last updated August 2,2000
Project Overview
The Integrated Training Area Management Program at the National Training Center and Fort Irwin, 36 miles north of Barstow, California has initiated a program to manage training areas in a sustainable manner. Over the next several years, a major portion of this program will entail revegetation and erosion control of disturbed areas. Services will include alternative windbreak design and construction, experimental treatments to determine the most effective means to seed and revegetate large areas and the control of surface and gully erosion on slopes.
The current project consists of two tasks, a large windbreak along the Langford Lake Main Supply Route (MSR) and a revegetation site 3.2 miles north of Red Pass Lake, referred to here as the Bunker site. The Langford Lake windbreak will serve as a dust control mechanism as well as forming a visible barrier to hinder further vehicle encroachment into the adjacent native vegetation. The Bunker site utilizes mounds of earth planted with native vegetation and placed around a disturbed area to discourage unnecessary vehicle traffic and promote natural revegetation within the protected area. These projects were executed in late May, June and early July 1998. The locations of these areas are shown in Figure 1.
Langford Lake Windbreak Site Description
This site is number 45 on the LRAM Erosion Control Plan and is located between UTM grid coordinates 41652E 95041N and 43046E 96007N at an elevation of 566 meters. It consists of a five-hectare plot that runs both adjacent and parallel to Langford Lake MSR on the southern side, covering a distance of 1 mile with a width of 80 feet (Figure 2). The northern side of the dirt road has a small ridge of compacted soil to prevent vehicles from leaving the road. The southern side of the road, however, has no variation in topography and is open to vehicles leaving the road in search of a smoother driving surface. As a result the road has been widened over time. One intent of this project is to stop the vehicular traffic from widening the road on the southern side.
Figure 2. Langford Lake site.
The soil is sandy but highly compacted due to vehicular traffic. The site slopes slightly to the southeast and is subject to sheet and small wash runoffs after the occurrence of moderate precipitation. Possibly compounding the effects of erosion, the water runs across Langford Lake MSR and increases its rate of flow due to compaction of the road before it reaches the site. There are essentially no plants established on the plot due to damage incurred by previous vehicle traffic. The surrounding vegetation to the south and north of the road, however, is Creosote bush scrub consisting mainly of Larrea tridentata, Ambrosia dumosa and Encelia frutescens.
Langford Lake Windbreak Materials and Methods
National Guard engineers accomplished the heavy equipment work at the site in mid-March 1998. They ripped the soil surface to a depth of three feet and built 44 parallel berms 100 feet long which point towards the east at a 45 degree angle from the Langford Lake MSR. These berms were spaced approximately 100 feet apart and should provide erosion control, dust control and a visual/physical barrier to discourage vehicles from entering the site. From this juncture, Soil Ecology and Restoration Group (SERG) personnel performed the rest of the scope of work, which commenced on 26 May 1998 and was completed on 28 May 1998.
All berms were modified by SERG personnel using the Integrated Training Area Management (ITAM) tractor. The 100 foot long by three inch diameter sections of flexible perforated pipe to be used for irrigation were laid out adjacent to each of the 44 existing berms. Two foot high plastic Supertube shelters with varying diameters of three to five
inches were then anchored with rebar in each place where an outplanted shrub was to be planted. Next, the berm was shifted so the soil completely buried the pipe to a depth of 8-10 inches and partially covered the Supertubes. Each end of the pipe was kept elevated by tying it to a three foot rebar so the pipe would act as a stand-pipe when irrigation was conducted. Water was then transferred from a water truck (contracted through Equipment Leasing Co. of Barstow) to the flex pipe by a one and one-half inch hose and to the Supertubes through a garden hose. This served to pre-water the holes. The Supertubes were then removed from the berms where a small planting hole remained. The plant-band sized shrubs were then planted into the holes left behind by the Supertube shelters. Once the shrubs were planted, the Supertube shelters were replaced and secured with rebar in order to protect the shrubs from herbivory and desiccation. The shrubs were watered again via the flex pipe after planting. A three-inch pipe holds 0.38 gallons of water per linear foot. Thus, when full, a 100-foot pipe can hold 38 gallons of water. In this case, roughly 2.4 gallons of water is delivered to each plant per watering event.
A total of 704 plants, 16 shrubs along the south side of each berm at intervals of six feet, were planted. The native species included Isomeris arborea (220), Prosopis glandulosa (176), Atriplex canescens (110), Atriplex polycarpa (110) and Larrea tridentata (88). To maximize the windbreak effect, the tallest species (i.e. Prosopis) and the larger evergreen species (i.e. Larrea and Isomeris) were distributed evenly throughout the plot to create a consistent wind barrier.
Bunker Revegetation Site Description
This site, number 60 on the LRAM Erosion Control Plan, is a quadrangle of about 9 hectares located at UTM grid coordinates 59920E 08970N at an elevation of 586 meters (Figures 3 and 4). The site has a slight slope which drains from west to east. Along the west side of the plot, previous engineering work has left a section of artificial mounds and depressions. The soil is sandy with light to moderate compaction except where roads pass through the plot creating areas of greater compaction. These interior roads were ripped to a depth of one foot by ITAM personnel, and the roads that form the perimeter of the plot have been improved to encourage vehicle traffic to remain on established tank trails. Vegetative cover on the site is spotty, with the most dense perennial growth along the north side and the least growth along the eastern side. Perennial species composition near the plot consists primarily of Larrea tridentata,Ambrosia dumosa, Ephedra nevadensis and Hymenoclea salsola. Diversity of annual species is high.
Figure 4. Bunker site from different vantage points.
Bunker Revegetation Site Materials and Methods
Work at the Bunker site commenced on 2 June 1998 and was completed on 15 July 1998. In order to create a visible barrier to discourage vehicular traffic from entering the plot, a series of 165 mounds were constructed around the plot perimeter. The distance between the mounds was largely dependent on the density of the existing vegetation, but on average the mounds were spaced every 5 meters. The one exception to this was along the western perimeter of the plot, where the presence of an unexploded bomb in the road impeded the progress of work and, as a consequence, a 60 meter long area received no mounds. Each mound was two to three meters long, one meter wide and slightly under one meter high. An average of five plants were planted on or around each mound.
Two irrigation systems were used on the mounds. Six hundred and twenty five plants in 125 mounds were irrigated with 25 foot long sections of three inch flexible pipe laid out in a circular pattern. Both ends of the pipe were kept vertical to act as irrigation stand-pipes by being tied to a three-foot rebar (Figure 5B). Each pipe was perforated five times by hand using a screwdriver, allowing all five plants at each mound to be watered close to the root zone. The stand-pipes could then be watered with an inch and one-half hose attached to a water truck. On average, each plant receives approximately 1.9 gallons of water per watering event.
One hundred and ninety nine plants in 40 mounds were irrigated with four inch diameter, 15 inch long PVC "deep pipes" installed with each shrub as it was planted (Figure 5C). Each deep pipe can be watered individually with a garden hose attached to a water truck. A four-inch tube holds 0.66 gallons per linear foot so each plant will receive approximately 0.83 gallons of water per watering event.
In addition, a section within the interior of the site along the eastern edge was established where 50 shrubs were planted and irrigated using one-half-inch diameter drip irrigation tubing (Figure 5D). Each section of tubing is 100 feet long and irrigates 25 plants at one meter intervals. Each plant was installed with a four-inch diameter by 15-inch long PVC deep pipe reservoir which is filled from the one-half-inch tubing through a smaller one-quarter inch tube. In this case, like the deep pipe mounds, each plant will receive approximately 0.83 gallons of water per watering event. The advantage of the dripline irrigation system is that it allows for establishment of plants in the interior of the plot with one point watering from the plot perimeter, minimizing disturbance.
To help promote revegetation in the plot interior, some of the depressions created by the engineering work previously mentioned were planted to take advantage of their water catchment capabilities. These plants were given deep pipe systems similar to the deep pipe mounds. However, unlike the deep pipe mounds, water must be delivered to the basin plants using a garden hose, a water pump and a 180-gallon portable water tank in the back of the SERG pickup truck. In this case, like the deep pipe mounds and irrigation lines, each plant will receive approximately 0.83 gallons of water per watering event.
A total of 989 plants were planted, including Ambrosia dumosa (250), Larrea tridentata (200), Encelia frutescens or farinosa (100), Hymenoclea salsola (100), Ephedra
nevadensis (100), Senna armata (75), and eight minor species (164).
Figure 5. Diagram of plantings done at bunker site.
Project Monitoring and Maintenance
The project schedule is shown in Table 1. All installation work for both tasks was completed by 15 July 1998. Watering was conducted using a contracted water truck and commenced three weeks post-planting and continued at approximately three week intervals until final monitoring of plant survival occurred. Final plant survival data was collected six months post-planting; 18 November 1998 for the Langford Lake site and 31 December 1998 for the Bunker site. At the time of final monitoring, Supertubes were removed from the plants. Three Supertubes per berm were left at Langford Lake and one Supertube per mound was left at the Bunker site to notify the drivers of passing vehicles that a restoration project was in the area. Troops are apparently recognizing Supertubes as indicators of plant revegetation areas.
Results
Langford Lake
Six months after planting the overall survival at Langford Lake was 74 percent. All species except Isomeris arborea responded well to the perforated pipe irrigation technique (Figure 6). The berms retained their shape though they did shrink slightly due to settling of the soil and wind erosion. In several areas, after a fairly large storm, the berms were unable to hold up to rushing water from the small washes and erosion occurred. Areas subject to sheet runoff had no problems with erosion, which suggests that berms can break up the flow of water under mild runoff circumstances. At several locations tactical vehicles crossed the site, but no occurrences of multiple berms being damaged by a vehicle running parallel to the road were seen. Damage to the planted shrubs was minimal, with less than ten fatalities. Langford Lake six month survival visual observation suggested that survivorship was higher at the east end of the plot. It was found that survival was significantly higher (chi-square contingency test, p<.05) in the higher numbered rows with rows 23-44 having a survivorship of 85% while rows 1-22 had a survivorship of 62%.
Bunker site
A chi square contingency test with a confidence level of 95 percent demonstrated a significant difference between several of the irrigation techniques used at the Bunker site (Table 2). Six months after planting, overall survival at the Bunker site was 70 percent, ranging between 42 percent and 75 percent. (Figure 8).Table 2. Bunker site chi square contingency results.
A number of shrubs planted on the mounds were damaged by vehicles, primarily on the side of the mound facing the road. In one case, a vehicle ran over five consecutive mounds, damaging two to three shrubs per mound. The mounds on the corners were also subject to damage as some vehicle operators cut the corner. In all, 38 plants were destroyed by vehicles, 24 on the flex pipes mounds and 14 on the deep pipe mounds. Tracks were also seen in the interior of the plot, but no damage was noted to the deep pipe basins.
During the watering trip on 19 November 1998, the one and one-half inch supply valve on the 2,000-gallon water truck (rented from Deloss Equipment Rentals of Barstow) broke after watering 33 mounds. Since there was no way to stop the release of water, the truck drove along the perimeter of the site and flood irrigated another 65 mounds with water before the supply was exhausted. That left another 67 mounds, all irrigation line shrubs and all basin shrubs without water until the next watering trip on 18 December 1998. At the end of six months, the mounds that received the proper irrigation technique on 19 November had a survival rate of 75 percent. The mounds that were flood irrigated had a 77 percent survival rate while the mounds that received no water had a 71 percent survival rate. A chi square contingency test demonstrated no significant difference in survival between the mound plants that received water and those that did not
During the last watering trip on 18 December 1998, Supertubes were removed from 60 of the mounds. Upon returning to the site on 31 December 1998 to conduct a final survival count, it was found that a number of plants no longer protected by Supertubes had been subjected to herbivory by rabbits. It was determined that 73 percent of the mound plants subjected to herbivory survived while 75 percent of the mound plants still protected by Supertubes survived. A chi square contingency test showed no significant difference.
Discussion and Recommendations
Langford Lake
Final survivorship at the Langford Lake site was 75 percent after six months (Figures 9 and 10). This is comparable to the perforated pipe watering technique results we have seen at other sites. On Fort Irwin, 87 percent survival was seen at the Fifth street windbreak site after eight months and 75 percent after six months at the Bunker site. At a similar site at the Marine Corps Air Ground Combat Center in 29 Palms, 87 percent were alive after nine months. All sites received irrigation water on average of once per month. Both the 29 Palms site and the Fifth street windbreak site at Fort Irwin were planted in October of 1997 with each having an 87 percent survival rate. The Langford Lake site and the Bunker site at Fort Irwin were planted in May and July 1998, respectively, and each had a 75 percent survival rate. The fall planting survival rates are higher for three possible reasons. First, plants received supplemental water from the winter rains. Second, plants received even more precipitation than usual because 1997/1998 was an El Niño year. Lastly, the plants were able to take advantage of the winter growing season to lessen the shock of transplanting and become established in the native soil prior to the hot summer months. Many desert plants have a tendency to go dormant during the long hot days of summer. It appears that it may be best to plant in the fall rather than in late spring or early summer because irrigation water is not as efficient as natural precipitation.
Figure 9. Langford Lake six months after planting.
Figure 10. Close up views of Langford Lake site after planting.
It was also noted at the Langford Lake site that the southern section (rows 1-22) had a lower survival rate than the northern section (rows 23-44). There are several possible explanations. The first concerns the fact that planting by SERG personnel began in the southern section. Since several new SERG personnel had limited or no experience planting with plant bands or half-highs, it may have taken time for them to perfect the proper planting technique. Hence, by the time the new personnel reached the northern section, they may have become more competent with their planting skills. Experience from previous restoration projects has shown that planting technique can have as much as a 90 percent affect on plant survival in desert environments.
Second, perhaps more Isomeris arborea were planted in the southern section than in the northern section. Unfortunately, due to the loss of field notes during a vehicle break-in, data is not available for actual species locations at Langford Lake. In general, however, Isomeris arborea does not transplant well. In the future, it might be worth while to try direct seeding of Isomeris arborea next to the perforated pipe so that the seeds receive irrigation water and have a greater chance for germination and growth. Once germinated and in place, the Isomeris arborea seedlings will not have to deal with the shock that comes with transplanting.
A third possible explanation concerns the fact that brown colored Supertubes were used in the southern section while pink colored Supertubes were used in the northern section. Perhaps the difference in color created different light intensity and humidity environments, with the pink color being more favorable. Future research into the effects of color differences of plant protective devices should be conducted to determine if, in fact, such differences significantly affect plant survival.
Lastly, since the water supply valve is on the driver's side of the water truck, the water truck driver normally started at the north end of the site and worked towards the southern end. Watering this site was normally a full day operation. It is possible that the water truck operator was more thorough in ensuring that the irrigation pipes were completely filled with water during the beginning of the workday and was slightly less thorough as the end of the day approached. Such actions would lead to the southern section receiving less water than the northern section, possibly resulting in a lower survival rate.
As stated earlier, there was not a great amount of vehicle damage to the site. The berms worked well in deterring vehicles from driving parallel to the road along the eastern side. The berms did not, however, deter the vehicles from driving across the plot to get to trails on the other side. It is recommended that with long narrow sites such as Langford Lake, clearly marked trails for vehicles to cross the site should be constructed to guide drivers through the site with minimal damage.
It is uncertain whether plantings have reduced the creation of airborne particles because no testing has yet been conducted. At this point, however, it can assumed that dust reduction is minimally successful since the denuded area has been reduced in overall size through the mound planting and the establishment of volunteers plants, such as Encelia farinosa.
Bunker site
Overall survival at the Bunker site after six months was 70 percent (Figure 11), five percent less than the Langford Lake site. Perhaps it was the difference between a late spring and an early summer planting, but more than likely, the difference lies in irrigation techniques. The perforated pipe plantings enjoyed the greatest success at 75 percent. This survival rate was significantly greater than the irrigation line plantings at 58 percent and the deep pipe basin plantings at 42 percent, but not significantly greater than the deep pipe mounds at 71 percent. Perhaps this indicates the benefits of mound planting. The fact that the mounds did not receive surface water, only "deep" water administered directly to the root zone, meant that the mounds could act as an insulating barrier to slow down the evaporation rate of water. The irrigation lines and deep pipe basins did not have the luxury of an evaporation buffer zone and were therefore more susceptible to evapotranspiration. The additional water provided by the more water efficient mounds probably led to the increased survival rate.
The major difference between the flex pipe and the deep pipes was the amount of water administered to each plant during each watering event. Flex pipe plants received 1.9 gallons while deep pipe plants received 0.83 gallons per watering event; twice as much water with the flex pipe method. Not surprisingly, results were highly successful with the flex pipe method, with survival from the deep pipe technique slightly lower. When taken in combination with the results of the deep pipe basin survival rate, however, it appears that the use of mounds is the key factor for high survivorship. It is recommended, however, that future mounds along MSR’s be constructed slightly offset along the road to help reduce damage from vehicle operation.
The use of deep pipes with the irrigation line technique was not significantly different from the deep pipe mounds or deep pipe basins. The survival rate of the deep pipe mounds, however, was significantly higher than the deep pipe basins. This suggests that deep pipes can have a wide range of results, and care must be taken to utilize them only under favorable conditions. A problem that occasionally occurs with deep pipes is the accumulation of sand inside the pipes. This may have an affect on survival rates and future testing of possible covers to prevent "sanding up" is recommended.
There were some troubles with the irrigation line system. Initially, there was an uphill flow from the road, so the receptacles had to be placed on the end of the line within the interior of the plot. Also, no emitters were placed on the irrigation line to control the flow of water.
Consequently, some plants would receive an excessive amount of water while other plants received little water. When using irrigation lines, in line emitters and a pressurized water source to administer the water should be used. This technique was practiced for the fall 1998 project conducted by SERG at Fort Irwin. We found a 4,000-gallon water truck with its power-take-off and adjustable idle speeds provided the power and control needed to operate such an irrigation line system effectively, and has since continued to be used.
Not only were the basins placed in the most remote area of the site where watering was the most difficult, but the soil had a more sandy texture than at either the irrigation lines or the mounds. When watered, the water would soak in immediately. There was no pooling in the basins along with very quick draining of the deep pipes. This suggests that the soil in the area has poor water retention capabilities and water probably drained beyond the root zone of the newly planted shrubs, leading to many plants dying from desiccation. To offset such drainage problems, it is recommended that a covering be added to the bottom of the deep pipe prior to installation to slow down/prevent the rapid loss of water through porous soils. Testing of various types of material could be done at future restoration sites.
Some plants at the Bunker site went two months without water but showed no significant effects on survivorship. Fortunately, this "drought" occurred in the fall between the middle of October and the middle of December. This brings up the issue as to whether or not irrigation is necessary every month in the fall, winter and/or spring for plants that are semi or completely established. With increased knowledge of watering events and amounts of water administered to each plant in relation to survivorship, time and money will be saved while still achieving satisfactory results.
When some of the Supertubes were removed two weeks before monitoring, herbivory occurred, particularly on the Ambrosia dumosa, Atriplex and Encelia species. This reduced survival by two percent over two weeks between Supertube removal and final survival monitoring, though the reduction did not prove to be statistically significant. Yet, if such a trend proceeded at a loss of one percent plant per week, results of herbivory in the long run could be devastating. Thus, the use of Supertubes appears justified. A downside of Supertubes, however, is that they alter the morphology of the plant. Instead of a rounded, low level shrub with small leaves, Supertubes can form a tall cylindrical plant with large fleshy leaves. Once the Supertube is removed from the plant, it is subject to three possible hardships. First, an increased chance of herbivory because the well irrigated plant is more succulent than its nearby unprotected neighbors. Second, the plant is more susceptible to wind damage due to its tall shape with possible root damage as the stems are moved around by the wind or the plant may be blown over and buried by drifting sand. Lastly, the plant's pattern of photosynthesis and transpiration must change. Future research should include an experiment with a larger, mesh type of protective device. This would allow the herbivores to eat some, but not all of the plant. In addition, it would allow for the plant to become adapted to the desert environment at a less traumatic pace once it has recovered from the shock of transplanting.
