Soil Ecology and Research Group last update June 10, 1999

Point Loma

Fleet Combat Training Center

Fleet Combat Training Center, Pacific (FCTCP) is situated on 91 acres located on the northwest corner of the Point Loma Peninsula in San Diego, California Approximately 40 percent of the area is developed with buildings and roads. The remaining area consists primarily of Maritime Succulent Scrub and Southern Maritime Chaparral vegetation communities. Undisturbed areas of vegetation on FCTCP are threatened by two main factors: human disturbance through the creation of roads, parking lots and buildings; and the intrusion of nonnative vegetation such as Acacia cyclops (acacia) Chrysanthemum coronarium (chrysanthemum) and Carpobrotus edulis(ice plant).

In 1997, the Soil Ecology and Restoration Group began restoration research on a 1.5 acre site on FCTCP. The area was previously cleared of acacia by the Youth Conservation Corps and left bare and prone to erosion with sediment building up on an adjacent road. Studies were established to test the effectiveness of the following biodegradable erosion control methods; jute netting, Curlex matting, pitting and mulch, heavy planting, mulch, coir fencing and no alteration (control). Methods were analyzed for their ability to prevent sediment loss and to enhance native plant seed germination. Additionally, the effects of various types of containers on outplanting success was measured. Plant container type plays a role In the ease of care in the greenhouse and initial survival of seedlings after outplanting. Container size, shape and material may also affect root growth and development, factors important in plant establishment. Important criteria in selecting containers are space efficiency, cost of the container, amount of soil needed and hours of labor necessary to maintain plants. This study combines results from four different restoration sites on Point Loma: one on Fleet Combat Training Center Pacific, two on United States Submarine Base and one on Space and Warfare Research Command. Soil properties on the site were also measured for changes in soil ammonium, pH, nitrate, total nitrogen, percent organic matter and soil texture over the one year period of the project.

Results from these studies will provide information for effective biodegradable erosioncontrol methods on future restoration projects at Fleet Combat Training Center, Pacific. In addition, information gained from the plant container study will be useful forgreenhouse and restoration managers in determining plant containers that are not onlysuccessful for coastal sage plant establishment, but also cost effective and space efficient.

Study Site

The 1.5-acre study site is located adjacent the northern fence of FCTCP bordering Point Loma Nazarene College. The site is separated into northern and southern sections by a service road running east and west. The southern section is one-half acre in size with a northeast facing slope of approximately 40-degrees, no vegetation and severe erosion gullies causing sediment to accumulate onto the service road. The one-acre northern section of the site faces southwest with a slope of 40-degrees. Along the top of the northern slope is a flat area that is approximately 25 feet wide and 500 feet long. This section of the site was covered with acacia trees and iceplant. Surrounding vegetation includes landscape plants to the east and undisturbed native Maritime Succulent Scrub and Southern Maritime Chaparral to the south.

Experimental Design
Erosion Control
The erosion control experiments consisted of seven 2-meter x 5-meter plots in wood frames established on the south slope. A nylon bag was placed at the bottom of each plot to catch sediment after each storm. Methods tested include: pitting and mulch; heavy planting ( 13 plants/plot), Encs-2 (Bonterra); jute netting: Curlex (American Excelsior); coconut fiber fences (Belton): and no erosion control (control). Both jute and Curlex mats were installed using 6-inch metal staples. Plots were hand seeded with locally collected native coastal sage seed (Table I ) measured to yield 100 live seeds per m- and covered with seven gallons of cocoa mulch to a depth of two to three cm on each plot to prevent seeds from being blown away. Sediment loss was measured after each storm using a spring scale. If sediment loss was less than 30 pounds, a Chatillion 30 pound scale with one quarter pound precision was used. For sediment build up in excess of 30 pounds, a Hanson 100 pound spring scale with a precision to 1 pound was used. Dry weight of the soil was determined by collecting approximately 10 grams of soil from the nylon bags and drying it in an oven at 60 degrees (F) for 24 hours. Seedlings were counted after four months to determine percent germination.

A second set of erosion control experiments were set up on the 40 degree slope on the northern section of the site. Six test plots, 8 feet wide by 25 feet long, compared the effectiveness of jute netting and Curlex. Additionally, four-inch deep ditches were constructed for the installation of 10 inch wide coconut fiber fences. Once fences were laid the ditches were backfilled. Twelve inch wooden stakes were used as anchors with the fences tied to the stakes with twine.

Container Planting

Five hundred and twenty-one coastal sage seedlings grown at the San Diego StateUniversity greenhouse were planted between 22 December 1997 and 16 March 1998(Table 3). Approximately 101 seedlings were planted on the south slope and theremaining 420 on the north area. The two hundred and twenty-two seedlings used in the container study are included in this number. The remaining 483 plants used in thecontainer study were planted on the US Submarine Base and SPAWAR. Basins with aradius of approximately I2 cm were created around each plant to hold water. Plantprotection in the form of Treepees was placed on all seedlings less than I2 centimeterstall to prevent herbivory.

Results
Total rainfall during the erosion control experiments (December 1997 through April 1998) was 14.1 inches as measured by rain gauge on Fleet Industrial Supply Command on the east side of the Point Loma Peninsula. Cumulative sediment loss for each erosion control treatment was converted to pounds of sediment lost per acre per inch of rain. The least amount of sediment loss, 322 pounds, occurred with the Curlex blanket. The greatest amount of sediment loss (9,474 pounds) occurred in the pitting and mulch plots, almost double the amount (4,994 pounds) of the control.

Jute versus Curlex experiments on the north side of the road also proved Curlex netting toreduce sediment loss more effectively than Jute netting ( 346 pounds and 249 pounds respectively). Coastal sage seed germination was greatest under the cocoa mulch alone treatment at 13.1 percent as compared to control with 0.1 percent. The Curlex germination was also high at 11.2 percent.

Overall survival of container planted seedlings as of 16 September 1998 was 81 percent (Table 4). Malacothamnus fasciculatus had the highest percent survival at 100% and Euphorbia misera and Mammillaria dioica the lowest at 41 percent and 25 percent respectively. Overall total percent cover on the revegetation site was approximately 20 percent.

Based on the results of the study, an attempt was made to combine the space saving quality of plant bands and higher percent survival of plastic containers. Plastic plant bands were constructed by cutting square plastic rain gutters into 8" x 2.5" x 2.5" containers. Seedling volume was measured in the paper plant bands and plastic plant bands in the greenhouse after three months growth. Plastic plant bands showed an almost twofold increase in volume over the paper plant bands.

Soil analysis tests showed soil texture on the north side of the road as sand and the south of the road as sandy loam. Soil pH and percent organic matter did not change from October 1997 through July 1998 so the three sample dates were averaged. Total nitrogen was higher on the north side of the road, but decreased over time on both sides of the site.

Discussion
These biodegradable erosion control studies appear to demonstrate that Curlex coconut fiber fences with mulch and jute netting are the most effective measures in preventing sediment loss under conditions of high rainfall for Southern California. Curlex matting reduced erosion significantly better than jute netting. Curlex and Cocoa mulch alone provided the greatest germination rate for coastal sage seeds, probably by keeping the soil moist and preventing seeds from blowing away. However, Curlex does have its drawbacks. Curlex matting is held together by a photodegradable plastic mesh that becomes unsightly over time. Curlex is also not as durable under foot traffic as jute netting.

Initial plant survival was successful with overall survival at 81 percent. Survival of Ceanothus verrucosus and Cneoridium dumosum was above average compared to previous experience with these species. Low survival for Ferocactus viridescens was most likely caused by small seedling size(2-3 cm. diameter). There was also a visible difference in size of plants between the north and south side of the road within one month. Seedlings m the loamy sand found on the south side of the road were smaller (by approximately 25 cm. ) in general than the seedlings growing in the sandy soil on the north side of the road. A possible explanation could be higher compaction on the south side of the road due to grading by heavy equipment before the project began or, more probably, the greater amount of available nitrogen found on the north side of the road providing an initial growth spurt for the newly planted seedlings.

The container outplanting study demonstrated that plastic one gallon pots provided the greatest transplant success (89%) of the containers tested. Other plastic containers tested such as green and black square four inch containers provided success above 75% while using less space than one gallon containers or half highs in the greenhouse. Survival from the peat pots was low and required the greatest amount of maintenance. Liners are small and require little greenhouse space and effort when planting, though transplant survival was barely above 50%. Survival rate for plants from half highs was not any greater than in plant bands, while the cost and amount of space required for half highs is near double that of plant bands. It is possible that a major reason that paper containers have lower success than plastic is that they absorb and maintain water more than the plastic leading to the development of root rot. Plastic plant bands appear to have promise by providing better plant growth than paper and are also being efficient space savers.

Soil analysis indicate that the northern and southern sections of the restoration sites have similar pH readings, both slightly basic, possibly indicating the effects of salt spray. Organic matter is slightly higher on the northern section, but not significantly different. This is reasonable since the northern section had previously been covered with a layer of eucalyptus leaves which should add to the organic matter content of the soil. The nitrogen readings, however, indicate a definite difference between northern and southern soils. There is a tremendous swing in available nitrogen levels, for both ammonium and nitrate, for the northern section while the available nitrogen levels for the southern section show only a small change over time. Total nitrogen on the other hand remains fairly equal for both sites, indicating that the swing in levels of nitrogen are internal changes only with no external inputs appearing. High available nitrogen swings with no actual changes in total nitrogen indicate a soil dominated by easily mineralized carbon compounds, such as annual exotic grasses and ice plant. Low available nitrogen swings, such as found on the southern site, indicate a soil mineralization system dominated by highly recalcitrant carbon compounds, such as native perennial shrubs. The soil analysis results would therefore seem to indicate that the southern site has experienced much less impact to its soil ecosystem than the northern site. This means that more time and effort may be required to restore the northern site to a coastal sage scrub habitat than will be required for the southern section of the site.

Conclusions and Recommendations
Proper selection of erosion control methods depends upon slope steepness, slope aspect,soil texture, amount of foot traffic, revegetation methods available and budget. In thisstudy, ground covers such as jute netting and Curlex provided the best protection forpreventing sediment loss. However, erosion control materials with plastic, such asCurlex, are not highly recommended due to the unsightly appearance created as theydegrade. Slopes experiencing heavy foot traffic are best covered with jute netting or anequivalent durable material.

Cocoa mulch is highly recommended as an amendment to be added when direct seeding is used. The mulch provides cover to retain soil moisture and prevent seed from blowing away with only a thin application (approximately 2-3 cm. in depth).

One gallon plastic containers were the most efficient of the containers tested. Liners proved to have the lowest survival rate, therefore seedlings in liners purchased from a retail greenhouse should be immediately transplanted to larger pots for use at a later date. Though half highs have proven extremely successful in the desert, smaller containers appear more efficient for coastal sage revegetation, costing less and requiring less greenhouse space. Although no one container is suitable for all conditions (Bainbridge et al., 1995 ). plastic containers appear to yield the highest transplant survival rate for coastal sage plants. Plastic plant bands would combine the space efficiency of paper plant bands and the higher survival rates of traditional plastic containers. Further research in the manufacturing and use of plastic plant bands could prove to be highly beneficial in saving space and reducing costs.

Implementation of a native plant revegetation project during the El Nino yeardemonstrated both benefits and drawbacks. Many plants received above averageprecipitation allowing them to thrive. However, some plants, such as cactus andsucculents, received too much water as the soil became saturated due to inadequatedrainage in some areas. This may have led to the low survival rate experienced by cactusand succulents which are adapted to low rainfall. Excessive precipitation and poor drainage possibly resulted in root rot and low survival rates. During future El Nino years,basins around all plants are not recommended due to saturation of the soil and lack ofdrainage. These should be replaced with deep pipes, which will also improve wateringefficiency during the summer.

Native plant restoration on this site has demonstrated initial success. If the winter of1998/1999 produces at least average rainfall, plants should be able to survive thefollowing summer. However, if rainfall is low during the winter, container plant survivaland percent cover may suffer the following summer (1999) without supplementalirrigation. Additionally, control of exotics for a second year would assist in the recoveryof the site.

References
Bainbridge, D. A., M. Fidelibus and R. MacAller. 1995. Techniques for plantestablishment in arid ecosystems. Restoration and Management Notes. 13(2):190-197.