Soil Ecology and Research Group last update July 29, 2003

REVEGETATION AND EROSION CONTROL OF
RED PASS MSR
NATIONAL TRAINING CENTER
FORT IRWIN, CA 92310

Project Overview

The National Training Center at Fort Irwin, CA is a training facility for the United States Army. Located 35 miles northeast of the city of Barstow, CA, Fort Irwin occupies an area of nearly 643,000 acres within the Mojave Desert. Training activities conducted at the installation provide units and commanders the opportunity to practice large-scale war fighting skills in a realistic environment. Ground maneuvers, live-fire exercises, and force on force activities damage the native vegetation of the Mojave Desert creosote/bursage scrub habitat, which in turn causes dust and erosion problems.

The Integrated Training Area Management (ITAM) Program is responsible for land management to identify and repair critical areas on the post. Projects proposed by the ITAM program combine both re-vegetation and erosion control to mitigate the environmental impacts of training activities. Dust contributes to poor air quality as well as reduced visibility. Controlling levels of particulate matter less than 10 microns (PM 10) is of particular importance, as long-term exposure to these tiny particles is a health risk to people both on the base and in surrounding communities.

This project involved reducing the width of a portion of Red Pass Main Supply Route (MSR), a heavily used travel corridor, to both protect the remaining vegetation along the eastern side of the trail and reduce wind erosion. Dust created by traffic on this heavily used trail poses a hazard during training activities due to reduced visibility and also contributes to off-post air quality issues. Increasing vegetation along the downwind side of the trail was intended to improve air quality by trapping fugitive dust from the trail surface. Revegetation included transplanting greenhouse-grown native shrubs and direct seeding. Straw wattles were also used in an attempt to decrease surface erosion in numerous drainages across the trail.

Site Description

Red Pass MSR is a travel corridor located near the eastern border of Fort Irwin National Training Center (Figure 1). The site is thirty-five kilometers from the Cantonment area centered at UTM Grid Coordinates 558750 E 3909750 N. A 2.57 kilometer portion of the MSR was designated for rehabilitation, encompassing an area of approximately eighteen acres. Heavy use of the trail during training activities has destroyed native vegetation along the sides, making it extremely wide.

The restoration design for the site (Figure 2) involved narrowing the trail by re-vegetating a thirty-meter wide strip on the east side of the MSR. The site was ripped prior to implementation to relieve soil compaction, increase water infiltration, and create micro-sites for wind blown seeds and dust. Sand berms were created throughout the thirty-meter by 2.57 kilometer strip to deter use of the east side of the trail. Several smaller trails that intersect the MSR remained open for use, and berm locations were adjusted accordingly. Greenhouse-grown native shrubs were transplanted on the western edge of the restoration area to create a more permanent trail boundary and create a visual barrier. The area between the transplanted shrubs and the existing vegetation to the east of the trail was seeded with a native annual and perennial seed mix. Straw wattles were installed in several natural drainages from west to east to reduce surface erosion within the site.

Site-specific information includes soil type and vegetative species composition. The soil is of the Cronese series and consists of ten to twelve inches of fines at the surface, with a few two- to three-inch diameter rocks found throughout. Soil in the top six inches is heavily compacted. Within the drainages, there is an additional four to five inches of loose, coarse gravel on top of the compacted layer (See Appendix A for a more complete soil series description). A few native species, including Larrea tridentata (Creosote bush), Ambrosia dumosa (Burro weed), and Hymenoclea salsola (Cheese bush), inhabit the area adjacent to the site.

Figure 2. Project design of Red Pass MSR.

Materials and Methods

Site Preparation
On 28 June 2001, site preparation began with ripping a thirty-meter wide by 2.57 kilometer long section of the trail using a D-6 bulldozer. Intersections with smaller trails were not ripped. The ripping bar used on the bulldozer created furrows to a depth of approximately two feet. The area was ripped with a single pass, so areas between the furrows remained fairly compacted.

Seventy-five earthen berms were created at approximate 100-foot intervals within the ripped area. On the 2nd and 3rd of July 2001, a D-6 bulldozer was used to push the soil into three-foot high, 100-foot long mounds. The berms were placed at a 70º angle from the edge of the existing vegetation to form diagonal berms and create more of a visual deterrent. Along each side of the smaller trails that remained open, a 100-foot long diagonal berm was built. This did not always allow for one berm at every 100-foot interval, and spacing had to be altered in order to total seventy-five berms for the site. The angle of these berms was also altered as necessary to delineate the entrances to the cross trails and facilitate their access.

Drip irrigation line was laid in a serpentine pattern on a ten to fifteen-meter wide strip along the western edge of the ripped area. A total of 11,000 feet of 1/2" polyethylene tubing was used to cover the site. This was divided into eighteen individual lines. Sixteen-liter per hour emitters were installed every eight to ten feet to facilitate irrigation of each plant.

Planting
Since soil between each furrow remained heavily compacted, plants were planted only within the furrows. A depression was created under each emitter to hold water during pre-watering. The line was pre-watered for one-half hour, delivering two gallons to each hole. The moist soil was then shoveled out and a shrub transplanted under each emitter. During planting, an additional three gallons was used for each plant (total of five gallons per plant). A twenty-inch diameter circular basin was created around the base of each plant. The shrubs were then protected with Treepee Quicone ® plant protectors.

A total of 1229 native desert shrubs were installed between 26 July 2001 and 10 October 2001, although initial contract specifications required only 1100 plants to be installed. Modifications were made to restoration plans for Pioneer Trail (NTC contract N687114-99-D-6602/0012) in order to overcome challenges encountered at the site, and an additional 129 plants from that project site were added to the Red Pass MSR contract. Table 1 lists the species composition of shrubs planted at Red Pass MSR.

Each plant has been watered with two gallons on a monthly basis since the final planting date, with the exception of one month. Irrigation proposed for 19 September 2001 was cancelled due to denied civilian access and increased security measures at the Fort as a result of terrorist events that occurred 11 September 2001. This resulted in 1139 of the plants installed at Red Pass MSR not receiving water for two months. However, initial visual inspection of the plants on the next site visit showed no significant negative impact from this delay.

Seeding
A fifteen to twenty-meter strip of ripped area situated between the transplanted shrubs and existing vegetation to the east of the MSR was seeded with 214.72 bulk pounds of seed mix on 13 December 2001. The mix was composed of native annual and perennial seed (see Appendix B for species composition). In order to ensure equal distribution of the seed over the length of the site, seed was mixed with 225 pounds of cactus mix for an approximated 1:1 ratio. The mix was broadcast by hand over the twelve acres.

Erosion Control
Fifty straw wattles were installed at the Red Pass MSR restoration site. The majority were installed in the northern end of the site, where potential surface erosion appeared highest. Soils at the north end were shallower and drainages

Table 1.
Species planted at Red Pass MSR.

from the hill west of the site were more prominent. Some of the twenty-five-foot lengths were cut into halves or thirds to adequately fit the natural drainages. The remaining wattles were installed in depressions that were created when building the berms (Figure 3). When the soil was pushed up with the bulldozer, a trench was created on the side from which it was pushed. In an attempt to reinforce the berms, small pieces of wattles were installed next to the berms at an angle that would help divert runoff to the adjacent planted areas.

Figure 3. Installation of wattles in trench adjacent to berm.

On 9 and 10 October 2001, initial attempts to dig trenches for the placement of wattles using pick axes and shovels failed because the soil was too compacted. On 11 October 2001, a mechanical trencher was used to create trenches long enough to fit each wattle piece (Figure 4). Three-eighths inch thick, three-foot lengths of re-bar were used to secure the wattles in their trenches. Wattle installation was completed on 6 and 7 November 2001.

Results

Planting
The overall one-year survival rate for Red Pass MSR is 29.4%. This is due partly to the low initial survival at the six months mark (53.4%) as well as to vehicle damage to the entire site documented on 16 October 2002. The damage from the site being run over was so extensive at this time it became impossible to determine direct responsibility for mortality. Survival rate was calculated without accounting for those run over and without calculating an adjusted survival rate.

Figure 4. Mechanical trencher used to install wattles.

Larrea tridentata, Ambrosia dumosa and Eriogonum fasciculatum were the only three species with over 50% survival. The survival rates of Brickellia incana, Lycium andersonii, Prosopis glandulosa and Thamnosma montana were all within the 40-50% range. Atriplex polycarpa, Ephedra nevadensis, Hymenoclea salsola and Lepidium fremontii all had 20-40% survival rates. Of the species planted in significant numbers (740 individuals), Atriplex canescens (5.2%), Isomeris arborea (2.2%), and Salazaria mexicana (9.6%) experienced the largest decrease in survival after six months and the lowest overall percent survival. Several other species had very low survival rates but were planted in small numbers (Cercidium floridum, Chilopsis linearis, Ericameria cooperii, and Sphaeraclea ambigua). Because of the low survival rate of these species, it is probable that they will not be adequately represented in the species composition of the site (Table 2).

Table 2.
Survival of Species planted at Red Pass MSR.

Seeding
At the completion of one year there has still been no seed germination. The furrows that trapped the seed as it was sown have filled in with sand to a depth of six or more inches due to the heavy winds that occurred after seeding was accomplished. Failure of the seeds to germinate is probably due to a lack of sufficient rainfall through most of the year and one occasion of heavy rainfall which caused significant runoff (Figure 11). It is suspected that the seed has been dispersed by wind, water or wildlife to areas other than the restoration site or is buried too deep beneath soil surface to germinate on site.

Erosion Control
The wattles appeared to be effective at first. However, there had been no substantial rainfall event in the first six months of maintenance. Since that time many of the wattles have now been buried by loose sand (Figure 5) or run over by tanks to ground level (Figure 6), rendering them ineffective. Although the primary objective of the berms was not erosion control, they appear to have aided in trapping soil. However, they do not seem to have created a deterrent to vehicle traffic, the initial purpose. A site visit in October 2002 found the majority of berms had been run over numerous times.(Figure 7).

Figure 5. Wattles buried by loose soil.

Figure 6. Wattle run over by training vehicles.

Figure 7. Berms run over by training vehicles.

Conclusions and Recommendations

The plants at Red Pass MSR had a very low survival rate. Poor soil conditions, timing of planting, lack of precipitation and several other factors contributed to low survival. The soil at this site was extremely compacted due to vehicle use and naturally occurring calcic soil horizons. Plant survival might have been higher if the site had been ripped more than once to create better planting conditions and encourage infiltration.

Problems were encountered with watering at this site. The first problem was that the planting began in the hottest part of the summer after which the installation was closed for two months in the wake of the September 11th terrorist attacks. Consequently the plants received no water for two months after their initial irrigation. A visual inspection of the plants on the next site visit was surprising because the plants all appeared to be doing quite well. However, the plants soon began to decline and survival was 53.4% after six months. This could be explained by possible over-watering at the time of planting.

Ripping the site prior to implementation was helpful for planting, although cross-ripping or double-ripping would have reduced soil compaction to a greater extent. Planting within the furrows was very efficient. The soil was loose and digging was easy. Pre-watering within the ripped area allowed the water to penetrate deep into the soil. Generally, when pre-watering, it takes quite a while for the two gallons to percolate before planting can commence. When pre-watering the holes in the ripped zone, water percolated quickly and planting could begin almost immediately after disconnecting the hose from the irrigation line. However, the plants received too much water during pre-watering because the field crew could not keep up with the water truck during planting. As a result each line received much more than five gallons of water at the time of transplant. The large amount of water initially provided followed by two month with no precipitation or supplemental irrigation probably increased the degree of transplant shock experience.

The result was that the shoots grew very fast and appeared to be healthy at first inspection. However, it is likely that the roots did not grow at a proportional rate to the shoots because due to poor soil quality and compaction. Since the site was ripped only once, there were rows of soft soil created between rows of heavily compacted soil. The rows of hard soil helped retain water from the initial pre-watering/watering in the soft furrows and The plants were planted in the rows of soft soil and the first two months conditions for growth were, in general, favorable until the roots met with the hard soil. At this point the roots could no longer support the shoots and the plants died back. This is supported by the observation that many of the plants displayed foliage only at the top where sunlight was available through the treepee while the stems dropped foliage to conserve energy and resources (Figure 8). This is a common occurrence with plant protectors but seemed to be more prevalent at this site.

The use of drip lines was a very ineffective way of watering at this site because of animal disturbance and the size of the site. Coyotes regularly chewed through the drip lines (Figure 9) and ravens pulled the emitters out of many of the lines. The time and money spent fixing the lines soon became excessive. Watering from the drip lines was halted and, after consideration of the possible options, it was determined that use of a large water truck outfitted with a side sprayer would be the most effective method of irrigation at that point. This method proved to be much more efficient due to the size of site, although there was no way to ensure that all plants received ample water. There were also concerns that blasts of water from the side sprayer could disrupt the seeding portion of the project. However, at the point at which this method was adopted, there had still been no signs of seed germination and much of the seed had been buried in the furrows or blown away by the wind.

Figure 8. Seedling conserving energy by supporting foliage only at site of direct photosynthesis.

Figure 9. Drip line damaged by coyotes.

An additional problem was a severe lack of precipitation. Rainfall was well below average for 2001/2002 (Figure 10). The build-up of wind blown sand in the plant protectors may have also been a factor in the poor plant survival at this site. Plants that were deeply buried by sand also were more likely to be attacked by molds and insects. Vehicle tracks had initially damaged some of the plants at the edge of the site near the main trail early on (Figure 11). However, more extensive damage was documented in October 2002. Signs or cyber stakes may be helpful in the future to deter vehicles from entering the sites and creating a buffer zone so the plants are not so close to the trails.

The two plants that had the highest survival rates at the six-month point, Prosopis glandulosa and Lycium andersonii, had relatively high survival rates at the time of the one year monitoring when overall survival is taken into account. Both have very woody stems and protective thorns. The fact that they both have these characteristics seems to have helped them survive during a dry year In additiona the thorns may have reduced herbivory on Lycium andersonii. Even

Figure 10. Inches of precipitation at Red Pass Lake.

Figure 11. Initial vehicle damage of plants bordering the main trail at Red Pass MSR.

though Prosopis glandulosa typically experiences preferential browsing, the shrubshelters may have reduced this pressure.

The species that has the lowest survival rate at the six month point, Hymenoclea salsola (32.6%), has a very soft stem during its early growing period, making it weaker in respects to it's ability to tolerate droughts. Hymenoclea salsola also lacks any defensive thorns and is thus subject to intense browsing. However, the survival rate has not dropped much since in the final six months (32.0%) suggesting that the species is better able to tolerate conditions once it has established and developed a woody stem. After one year it appears that the plant species that have woody stems and defensive thorns appear to have higher survival rates than plants without these characteristics. The obvious exception is Isomeris arborea, which typically experience high mortality in the first few month following transplanting, but very low mortality thereafter. Poor conditions for establishment described previously could have been responsible for the drop in survival from 46 individuals at the time of planting, to 23 individuals at six month monitoring to 1 individual during the final annual survival count.

The seeding project has been unsuccessful so far. After almost one year there are still no signs of seed germination and much of the seed has been buried by sand or blown off site. In addition to relieving compaction and increasing water infiltration, the furrows in the ripped zone created temporary micro-sites for seeds. On 14 March 2002, observations of seeding success were taken. After three months, much of the seed remained trapped in the furrows of the site. However, there were no signs of any seeds germinating, most likely due to lack of precipitation. In the following months it was noted that the furrows began to fill in with soil (Figure 12). Most desert species germinate at a depth of just a centimeter or two, thus poor germination rates can be expected from seeds buried too deeply by the build-up of wind blown sand.

Again, lack of rainfall this past winter season greatly affected the outcome of the project. Annual variability of winter precipitation is always a major factor for seeding success in the Mojave Desert. One normal wet season may cause

Figure 12. Ripped furrows filled with windblown sand.

germination of remaining viable seed, however, there are several factors that may decrease the chances of success in the future even if a normal wet season occurs. First, if the seeds are buried too deep underneath sand, they may not be able to germinate. In addition, seed viability will decrease over time. Overall, the chances of seed germination lessen with each year.

Sand has built up around the berms and also filled in the surrounding areas of the site. The furrows that were created with the bulldozer to loosen the compacted soil have filled in with six or more inches of soft sand. The accumulation of soft loose sand behind the wattles may have served to slow and capture some runoff during future rain events. However, the majority of the wattles have now been run over by tactical vehicles and are unlikely to cause any resistance to erosion. Erosion due to water flow is not evident at the site due to the very dry year.

Vehicle damage may have had the greatest impact on the poor outcome at this site. On 16 October 2002 a site visit was conducted to determine the one-year survival for the completion of the project. At this time it was discovered that there had recently been heavy damage done to the site by many vehicles, possibly a convoy (Figure 13). It appears that the vehicles, including tanks, had approached the site from the southern end where the trail is still quite wide. The tracks show that the many vehicles proceeded over the entire site, occasionally even diverting in order to run over treepees and wattles throughout the site (Figure 14). Although some live plants were found underneath the flattened treepees, there were other sections in which no plants were found at all (Figure 15). The berms and wattles did not appear to create any deterrent to the vehicle traffic as can be seen by the continued tracks over and, at times, through them (Figure 16).

Figure 13. Vehicle damage to the site.

Figure 14. Diverting vehicle tracks and damaged plants.

Figure 15. Sections devoid of outplantings following maneuver damage.

Figure 16. Berms destroyed by repeated vehicle damage.

It is unfortunate the extensive vehicle damage occurred immediately prior to the scheduled one-year survival count because it has made it very difficult to determine responsibility for the extremely low survival rate. The total survival rate of 29.4% was not sufficient to fulfill the agreed upon contract. After discussing possible options for remedial measures, it was determined that the many compounded problems at this site make remedial planting at Red Pass a poor option. Instead, it was determined that any possible repairs to the Red Pass restoration site would be implemented by the ITAM field crew and SERG would be responsible for the planting of additional seedlings at the Old Harry landform site (Contract # N68711-99-D-6602).

At the six month period the survival rate at Red Pass was 656 plants, or 53.4%, well below the required 860 plants (70%). At the time of the one-year survival count in October 2002 there were only 361 plants (29.4%) found. At a meeting between Ruth Sparks, Taura Huxley and Dana Morin on 11 December 2002, the high mortality was determined to be a product of inadequate reduction of soil compaction, areas of poor soil quality, lack of precipitation, wildlife damage to irrigation lines and destruction of plants by vehicles. SERG accepted responsibility for a portion of the plants lost below the acceptable 70% survival and an additional number of 400 plants, to bring the total to 761 (61.9%), was agreed upon to be planted in sparse areas at the Old Harry landform restoration site.

There are three major difference between the Red Pass MSR site and the Langford Lake windbreak site, a successful site implemented May 1998 (Plant Restoration and Erosion Control N68711-98-Q-5725 at National Training Center Fort Irwin, CA). First, the Langford Lake site was picketed with cyber stakes, although this did not completely deter all vehicle traffic. Second, the Langford Lake was planted entirely with perforation pipes. This technique has several advantages which contributed to the high survival of the site (75%). The soil was ripped to a depth of three feet prior to berm construction, similar to Red Pass site. However, because of perforated pipe installation, the berms were shifted several times using a tractor, most likely further relieving soil compaction. The seedlings were then planted in these mounds above the perforated pipes in soft soil. Irrigation through the perforated eliminated evaporation and allowed for the seedlings to maximize uptake of water. Previous monitoring at other sites at Fort Irwin have shown a significant benefit to perforated pipes use. Finally, Supertubes reinforced with rebar were used as opposed to the treepees used at Red Pass MSR. The plants on top of the mounds with the larger plant protectors with rebar may have acted as a better deterrent to vehicles. There were no reports of vehicle damage parallel to the MSR, only perpendicular in attempts to find other trails at the Langford Lake site. This site and the Bunker Revegetation site (75%) were both planted in the summer of 1998 and both sites showed a decreased survival to similar sites which were planted in the fall (Fifth street windbreak and 29 Palms site, both 87%).

In conclusion, many problems were encountered at the Red Pass MSR restoration site: denied access for two months after the terrorist attacks; planting in the hottest part of the summer; over-watering at the time of planting; not ripping the site enough times to relieve soil compaction; wildlife damage to the driplines; and the build-up of wind blown sand at the site all made a negative impact on the outcome of the planting and seeding parts of the project. In addition, lack of vehicle deterrents such as signs or cyber stakes and its close proximity to a heavily traveled trail made the site particularly vulnerable. Recommendations for future projects are to not plant in the hot summer months, not over-water at the time of planting and rip the site several times so no furrows are left behind effectively reducing soil compaction. The use of Rainbirds instead of dripline on large-scale restoration sites such as this one is also recommended along with adequate marking of the site to reduce vehicle damage.