective methods of eradication. Habitat creation has entailed the installation of erosion control devices and the outplanting of species that are native to the area. Erosion control and revegetation occurred between January and February 2003. The final five months of the project focused on maintenance and monitoring of the site and outplanted seedlings.
Point Loma is a four-mile long peninsula located at the entrance of San Diego Bay. Land use is divided between U.S. Navy, U.S. National Park Service, Department of Veteran’s Affairs, City of San Diego and the University of California. The U.S. Navy is the largest landholder on Point Loma. Because of unique climatic and geological factors, sensitive and diverse biological communities occur on Point Loma. Many of these communities remain intact because of limited development and limited public access that has resulted from the presence of the U.S. Navy on the peninsula. In 1995, landowners on Point Loma jointly established the Point Loma Ecological Reserve in an effort to preserve sensitive biological resources.
In July 2002 Southwest Division, Naval Facilities Engineering Command contracted the Soil Ecology and Restoration Group to perform habitat enhancement of native maritime chaparral on Point Loma. The purpose of the habitat enhancement was to remove invasive species threatening the area and to increase both the diversity and density of natives. These activities were expected to further repair the damaged ecological cycles by autogenic means.
Two areas on the west-side of Point Loma were designated as restoration sites. The first site was a fairly steep five acre site located adjacent to the Rosecrans National Cemetery. Efforts at this site concentrated on the physical removal of exotic tree species such as Golden Wattle (Acacia longifolia), Lollipop tree, (Myoporum laetum) and non-native pines, and the application of herbicide to several acres of ice plant, (Carpobrotus edulis). The second site, located next to the Fleet Combat Training Center, Pacific recreation field, was selected for habitat restoration efforts and is referred to as the “U-shaped gully site”. This site, located off Electron Drive, encompasses slightly less than one acre and consists of a gully that was covered in dead brush, ice plant, acacia, and eucalyptus. Few natives were present. The adjacent vegetation community is identified as southern maritime chaparral (Integrated Natural Resources Plan for Naval Base, Point Loma, 2001 and personal observation). Restoration efforts at this site concentrated on both exotic species removal and the re-establishment of native species through the transplanting of greenhouse grown species germinated from locally collected seed.
COLLECTION OF GEOGRAPHICAL INFORMATION
GPS coordinates were taken and data was used to create a map for the exotic removal site (Figure 1). Perimeters run adjacent to the Fort Rosecrans National Cemetery and encompass approximately five acres of disturbed land.
During initial evaluation of the U-shaped gully site, perimeters were determined to be the drainage area from the southwest corner of the gully to the bottom of the gully, the south-facing slope, and the flat area along the top bordering the parking lot. GPS coordinates for the perimeter were recorded and GIS technology was used to map the area (Figure 2). Borders were then marked with blue pin flags.
The first site, made up of five-acres, bordered Fort Rosecrans National Cemetery and had a ground cover of nearly 100% ice plant. Ice plant found on the north-west-facing slope was up to two to three feet thick, as was the ice plant found on a one-acre portion at the far south end of the site.
The flat area bordering the fence line was covered with Golden Wattle, Lollipop trees, and non-native pines. These exotics were found from the far south end to the northern most point of the site. Lemonade berry (Rhus integrifolia) and California buckwheat (Eriogonum fasciculatum) were the only natives present in this area.
The bottom of the gully, in the northern half of the site, contained the largest Acacia found on site. This exotic tree was approximately twenty-feet tall and covered an area of approximately fifty square feet. Lemonade berry was the most dominant native on this of the site.
On the second site, the west-facing slope of the U-shaped gully was a steep sandy area with scattered stands of California buckwheat and lemonade berry. Ice plant was present on both the west-facing and south-facing slopes. California brittle brush (Encelia californica) was the dominant native found in this area. The flat area bordering the parking lot was a sandy strip consisting of landscaping plants such as the blue gum tree (Eucalyptus globulus) and traces of ice plant.
The area at the bottom of the gully was initially filled with dead brush, ice plant, and acacia sprouts. The dead brush and ice plant were removed manually and acacia sprouts treated with herbicide. Only at the lower end of the south-facing slope, just above the bottom of the gully, were any natives found. Lemonade berry and California brittlebush were dominant. The lack of natives was probably due to the thick layer of ice plant initially found on site. Also, a concrete drain that ends near the bottom of the gully would also have discouraged native colonization.
The flat section at the top of the south-facing slope was a bare sandy area sprouting some exotic grasses prior to site preparation. Very few natives were found in this area, probably due to the construction of the parking lot adjacent to the area. The construction seems to have contributed to compaction of the soil making it difficult for native seed to germinate and grow.
Exotic species removal at the site adjacent to Fort Rosecrans National Cemetery fell into two categories. First, all non-native tree species were cut down and removed to the San Diego City landfill. These included fourteen acacia trees, approximately fifteen to twenty feet tall; eight pine trees, ranging from three to eighteen feet tall; and twelve myoporum trees, twelve to fifteen feet tall. All were cut down and reduced to manageable sizes through the use of gasoline-powered chain saws. Since all qualified as green waste, it was transported to the City of San Diego’s Miramar landfill and placed in the green waste section for recycling.
The second category of exotic species removal was ice plant, mainly Carpobrotus edulis. Since most of the five-acre site was covered with ice plant, its removal was essential to the area’s ability to naturally restore itself. In areas where small native seedlings were growing within the ice plant mats, the ice plant was removed by hand to prevent damaging the seedlings through the use of herbicide. This dead ice plant was then spread over the bare areas of the site, caused by the removal of non-native tree species described above, to aid in erosion control. The ice plant areas where no native seedlings were noticed were treated with the herbicide Roundup Pro. The dead ice plant was left in place to aid in the control of possible erosion.
The goal of the exotic removal from this site was twofold. The project site is bordered on one side by the Fort Rosecrans National Cemetery and on the other three sides by the Point Loma Ecological Reserve. Removal of exotic species from this site will not only assist the site to restore itself naturally, but will prevent exotic species from invading into the high quality, undisturbed maritime coastal sage scrub habitat located within the Reserve. Target invasive species found at the U-shaped gully site such as ice plant and acacia, considered a threat to natives, or those whose presence was thought to deter the establishment of native flora, were removed from the site. In areas on the steeper part of the slope, ice plant was treated with herbicide and the dead mats left to aid in erosion control and decrease soil disturbance. Herbicide was applied January 2003 and April 2003. Other non-native species found on site were cut down and manually removed.
The resulting biomass from the manually removed ice plant was placed in garbage bags and disposed of at Miramar landfill. A duff litter layer, approximately four to six inches deep, remained following the manual removal of the live ice plant mats. Approximately fifty 33-gallon trash bags, filled with ice plant and small acacia sprouts, were removed from the site in a 24-foot stake bed truck and hauled to the Miramar landfill where it was disposed of as greenwaste.
To prevent additional soil disturbance and erosion, jute netting was installed. The jute was cut into strips ranging from four to ten feet in length (Figure 3). The cut edges were folded under and placed on the ground in a cross directional patchwork. The individual strips overlapped by four inches. This design was meant to reduce undercutting beneath the jute netting and prevent the formation of gullies that had been noted to occur along the seams at other restoration sites with sandy slopes. Metal staples and bamboo poles were used to secure the netting on all edges and in areas where the soil texture was particularly fine. Existing native seedlings were carefully pulled through the jute and the netting around them secured with staples. Holes were cut in the jute netting, two to four feet wide in a random pattern. These holes, where greenhouse raised seedlings were later planted, were placed randomly in order to create the most natural setting possible.
Figure 3. Fieldworker laying a cut strip of jute.
The plant species palette for the U-shaped gully site was determined from the species diversity found on the reference site. The reference site chosen was an undisturbed area immediately south-west of the restoration site. Seed and cuttings were collected from the immediate area on and around the site. Seedlings were propagated at the SERG greenhouse at San Diego State University. Cuttings were 15 to 20 cm in length, cut at an angle at the bottom and straight at the top. First placed in sand flats until roots sprouted, the cuttings were then transplanted to containers with a 1:1:1 (super soil: vermiculite: sand) potting mix. Species breakdown for the site is presented in Table 2.
Seedlings were watered three times each week and fertilized once each month for five months. Water and fertilizer were reduced two months prior to planting and plants were removed from under the shade cloth two weeks prior to planting to allow hardening off to occur.
Number of species planted on site.
Outplanting took place in February 2003. Holes were dug with shovels and post-hole diggers (Figure 4). Each hole was dug approximately 12 to 18 inches deep and 10 inches wide. One seedling was planted in each hole for a total of one hundred and fifty seedlings. Each seedling received at least one gallon of water at the time of transplanting. The soil around each plant was well compacted to reduce shock. A basin of twenty-eight inches in diameter was constructed around every outplanting. As shown in Figures 5 and 6, each plant received a Treepee shrub shelter to prevent herbivory.
Immediately following outplanting, two lines of irrigation tubing were installed on site. The lines were placed so that each plant was provided with a drip emitter. The irrigation lines were secured with metal staples and, in extremely sandy areas, reinforced with bamboo stakes. During supplemental irrigation the lines were opened for 1/2 hour allowing each plant to receive approximately 3 gallons of water.
Figure 4. Fieldworker digging a hole where a seedling will be outplanted.
Figure 5. Outplantings on south and west-facing slopes, February 2003.
Figure 6. Outplantings at the base of the gully, February 2003.
Maintenance of the site consisted of supplemental irrigation of the outplantings by hand watering and use of the drip/irrigation line, and the monitoring of re-emerging invasive species and subsequent eradication or removal. At the time of each visit to the site, all invasive species were identified, removed, and properly disposed. The outplanted seedlings received supplemental irrigation, unless unnecessary due to natural precipitation, once every two weeks from the time of outplanting through August 2003. Results from previous coastal sage scrub restoration efforts have demonstrated the need for supplemental irrigation throughout the first summer. Following the first summer outplantings were able to survive with natural precipitation. Each outplanting was given one to three gallons of water per irrigation event.
During spring monitoring, no ice plant resprouts were found, however, crown daisy (Chrysanthemum coronarium) was found sprouting over the entire site. This exotic has been known to invade urban coastal areas, vacant lots, and filled areas, (areas under construction where the uneven ground has been backfilled to make the ground flat). Any exotic species found were treated with herbicide or manually removed before they went to seed. Eliminating invasives early prevents future sprouting from seed. With the exception of the crown daisy, no other invasive species were able to establish on site for the duration of the project.
Extremely loose soil conditions made it necessary to install 3-foot bamboo poles to aid the staples in fastening the jute netting to the slope (Figure 7). Following planting, natural rainfall events caused continued erosion beneath the jute in areas on the south side of the west-facing slope (Figure 8). Outplantings in this area were monitored closely and soil was replaced around the water basins during maintenance visits in 2003. Basins needed to be consistently repaired in order for the outplantings to receive and retain a sufficient amount of water for survival (Figure 9). Moreover, a landscape sprinkler head, located in the center of the west-facing slope, appears to have an underground leak causing the soil directly south of the sprinkler head to erode beneath the jute netting (Figure 10).
Figure 7. Three foot bamboo poles installed to secure jute in soft soil.
Figure 8. Slope continues to erode beneath jute netting.
Figure 9. Plant basin eroding away due to loose soil conditions.
Figure 10. Area directly beneath sprinkler head continues to erode.
Success on site was determined by reduction in presence of invasive species, recovery and recruitment of native vegetation and survival of outplanted seedlings.
Exotic eradication and removal at the five-acre site adjacent to Rosecrans National Cemetery was very successful considering no follow-up monitoring or maintenance was performed. Approximately 70 % of ice plant treated with herbicide was successfully exterminated. Golden Wattle and Lollipop tree resprouts have been reappearing along the fence line along with non-native pines. In order to prevent continued exotic resprouting, follow-up herbicide treatment is necessary. The overall re-emergence of exotics is minimal compared to their original size and abundance.
The U-shaped gully site has been determined a success through a survival count (Table 3). Plants showing low survival such as laurel sumac and wart-stemmed ceanothus typically have low transplant survival but high recruitment due to seed dispersal. A large number of recruits have sprouted, particularly goldenbush, lemonade berry, and California brittlebush, making up for lost outplantings and demonstrating the ability of autogenic repair, or site success.
Survival on site.
DISCUSSION AND RECOMMENDATIONS
Exotic removal and eradication at the five-acre site adjacent to Rosecrans National Cemetery was completed. Although additional maintenance or monitoring is not currently funded, it is suggested that continued herbicide application of resprouts be accomplished over the next 1-2 years. Without ongoing treatment, the long term success of the site is in jeopardy.
Due to the size of the U-shaped gully site, work on the project progressed quickly. Exotic plant and dead brush removal were completed as scheduled. Erosion control took longer than expected due to unforeseen complications with extremely loose soil conditions.
While a problem for erosion control, the moist, loose soil was perfect for planting. Immediately after outplanting the seedlings received a steady amount of natural rainfall during the month of February and into the middle of March, making supplemental irrigation unnecessary until early April.
During spring monitoring 2003, outplantings on the top of the south-facing slope were noted to be surviving well despite the rough soil conditions. A significant number of volunteers, particularly goldenbush, had sprouted over this entire area, already displaying successful recruitment (Figure 11). Outplantings on the bottom of the gully have thrived as well (Figure 12 and 13). The elimination of exotic germination should help them to out-compete future colonization of exotics through preemptive means. Additional monitoring to be conducted under a separate maintenance contract should reveal an increase in abundance and diversity of native plants on site.
Figure 11. Golden bush recruit.
Figure 12. Deerweed established in ice plant litter duff.
Figure 13. Outplantings at the bottom of the gully.
Overall project success was exceptional. All exotic species eradication and erosion control treatments were extremely effective; in fact, there have been no ice plant resprouts since removal. Total survival for the site was 86.8%. Survival will be monitored for an additional year to address and remedy any problems encountered. Cover will be calculated and reported under a separate contract. An overall survival result of 70% was the project's goal. Success at the species level was determined by survival and/or overall representation of the species composition on-site. In addition, a great number of volunteers, now present on-site have displayed immediate success and potential for future recruitment and colonization of native flora for the area.
In general, the site has demonstrated resiliency and potential. The ability
of many of the existing natives to establish on a once bare slope encroached
with ice plant and various dead brush and debris is encouraging. The quick recruitment
and fast growth of new seedlings demonstrates high success. The high level of
native recovery and recruitment and the low amount of exotic establishment on
site suggests that future outplanting will not be necessary in order to maintain
the level of success the site has accomplished.
Monitoring of erosion and erosion control will continue through a separate contract. The area on the west-facing slope directly beneath the sprinkler head will be closely monitored. Any further evidence of an underground leak in the irrigation system will be recorded and reported promptly. Exotic plant monitoring will also continue. Invasive species that sprout will be eradicated by the necessary method. It is expected that with a minimum of further maintenance and monitoring, this site will continue to be successful.
LIST OF PERSONNEL AND RESPECTIVE ROLES