Connectivity and corridors, Habitat management, Restoration
Plant and Topsoil Salvage Methods for Revegetation after Road Disturbance in Lake Mead National Recreation Area
Case Study by the Conservation and Adaptation Resources Toolbox
Status
Ongoing

Location

States

Nevada

Ecosystem

Desert

Subject

Connectivity
Deserts
Parks
Plants
Recreation
Restoration
Roads
Vegetation

Introduction

A plant in the desert in a circular fence enclosure
Image Details

Lake Mead is a 563,513-hectare (1,392,471-acres) National Recreation Area managed by the National Park Service (NPS) in southeastern Nevada and northwestern Arizona. Lake Mead has the largest water capacity of any reservoir in the United States. Water flows into Lake Mead from the Colorado River, ephemeral washes during storm events, and storm drains and a wastewater treatment plant in Las Vegas, Nevada. Lake Mead lies within the Mojave Desert, which contains perennial shrubs such as creosote bush, white bursage, and desert holly. These plants provide habitat for species including the desert tortoise, desert plantain, other native annual plants, and pollinators.

Key Issues Addressed

Maintaining the aesthetic of National Park lands is important for recreation. Disturbances, such as road maintenance, remove mature perennial shrubs and native vegetation that provide important ecosystem services. In 2008-2009, a maintenance project was implemented in the upper reach of Lake Mead National Recreation Area to widen and straighten Northshore Road. Collaborators are attempting to restore areas affected by maintenance activities in order to re-establish habitat that might not recover otherwise and to test methods that mitigate disturbance-related impacts. 

Project Goals

  • Balance biodiversity conservation and aesthetic restoration in a nationally protected area
  • Determine best methods for successfully revegetating sites after disturbance
  • Identify plant species and lifeforms that survive salvage and outplanting activities

Project Highlights

Soil Salvage: Salvaged topsoil retains microbial communities, often formed in special association with plant species, which are critical for improving survival of certain plants in harsh environments

  • Plant and Soil Salvage: Prior to the construction of the new Northshore road, 2,105 plants were salvaged, including 23 species of cacti, grasses, forbs, and shrubs. Topsoil was scraped from the top 5-20 cm of the soil surface and stored on site for later re-distribution. After plant collection, roots were subjected to one of three treatments:

    • Root stimulating hormone (IBA);
    • A slurry of watersorb water crystals, which slowly releases water to the roots;
    • Either a dip or overnight soaking.

  • Nursery Survival Determination: For one year, salvaged plants were kept in pots at a nursery located near the study site. The plants were drip irrigated, receiving a total of 3 cm of water daily. After a year, plant survival in nursery conditions was determined. A determination of plant survival under nursery conditions was made at the end of the year.

  • Field Study: A 5-cm thick layer ofsalvaged topsoil was spread in 3/4 of the area where the road was removed. Surviving salvaged plants were transplanted and enclosed within 1-m tall circular mesh cages. Each plant was randomly assigned a watering treatment: DRiWATER, hand watering, or no further watering at time of planting. DRiWATER packets were buried and angled towards the root zone of individual plant species; Packets were replaced monthly from May through September and every three months from October through April. Once a month, hand watering treatments supplemented 0.5 L of water to each plant receiving this treatment.  

  • Tracking Field Survival: Vegetation surveys were conducted 3, 15, and 27-months after transplanting. During the final assessment, the number of natural recruits in both topsoil amended and non-amended areas were counted.

Lessons Learned

An individual crouches by some plants in fenced enclosures in a desert
Image Details
  • The overall transplanting success rate was 27%, including salvage to nursery and nursery to outplanting. However, the project was successful as an experiment to determine best methods for plant salvage and revegetation of disturbed sites at the park.
  • Forty-eight percent or 1,017 of plants survived salvage and nursery storage. Surprisingly, 143 new recruits emerged the year the plants were in the nursery which increased the number of plants for future transplant to 1,160. Ultimately, a total of 1,153 plants were transplanted in the field.
  • Applying IBA, water (soaking overnight or dipped), a slurry of water sorbed crystals, and IBA+slurry to the roots did not significantly increase survival of salvaged plants in the nursery at lifeform or species level.
  • Shrub survival decreased when roots were soaked in water overnight.
  • The following species survived salvage with no water treatment:
    • White bursage (Ambrosia dumosa)
    • Desert globemallow (Sphaeralcea ambigua)
    • Creosote bush(Larrea tridentata)
  • Although the survival of the following species was low regardless of treatment type, these plants survived salvage and nursery storage:
    • Torrey’s Mormon tea (Ephedra torreyana)
    • Desert trumpet(Eriogonum inflatum)
  • In the field, 56% of plants survived transplanting where salvage topsoil was placed. This was similar to survival of irrigated plants. Survival was 25% in areas without salvage topsoil.
  • Irrigation treatment effects on plant survival varied across species and lifeforms.
    • The survival of white bursage was similar with DRIWATER and hand watering treatments. The survival of desert globemallow increased the most with hand watering.
    • At the lifeform level, survival was 65% higher for transplants receiving hand watering and DRIWATER treatments versus those that received no irrigation.
    • Survival rate increased with irrigation for:
      • Creosote bush (Larrea tridentata)
      • Desert globemallow (Sphaeralcea Ambigua)
      • Brownplume wirelettuce (Stephanomeria pauciflora)
      • White bursage (Ambrosia dumosa)
  • At 27-months, 571 (50%) of the transplants survived, with most mortality during the first 15 months.
    • Cactus species that best survived both salvage and transplanting were:
      • California barrel cactus (Ferrocactus cylindraceous)
      • Buckhorn cholla (Opuntia acanthocarpa)
      • Beavertail prickly pear (Opuntia basilaris)
      • Johnson’s bee-hive cactus (Sclerocactus johnsonii)
    • Forb species that best survived both salvage and transplanting were:
      • Desert globemallow (Sphaeralcea Ambigua)
      • Brownplume wirelettuce (Stephanomeria pauciflora)
    • Shrub species that best survived both salvage and transplanting were:
      • Shadscale saltbush(Atriplex confertifolia)
      • White bursage (Ambrosia dumosa)
      • Desert holly (Atriplex hymenelytra)
      • Creosote bush (Larrea tridentata)
      • Virgin river brittlebush (Encelia virginensis)
    • Big galleta (Pleuraphis rigida), a grass species, survived salvage and transplanting
  • For the most part, species that survived salvaging were also likely to survive transplanting.
  • Transplanting resulted in increased density of perennial plants compared to only placement of salvaged topsoil.

Next Steps

  • Determine whether flowering and seed production of surviving transplants will facilitate expansion of plant populations and provide sufficient food resources for desert biota
  • Compare the presence of shady, cooler, microclimate between undisturbed and restored desert ecosystems to evaluate the effectiveness of revegetation efforts
  • Optimize salvage costs and benefits by adjusting methods to only salvage the topsoil beneath perennial shrubs
  • Restore disturbed areas with the best performing species and treatments
  • Test the placement of DRiWATER packages at different depths and angles to optimize the utilization by plants

Funding Partner

Resources

Contact

Case Study Lead Author

  • Andrea Lopez, CART Graduate Research Assistant, University of New Mexico

Suggested Citation

Lopez, A. (2018). “Plant and Topsoil Salvage for Revegetation in Lake Mead National Recreation Area.” CART. Retrieved from https://www.fws.gov/project/revegetation-after-road-disturbance-lake-mead.

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