last update April 15, 2001
Space and Warfare Research (SPAWAR), previously Naval Command, Control, and Ocean Surveillance Center (NCCOSC), is the largest of the naval commands situated on the Point Loma Peninsula in San Diego, California (Figure 1). SPAWAR has divisions located on the eastern and western sides of the peninsula as well as the southern tip for a total of 500 acres (Point Loma Natural Resources Management Plan, 1994). Three hundred acres of SPAWAR land are located in the Point Loma Ecological Reserve designated for conservation and preservation (Natural Resource Conservation, 1995). In 1996, approximately 10 acres of land located on the western side of the peninsula was sold to the City of San Diego Wastewater Treatment Plant to build two water tanks and a water pipeline. In exchange, SPAWAR received funding to restore and enhance areas of the reserve. As part of this agreement, a three-acre area north of the water tanks and west of Fort Rosecrans Nationa] Cemetery was selected for restoration and a letter of agreement was written between the Soil Ecology and Restoration Group (SERG) from San Diego State University and the United States Navy to conduct research on native plant revegetation on this site.
City maintenance crews removed invasive exotic vegetation such as Acacia cyclops (acacia), Carpobrotus edulis(ice plant) and Myoporum laetum(myoporum) leaving the slopes bare and prone to erosion. SERG research included experimenting with erosion control methods such as; jute netting, Bonterra ENCS-2 straw matting, punched straw, Excelsior Curlex blanket, coir fencing and straw flake dams. Testing was done under extreme weather conditions for Southern California due to an El Nino during which San Diego received almost double the average annual precipitation. Soil samples of the site and surrounding undisturbed area were analyzed for soil texture, percent organic matter, nitrate. ammonium, total nitrogen and pH. The slopes w ere container planted with 1095 maritime succulent scrub seedlings to match the surrounding undisturbed area. Container size and type of each plant was noted and outplanting survival was monitored to determine the effects that nursery containers have on outplanting survival. In addition, a comparison of percent cover of native and exotic vegetation was made between hydroseeding and container planting.
Monitoring and maintenance of the site continued through October 1999. The results of these studies will provide information for future restoration on Point Loma while enhancing the land in the reserve.
The restoration site is a three-acre area located on the west side of the Point Loma peninsula. Fort Rosecrans National Cemetery on Cabrillo Monument Road borders the site to the east, the San Diego City Wastewater Treatment Plant pipeline to the south and native undisturbed maritime succulent scrub vegetation to the west. Approximately two- thirds of the site is on a 90 foot long, 40 degree, northwest-facing slope. The slope is separated by a ten foot wide shelf into two sections: 50 feet on top and 40 feet below. The second slope is 20 feet long facing southeast at an angle of 35 degrees. The area was covered in ice plant, acacia and myoporum trees. The surrounding area is dominated by Cneoridium dumosum (Spice bush), Rhus integrifolia (Lemonadeberry)Eriogonum fasciculatum (Flat-top buckwheat) and Euphorbia misera (Cliff spurge). There are also populations of the rare cactus species Opuntia parryi var. serpentina (Snake cholla) and Ferocactus viridescens (Fish hook cactus).
In July 1997, the City of San Diego maintenance crews removed all exotic vegetation, leaving a small portion of dead ice plant at the bottom of the northwest-facing slope. Two hundred and fifty feet of PVC pipe was installed by SERG from the southeast corner of the cemetery fence along the top of both slopes to supply water for a drip irrigation system.
Eighteen 23 feet wide by 48 foot long plots were set up testing jute netting, Curlex matting(AmericanExcelsiorCompany),Belton ENCS-2 straw matting and punched straw on the upper portion of the northwest facing slope. The same design was used for the lower portion of the slope, except plots were 40 feet long instead of 48 feet. The jute, Curlex and ENCS-2 were installed using six inch metal staples three to four feet apart. Punched straw was installed on the slope in a fish scale pattern using a shovel to create a slot for the straw.
The southeast-facing slope was divided into three test plots 25 feet ~vide by 20 feet long. These plots tested coir fences with cocoa mulch, straw flake dams and coir fences without mulch. Four-inch deep ditches were constructed for the installation of 10 inch wide coconut fiber fences. Once fences were laid the ditches were back-filled. Twelve inch wooden stakes were used as anchors with the fences stapled to the wooden stakes using a staple gun. Cocoa mulch was surface applied above the coconut fiber dams to a depth of approximately 1 inch. Ditches, 3-4 inches wide and 6 inches deep, were created to install the straw flake check dams. Straw flakes were peeled off bales and placed vertically in the ditches, back filled, and hand compacted leaving approximately 8 inches of straw above ground.
The jute, Curlex, ENCS-2 and punched straw methods were analyzed for container plant survival and erosion control. Straw flake dams and coconut fiber dams were analyzed for reduction of sediment loss. Due to the large size of the plots and the length of time required for planting, sediment loss was measured qualitatively by the amount of sediment at the base of the slopes and the formation erosion gullies.
A comparison of exotic and native vegetation cover was conducted between the container planted restoration site and an adjacent hydroseeded area. The pipeline to the south of the restoration site was hydroseeded by the City of San Diego in December 1997, concurrent with container planting on the restoration site. Three random measurements were made in July 1998 using a ten square-meter quadrat separated into one meter2 grids to determine percent cover of native and exotic plants sprouting in the hydroseeding area. The same sampling procedure was used to take three random samples on the restoration site: one immediately adjacent to the hydroseeding area; one in the middle of the site approximately 70 meters away from the hydroseeding; and one at the far end of the restoration site approximately 300 meters away from the hydroseeding site. Percent cover of native and exotic species in the hydroseeding area and in three sections of the restoration sites was calculated and graphed.
Three soil samples were taken from the restoration site and three from adjacent undisturbed vegetation in August 1997, December 1997 and May 1998. All of the December and May samples were analyzed for total nitrogen, organic matter, phosphate, ammonium, nitrogen, pH and soil texture. The August samples were sent to A&L laboratories in Modesto, California for analysis of percent organic matter, pH and nitrate.
A total of 705 plants from twelve coastal sage species were grown in eleven different nursery containers (Table I ). Three-hundred and eighty-two of these seedlings were included in the 1095 seedlings planted on the SPAWAR restoration site. The remaining 323 seedlings were planted on 2 sites on the United States Submarine Base and I site on Fleet Combat Training Center Pacific, both located on Point Loma. The containers were made of either plastic, paper, peat or PVC pipe. The plants were individually labeled on four sites on Point Loma, California during Fall/ Winter 1997/1998. After approximately three months, plant survival was measured. The average survival from each container type was calculated and graphed.
Table 1. Container types used in outplanting
|Container Name||Material||Manufacturer||Dimensions (in.)*|
|Peat pot||peat||Jiffy Products||12.6 x 4|
|Half high||PVC||SERG||28 x 18|
|One gallon||plastic||McConkey||28 x 7.5|
|Plant band||paper||Monarch Manufacturing Inc.||2 x 2 x 14
3 x 3 x 10
2 x 2 x 8
|Four inch black||plastic||McConkey||3.5 x 3.5 x 6|
|Four inch green||plastic||McConkey||4 x 4 x 3.5|
|Liner||plastic||McConkey||2 x 2 x 3.5|
|Tall one||plastic||Stuewe & Sons Inc.||4 x 4 x 13.5|
|Three inch green||plastic (thin walled)||McConkey||3 x 3 x 3.5|
*dimensions on square containers are length x width x height.
dimensions on round containers are circumference x height.
A total of 1095 coastal sage seedlings were planted on the revegetation site between October 1997 and April 1998 (Table 2). Plants were grown at the San Diego State University greenhouse and Tree of Life Nursery from seeds collected on Point Loma.
Table 2. Native plant species container planted
|Species||Common Name||Number Planted|
|Artemisia californica||California sagebrush||125|
|Baccharis sarothroides||Broom baccharis||30|
|Ceanothus verrucosus||Wart-stemmed ceanothus||62|
|Cneoridium dumosum||Spice Brush||23|
|Dudleya lanceolata||Coastal Dudleya||4|
|Encelia californica||California encelia||127|
|Eriogonum fasciculatum||Flat-Top buckwheat||119|
|Euphoribia misera||Cliff spurge||112|
|Ferocactus viridescens||San Diego barrel cactus||59|
|Malacothamnus fasciculatus||Chaparral mallow||39|
|Malosoma laurina||Laurel sumac||64|
|Mammillaria dioica||Fishhook cactus||13|
|Opuntia littoralis||Coastal prickly pear||11|
|Opuntia parryi var. serpentina||Snake cholla||50|
|Pinus torreyana||Torrey pine||2|
|Rhus integrifolia||Lemonade Berry||62|
|Salvia mellifera||Black sage||114|
|Yucca schidigera||Mojave yucca||4|
Approximately 600 seedlings planted without protection from herbivory and weather dried out and lost their leaves immediately after planting due to high winds from the west. Treepees and tubex were placed around these plants, allowing them to recover and resprout new leaves. The remaining 495 seedlings were covered during planting.
Maintenance and Monitoring
A drip irrigation system using 1/2 inch supply tubing connected to 1/4 inch drip tubing and one gallon per hour drip emitters was installed to approximately 1000 plants. Cacti and dudleya were not connected to the drip system because excess water during the summer can cause root rot due to the drought tolerant nature of these plants. Fifteen centimeter long deep pipes were buried with each plant to direct the water from the drip system to the plant roots and prevent run off. Water to the drip system was turned on for one hour every two weeks between May 1998 and October 1998. The site was weeded monthly from August 1997 through April 1998 and twice a month May 1998 through October 1998. Treepees and tubex were removed once plants had outgrow them.
Sediment loss and erosion gully formation on the erosion control plots was least on the Curlex mat plots. Punched straw plots experienced the greatest amount of erosion with sediment build up of 20 centimeters at the bottom of each slope with 3 to 10 erosion gullies, 6 to 8 cm wide, forming per plot. Container plant survival was greatest in the Curlex matting at 100 percent suNival and lowest in the punched straw with 69 percent survival (Figure 2). The difference in container plant survival between the jute netting and ENCS-2 was minimal at 86 and 87 percent respectively.
Figure 2. Percent survival of container planted seedlings in various erosion methods.
Coir fencing with cocoa mulch and without cocoa mulch and the straw flake dams performed equally well in preventing sediment loss measured by a lack of sediment build up at the bottom of the slope and the absence of erosion gullies. There was no significant difference in container plant survival between the coir fencing with and without cocoa mulch and the straw flake dams.
After two years, the jute netting showed less wear than the ENCS-2 and Curlex netting while the punched straw was almost completely degraded (Figure 3). Of the two fencing material
Figure 3. Jute netting (top), ENCS-2 (middle) and punched straw (bottom) in October 1999.
tested, the coir netting remained intact better than the straw, but the fencing still remained functional.
The greatest number of exotic seedlings sprouted in the hydroseeding area and on the restoration site adjacent to the hydroseeding (Figure 4). The least number of exotic seedlings sprouted on the north section of the restoration site, which was the farthest from the hydroseeding area Resprouting of acacia seedlings is the greatest problem on the site, howeverBrassica nigra and Carpobrotus edulis are also prevalent (Table 3). The hydroseeding also proved to be a poor erosion control method yielding erosion gullies of up to 18 centimeters wide and 15 feet long (Figure 5)
Figure 4. Native and exotic plant species comparison between
hydroseeding and restoration site.
Table 3. Exotic plant species found in
hydroseeding area and on restoration site.
|Atriplex semibaccata||Australian saltbush|
|Avena sp.||Wild oat|
|Bromus rubens||Red brome|
|Carpobrotus edulis||ice plant|
|Melilotus albus||White sweet colver|
|Mesembryanthemum crystallinum||Crystal ice plant|
Figure 5. Comparison between area container planted by SERG and area hydroseeding by City of San Deigo contractor in September 1998.
Soil test results demonstrated a significant difference in pH between the restoration site and the surrounding undisturbed area. The pH of the soil in the disturbed area was alkaline with a mean of 7.4. The mean pH of the surrounding undisturbed area was acidic at 5.4 (Figure 6). Percent organic matter was higher in the undisturbed area, however not significantly. Nitrate in the soil increased during the spring months, while the ammonium decreased. Total nitrogen increased on the undisturbed plots and decreased slightly on the site. There are only two data points for ammonium and total nitrogen due to the absence of tests run by A&L laboratories. Soil texture in both the undisturbed area and disturbed site was loamy sand or sandy loam.
Plant survival was highest in plants which were grown in the plastic pots: 1 gallon (89%), Tall Ones (75%), 4 inch green (81%) and 4 inch black (79%). The average survival in the half highs (75%) was the same as the paper plant bands. Peat pots are easily transplanted, but transplant survival (71%) was lower than the paper containers. In addition, peat pots required the most maintenance of all containers tested due to increased evaporation, requiring water twice daily. The lowest plant survival was from the liners (57%) (Figure 7).
Seedlings grew faster in plastic containers in the greenhouse, but paper plant bands are more compact and save space. Based on the results of this 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 for both paper plant bands and plastic plant bands in the greenhouse after three months growth. Plastic plant bands demonstrated an almost two-fold increase in volume over the paper plant bands (Figure 8).
Figure 6. Results of soil nutrient tests comparing the disturbed restoration site and surrounding undisturbed area.
Figure 7. Container plant survival of seedlings outplanted from eleven different plant containers. The first four are above 75%.
Figure 8. Comparison of plant volume in paper and plastic containers.
Overall plant survival of container plants on the revegetation site was 71 percent (77 live plants out of 1095) as of 30 September 1998 (Table 4). Percent cover of native vegetation ranged from approximately 15 percent to 25 percent (Figure 8).
Table 4. Percent survival of container plants
as of 30 September 1998.
|Species||Common name||Percent survival|
|Artemisia californica||California sagebrush||88|
|Baccharis sarothroides||Broom baccharis||90|
|Ceanothus verrucosus||Wart-stemmed ceanothus||45|
|Cneoridium dumosum||Spice bush||35|
|Dudleya Ianceolata||Coastal Dudleya||50|
|Encelia californica||Califronia encelia||71|
|Erigonum fasciculatum||Flat-Top buckwheat||71|
|Euphorbia misera||Cliff Spurge||63|
|Ferocactus viridescens||San Diego barrel cactus||36|
|Malacothamnus fasciculatus||Chaparral mallow||90|
|Malosoma laurina||Laurel sumac||58|
|Mammillaria dioica||Fishhook cactus||62|
|Opuntia littoralis||Coastal prickly pear||100|
|Opuntia parryi var. serpentina||Snake cholla||88|
|Pinus torreyana||Torrey pine||100|
|Rhus integrifolia||Lemonade berry||72|
|Salvia mellifera||Black sage||77|
|Yucca schidigera||Mojave Yucca||100|
Figure 9. Restoration site on SPAWAR in August 1997 before revegetation and October 1999 two years after revegetation began.
Erosion control experiments demonstrated that Curlex netting proved most effective in reducing sediment loss and aiding in container plant survival. ENCS-2 and jute netting appeared to be equivalent in these tests. Punched straw, although the least expensive, was the least effective at reducing sediment loss and promoting container plant survival. In addition, the punched straw did not provide traction for walking on the slopes during planting and maintenance. Jute netting was more durable than the Curlex and ENCS-2 as it remained intact under foot traffic and appears to last longer over time. There were no differences in sediment loss or container plant survival between coir fences with and without cocoa mulch and straw flake dams.
Although biodegradable erosion control methods such as jute, Curlex, ENCS-2 and container planting are more expensive than hydroseeding, they promote a more accurate restoration of an area and provide results in a shorter period of time. Hydroseeding on the adjacent pipeline failed as erosion control, resulting in erosion gullies greater than 18 centimeters wide and over 1O meters long. In addition, the percent cover of exotic species was almost double in the area hydroseeded as compared to the northern end of the restoration site.
The difference in soil pH between the restoration site and the surrounding undisturbed area may be due to salt uptake by the plants in the undisturbed area. Salt from the ocean air may be accumulating on the restoration site, increasing the soil pH. Organic matter was not significantly different between the restoration site and adjacent undisturbed area probably due to the restoration site being previously covered by acacia, adding litter to the soil surface. The increase in available nitrate in the soil on disturbed sites over undisturbed areas is probably the result of higher mineralization rates occurring from the more easily decomposable exotic annuals compared to the more recalcitrant native shrubs. Measuring available nitrate over time is a good indication of the success of a coastal sage scrub restoration project.
The container outplanting study demonstrated that plastic one gallon container provided the greatest transplant success (89%) of the containers tested. Other plastic containers tested such as green and black four inch(squared) containers provided success above 75% while using less space in the greenhouse than one gallon containers or half highs. 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, however transplant survival was below 60%. The survival rate for plants grown in half highs was no greater than plants grown in plant bands, while the cost and amount of space required for half highs is near double that of plant bands. A possible reason paper containers have lower success rates than plastic is they absorb and maintain more water 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 more efficient at saving space than other plastic containers.
Percent survival was lower that expected during the El Nino year due to the loss of plants in the punched straw erosion control treatment. However, surviving plants made up for the low survival with rapid growth, leading to a healthy percent cover. A factor leading to the loss of container plants was some seedlings being initially buried in silt collected by the basins created to catch water. To remedy this, basins were broken down and deep pipes installed to focused water from the surface to the roots, preventing run off. The drip system installed was effective, but installation was time consuming and requires continuous maintenance with either the emitter disconnecting from the 1/4" tubing or the 1/4" tubing detaching from the 1/2" tubing.
Conclusions and Recommendations
Punched straw is not recommended as an erosion control method. Although the cost of material is less than jute or Curlex netting, punched straw requires more labor for installation than these other methods and yields poor results. Jute is recommended on areas that experience high levels of foot traffic, however Curlex matting or an equivalent is recommended for an area that has been seeded and encounters low foot traffic.
Hydroseeding as the only means of restoration is not recommended. It may be useful for easily germinated plant species such as Encelia californica and Eriogonum fasciculatum, but container planting is recommended for woody species such as Rhus integrifolia and Cneoridium dumosum. Seed used in the hydroseed mixture should be carefully selected to be weed free. This will avoid introducing competition from exotic species for the native plant seedlings.
One gallon plastic containers were the most efficient of the containers tested and are highly recommended for use in future coastal sage restoration efforts. 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 appear to combine the space efficiency of paper plant bands with the higher survival rate 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.
Irrigation on slopes is highly recommended to reduce damage to the slope from water run off and increase plant survival. It is recommended that in future projects, 1/2 inch irrigation be installed on slopes with seedlings planted next to the tubing and drip emitters attached directly to the 1/2 inch tubing. This will save time and money by eliminating the installation of 1/4 inch tubing and decrease the potential for problems by reducing the number of components in the irrigation system.
Additional soil samples will be taken in 1999 to monitor any changes in the restoration site as percent cover of native species both from container planting and recruits increase.