Soil Ecology and Restoration Group

FINAL REPORT

REVEGETATION AND EROSION CONTROL FIELD AMMO
SUPPLY POINT AND
BIKE LAKE NORTH SITE AT
NATIONAL TRAINING CENTER
FORT IRWIN, CA 92310

PROJECT OVERVIEW

The National Training Center (NTC) at Fort Irwin is located 35 miles northeast of the city of Barstow, San Bernardino County, California. Fort Irwin encompasses an area of nearly 643,000 acres in the Mojave Desert floristic province. The NTC is dominated by creosotebush scrub, but also contains saltbush scrub, mesquite bosques, alkali playas, dunes, native grasslands, and Mojave Desert washes.

As a result of ground maneuvers, live fire exercises, and force-on-force military training activities, many of the vegetation communities present at the NTC have been disturbed or severely degraded. Furthermore, training activities may have also damaged the cryptogamic soil crusts, a thin crust of algae, fungi, lichen, and other micro-organisms which bonds the soil surface together. After the vegetation and soil crust have been disturbed or damaged, the newly barren surfaces are subject to an accelerated rate of erosion from the normal forces of wind and water. Once the erosion process has begun, the effects will continue to intensify unless corrective action is taken. In severely damaged areas, nitrogen and organic contents are decreased and the soils become more alkaline, making it harder for plants to reestablish in an already harsh environment. Training activities need to be managed to minimize negative environmental effects, with those effects mitigated through rehabilitation activities to insure that the end result is not the loss of realistic conditions for desert warfare training. Land mamagement activities should also address training hazards including low visibility from excessive dust and gully formation due to water erosion.

The Integrated Training Management Program has established a long-term program (1997-2005) to manage areas in a suitable manner. A major portion of this program includes re-vegetation and erosion control of disturbed lands. For this project two sites located near the cantonment area of the NTC (Figure 1) were chosen. The first site is 20 acres in size and is located adjacent to the Field Ammo Supply Point. The second site is 15 acres and is located north of Bicycle Lake, at the base of Mount Teifort.

((Figure 1))

Figure 1:

SITE DESCRIPTIONS

Field Ammo Supply Point

This site encompasses approximately 20 acres and is located 4.5 km to the southwest of the Cantonment area at UTM grid coordinates 530900 east/ 389660 north (Figure 2). The site is directly adjacent to an ammo supply area and receives heavy traffic on roads that bisect it and also border it on all sides. The soil is of the Arizo series and is a gravelly fine sand with low to moderate compaction (Appendix B). Initial damage occurred at the site in August 1999 as a result of unauthorized engineering activity (Figure 3). Since that time erosion and gullying have become noticeable along the perimeter roads and the site is still being damaged by current off-trail vehicular travel. The heaviest disturbance of the site occurred in two locations; the western end, where encroachment from the road has all but completely destroyed the native vegetation/shrubs (Figure 4), and an area on the eastern side (approximately 300'x 10'x 3’) where a large double trench had been excavated (Figure 5). A preliminary plant survey of the area, conducted on 17 May 2000, found the following four species to be dominant at the site: Larrea tridentata, Ambrosia dumosa, Atriplex polycarpa and Hymenoclea salsola. The exotic grass Schismus was also present, but not in overwhelming amounts. A complete list of plant species is found in Table 1.

Bicycle Lake North

This site is located 7.8 km to the northeast of Cantonment at UTM grid coordinates 536025 east/ 3906550 north and covers an area of 15.48 acres (Figure 6). The topography is flat with no signs of water erosion apparent. The soil is of the Arizo series and is a gravelly fine sand with moderate compaction. Roads border the site on all sides and vehicle tracks into the area are noticeable at two points along the northeastern edge (Figure 7). With the exception of the northern and eastern edges of the site, the damage is fairly heavy, with no adult native shrubs present (Figure 8).

Figure 2. Ammo Supply Point (ASP) project site.

((Figure 3))

Figure 3. Vehicle disturbance at ASP site.

Figure 4. Trail through the ASP site before closure.

Figure 5. Large trench on eastern side of the ASP site.

Table 1. Species identified at ASP site as of 17 May 2000

Figure 6. Bike Lake project site.

Figure 7. Vehicle tracks at Bike Lake site.

Figure 8. Barren central area of Bike Lake site.

Revegetation is necessary to stabilize the soil and reduce wind erosion that might affect operations at the nearby Bike Lake Army Airfield (Figure 9).

A preliminary survey of the area, conducted on 28 June 2000, found the following four native species to be dominant at the site: Ambrosia dumosa, Hymenoclea salsola, Atriplex polycarpa and Larrea tridentata. Unfortunately, two non-native species, Schismus and Salsola, are present in large numbers and cover the majority of the site. Table 2 lists all plant species found at Bike Lake North site.

Figure 9. Plane approaching Bike Lake Airfield.

Table 2. Species identified at Bike Lake site as of 28 June 2000

*( Denotes non-native species)

MATERIALS AND METHODS

Field Ammo Supply Point

This project was designed to re-establish vegetation and repair engineering damage on an area adjacent to the ammo re-supply point near Langford Lake road. The goal of this was to reduce both wind and water erosion, and prevent further damage by restricting access through the site from the surrounding road network. To accomplish this, all trails crossing the site were closed, barriers were installed to slow surface water runoff, and a total of 668 native shrubs were planted in the more barren areas. Work at the site was started on 24 May 2000, and planting was completed on

11 June 2000.

There were two main trails bisecting the site with two other minor trails branching off. Access to these were closed through a combination of methods, including the construction of six (6) mounds, 1,410 feet of berms and twenty-seven (27) catchments at the entrances to the trails. The full length of the trails (approximately 1.05 km) was then pitted using the John Deere tractor and agricultural disker provided by ITAM. This same tractor was used to construct the berms, mounds, and catchments.

Around the perimeter of the site, thirty-one (31) straw wattles were installed in pre-existing washes. The wattles ranged in size from fifteen to twenty-five feet long and were placed perpendicularly across the small washes. This was done in an attempt to slow water traveling across the surface of the site, and to trap sediment. Each wattle was dug in approximately 4-6 inches and held in place with three to four lengths of 3-foot rebar (Figure 10).

Twenty-four (24) catchments were constructed around the perimeter of the site to deter vehicle traffic into the area (Figure 11). Each catchment is approximately 20 feet across, three feet high and received four native plants. The shape and design of the catchments created a nearly continuous berm with basins at approximately fifty foot intervals. These catchments are close enough to the road to be hand watered so irrigation tubing was not necessary. The rest of the site was divided up into five main areas of damage.

In the large, engineered double-trench area along the eastern border, 36 cross berms were created by hand to divide the trench into catchments/basins where 76 shrubs were then planted. In Area 4, located in the center of the project site, 202 shrubs were planted in pre-existing depressions. In the remaining areas, plants were placed in pairs in basins that were constructed approximately one meter in diameter. Thirty-two (32) basins were also constructed in Area 1 in the northern corner, 40 basins in Area 2 on the eastern edge, and 73 basins in Area 3 in the heavily damaged southwestern side. The species types and number of individuals planted are outlined in Table 3.

Figure 10. Installation of wattles at ASP site.

Figure 11. Tractor constructing catchments at ASP site.

TABLE 3. Species and quantities planted at ASP site

In each of the five areas described above (not including the catchment plantings), 1/2-inch polyurethane irrigation tubing with 4.0 gallon/hour emitters was installed in a nonlinear pattern. Five hundred fifty-nine (559) plants were placed along these irrigation lines in the five different areas. Each hole for the plants was dug with a gas-powered auger and then pre-watered with 2-10 gallons of water.

Monitoring of the project site continued for six months after the final planting date. During this time, the plants were watered with approximately two gallons each on a monthly basis as necessary. Any repairs needed were made at the same time as watering (approximately 1-2 litres per plant). The final survival count was conducted on 28 December 2000

Bicycle Lake North

This project was different from the ASP site in several ways. Although the Bike lake site was also designed to re-establish vegetation, there was little engineering damage to the area. With over five acres of the site all but completely devoid of any perennial shrubs, the goal of reducing both wind and water erosion had to be achieved through different means. To accomplish this, two faint trails crossing the site were closed, a total of 612 native shrubs were planted along the edges to prevent incursions, and broadcast seeding was used to supplement the depleted native seed bank. Work at the site was started on 12 June 2000, planting was completed on 27 June 2000, and seeding was conducted on 27 December 2000. Species and number of individuals planted are outlined in Table 4.

In the heavily disturbed center of the site, two two-acre seeding plots were established. The seeding mix used was supplied by the ITAM office and mixed in a 1:3 ratio with standard cactus mix, to obtain a more even application (Appendix C). The first plot was supposed to receive a new method of straw crimping to prevent wind action from blowing all the seed away. However, during the testing of our modified straw-planter (Figures 12 & 13) at the site, it was found that it did not perform well in the dry, compacted soil. Instead, the hay (66 bales) was broadcast by hand and then driven over with a mechanical pitter to partially incorporate the hay into the soil surface (Figure 14). The pitter was supplied by ITAM and pulled behind a HMMWV. The two acres were then broadcast seeded by hand. The adjacent two acre area was seeded first, and then treated with a surface tackifier. The brand-name polymer Soil Sement was used (Appendix E). It was applied in two coats by a licensed sub-contractor using a five thousand gallon spray truck.

On the eastern side of the project site, fifteen relatively large and intact shrubs were identified to serve as foci for the planting of vegetation islands (Larrea protection zones or LPZ’s). This was accomplished by choosing 15 pre-existing, mature Larrea tridentata shrubs, and planting 6 native shrubs around each Larrea in a circular pattern (Figures

TABLE 4. Species and quantities planted at Bike Lake site

Figure 14. Broadcasting straw by hand at Bike Lake

Figure 15. Larrea before LPZ planting at Bike lake

Figure 16. Larrea after LPZ planting at Bike Lake

Figure 17. Planting along irrigation line at Bike Lake.

This same technique was duplicated on the southern boundary of the site where an additional 165 shrubs were planted. In this section, however, the irrigation lines run perpendicular to the road.

In addition to the initially proposed work, two additional studies were also conducted at the Bike Lake site. The first study was a comparison of plant protectors. This was implemented to determine the effects that different designs of plant protection devices have on plant survival rates. Along the western irrigation lines, 120 Larrea tridentata shrubs were randomly chosen for this study and marked with a red pin flag. Each plant received one of the following protectors: 1) diamond-mesh, photo-degradable tube (Figure 18-a); 2) TreePee II, self -staking, eighteen inch cone (Figure 18-b);

3) twelve inch Tubex (Figure 18-c); 4) twenty-four inch Tubex (both standard colors of Tubex were used: tan and brown) (Figure 18-d). Thirty of each type were used. A dark gray type of Tubex and a white small diameter mesh protector were also used at the site, but not in large enough sample sizes to generate accurate data (Figure 19).

Figure 18. The four different protection devices used in the comparison study.

Figure 19. Two other plant protectors also used at Bike Lake.

The other study is a long-term observation and analysis of microclimates around Larrea tridentata shrubs (Appendix D). Data from this experiment is just beginning to be collected so no results are available at this time.

Monitoring of the project site continued for six months after the final planting date. During this time, the plants were watered on a monthly basis when necessary. Any repairs needed were made at the same time as watering. The final survival count was conducted on 19 January 2001.

RESULTS

Field Ammo Supply Point

After one year, overall survivorship at the Field ASP site was 484 plants out of a total of 664 for a survival percentage of 73% (Table 5). The total of 664 is an adjusted number calculated by subtracting the four plants killed by vehicular damage from the original contract total of 668 shrubs.

Survival by treatment varied from a low of 64% for the single basin plantings, to a high of 80% for those paired in basins. Shrubs planted in the chevron shaped catchments had a survival rate of 74% (Table 6). Using the statistical analysis program Super

TABLE 5. Survival by species at ASP site.

TABLE 6. Survival by treatment at ASP site.

TABLE 7. ASP Site ANOVA Spreadsheet

ASP Site ANOVA Spreadsheet

The road closures were completely effective in keeping vehicles off of the closed trails. However, new vehicle incursions beginning on 17 July 2000 were made into the site via a sandy wash.

After a heavy rain event and subsequent flooding, the wattles performed relatively well. Eleven of the thirty-one wattles needed repairs, and one needed to be replaced entirely.

As for the catchments, after the flood event, 46% of the original length of catchments was left intact. Four catchments were gone entirely, while six others were left with 30% or less of the original footage. Nine of the catchments were 90% intact or more. All catchments did collect large amounts of silt and sediments, in some cases enough to bury the shrubs

Bicycle Lake North

After six months, overall survivorship at the Bike Lake site was 479 plants out of a total of 612 for a survival percentage of 78% (Table 8). Survival by species was worst for the grass Acnatherum hymenoides at only 4% and Lepidium fremontii at 46%, while Atriplex canescens successfully established at 90%. Survival by treatment varied from a low of 41% for the LPZ plantings to a high of 100% for those at the road closures.

Shrubs planted along the drip lines had a survival rate of 84% (Table 9). Using the statistical analysis program Super ANOVA, a significant difference (p-value < 0001) was found between the LPZ's and the other two planting treatments (Table 10). Using Fisher's Protected Least Significant Difference (LSD) test, the greatest difference in survivorship rates was found to be between the plants in the LPZ's and the two other treatments, both with p-values ¾ 0.0001. There was no significant difference in survival between the drip line plantings and the road closures (p-value = 0.0687).

TABLE 8. Survival by species at Bike Lake site

TABLE 9. Survival by treatment at Bike Lake site

Table 10. Bike Lake ANOVA Spreadsheet

The results for the plant protector comparison were interesting. Out of the thirty plants chosen for each of the four types of protectors, the TreePee faired the best with a 93% survival rate. This compares with 87% for the mesh tubing, and 83% for both of the Tubex lengths (Table 11).

In the seeding treatment that received the tackifier, the seed was applied and spread with Soil Sement in less than two hours with no installation

TABLE 11. Bike Lake Plant Protector Survival Study Results

problems. The other site, which initially was to have straw applied mechanically with a mechanical planter, was implemented by a different method than planned. The mechanical planter was unable to penetrate into the highly compacted and rocky soil of the site to a depth necessary to secure the straw bundles. It was then decided to broadcast the straw by hand over the site and to partially incorporate it into the soil by using a pitter pulled over the site. It appears that this second option has been successful in creating a surface that will prevent seed from being blown away.

CONCLUSIONS

Ammo Supply Point

The 29 August 2000 rain event provided an opportunity to see how the different techniques used at the ASP site held up to extreme conditions. Rainfall totals were not taken directly on site but the nearby meteorological stations at TA Bravo and Langford Lake received .57 and .24 inches, respectively. Most of this rain fell in a two-hour period, so flash flooding likely occurred.

The catchments held up fairly well considering the amount of water traveling across the surface. They did collect water and sediment as planned, but some were insufficient for the amount of runoff coming from the Field ASP. A few of the plants in some of the failed catchments were washed away, Tubex and all, without a trace (Figure 20). One of the catchments was washed out so badly that there was actually some debate on its original location. The catchments that held up, however, had much more healthy, robust plants at the close of the monitoring period than any of the other treatments due to the amount of passively collected water.

The wattles were equally successful under intense flood conditions. Only three out of the original thirty-one failed completely (one was found about 150 feet down the road from where it was originally installed), and the repairs to most of the others consisted of pounding in a new piece of rebar (Figure 21).

The rain event also resulted in differential survival rates between the two irrigation line treatments. Area 4 and the double-trench were hardest hit by flooding due to the hydrology of the site. It is estimated that 87% of the plant mortality occurring in the double-trench was due to flooding. Plants were buried with two to fourteen inches of sediment (Figure 22). Also in area four, a large section was washed out, killing twenty to twenty-five shrubs (Figure 23).

As with the Nelson Lake site, the coyotes quickly developed a taste for polyethylene tubing (Figures 24 & 25). During one visit to the site at the end of July, over one hundred twenty breaks were found in the lines. After repairing those breaks, it was decided the lines should be buried. Using a shovel and a wheelbarrow, the irrigation lines were covered with approximately one half inch of soil. This prevented future coyote damage, and also prevented the lines from being washed away during the flood event.

Figure 20. Washed out catchments at ASP.

Figure 21. Blown out wattle after rain event at ASP.

Figure 22. Silted up double trench at ASP.

Figure 23. Partially buried treepee at ASP.

Figure 24. Coyote damage to irrigation line at ASP.

Figure 25. Coyote prowling irrigation lines at ASP.

Bicycle Lake North

Mortality was highest in the Larrea Protection Zone (LPZ) plantings (59%), with several different factors possibly accounting for such results. First, it has been noted in past SERG studies that environmental conditions and techniques used during planting can greatly affect mortality of individual shrubs. LPZ's were the last treatment planted at this site, planting having occurred in late June, when temperatures were in excess of 100 degrees Fahrenheit. In these conditions, exposure to excessive heat and sunlight during planting, even for brief periods, can greatly reduce a shrub's chances for survival. Another factor is the disproportionately large number of Indian rice grass, Acnatherum hymenoides, planted in the LPZ's, which completely failed to establish in any of the treatments at the site. Most importantly, however, in the last three SERG projects where LPZ's have been used, they have had an average survival rate of only 47%. This compares to an average of 81% survival along irrigation lines at these very same projects. These kinds of numbers lead us to believe that there might be more important factors at work, such as the root system of the mature Larrea plant that is the focus for the LPZ's. Even with basin sizes increased in volume by 100%, such well-established root systems might be drawing up water that would otherwise be available for the transplanted shrubs

(Figure 26).

Mortality was non-existent at the road closure plantings, with a survival rate of 100%. This could be due to the fact that it was about 20 degrees cooler when these shrubs were planted and that they received more water than the other plants. During the pre-planting, each hole was augered to a greater depth and width than the other treatments and watered with at least ten gallons. Each plant then received at least five gallons immediately after planting. Most of the other plants at treatments other than the road closures initially received about half that amount.

The results of the plant shelter study were a surprise. As noted above, the TreePee protected shrubs had a 90% survival rate compared to the Tubex covered plants 80%. However, when the survivorship for the total number of shrubs in Tree Pees and Tubex along the western edge of the study site were included, this difference was even more apparent. Out of one hundred forty-one plants in TreePees, only six died. This compares to thirty-one out of one hundred thirty-nine plants that died in the full height Tubex. This might be due to two different factors. First, the TreePees are cone shaped and of a larger diameter than the Tubex, allowing for a more natural growth form. Secondly, the TreePees are a lighter color than the Tubex, preventing possible overheating in the summer sun.

Figure 26. Increased basin diameters at Bike Lake.

It appears that the use of the Soil Sement tackifier and the hand broadcasted straw with pitter are both appropriate methods by which to treat large seeded areas to prevent the seed from being blown away. Though it is too early to determine the success of each method concerning germination rates, monitoring of the site over the next several years should provide this information. Though unsuccessful in this first attempt, the use of a mechanical planter for installation of straw bundles might still be a viable restoration method on more sandy soil sites.

RECOMMENDATIONS

Field Ammo Supply Point

Wattles have again proved their success and usefulness in slowing water and trapping sediment flowing across a site. However, it would help to stabilize the wattles by using more rebar, perhaps one piece for every 3 feet of wattle used.

The catchments continue to prove to be a good means to increase water and soil organic matter for the shrubs planted in them. They should continue to be used, but care must be taken when placing them on slopes where runoff may be too severe for them to be effective.

As for the irrigation lines, both of the basin sizes had good success. However, looking at the individual plant sizes and vigor, it appears that the plants in the double basins performed better. It is suggested that in a future study, a comparison model be set up whereby the vigor of the plants for both basin sizes can be compared through long term monitoring. It is possible that after only six months, even slight differences in rates of vigor can contribute greatly to a plants long term survivability.

Bicycle Lake North

In regards to the plant protection study, it is recommended that further studies be conducted comparing Tree Pees and Tubex. A study measuring the internal temperatures of different colors and diameters of Tubex should also be conducted to determine if overheating could be a factor in mortality. Furthermore, the effect of the interior vs. exterior placement of the rebar on temperature of the Tubex should be examined.

Current results suggest that more sites be designed utilizing the paired-plant basins along irrigation lines. More testing should be done with them to find out if this method will consistently out-perform the single-plant basin design.

In regards to the Larrea Protection Zone plantings, it has again shown to be the least productive method for out-planting survival. Planting around dead Larrea shrubs may be attempted to overcome previously mentioned detriments. This would possibly give the transplanted shrubs the benefits of increased organic matter in the upper soil horizons, without having to compete for water with a large well-established root system.

For the two seeding treatments at the project site, a long-term monitoring program should be instituted. Comparisons of seedling establishment rates between the two plots between the two plots should be made for future integration with site rehabilitation activities. In terms of time and money, the tackifier treatment was superior to the straw treatment. It might be beneficial to re-examine the modified straw planter method at a different site after rainfall. Moister soil might allow better penetration of the blade necessary to properly hold the straw bundles in place.

Pepsis formosa on Petalonyx sp. at ASP site.