Natural drainage takes place in soils where the hydraulic conductivity values are either uniform or increase with depth. Visual evidences of inadequate drainage include surface wetness, lack of vegetation, crop stands of irregular color and growth, variations in soil color, and salt deposits on the ground surface. A lack of natural drainage often causes a high water table and, under some conditions, can cause surface ponding of water. Soils that have a slowly permeable subsoil, rock formation, or compact (hardpan) layer below the surface (either within the normal root zone of plants or at a greater depth) restrict drainage. Compact layers can result from human activities or can occur naturally. Also soils in arid and semiarid areas may have high water tables, which indicates restricted drainage and leads to salt accumulations.
Drought can increase erosion and the occurrence of wildfires. Decreased vegetation is the main cause of erosion due to drought. To help plan for and manage drought impacts the U.S. Drought Monitor (produced in partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration), provides drought impact reports, indicators, drought indices, rainfall, vegetation/temperature outlook, and soil moisture information.
Erosion refers to the loss of soil as a result of the forces of gravity, water, ice, or wind acting upon the surface of the soil. Geological or natural erosion occurs under natural environmental conditions and geological processes. Accelerated erosion occurs as a result of the influence of humans and/or animals. Major disturbance events, such as wildfires, can accelerate erosion. Maintaining adequate plant cover to protect a watershed, reducing compaction, and using good road building practices are the best ways to minimize accelerated erosion. For information regarding soil erosion monitoring and assessment see Technical Note 438 Upland Soil Erosion Monitoring and Assessment: An Overview June 2011.
Invasive Species, including weeds, can increase erosion by killing native ground level plants that normally hold soil and can alter the amount of nutrients in soils, thus impacting the plant and animal life in the area. One of the Bureau of Land Management’s (BLM’s) highest priorities is to promote ecosystem health and one of the greatest obstacles to achieving this goal is the rapid expansion of weeds across public lands. These invasive plants can dominate and often cause permanent damage to natural plant communities. The BLM works with State, Federal and local partners to reduce the spread of invasive species, with an emphasis on early detection of and rapid response to new invasions in order to reduce the need for larger, more expensive treatments later on.
Loss of organic matter decreases soil functions including soil fertility and plant productivity. Organic matter improves the ability of the soil to store and supply nutrients, water, and air, thus supporting plant growth. Wind and water erosion increase losses of organic matter. Erosion breaks down soil aggregates, exposing organic matter to decomposition and loss. Organic-rich soil from the surface layer can be carried away by runoff or wind. Overgrazing reduces the amount of plant energy available for the growth of new roots, which provides much of soil’s organic matter. Trampling also breaks up soil aggregates, exposing organic matter to decomposition and loss through erosion.
Strategies that the Bureau of Land Management (BLM) may use to help to maintain soil organic matter includes increasing or maintaining plant production, protecting the soil from erosion by maintaining or increasing the plant cover and reducing the amount of bare soil, and properly managing grazing, fire, and vehicle use to promote the desired plant community and protect the soil from erosion.
Salinization is the process by which water-soluble salts accumulate in the soil. Salinization is a resource concern for the Bureau of Land Management (BLM) because excess salts hinder the growth of some plants by limiting their ability to take up water. High levels of salt in the soil have a similar effect as drought because water is less available for uptake by plant roots. Salinization may occur naturally or because of conditions resulting from management practices. Salinization can be avoided or reduced by promoting adequate infiltration and permeability, including building organic matter for soil aggregation and avoiding compaction. Soil salinity can be estimated by measuring the electrical conductivity of the soil solution. For additional information see the USDA Soil Quality Resource Concerns Information Sheet: Salinization.
Soil Compaction can result from trampling of livestock, big game animals or humans, or by operation of mechanical equipment or vehicles across the soil surface. Compaction reduces infiltration, available water capacity, aeration of plant roots, and habitat requirements for some soil organisms. Compaction can increase runoff, erosion, and resistance to plant root growth. The degree of soil compaction can be determined by the soil bulk density. For additional information see USDA Rangeland Fact Sheet 4 — Compaction.
Wildfire impacts go beyond burnt vegetation. The potential for severe soil erosion and accelerated water runoff exists after a wildfire due to the lack of plant material to stabilize the soil. Soil erosion and water runoff can cause severe damage to property and pose safety hazards. Where soil erosion potential is high after a fire, the Bureau of Land Management (BLM) can use soil stabilization techniques that can protect water quality, property values, and human life and safety. Examples include spreading straw mulch on unstable slopes, straw bale check damns, or straw wattles.