Soil Ecology and Research Group last update August 5, 2003

IMPLEMENTATION REPORT

INVASIVE SPECIES CONTROL AND
NATIVE HABITAT ENHANCEMENT
Veldt Grass and Mustard Sites

NALF SAN CLEMENTE ISLAND

Background
Two exotic species have gained a foothold on the island and are in the process of expanding their range at the expense of the surrounding native habitat (Figure 1). The first species, Ehrharta calycina, or veldt grass, is a native of south Africa that has become established at the north end of the island. The veldt grass is currently spreading into the undisturbed native maritime desert scrub that is dominated by Lycium californicum (box thorn). The second exotic species, Brassica nigra, or black mustard, has become established along China Canyon Road on the southern end of the island and has quickly spread into the adjacent native grasslands.

Initial estimates of the sizes of these populations were approximately 25 acres for the Brassica nigra site and 6 acres for the Ehrharta calycina site. Favorable weather conditions and additional discoveries have increased these population estimates significantly. The current size estimate for the Brassica site is approximately 45 acres. Two additional Ehrharta calycina sites have been identified of approximately 1.6 acres and 3.4 acres and the fuel farm site has been reassessed at approximately 12.4 acres.

Methods
To prevent the continued spread of exotic species in both these areas, the veldt grass and black mustard were/are being removed and replaced with appropriate native species. Appropriate native species for both grassland and maritime desert scrub habitats have been grown at the San Clemente Island Native Plant Nursery from locally collected seed. Local soil from adjacent undisturbed habitat has been used to inoculate the seedlings with necessary mycorrhizal fungi during their germination and early growth.

A strong showing of native annual plant species at the Brassica nigra site caused a reassessment of initial plans to carpet spray the area with herbicide. Higher than average rainfall in the current year (150% above average) resulted in the germination and growth of a dense understory of native forbs including Trifolium palmeri, T. fucatum, Lupinus succulentus, Calandrinia ciliata and Stebbinsoseris heterotheca throughout much of the area supporting Brassica nigra. Therefore, a combination of herbicide and mechanical treatments were employed to reduce the population of Brassica and mitigate the collateral damage to the reproductive success of the native species. Areas of dense Brassica populations with little native understory and areas along the roadsides were sprayed with herbicide, while string trimmers were employed to remove the flower and seed heads of the Brassica before viable seed could be produced in areas with strong native growth.

Once each site has been prepared as described above, approximately 400 seedlings per acre are being out-planted. A temporary drip irrigation system will be established for the maritime desert scrub seedlings at the veldt grass site to assist them through the first hot dry summer. This will also allow supplemental water to be directly applied to each seedling, decreasing the germination of weedy species that is prevalent with overhead or flood irrigation. This system will be removed after the first year. No supplemental irrigation system will be used for the grassland site since the grass seedlings will become established much quicker than the maritime desert shrubs.

Both sites will be maintained and monitored during the first year for additional weed control, if necessary, and seedling survival and growth. Two 100 meter long transects at the veldt grass site and five 100 meter long transects at the black mustard site will be established upon completion of planting. These will be used in conjunction with a modified California Native Plant Society (CNPS) sampling protocol to analyze restoration success through the determination of species diversity and cover.

Progress of Work
Weather conditions and restricted site access has delayed the completion of this project and work is ongoing. Project implementation began in July 2002 with the collection and propagation of native seed. Nursery production and maintenance of native plants has continued to date.

Figure 1. Location of restoration sites.

Brassica Site Summary
Progress to date includes the treatment of approximately 31 acres of Brassica nigra (Table. 1). Two treatments have been employed. Herbicide applications have been made in areas supporting few native species and along roadsides (Figures 2), and Brassica flower/seed heads have been cut to reduce the production of viable Brassica seed in areas supporting significant native plant populations (Figure 3). A total of 9.8 acres were sprayed with 2% glyphosphate solution. A total of 174 gallons of herbicide solution were applied to the site. Special emphasis was made to reduce the Brassica population along the roadside, as roads serve as corridors for the dispersal of seed. Herbicide application occurred during the elongation and flowering stage of the target species phenology and resulted in high kill (Figure 4). Figure 5 delineates treatment dates and locations for the Brassica site.

Table 1.
Summary of Brassica site treatments

Figure 2. Herbicide application at Brassica nigra site.

Figure 3. Cutting the flower and seed heads of the Brassica nigra before viable seed.

Figure 4. Brassica nigra site post-treatment.

Figure 5. Brassica nigra treatment site.

Ehrharta Site Summary
Progress to date includes the treatment of approximately 17 acres of Ehrharta calycina and the installation of approximately 1300 native plants. A total of 17.4 acres were sprayed with 2% glyphosphate solution. A total of 322 gallons of herbicide solution were applied to these three sites (Table 2).

Table 2.
Summary of Ehrharta site treatments

Approximately 1800 native maritime desert scrub plant species were installed at the West Cove and Chad's Bluff sites, June 5-9 and June 19-21 respectively (Table 3). The planting site were prepared by first clearing a continuous strip approximately 1.5 - 2.0 meters wide through vegetation and duff with a gas powered string trimmer. These clearings facilitate the installation of irrigation lines and reduce resource competition for plantings. Irrigation tubing was stretched the length of the clearings and drip emitters were installed. Planting holes were dug at approximately one-meter intervals in the center of the cleared strip. Digging was done primarily with a six-inch diameter power auger and cleared with a post-hole digger.

Prior to planting, each hole received approximately 1.0-1.5 gallons of water via the irrigation system. After the water was allowed to percolate, plants were installed in each hole and a shallow berm of approximately 0.5-meter was constructed around each plant to retain irrigation water. After installation, each plant received an additional 1.0-1.5 gallons of water. Restricted site access has delayed the completion of plantings at the Ehrharta Fuel Farm site. It is expected that access will be made available to complete these plantings by July 31, 2003. Figure 6 delineates the Ehrharta treatment sites.

Table 3.
Species and quantities planted at Ehrharta treatment sites.

Figure 6. Ehrharta calycina treatment sites.

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Scope of Work (October 29, 2002)

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