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Rangeland Assessment and Monitoring Committee

Evaluating Rangeland Sustainability: The Evolving Technology

The Task Group on Unity in Concepts and Terminology

Membership of the Task Group on Unity in Concepts and Terminology was established by the Society for Range Management Board of Directors in 1989.

Reprinted from Rangelands, 17(3), June 1995 with permission


E. Lamar Smith
University of Arizona
Tucson, Arizona

Patricia S. Johnson
South Dakota State Univ.
Brookings, South Dakota

George Ruyle
University of Arizona
Tucson, Arizona

Fred Smeins
Texas A&M University
College  Station, Texas

Dick Loper
Lander, Wyoming

Dick Wetsell
Pawhuska, Oklahoma

Dennis Child
Washington, D.C.

Phillip Sims
Woodward, Oklahoma

Ray Smith
Bureau of Indian Affairs
Herndon, Virginia

Len Volland
USDA Forest Service
Portland, Oregon

Miles Hermstrom
U.S. Forest Service
Lakewood, Colorado

Everet Bainter
Casper, Wyoming

Arnold Mendenhall
Soil Conservation Service
Lincoln, Nebraska

Jennifer Haley
National Park Service
Boulder City, Nevada

Keith Wadman
Soil Conservation Service
Washington, D.C.

Dave Franzen
U.S. Fish and Wildlife Service
Lakeview, Oregon

Milt Suthers
U.S. Fish and Wildlife Service
Evergreen, Colorado

John Willoughby
Bureau of Land Management
Sacramento, California

Ned Habich
Bureau of Land Management
Lakewood, Colorado

Tom Gaven
Nation Park Service
San Francisco

The current condition and trend of American rangelands continues to be a topic of controversy and confusion. National reports on range condition have often provided different interpretations of the same data and are of limited utility for planning, budgeting or making policy decisions. The deficiency in these reports stems partly from lack of uniformity in the approaches used to measure range condition and the terminology used by the various land management agencies. A larger problem is that the attributes measured and their interpretation are not consistently related to the land management objectives. Further the concepts on which range condition have been based has not evolved along with the current theory about the nature of ecosystem changes.  

Methods used in the inventory and evaluation of rangelands have not kept pace with the developing ecological theories of plant succession. While an understanding of how vegetation change occurs and likely pathways for change is vital for good rangeland management, Clementsian-based successional theory is an inappropriate model of vegetation change on many rangelands, particularly those of the and West. Interpretations of successional status, or seral stage, are not adequate to assess whether or not rangelands are properly protected from site degradation, meeting management objectives or other characteristics related to biological diversity or nutrient cycling.

Protection and long-term sustainability of the natural resource base are major objectives in rangeland management. Currently, there is no consistent indicator of site protection or soil stability. Further, little can be interpreted regarding site protection or soil stability from reports in which the many rangeland sites of a region are lumped together and millions of acres in excellent, good, fair and poor condition (or climax, high seral, etc. stages) are enumerated. This is further exacerbated by the inconsistent use of terminology throughout the profession.

Fig. 1. Concept of site conservation threshold for a particular ecological site. The measurable attribute influencing erosion may vary depending upon characteristics of the site. The response curve is hypothetical, but illustrates a threshold level (shaded area) of site protection below which allows for an increase in the rate of soil erosion.

Recognizing that these problems are hampering effective communication and decision making in the management of rangelands the Society for Range Management Board of Directors established the Task Group on Unity in Concepts and Terminology (Table 1). The principal task was to develop solutions to the problems related to the evaluation, interpretation and reporting of rangeland condition and trend information and seek, through the Society for Range Management, commonality and unity in terminology and methodology. The purpose of this article is to provide an update on the findings of this Task Group and report those items the SRM's Board of Directors has approved as standards and guidelines for the profession.

The deliberations of the Task Group were open discussions involving membership from throughout the SRM and with the input from private and public rangeland managers, researchers and administrators. The membership of SRM was kept abreast by notices in the Trail Boss, symposia at annual meetings and by keeping the SRM Board of Directors abreast of all discussions. The Task Group used the consensus approach to all decisions made and fostered input at every stage of the discussions.

The Basic Resource 

The most important and most basic physical resource on rangelands is the soil. If excessive soil is lost, the potential of the site is changed. The site is no longer capable of supporting the same variety of plant communities it once produced. Avoidance of accelerated erosion due to land management should be the underlying goal. We define "accelerated erosion" as when the loss of soil is significantly greater than the "normal" or "geologic" erosion for the site. Erosion is, however, extremely difficult—some would argue impossible—to measure. Since the plant community is integral to protection of the soil, has characteristics that can be measured, and is the factor most readily managed and manipulated on a site, the Task Group agreed that it should be a primary focus for determinations of site protection.

Evaluation Approach 

The Task Group developed an approach to the assessment of rangelands which concentrates on the dual objectives of land managers to meet management objectives while conserving long-term environmental options through site protection. The result of our efforts is a conceptual framework for evaluating the status of rangelands. it is just that, a framework, and not a finished product. We can, however, begin to use this framework with current knowledge, and continue to refine the system as our knowledge expands through research and experience. This approach has the following guidelines:

Guideline #1: Ecological Sites 

Rangelands are to be classified into ecological sites as a basis for rangeland inventories, assessments, and extrapolation of research and management experience.

The capacity of rangeland to produce vegetation is determined primarily by climate and soil. Given a general climatic pattern, soil properties reflect the integrated effects of topography, geology, and geomorphic and land use history, thus determining the ability of the land to supply moisture and nutrients to plants. An ecological site is defined as a kind of land with specific physical characteristics which differs from other kinds of land in its ability to produce distinctive kinds and amounts of vegetation and in its response to management. This is an appropriate land classification regardless of the type of land being considered (e.g. grassland, woodland, forestland, even cropland) and it is not restricted to evaluation of rangeland for any particular use. All rangelands, both public and private, should be classified by ecological sites.

Recognition of land types which differ significantly in their ability to produce vegetation, either kind or amount, is fundamental for predicting response of vegetation to nature's forces or to management practices and for extrapolating research and management experience to the landscape. Differences in any of the physical or cultural factors significant to management would constitute the basis for recognizing a different ecological site.

Fig. 2. Multiple plant communities identified for a hypothetical, ecological site are illustrated both above (I-V) and below (A and B) the site conservation threshold. Arrows indicate possible transitions among plant communities due to natural processes or management.

Guideline #2: Site Conservation Threshold (SCT) and Site Conservation Rating (SCR)

Vegetation communities should be evaluated as to their effectiveness in protecting a site from accelerated erosion. The point at which erosion appreciably accelerates due to management influences would be called the Site Conservation Threshold (SCT) (Figure 1). For example, as ground cover decreases on an ecological site (Figure 1), erosion increases. At some cover value the rate of erosion accelerates. This point is the SCT. There will be some uncertainty in the estimation of SCT for an ecological site, thus the gray zone around SCT (Figure 1). The SCT may be estimated using one or more parameters of the vegetation (for example, canopy cover, basal area, density, lifeform, species, biomass) as well as soil surface characteristics. The SCT, and the parameters used to measure it, would be very specific to the ecological site.

Vegetation occurring on a particular site would be evaluated in relation to the criteria for the Site Conservation Threshold for that site. Those situations where the community meets the criteria for protection of the site would be assigned a Site Conservation Rating (SCR) of "sustainable"; all others would be "unsustainable." Ecological sites having an SCR of unsustainable may not have necessarily suffered a significant loss in site potential. This potential will be lost eventually, however, if the kind, amount or pattern of vegetation is not altered. If continued long enough, the site potential will be changed permanently and sufficiently to require the description of a new ecological site.

Guideline #3: Desired Plant Communities (OPC)

An ecological site may support several different plant community types at different locations or times (Figure 2). These plant communities may differ in species composition, life forms, or other attributes. Vegetation communities which have a Site Conservation Rating (SCR) exceeding the Site Conservation Threshold (SCT) (Figure 2) are considered to adequately protect the site from accelerated erosion, even though the rates of erosion may differ. Plant communities with an SCR of sustainable may be selected as the management goal Desired Plant Community (DPC) for that site based solely on management objectives, not on erosion rate. Characteristics of the community are determined by the nature of the site, the land use history, "natural" factors such as fire, drought, flood, wildlife, etc., and their interactions. Community structure may remain fairly stable over time or it may change in the direction of another community type due to management or natural processes.

Communities capable of occurring on a site which have site protection above the threshold Site Conservation Threshold (SCT) are acceptable management goals because any of these communities will provide sufficient site protection from accelerated erosion to maintain future management options. The choice of community type as a management goal on any particular site, i.e. the "desired plant community", depends on the goals of the landowner or manager. The SRM defines Desired Plant Community (DPC) as "the plant community, of the several that may occupy a site, that has been identified through a management plan to best meet the plan's objectives for the site."

Any plant community which provides site protection in excess of the site conservation threshold Site Conservation Threshold (SCT) could be chosen as the Desired Plant Community (DPC) and management would aim to alter current vegetation in that direction (Figure 2). Desired Plant Communities should be based on actual vegetation which has been observed to exist on particular ecological sites.

Plant communities which provide site protection below the (SCT) should not be selected as (DPCs). By definition, these plant communities are undesirable since they will not protect the site from accelerated erosion. Through management these plant communities may be converted to a plant community above the (SCT), but if soil loss is sufficient the former potential may be unattainable.

Management objectives should be defined in terms of a Desired Plant Community for each ecological site, and the Vegetation Management Status be reported in terms of similarity to and trend toward or away from the selected DPC. Management has basically two objectives, to conserve to the extent practicable the long-term potential of the site to produce vegetation, and to produce in the shorter term those combinations of goods and services desired from the land. The desired plant community should meet both of these objectives.

The following series of photographs further demonstrate these concepts. These photographs illustrate a series of plant communities providing various levels of soil protection. Plant communities photographed are on the same ecological (range) sites within each set. The sites are located in Arizona (AZ1-8) and Oklahoma (OK1 -8).

Arizona Set - Arizona Loamy Upland Ecological Site

Oklahoma Set - Oklahoma Loamy Prairie Ecological Site

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