Soil Ecology and Research Group last update September 29, 2003

BALLFIELD INSTALLATION REPORT FOR THE
INVASIVE SPECIES CONTROL AND NATIVE HABITAT
ENHANCEMENT AT FLEET COMBAT TRAINING
CENTER, PACIFIC NAVAL BASE POINT LOMA

Background

The primary forms of habitat disturbance on Fleet Combat Training Center, Pacific (FCTCP) are water erosion and exotic plant species such as Eucalyptus spp., Acacia spp., Carpobrotus spp. and smaller Mediterranean annual plants such as Bromus spp. and Avena spp. Both of these disturbance types result from impacts sustained during the construction of roads, facilities, and utility corridors. Both types of disturbance can lead to the degradation of nearby undisturbed areas, increasing the loss of already scarce native habitat.

The dominance of exotic plant species is apparent in the areas adjacent to large expanses of undisturbed habitat that are susceptible to invasion by exotic species. The western slope of the recreational field at FCTCP is an area of several acres dominated by Chrysanthemum coronarium, Carpobrotus edulis, Atriplex, semibaccata, Salsola tragus, and exotic annual grasses. Over the past two years a dominant exotic, Acacia cyclops, has been removed from the site leaving large areas of the slope bare or lightly vegetated, thus making it highly susceptible to erosion.

Indications are already apparent that exotic invasion is occurring as non-native grasses and other exotic species are beginning to appear in the native habitat found on the slope west of the recreation field. This restoration site, called the Ballfield site (Figure 1), is slightly under one acre in size and required timely restoration efforts in order to prevent the further spread of exotic species, the subsequent loss of additional native habitat, and the loss of soil due to the effects of erosion. Such impacts were already being seen in the U-shaped gully located northwest of the recreational field, where erosion gullies are forming along the northern side.

Due to the condition of the Ballfield slope, restoration efforts were conducted in three phases. The first phase was the eradication of exotic plant species. The second phase was the establishment of biodegradable erosion control materials and the third phase was the revegetation of the slope with native coastal sage scrub and maritime succulent scrub species germinated from locally collected seed. The Ballfield site will be maintained and monitored for one year after planting. Table 1 provides the timeline for all restoration activities.

Table 1.
Timeline of restoration activities.

Site Preparation

Eradication of Exotic Plant Species
Soil Ecology and Restoration Group (SERG) personnel prepared the Ballfield site for out-planting by eradicating all exotic plant species that occurred on or immediately adjacent to the site. Located on site were large exotic plant species such as Acacia trees, an Arundo donax stand (Figure 2), and a palm tree (Figure 3); and smaller exotic plant species such as C. edulis, C. coronarium, A. semibaccata and S. tragus. The larger exotic plant species were partially cut down by hand and the remaining stumps were sprayed with herbicide (Roundup-Pro). The smaller exotics were removed by hand or with a weed-whacker. Located adjacent to the site (northwest side) were two Pittosporum spp. trees, which were also removed using the same methods as the larger exotics.

Figure 2. The Arundo stand on the northern side of the site.

Figure 3. Palm (left and center) and Acacia (right corner) tree cuttings.

Erosion Control
Once all exotic plant species were removed, the slope became highly susceptible to soil erosion. Therefore, biodegradable jute netting was installed to control erosion (Figure 4). Jute was stapled onto the site in a patchwork fashion to better contour the slope and to prevent gullies from forming between the sheets of jute (Figure 5). The jute was cut lengthwise in pieces ranging from 4-6 feet. Six-inch steel staples were used to attach the jute and the borders of each jute piece overlapped neighboring jute pieces by approximately 2-3 inches.

Figure 4. SERG personnel installing jute onto the slope.

Figure 5. Jute netting installed in a patchwork fashion.

Revegetation

Propagation of Native Plants
SERG personnel collected seed from Point Loma to propagate native coastal sage scrub and maritime succulent scrub plant species in 2”, 3", or 4” plant bands. The size of the plant band used depended upon the rate of growth of each species. Native seeds were propagated in the SERG greenhouse at San Diego State University. The quantity of container plants grown was sufficient enough to achieve densities similar to those of native plant species in undisturbed coastal sage scrub and maritime succulent scrub near the restoration sites within three years after planting. Two hundred plants were out-planted to meet this objective.

A reference transect was established in an undisturbed habitat north of the Ballfield site. The reference transect is shown in Figure 1. Point-intercept monitoring was performed on this transect line to determine the species composition of a nearby undisturbed area (see Appendix I for results). Data collected from the transect was used to determine the percent cover of each native plant species, which in turn helped determine the number of each species needed to be grown and planted. Table 2 is a list of plant species and quantities out-planted on the site. The following is a list of plant species that were originally included in the list, but were unsuccessful in germination: Artemisia californica, Cneoridium dumosum, Dudleya lanceolata, Gnaphalium bicolor, Lessingia filaginifolia, Rhamnus crocea, and Viguiera laciniata.

Table 2.
List of species, quantities, and container sizes of plants out-planted on the Ballfield site.

Out-Planting
During February 2003, SERG personnel out-planted 200 seedlings (Figure 6). Holes were dug with shovels and plant basins were molded by hand. Plant protectors, either treepees or mesh tubing, were placed around each seedling to discourage herbivory and to maintain a greenhouse-like microclimate (Figure 7 and 8). The mesh protectors were placed mainly around younger, smaller seedlings that required more direct sunlight. Immediately after planting, each seedling received approximately 2 gallons (4 liters) of water.

SERG personnel installed a temporary drip irrigation system that delivers water directly to the basin of each seedling to improve plant survival through the first dry season after planting (Figure 7 and 8). The drip irrigation system consists of 1/2" drip tubing and 8 liters/hour emitters. The drip-line was installed in February 2003, but became operational in April 2003 because the rains in February 2003 and March 2003 made supplemental irrigation unnecessary.

During supplemental irrigation, the drip-line gives each plant approximately 1 gallon (2 liters) of water. Drip irrigation was used instead of overhead or flood irrigation to decrease the germination of weedy species and hand watering will be avoided to prevent soil compaction and additional soil erosion on the slope. The drip irrigation system will be removed at the end of the first year after planting.

Figure 6. SERG personnel out-planting seedlings.

Figure 7. Completed installation of jute netting, drip-line, plants, and plant protectors.

Figure 8. South side of the Ballfield site.

Maintenance and Monitoring

The Ballfield site will be maintained and monitored for one year after planting. From February 2003 to February 2004, the plants will be watered twice each month and each basin will receive approximately 1 gallon of water. Any damage to the drip irrigation system will be repaired and the site monitored for reoccurring weeds. Weeds will continue to be removed by hand or sprayed with herbicide as necessary. Since being removed in October 2002, herbicide has been applied twice to the Acacia tree stumps and the Pittosporum tree stumps. The palm tree stump was not sprayed because it was considered non-viable after being cut down. The rains in February and April 2003 increased the growth of herbaceous weeds throughout the site; therefore, herbicide was applied in those months. Herbicide was also applied four times on the Arundo donax stand because new shoots continue to grow (Figure 9).

Plant survivorship was recorded in May 2003. Table 3 lists the species survival count and survivorship percentage. Of 200 plants, 17 died. Approximately 5-8 of those plants were "washed" off the slope due to erosion problems caused by floodwater (in February 2003) running off the construction site adjacent to the project site. The remaining 9-12 plants died from natural causes.

Figure 9. New Arundo shoots growing out of the jute.

Table 3.
List of species out-planted in February 2003.

Observations Made and Problems Encountered

During the late February 2003 rains, two existing gullies on site were eroded further as a result of the parking lot construction on the ballfield. Pooling water, east of the ballfield running track, created flowing streams down the gullies (Figure 10). These streams pushed soil, rocks, and other debris down the slope, which pulled the jute netting off the site (Figure 11). The pieces of jute that were pulled off completely were located mainly at the end (west border) of the site. While other pieces toward the top (east border) remain partially attached, but filled with eroding soil and debris (Figure 12).

Another problem caused by the rains occurred in early March 2003. The rains created a mudslide that covered a third gully, which affected a section of jute that is approximately 5 m x 22 m (Figure 13 and 14). In this section, 5-8 plants were "washed" away and a section of drip-line was displaced (Figure 14 and 15). The drip-line has been re-attached and another layer of jute was installed to cover the mudslide section for reinforcement (Figure 16). In addition, pieces of rolled jute, mimicking wattles, have been placed along the fence above the gullies to slow the flow of future pooling water.

The gravel parking lot that is now located on the Ballfield site is crowned so water will continue to runoff the lot and onto the project site. No considerations have been made for drainage of the parking lot, leaving the restoration site open to future damage from runoff similar to what occurred during the months of March and April of this year. If corrective action regarding the parking lot drainage is not accomplished, the restoration site will continue to be impacted by the heavy runoff and erosion problems will be inevitable.

Figure 10. Pooling water from the construction site, east of the running track, flowing
into the north gully.

Figure 11. The top of the north gully. Pooling water from the construction site pushed
rocks and debris into the gully, pulling the jute off the slope.

Figure 12. Piece of jute partially attached to the slope and filled with soil, rocks, and
debris.

Figure 13. The mudslide caused by the March 2003 rains as viewed from the top (east)
of the site.

Figure 14. The March 2003 mudslide with two fallen plant protectors (center and left) as
viewed from the west.

Figure 15. Plants and plant protectors "washed" away by the mudslide.

Figure 16. The reinforcement of the mudslide section with another layer of jute netting.

Future Proposed Site Visits

Supplemental irrigation of plants will continue twice each month from May 2003 until February 2004. The weeds on site will be continuously monitored for re-growth and herbicide will be re-applied as necessary. In addition, plant protectors constraining the morphology of a plant will be removed.

The success criteria will be determined by percent plant survivorship. At the end of the monitoring period, container plant survivorship will be 60%. Since survivorship is currently 92% (Table 2), the plants "washed" away in the mudslide were not replaced. If survivorship is below 60%, SERG will plant additional container stock and monitor the site for another year to ensure that survivorship reaches 60% of the number of plants installed during the first planting season.