USDI Indicators of Rangeland Health (2000)

Area of Focus

Forest and Rangeland Frameworks

This framework for evaluating rangeland health was developed by an inter-agency consortium of scientists from the Bureau of Land Management, the Natural Resources Conservation Service, the US Geological Survey, and the Agricultural Research Service. It describes the use of ecosystem attributes to evaluate rangeland condition in comparison to reference conditions.

Ecological processes include the water cycle (the capture, storage, and redistribution of precipitation), energy flow (conversion of sunlight to plant and animal matter), and nutrient cycle (the cycle of nutrients such as nitrogen and phosphorus through the physical and biotic components of the environment). Ecological processes functioning within a normal range of variation will support specific plant and animal communities. Direct measures of site integrity and status of ecological processes are difficult or expensive to measure due to the complexity of the processes and their interrelationships. Therefore, biological and physical attributes are often used as indicators of the functional status of ecological processes and site integrity.

The National Research Council (1994) publication, Rangeland Health, New Methods to Classify, Inventory, and Monitor Rangelands defined rangeland health as: "the degree to which the integrity of the soil and ecological processes of rangeland ecosystems are maintained."

Indicators are components of a system whose characteristics (e.g., presence or absence, quantity, distribution) are used as an index of an attribute (e.g., rangeland health) that is too difficult, inconvenient, or expensive to measure. Just as the Dow Jones Index is used to gauge the strength of the stock market, so different combinations of the 17 indicators are used to gauge soil/site stability, hydrologic function, and the integrity of the biotic community of selected rangeland ecological sites. Each of the indicators is followed by five descriptors with a narrative that the evaluator(s) reviews prior to agreeing on an appropriate category for each indicator.

Indicators

Amount of plant litter
Litter is any dead plant material that is in contact with the soil surface. That portion of the litter component that is in contact with the soil surface (as opposed to standing dead vegetation which is not) provides a major source of the soil organic material and the raw materials for onsite nutrient cycling. Litter also helps moderate the soil microclimate and provides food for microorganisms. The amount of litter present is also a factor in enhancing the ability of the site to resist erosion.
Annual plant production
Aboveground biomass (i.e., annual production) is an indicator of the energy captured by plants and its availability for secondary consumers in an ecosystem given current weather conditions. Production potential will change with communities or ecological sites, biological diversity, and with latitude. Annual production of the area of interest is compared to the site potential from the rangeland ecological site description and/or the ecological reference area(s).
Bare ground compared to expected
Bare ground is exposed mineral or organic soil that is susceptible to raindrop splash erosion, the initial form of most water-related erosion. It is the opposite of ground cover, which is the percentage of ground surface covered by vegetation, litter, standing dead vegetation, gravel/rock, and visible biological crust (e.g., lichen, mosses, algae), meaning everything except bare ground.
Compaction layer
A compaction layer is a near surface layer of dense soil caused by the repeated impact on or disturbance of the soil surface. Compaction becomes a problem when it begins to limit plant growth, water infiltration or nutrient cycling processes. Farm machinery, herbivore trampling, recreational and military vehicles, foot traffic, or any other activity that repeatedly causes an impact on the soil surface can cause a compaction layer.
Functional/structural plant groups
Functional/structural groups are a suite of species that because of similar shoot (height and volume) or root (fibrous vs. tap) structure, photosynthetic pathways, nitrogen fixing ability, or life cycle are grouped together on an ecological site basis. factors that change ecosystem composition, such as invasion by novel organisms, nitrogen deposition, disturbance frequency, fragmentation, predator decimation, species removal, and alternative management practices can have a strong effect on ecosystem processes.
Gully formation
A gully is a channel that has been cut into the soil by moving water. Gullies generally follow the natural drainages and are caused by accelerated water flow and the resulting down-cutting of soil. Gullies are a natural feature of some landscapes, while on others management actions (e.g., excessive grazing, recreation vehicles, or road drainages) may cause gullies to form or expand.
Invasive plants
This indicator deals with plants that are invasive to the area of interest. These plants may or may not be noxious and may or may not be exotic. Generally they are invaders or increasers to the site that can, and often do, continue to increase regardless of the management of the site and may eventually dominate the site. Invasives can include noxious plants (i.e., plants that are listed by a state because of their unfavorable economic or ecological impacts), non-native, and native plants.
Litter (dead plant material) movement
The degree and amount of litter (i.e., dead plant material that is in contact with the soil surface) movement (e.g., redistribution) is an indicator of the degree of wind and/or water erosion. The redistribution of litter within a small area on a site is indicative of less erosion, whereas the movement of litter offsite due to wind or water is indicative of more severe erosion.
Pedestals and/or terracettes (rocks and plants)
Pedestals and terracettes are important indicators of the movement of soil by water and/or by wind. Pedestals are rocks or plants that appear elevated as a result of soil loss by wind or water erosion. Pedestals can also be caused by non-erosional processes such as frost heaving or through soil or litter deposition on and around plants, thus it is important to distinguish and not include this type of pedestalling as an indication of erosional processes.
Plant community composition and distribution relative to infiltration and runoff
Vegetation growth form is an important determinant of infiltration rate and interrill erosion. The distribution of the amount and type of vegetation has been found to be an important factor controlling spatial and temporal variations in infiltration and interrill erosion rates on rangelands in Nevada, Idaho, and Texas.
Plant mortality/decadence
The proportion of dead or decadent (e.g., moribund, dying) to young or mature plants in the community relative to that expected for the site, under normal disturbance regimes, is an indicator of the population dynamics of the stand. If recruitment is not occurring and existing plants are either dying or dead, the integrity of the stand would be expected to decline and other undesirable plants (e.g., weeds or invasives) may increase. A healthy range has a mixture of many age classes of plants relative to site potential and climatic conditions.
Reproductive capability of perennial plants
Adequate seed production is essential to maintain populations of plants when sexual reproduction is the primary mechanism of individual plant replacement at a site; however, annual seed production of perennial plants is highly variable. Comparing number of seedstalks and/or number of seeds per seedstalk of native or seeded plants (not weeds or invasives) in the evaluation area with that produced on the associated ecological reference area (ERA) can be used to assess seed production.
Rill formation
Rills are small erosional rivulets that are generally linear and do not necessarily follow the microtopography as flow patterns do. They are formed through complex interactions between raindrops, overland flow, and the characteristics of the soil surface.
Soil surface loss or degradation
The loss or degradation of part or all of the soil surface layer or horizon is an indicator of a loss in site potential. In most sites, the soil at and near the surface has the highest organic matter and nutrient content. This generally controls the maximum rate of water infiltration into the soil and is essential for successful seedling establishment.
Soil surface resistance to erosion
This indicator assesses the resistance of the surface of the soil to erosion. Resistance depends on soil stability, microtopography, and on the spatial variability in soil stability relative to vegetation and microtopographic features. The stability of the soil surface is key to this indicator. Soil surfaces may be stabilized by soil organic matter which has been fully incorporated into aggregates at the soil surface, adhesion of decomposing organic matter to the soil surface, and biological crusts. The presence of one or more of these factors is a good indicator of soil surface resistance to erosion.
Water flow patterns and erosion
Flow patterns are the path that water takes (i.e., accumulates) as it moves across the soil surface during overland flow. Overland flow will occur during rainstorms or snowmelt when a surface crust impedes water infiltration, or the infiltration capacity is exceeded. These patterns are generally evidenced by litter, soil or gravel redistribution, or pedestalling of vegetation or stones that break the flow of water. Interrill erosion caused by overland flow has been identified as the dominant sediment transport mechanism on rangelands.
Wind-scoured, blowouts, and/or deposition areas
Accelerated wind erosion on an otherwise stable soil increases as the surface crust (i.e., either physical, chemical, or biological crust) is worn by disturbance or abrasion. Areas of wind erosion within a vegetation community are represented by wind-scoured or blowout areas where the finer particles of the topsoil have blown away, sometimes leaving residual gravel, rock, or exposed roots on the soil surface. Deposition of suspended soil particles is often associated with vegetation that provides roughness to slow the wind velocity and allow soil particles to settle from the wind stream.