Soil Ecology and Research Group last update July 29, 2003

RACETRACK TOC AND OLD HARRY RESTORATION
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 and rehabilitation of disturbed areas on the post. Projects proposed by the ITAM program combine both re-vegetation and erosion control to minimize 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 wind and water erosion and loss of vegetation around the Racetrack Firing Point and Old Harry land formation and protecting remaining vegetation at these sites. Dust created by traffic on East Range MSR (Main Supply Route) near the Racetrack site and on intermittent trails at both these sites poses a hazard during training activities due to reduced visibility and also contributes to off-post air quality issues. Increasing vegetation along these trails should improve air quality by trapping fugitive dust from the trail surfaces. Replacing vegetation in these areas also discourages vehicle travel off existing trails and provides some protection for remaining plants. Revegetation consisted of transplanting greenhouse-grown native shrubs. Berms and catchments were utilized at both sites to define trails, aid in moisture retention and deter water erosion.

SITE DESCRIPTIONS

Racetrack
The Racetrack site is an approximately 40-acre area bordered to the north by a large and frequently used cleared area, and the East Range Main Supply Route to the south (Figure 1). The site is 21.5 kilometers from the Cantonment area centered at UTM Grid Coordinates 547551 E 3913729 N. The site is dissected by three well defined trails running east to west and several more random trails running north to south. There is established native vegetation on most of the site that is being reduced by the use of less defined trails and random vehicle entry points.

The restoration design for the site (Figure 2) involved strategically placed berms and grouped outplantings within the three defined sections. Sand catchments were created as designated by ITAM (Integrated Training Area Management) personnel along the most southern trail parallel to the East Range MSR. Several smaller trails that intersect along the well-defined trails have remained open for use, and berms were created accordingly. Greenhouse-grown native shrubs were transplanted in groups throughout the site area to create more permanent trail boundaries.

Site-specific information includes soil type and vegetative species composition. The soil is of the Goldivide series and consists of granitic loam with moderate to high compaction (See Appendix A for a more complete soil series description). Native species found on site include Larrea tridentata (Creosote bush), Ambrosia dumosa (Burro weed), Hymenoclea salsola (Cheese bush) and Ephedra nevadensis (Mormon tea).

Figure 2. Racetrack TOC revegetation site.

Old Harry
The Old Harry site is an approximately 9.1 acre area to the south and the west of the Old Harry landform (Figure 3). The site is 15.65 kilometers from the Cantonment area centered at UTM Grid Coordinates 536300 E 3915400 N. The site consists of twelve sections, each between 0.3 acres and 1.5 acres. The sections radiate from the base of the Old Harry landform and are divided by well-defined trails intersecting with the trails immediately to the west and south of the landform. There is established native vegetation on much of the site that is being reduced by the use of less defined trails and random vehicle entry points.

The restoration design for the site (Figure 4) involved the outplanting of native greenhouse seedlings concentrated along the outer edges of the sections and within strategically placed catchments to better define trails. Berms 15 to 20 inches high were also created on the edges of the established roads as needed.

Site-specific information includes soil type and vegetative species composition. The soil at the Old Harry site is also of the Goldivide series and consists of granitic loam with moderate to high compaction. Native species, including Larrea tridentata (Creosote bush), Ambrosia dumosa (Burro weed), Hymenoclea salsola (Cheese bush) and Ephedra nevadensis (Mormon tea), were present on-site.

MATERIALS AND METHODS

Racetrack

Site Preparation
Site preparations occurred between 8 and 10 January 2002. Figure 5 shows part of the Racetrack site prior to implementation.

Figure 4. Adapted Old Harry revegetation site.

Figure 5. West view of section 3, Racetrack site

A D-6 bulldozer was used to build twenty catchments approximately two feethigh along the southern most trail bordering the East Range MSR. The bulldozer was also used to create a total of 4,360 feet of earthen berms approximately 20 inches high, as marked by ITAM personnel, to deter vehicle traffic along the trails throughout the revegetation area.

A total of fifteen soil samples were collected, five from each section. Due to high soil compaction a thin trowel was used to collect samples instead of a “T-auger”, possibly increasing the margin of error for results.

800 feet of 0.5 inch polyethylene drip irrigation line was installed in the two northeastern sections designated to decrease the width of an existing trail. Sixteen-liter per hour (4 gal / hr) emitters were installed at a more concentrated density at the northern and southern borders of the two sections with fewer emitters placed in the central areas to facilitate irrigation of each plant.

Planting
Holes for outplanting were dug with a power auger. Planting began 9 January 2002 and concluded 7 February 2002. All holes were pre-watered with two gallons of water prior to planting. An additional 3 gallons of water was used during transplanting. 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 510 native desert shrubs were transplanted. Seedlings were positioned in groupings along unauthorized vehicle entry points (Figure 6). Outplantings were also installed beneath each emitter along the irrigation line previously placed. Each plant has been watered with two gallons on a monthly basis since the final planting date. Table 1 lists the species composition of shrubs planted at the Racetrack site.

Figure 6. Northwest corner of Racetrack six months after planting.

Table 1.
Species planted at Racetrack TOC and East Range MSR.

Site Preparation
Site preparations occurred between 7 February and 4 March 2002. Figures 7 and 8 show two views of the site before implementation.

Figure 7. South view of Old Harry site prior to implementation.

Figure 8. West view of Old Harry site prior to implementation.

A D-4 bulldozer was used to build forty catchments approximately two feet high and six feet wide as well as a total of 6,685 feet of berms approximately 20 inches high in each section along the designated trails (Figure 9). Sections 1 and 6 were ripped with 1-2 foot ripping bars due to severe soil compaction, however, it appeared to have little affect so sections 2-5 were not treated.

An area to the northwest of the Old Harry landform designated for revegetation was moved due to the establishment of a new target pit adjacent to the site. On 13 March 2002 the missing section, section 12, was created to the south of section 6. The remaining sections retained their numbers.

A total of 6,685 feet of 0.5 inch polyethylene drip irrigation line was installed throughout the twelve sections of the site, one line per section. Sixteen-liter per hour (4 gal / hr) emitters were installed at 8-10 feet intervals along the lines to facilitate irrigation of each plant.

Planting
Holes for outplanting were dug with a power auger. Planting began 14 February 2002 and concluded 2 April 2002 (Figure 10). All holes were pre-watered with two gallons of water by means of irrigation lines prior to planting. An additional 3 gallons of water was used during transplanting. 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 775 native desert shrubs were transplanted. Seedlings were positioned in groupings of three to four plants in each catchment and one seedling was installed beneath each emitter along the irrigation line previously placed. Each plant has been watered with two gallons on a monthly basis since the final planting date.

Figure 9. Building catchments at Old Harry site.

Figure 10. Planting along irrigation line at Old Harry site.

In January 2003 it was determined that 400 additional shrubs would be planted at the Old Harry site in order to mitigate for the low survival and extreme vehicle damage incurred at the Red Pass site the previous year. Table 2 lists the species composition of shrubs planted at the Old Harry site originally and in February 2003. These shrubs were planted 10, 11 and 12 February 2003 under rainy conditions. The first survival data were taken in March 2003.

Table 2.
Species planted at the Old Harry site

The new shrubs were planted in three groups across the site. The first group of 125 shrubs was planted on the perimeter of a triangular section located between sections 1 – 6 and 12 to the northwest and sections 7 – 11 to the southeast. ITAM personnel seeded the interior of the triangle on 10 February 2003 and it was decided that planting shrubs around the perimeter would provide some degree of protection for the seeded area. The 125 shrubs in this section were planted in 29 clumps of 4 or 5 plants spaced roughly evenly around the two long legs of the triangle. The remaining shrubs were divided between the 12 previously planted sections as listed in Table 3. Within each section, shrubs were planted in clumps of 4 to 6 plants in regions of relative sparseness, as determined by earlier surveys (Figure 11). The plants were hand-watered after planting and covered with Treepees. Due to the ideal planting conditions

Table 3.
Distribution of shrubs added at Old Harry February 2003

(Figure 11)
Figure 11. Old Harry new plants between sections 6 and 12.

provided by the rain (Figure 12), the planting holes were not pre-watered, and the plants were given a smaller than normal amount of water after planting.

(Figure 12)
Figure 12. Planting conditions at Old Harry February 2003.

RESULTS

Racetrack

Planting
The overall one year survival rate for the Racetrack site was 72.55% (Table 4). Atriplex canescens and Lycium andersonii had the highest survival rates -- 100% and 94%, respectively. Ephedra nevadensis had an 82% survival rate, while Ambrosia dumosa, Hymenoclea salsola, Larrea tridentata, and Eriogonum fasciculatum had survival rates ranging from 70% to 80%. Brickellia incana, Encelia spp., Salazaria mexicana, Senna armata, and Sphaeralcea ambigua all had survival rates between 50% and 60%, and Krascheninnikovia lanata and Atriplex polycarpa had less than 50% survival. Five plants had been run over by vehicle traffic.

Table 4
Survival of plants at Racetrack and East Range TOC

Erosion Control
The catchments and berms appear to be moderately effective in discouraging traffic through the revegetation area. While there were few occurrences of tank or vehicle tracks off the well-defined trails in the first six months after planting, several groups of tracks were found throughout the site in Feburary 2003 (Figure 13). The incidents of vehicle traffic through the site did not appear to have increased substantially between February and the final survival count conducted in early April 2003.

(figure 13)
Figure 13. Vehicle damage at Racetrack and East Range TOC.

Between November 2002 and April 2003, there were a total of 4.04 inches of rainfall. The catchments and berms appeared to be mostly effective in deterring erosion. There were a few berms breached by running water (Figure 14), but in only one case was the erosion significant enough to effect the survival of the plants within the catchment (Figure 15).

(Figure 14)
Figure 14. Erosion damage at Racetrack and East Range TOC.

(Figure 15)
Figure 15. Breached berm and partially buried plants.

Old Harry

Planting
The overall one year survival rate for the Old Harry site was 87.06% (Table 5). Hymenoclea salsola and Lycium andersonii both had survival rates over 90%. Ambrosia dumosa, Eriogonum fasciculatum, Larrea tridentata, Atriplex canescens, and the Encelia spp. all fell within the 70 to 89% survival range. Atriplex polycarpa and Senna armata were 70% and 80% survival, and Ephedra nevadensis had a survival rate under 70% (Figures 16 & 17). Ten plants were run over.

Table 5
Survival of plants at Old Harry

(Figure 16)
Figure 16. Old Harry section 11 one year after planting.

(Figure 17)
Figure 17. Old Harry section 12 one year after planting.

Erosion Control
The catchments and berms appear to be moderately effective in discouraging traffic through the revegetation area. There were several occurrences of tracked or wheeled vehicle tracks off the well-defined trails, the majority of which were located in the northern part of the site where several defined trails converge. Sections 1 through 4 in particular sustained vehicle damage to berms, project signs, and siber stakes, and in April 2003, new tracks were also found running through the middle of the area seeded in February (Figure 18).

There was evidence of wind erosion at the southern half of the site, especially in the first six months after planting. Basins previously encircling the plants were blown away or buried on several of the lines, particularly within sections 9 and 10. The wind erosion noted during the first six months after planting did not appear to have increased substantially in the subsequent six months.

(Figure 18)
Figure 18. Vehicle damage at Old Harry site.

The catchments and berms appear to have been quite efficient in deterring water erosion during the periods of rainfall between January and April. Most of the obvious water damage was contained along the established trails. Several of the berms in the northern section had obviously succeeded in keeping the water flowing down the main trail along the base of the Old Harry landform instead of through the planted and seeded areas (Figure 19).

A) (Figure 19a)
B) (Figure 19b)

Figure 19. Erosion around berm bases in section 5 (A) and 10 (B).

CONCLUSIONS AND RECOMMENDATIONS

Survival is satisfactory at both Racetrack TOC and Old Harry landform revegetation sites one year following the completion of planting. Both sites have survival rates above the 70% survival established as success criteria, with survival at the Old Harry site being particularly good. The high survival rates can be attributed to several factors, the first of which is that the shrubs were planted between February and April when soil and air temperatures were still moderate. In the case of the February 2003 additional planting at the Old Harry site, the shrubs were actually planted in the rain -- optimum conditions for avoiding transplant shock. Second, although the soil at both sites was recorded as being severely compacted, the site preparations performed prior to planting seem to have mitigated this potential problem. In addition, berm and basin construction appeared to benefit the spring annuals by reducing soil compaction and providing good microhabitats for seed germination (Figure 20). Possibly most important is the fact that the area received approximately four inches of rain between October 2002 and April 2003, resulting in a significant increase in both the survival and growth rates (Figure 21).

A) (Figure 20a)
B) (Figure 20b)

Figure 20. Annuals growing in microhabitats provided by A) berms and B) basins.

(Figure 21)
Figure 21. Rapid growth of plants at Racetrack TOC and Old Harry sites.

The ample rainfall also had a few negative effects that should be addressed in future projects. Many shrubs outgrew the treepees more quickly than expected, resulting in odd growth forms that may require pruning to alleviate. (Figure 22). Another drawback of the rainfall was that it encouraged fungal growth inside the treepees and invasion of the treepees by insects attracted to the new growth (Figure 23). In years of good rainfall, all of these problems could be avoided by removing the treepees earlier as well as by reducing supplemental irrigation proportionately with rainfall.

(Figure 22)
Figure 22. Atriplex canescens (left) and Salazaria mexicana (right) shaped by Treepees.

(Figure 23)
Figure 23. Gnats, aphids, and ants on Eriogonum fasciculatum.

Another problem caused by the rainfall and the resulting rapid growth was that once treepees were removed and the basins around the plant eroded away it became difficult to determine whether the shrub was planted or naturally occurring and therefore whether it should be included in survival counts. It cannot always be determined based on the shrub location, and in years of good rainfall such as this, the shrubs can grow quickly enough to appear much older than they actually are. Even more difficulty arises in the case of dead shrubs which have their treepees removed, as this leaves no indication at all that a shrub was once planted there. Both cases lead to missing plants in the survival counts, and the problem increases with time as more treepees are removed. Perhaps the easiest way to avoid this issue would be to re-stake any outgrown or empty treepees next to the shrub until after the final survival count. Additionally, if treepees were labeled with the species abbreviations immediately after planting, dead plants would remain identifiable. Leaving all treepees in the field would have the additional advantage of maintaining a visual deterrent to vehicles for the duration of the project, although it would not help with the problem of intentional vandalism.

Vehicle damage was minimal in the first few months following planting, however, vehicle tracks were documented beginning September 2002 at Racetrack and October 2002 at Old Harry landform. Increasing the number of siber stakes used at each site might reduce instances of vehicle damage, but as illustrated in Figure 18, they may still be missed or ignored. The vehicle damage at Old Harry further exacerbated difficulties during irrigation, as the tires dragged the polyethylene lines, already chewed apart by wildlife, out of position. Fieldworkers have begun using wet seal tape on lines with puncture holes. This has been effective and appears to be an efficient way of repairing lines during irrigation. In general, above-ground irrigation lines do not appear to be an effective or efficient means of watering plants in areas with coyotes. The level of damage to the irrigation lines at both sites caused us to discontinue their use and switch entirely to hand-watering.

In conclusion, both Racetrack and Old Harry sites have been successful restoration efforts. Ideal planting conditions and adequate rainfall produced high survival rates and allowed us to judge the effectiveness of the erosion control measures. In addition to the usual difficulties with irrigation lines and vehicle damage, the wet winter emphasized issues not regularly encountered, e.g. plants rapidly outgrowing the treepees and being attacked by mold and insects, which will be useful knowledge to have for future projects that occur during relatively wet years. Pruning may be necessary for the plants badly shaped by the treepees, but otherwise no remedial measures seem necessary at this time.