The Interaction between Watershed Processes and Rangeland Health as a Function of Scale.

Updated 02/27/2009

Mark A. Weltz, Leonard J. Lane ¹, Mary R. Kidwell ¹, and H. Dale Fox ²

¹USDA-ARS Tucson, Arizona
²USDA-NRCS, Phoenix, Arizona

Rangeland health has been defined as the degree to which the integrity of the soil and the ecological processes of rangeland ecosystems are sustained (NRC, 1994). Three problems that limit current methods of evaluating rangeland health have been identified:

1. The use of the climax community.
2. Determining thresholds of change.
3. Reliance on change in plant composition and productivity as the sole indicator of change in the ecological state of rangelands.

Various procedures have been developed to assess rangeland health, including that of the National Resource Conservation Service which considers 17 attributes for three categories of soil stability and watershed function, presence of recovery mechanisms, and integrity of nutrient cycles and energy flow. Each attribute is qualitatively scored on the basis of five rating classifications which are assessed against a standard. The standard used is the NRCS’s Ecological Site Description. Our goal is to develop criteria to determine healthy, at risk, and unhealthy rangelands with respect to soil stability and watershed function, i.e. a methodology for assessing sustainable ecosystems (rangeland health). With this in mind we need to bring the concepts, theory and data from hydrology, soil erosion, ecological sciences and geomorphology together to address rangeland health issues. "Point" or "lumped" qualitative indicators of rangeland health must be extended to quantitative distributed measures at the watershed scale, new models and tools must be developed to provide quantitative assessments and science-based decision making for rangeland management.

First, we must recognize that different tools are required for different questions.

1. Time and resources available to address the question:
   Status (health) of an allotment vs. status of an ecoregion.
2. Time frame of concern:
   Annual monitoring vs. geologic time.
3. Precision and accuracy required:
   Occular estimates of standing biomass (qualitative) vs. clipping and Weighing standing biomass (quantitative) measurements.
4. Differing resource concerns:
   Water resource issues vs. habitat concerns.

Once the tools are identified, proper implementation of technology transfer depends on understanding the clients needs. This may include having knowledge of clients computer hardware, the complexity and compatibility of software, data requirements and databases, the time allocated to collect field data, the interpretation of data, and the training requirements for using computer software and field techniques.

In terms of rangeland erosion processes, the scale at which assessments are done will determine the rangeland attributes that must be measured (see Table 1).

* Attributes not presently included but necessary for watershed scale rangeland health assessments.

Once the rangeland health attributes, and potential stressor scenarios have been assembled the information must be processed to yield an assessment of rangeland health. For this we propose to link rangeland health research and technology transfer components based on an expert system (See Figure 1). An expert system is a computerized system which embodies databases, organized knowledge, and simulation models in an area of expertise to perform as a skilled, effective consultant. In this case the area of espertise is rangeland health; specifically soil/site stability. A proposed scenario for our prototype expert system is shown in Figure 2.

Watersheds are complex features, and regions within a watershed may behave very differently from one another. Consider a conceptual system where a watershed is divided into four regions based on stability and erosion: An (outer) area of diffuse sheet flow; an area of concentrated sheet flow; an area where water is directed along rills; and a gully area. There are four methods to analyze the relative contributions of each region within a watershed to determine one overall rating for the watershed as a whole:

• Uniform weight method: Area of land attributed to each region are weighted equally.
• Relative ranking: Area of land attributed to each region are ranked based on perceived importance
• Area weight method: Area of land attributed to each region are weighted based on the percentage of area occupied within the watershed.
• Process weight method: Area of land attributed to each region are weighted using a percentage value that is deemed appropriate for the processes that occur within each dedicated area of the watershed.

Another pivotal component of the system is the Decision Support System (DSS) which is an Excel spreadsheet based on the implementation of the rangeland health worksheet. It is a hierarchical multi-attribute tool for prioritization of management decisions. DSS technology allows each attribute to be independently evaluated within each category so there is no codependence of an attribute from one category to another (see Table 2).

The ARS and NRCS hope to develop better information on how conservation practices affect resource concerns on rangeland. This will be done through research on the Santa Rita Experimental Range, Walnut Gulch Experimental Watershed, and Audubon Research Ranch, Arizona; Jornada Experimental Range, Alamogordo Creek Watershed, New Mexico; Fort Carson Army Base, Fort Collins, Colorado; and La Campana Experimental Ranch, Chihuahua, Mexico. The components of rangeland health will be examined to determine how to best measure and evaluate ecosystem functions. Over the next several years, ARS will develop and begin long term research on soil stability and watershed function. The goal is to develop a methodology to assess rangeland health based on criteria to determine healthy, at risk, and unhealthy rangelands with respect to soil stability and watershed function.

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