4: Conservation and maintenance of soil and water resources

Soil and water underpin forest ecosystem productivity and functions. Forest ecosystems play an important role in the regulation of surface and groundwater flow and, together with associated aquatic ecosystems and clean water, they are essential to the quality of human life. The interaction of soil, water and topography influence the character and health of streams and rivers flowing through and from forests. Monitoring change in the chemical, physical, and biological characteristics of soil, water and aquatic systems provides valuable information to support sustainable forest management.

Forest management activities can significantly alter forest soils, water quality and associated aquatic habitats. Inappropriate management may result in soil compaction, the loss of the soil A horizon, loss of riparian buffering capacity, increased sediment loads in streams, degradation and destruction of aquatic habitats and altered flow regimes. Change in water flow can also create an increased risk of flooding or the complete desiccation of streams. Both have harmful implications for human safety, property, and economies. Soil and water resources may be protected through the allocation of land for that purpose or through appropriate management regimes and best management practices.

Associated 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.

Area and percent of rangeland with a significant change in extent of bare ground

Bare ground is exposed mineral or organic soil that is susceptible to raindrop splash erosion. Increases in bare ground and greater homogeneity of existing bare ground relate—directly—to a site’s susceptibility to accelerated wind or water erosion. The importance of bare ground as an indicator is a function of 1) its direct relationship to erosion risk, 2) its known value as an indicator of changes in land management and watershed function, and 3) the ease and economy with which this indicator can be monitored over extensive areas, particularly when using remote sensing methods.

Area and percent of rangeland with accelerated soil erosion by water and wind

Soil erosion by wind or water begins with the loss of all or part of the surface horizon. Surface horizons of soils are important to maintain because they contain the majority of the organic material and are the exchange medium for transferring nutrients from the soil to plants. This indicator will identify areas where erosion is greater than expected for the soils on a specified site.

Area and percent of rangeland with significantly diminished soil organic carbon

This indicator measures the soil organic carbon (soil organic matter) content of the soil and the carbon:nitrogen (C:N) ratio of the soil organic matter. The C:N ratio is a relative measure of soil organic matter’s potential for biological decomposition. Soil organic matter provides many benefits to the soil and is associated with the productive potential of soils and soil sustainability. Grazing management that ensures a healthy plant community can result in increased soil organic matter through increased carbon sequestration (Schuman et al. 2002).

Biologic Integrity Index for Forest Streams

Evaluate stream health and indirect watershed health. An index of biotic integrity (IBI) combines several metrics from stream monitoring data to evaluate overall stream health. The IBI index score has been shown to be correlated with different levels of human disturbance. Where data exists it can be evaluated against IBI scores for forested areas with unimpaired streams that serve as reference conditions.

Biological integrity of forest streams

This indicator will provide information in tabular, graphical, and map formats that integrates complex biological data into a single number that, together with reference condition information, indicates the degree of biological alteration or quality of a given water body. Maintaining high quality aquatic biological assemblages is very important to the public, and protecting those biota forms the basis for water quality standards. Although indirect or surrogate indicators are important, only biological indicators can directly assess biological condition.

Changes in groundwater systems

Because groundwater is a crucial source of fresh water, supplying the major source of drinking water for more than 50 percent of the U.S. population and 96 percent of the rural domestic supply of water, a case could be made that groundwater has a direct connection with social, economic, and ecological sustainability of rangelands. Groundwater is used for irrigated pastures that supply winter forage for livestock in many regions of the country. Many of the streams, rivers, and wet meadows in rangeland depend on groundwater and the connection between groundwater and shallow water tables. Down-cutting of mountain meadows can lower water tables and cause the replacement of water-loving vegetation with upland species.

Changes in the frequency and duration of surface no-flow periods in rangeland streams

This indicator annually measures the percentage of rangeland streams with at least one day of no-flow (also referred to as zero-flow) in a year, and, of those, the percentage that have a duration of zero-flow for a given period that is substantially longer or shorter compared with a long-term average. Together, these two variables describe the frequency and duration of surface no-flow periods. Stream-flow is critical in sustaining the habitat necessary for many rangeland plants and animals. Increasing no-flow periods can lead to loss of streamside vegetation and wildlife habitat for many rangeland species. No-flow periods can lead to loss of fish and aquatic animals.

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.

Conservation and Maintenance of Soil and Water Resources: Bulk density

The bulk density of a soil is inversely related to its porosity and depends on the mineral composition of the soil.. For example, sandy soils will have low bulk density and high porosity, whereas clayey soils will have the opposite. Soils can become artificially compacted, which will change their bulk density and porosity.