Soil Ecology Restoration Group

last updated July 7, 2000

FORT IRWIN - Plant Community Restoration

Background
The native plant windbreak is located within the cantonment area on Fifth Street The windbreak extends 0.5 miles on the south side of Fifth Street between UTM coordinates 530310E, 3900573N and 529800E, 3901203N at an elevation of 725 meters. The windbreak runs parallel to both a water drainage and vehicle road test route The windbreak is bisected in three places by tactical vehicle crossings. Topography on site is flat with a gentle drainage to the southeast. Soil on site varies from a highly compacted sandy loam that contains large amounts of fine dust, the result of heavy vehicle traffic, on the western end to a coarse loose sand on the eastern end.

Materials and Methods
The windbreak was implemented in three phases. These phases consisted of site grading, perforated pipe installation, and planting. Site preparation and grading was carried out using personnel and equipment arranged by ITAM. The objective of grading was twofold. First to cut a trench for the perforated pipe and second to erect a berm to discourage vehicle traffic from cutting through and damaging the plantings. This berm will also catch and direct rainfall runoff from Fifth Street and the roadside adjacent to the plantings. The trench was cut to a depth of between 30 and 40 centimeters and the berm raised to a height of 60 to 80 centimeters. A schematic of the grading and plant positions is shown in Figure 1.

After the trench was cut and berm erected, 800 meters of 3 inch 100 ft long sections. The ends were bent upwards and staked in place with rebar to create watering standpipes. After the standpipes were secured, short segments of the perforated pipe were buried by hand to keep the pipe in position while it was buried with a motor grader.

The windbreak was planted with six different native desert plant species: Honey Mesquite (Prosopis glandulosa), Screwbean Mesquite (Prosopis pubescens), Bladderpod (Isomeris arborea), Desert Willow (Chilopsis linearis), Palo Verde (Cercidium floridum) and Cat Claw Acacia (Acacia gregii). The numbers planted are summarized in Table 1.

The container plantings were placed 1.6 meters apart in a single row on the leeward (north) side of the berm [Planting on the leeward side of the berm places the plantings immediately adjacent to the perforated pipe, reducing the amount of hand watering required during establishment and provides protection against wind]. Watering basins were shaped by hand around each plant to facilitate initial hand watering. For the smaller plants, a two foot high Supertube(tm) treeshelter secured with rebar was used to protect each seedling. To increase visibility and discourage vehicle traffic from crossing over the berm, additional treeshelters were staked in placed alongside some of the larger plants.

Erosion Control Site

Background
The erosion control site is located in training area Bravo, just west of Fort Irwin Road, across from Painted Rocks at UTM grid coordinates 0522090, 3894890. The site is 940 meters in elevation with an eastern aspect and is situated on a 4 percent slope. The soil on the site is a sand with less than 1 percent organic matter The area was once cleared, graded and used as a temporary helicopter landing pad or maintenance area. Vegetation in the area has begun to recover but remains too sparse to stabilize the soil surface. Despite the relatively high plant species diversity in the areas surrounding the site, only two species, Ambrosia dumosa and Hymenoclea salsola, have successfully colonized the landing pad area. In addition to these two species, the predisturbance vegetation community probably included Larrea tridentata, Encelia frutescens, Pleuraphis rigida, Senna armata, and Achnatherum hymenoides. The many roads and trails on site were probably created with the landing pad and have continued to be used during training activities, but not maintained. The area directly and indirectly impacted by construction of the landing pad is approximately 21,870 square meters. The area indirectly affected is difficult to estimate and likely includes a significant portion of the local watershed. The best way to estimate this impact is to view it in terms of damage to roads and trails. If corrective steps are not taken, between one and two miles of vehicle trails downslope of the landing pad (that are now beginning to show signs of serious erosion) will become impassable to non tactical vehicles within the next few seasons. Vehicle traffic along these roads has already begun to cause trail widening and damage to intact native vegetation through vehicle detours to avoid the worst of these gullies. The formation of new vehicle trails in response to poor trail conditions will be the next step. The gully erosion control component of this project was implemented along the major vehicle trails in this area, helping to maintain trail integrity and reducing the likelihood of trail widening and new trail formation.

Surface runoff patterns and natural erosion were exacerbated by clearing the landing pad area. This initiated the formation of erosion gullies that now threaten vehicle trails farther down the watershed. By situating the landing pad at the top of the watershed just below a ridge of boulders, the natural vegetation buffer that prevented point concentrations of water from developing off boulders was removed. A surface treatment plot was installed on the former landing pad site. By situating the surface treatment plot in this area, a buffer that absorbs point source accumulations from the boulders will be restored, effectively treating the cause, not just the symptoms of the erosion control problem.

Materials and Methods
Surface Treatment Area
Before surface treatments were established, the soil surface was ripped perpendicular to the slope using a box grader attached to the ITAM tractor. This was done to eliminate shallow surface erosion gullies and improve water infiltration. Above the surface treatment area, check dams were installed in all gullies to diffuse and reduce runoff before it enters the plot. The 60m x 25m surface treatment plot was divided into three 20m x 25m quadrats. One quadrat was left untreated to serve as a control, the second quadrat was treated with punched straw, and coconut fiber fences were installed in the third.

The quantity of soil translocated thus effectiveness of the punched straw and coconut fiber fences in reducing soil erosion will be determined by random placement of five marked stakes. The amount of soil accumulated or lost from the treated areas will be calculated by measuring changes in the soil level at the end of the rainy season.

Gully Erosion Control
In the area surrounding the surface treatment experiment, check dams and barriers were constructed over approximately one mile of road which had erosion gullies. These check dams and barriers were constructed using a variety of materials, depending on the size and depth of each gully. In the small gullies straw flake dams and coir (coconut fiber) dams were installed. The straw flake dams were constructed in one of two ways. The majority of the check dams installed were constructed by inserting the straw vertically into a trench that was then back filled with soil. A smaller number were constructed by placing the straw horizontal to the soil surface and then securing it in place with wire wickets. Where available, rocks were incorporated into the straw dam construction. Behind a subset of each check dam type, marked stakes were installed to compare how effective the construction was at catching sediment. On larger gullies, straw bale dams were constructed using whole straw bales keyed into the sides of the gully. To determine the utility and effectiveness of old Christmas trees as an erosion control treatment, twelve Christmas trees were stuffed into the largest gully on the site and secured in place with t- posts.

Direct Seeding Site

Background
The seeding site is located just outside the cantonment area in training area Alpha-1, east of Fort Irwin Road at UTM grid coordinates 0526148E and 3898462N. The disturbed area is approximately 70,880 square meters in size, 860 meters in elevation and generally flat with a gentle drainage to the north. The area has loose sandy loam soil with very little soil organic matter. This training site was probably used to train engineers as evidenced by extensive digging and earth moving activities. The site is largely devoid of vegetation. Vegetation surrounding the site is primarily Larrea tridentata and Ambrosia dumosa scrub. There is relatively little Erodium and Schismus to compete with any seeded native species.

Materials and Methods
The extensive earth moving activities have left the site with an exaggerated topography containing mounds and depressions ranging between 1 and 3 meters in height and depth. This unnatural landscape was smoothed and recontoured using a bulldozer prior to pitting. The loose soil did not require decompaction of any kind although one section was ripped. In order to compare the effectiveness of different seeding rates, two portions of the site were seeded at different seeding rates. The eastern third of the site, approximately 28,000 square meters in area, was seeded at a rate of 250 live seeds/ meter square. The remaining area, covering approximately 42,000 square meters, was seeded at a rate of 100 live seeds per meter square.

The entire seeding site was pitted using the SERG soil pitter pulled by a Humvee provided by ITAM prior to seeding. In order to ensure an even distribution throughout the site, the seed was mixed 1:3 with a combination of cactus mix, planting mix and peat moss as a carrying agent. The species seeded, as specified in the contract, included: Achnatherum hymenoides, Ambrosia dumosa, Atriplex canescens, Senna armata, Encelia farinosa, Ephedra nevadensis, Hymenoclea salsola, Isomeris arborea, Larrea tridentata and Sphaeralcea ambigua. The quantities used are summarized Table 2.

In order to test the effectiveness of surface amendments and soil tackifiers on seeding success, fifteen 5x5 meter quadrats were randomly located within the 42,000 square meter portion of the site. Three blocks of four treatments and an untreated control will be compared following germination in the spring. The treatments include two different types of mulch - ground peat moss and redwood compost; and two soil tackifier treatments - Soil Sement and xanthan gum. In late May, at the end of the growing season, at least three sampling quadrats per block will be randomly laid out within the treatment areas and the number of seedlings counted and results analyzed. The size and number of sampling quadrats will be adjusted based on seedling density.

Revegetation Sites

Background
Revegetation sites north and south are located east of Painted Rocks in training area Charlie, at UTM grid coordinates 0525100, 3895900. The north site is located approximately 500 meters northeast of the south site. The southern site is roughly twice the size of the northern site. Taken together, both sites total roughly 70,700 square meters in area. The southern site encompasses approximately 47,000 square meters is at 950 meters elevation. The northern site encompasses 23,000 square meters and is at 970 meters elevation. Both sites have a southern aspect and a gentle (less than 3%) slope. The soils in the area are a loose sandy loam with less than 1% soil organic matter. Soil compaction was mild at the southern site, consequently the site did not require decompaction. The soil at the north site was extremely compacted and riddled with erosion gullies. The site was ripped with a motor grader prior to project installation to reduce soil compaction and alter surface runoff patterns. Judging by the amount of resprouting Larrea tridentata, disturbance on the southern site is recent and probably less than one year old, thus does not appear on the 1993 aerial photo. The north site as a disturbed site has a long history of use dating back to the 1940s, based on the spent shells and military artifacts present. The northern site is largely devoid of vegetation except for individual Psorothamnus arborescens and has very little topsoil remaining. The southern site contains a large number of trampled Larrea tridentata and Ambrosia dumosa shrubs. The vegetation surrounding both sites is primarily Larrea tridentata and Ambrosia dumosa scrub with scattered individuals of Achnatherum hymenoides, Encelia virginensis, Lycium andersonii, Lepidium fremontii, Opuntia basilaris, Thamnosma montana and Pleuraphis rigida. Of the approximately 2000 plants allocated for planting at the revegetation sites, 1200 were planted at the south site and 850 planted at the north site.

Materials and Methods
On the south revegetation site, an experiment was set up to determine the most effective microcatchment size for shrub establishment: 128 V-shaped catchments ranging in size from 2x2 meters to 5x5 meters were constructed perpendicular to site drainage patterns. Each catchment was planted with four shrubs spaced one meter apart. A total of 512 plants were planted in the catchments: 53 Ephedra nevadensis, 58 Encelia farinosa, 64 Hymenoclea salsola, 87 Ambrosia dumosa, 87 Atriplex polycarpa, 70 Isomeris arborea and 93 Larrea tridentata. To compare survival inside the catchments with outside, a total of 630 plants were planted outside the catchments. These were planted in clusters of five plants to facilitate watering and monitoring. Also set up at the south revegetation site was an experiment investigating the effects of mycorrhizal inoculum on shrub establishment.

Mycorrhizal fungi are naturally occurring symbiotic soil fungi that live in plant roots and have been shown to influence plant growth and survival in some semi-arid ecosystems. For restoration projects, there are two sources for mycorrhizal inoculum, field collected material and commercially available species. Differences between these sources are unclear. To determine whether the addition of mycorrhizal inoculum is useful in improving shrub establishment at Fort Irwin and which inoculum source is the most effective, an experiment was set up. In this experiment 20 Encelia frutescens plants were planted using no inoculum addition, 20 plants inoculated with mycorrhizal inoculum native to Fort Irwin, and 20 plants inoculated with a commercially available mycorrhizal fungus, Glomus intraradices. These 60 plants were randomly installed in a grid pattern with 2 meter spacing between individual shrubs. Plant height and survivorship will be recorded after 4 months, 6 months and 10 months to determine the effects of mycorrhizal inoculum additions.

The north revegetation site offers an opportunity to integrate container planting and seeding with erosion control. The north site is located on the shoulders of a small set of hills topped by rocky outcroppings. Training activities have disturbed the vegetation at the base of this hill. Where the rocks end, there is scant vegetation to prevent water concentrated by the rocks from flowing unchecked. A compacted trail that cuts across the top edge of the site only aggravates this problem by increasing surface runoff into the site.

When combined with heavy soil compaction and sparse vegetation, the result has been sheet erosion and erosion gullies cutting across the site and damage to a vehicle trail that passes along the southern perimeter. To slow and reduce the flow of water into the site, check dams were concentrated at the base of the rocks. To investigate the best construction techniques, these check dams were built in two different ways; using rocks alone and rocks interwoven with jute netting. In the larger wash areas that flow into the site, three different surface erosion treatments were applied to help absorb the additional runoff created by the trail that cuts across the north edge of the site. These surface treatments included jute netting, punched straw and the placement of rocks over 30% of the soil surface. In order to determine the effect of the surface treatments on seed establishment, these areas were lightly seeded using 10 to 20 live seeds / sq. meter. Covering the majority of the north site, 3x3 meter microcatchments were constructed to prevent the formation of new erosion gullies on the freshly graded site and to facilitate shrub establishment. At total of ninety 3x3 meter catchments were constructed. Half of these catchments were lightly seeded after planting to determine the effect of catchments on seed establishment. A subset of these catchments were treated with bark mulch and straw to determine the effect of surface amendments on catchment efficiency.

Results