Range Condition
Range condition describes an evaluation of the current status of rangeland vegetation. Condition assessments provide the framework to register information obtained by range inventories on the basic status of existing vegetation, and to gauge changes or range trend through monitoring. In addition, range condition is used as a guide to ensure sustainable land use, to determine carrying capacity and adjust stocking rates, to identify potential responses to range improvement programs such as brush control or reseeding, and to evaluate the best locations of fences and water facilities to improve utilization within a pasture.
In earlier days of rangeland management, range condition was a general term describing the status of resources at a site with particular reference to livestock grazing. Today, range condition usually carries a specific connotation, reflecting current status of the vegetation and soils occupying a site in comparison to the site potential expected if the climax vegetation was present. Therefore, an initial and critical step in evaluating range condition is to classify range sites to determine site potential.
The best-known procedure to assess range condition is the Quantitative Climax Method, used by the Soil Conservation Service (now Natural Resources Conservation Service) since the 1950s. This method compares species or species groups in the existing vegetation with that expected in the climax vegetation, to give a percentage reflecting the similarity between the two. A value close to 100% indicates that species composition of the existing vegetation closely reflects the composition of the climax vegetation, whereas lower values indicate a greater level of departure from perceived climax conditions. Although range condition is evaluated on a continuous scale from 0% to 100%, arbitrary classes are generally reported to illustrate range condition (Table 1).
| Range Condition Class | Percent of Climax |
|---|---|
| Excellent | 76 -100 |
| Good | 50 - 75 |
| Fair | 26 - 50 |
| Poor | 0 - 25 |
However, assumptions and interpretation of the quantitative climax method of range condition assessment presently attract widespread criticism and dispute for a number of reasons.
a. Founded on inapplicable theories of plant succession - the current ecological approach using the climax vegetation as the benchmark to compare current vegetation status reflects a historical acceptance of the Clementsian theories of plant succession. Under these ideas, vegetation is expected to recover to an original climax composition following the reduction in grazing. However, these patterns are rarely apparent in many arid and semiarid vegetation such as creosote (Larrea tridentata) flats, or former grasslands now infested by mesquite (Prosopis spp.), but instead better conform to the widely accepted 'state-and-transition' model that is the basis of current ecological theory. Other approaches to evaluate resource status, such as the site conservation rating, desired plant community, and rangeland health initiatives, are evolving as an attempt to accommodate the non-linear responses to disturbance observed in the vegetation on many rangeland areas.
b. Sensitive to choice of benchmark - comparing current vegetation to potential productivity is both a strength and a weakness of range condition assessment. Site potential is highly meaningful to evaluation and management, because it provides the ultimate benchmark against which to base expectations regarding the type and amount of vegetation, natural erosion rates, comparisons of current site productivity, and alternative land uses. However, a realistic evaluation of range condition relies on selecting a benchmark that genuinely reflects potential site productivity. For example, sites of inherently low potential will always be categorized in 'poor' condition if inadvertently compared to a benchmark of intrinsically higher potential, even when there is no capacity to improve.
c. Disregards nonnative species - in some agencies (particularly Natural Resources Conservation Service), range site potential excludes the presence of non-native species. This approach results in an automatic penalty at locations dominated by nonnative species, such as Lehmann lovegrass (Eragrostis lehmanianna) in the Southwest, crested wheatgrass (Agropyron cristatum) in the Intermountain Basin, or the Californian annual grasslands. In many cases, these non-native species contribute a significantly to the vegetation, offer forage and habitat for livestock and wildlife, and provide valuable soil protection.
d. Excludes other important attributes influencing resource status - sustaining the productive potential at a site depends on maintaining the integrity of all resources, especially the soil. Current methods based comparing species composition are insensitive indicators of soil responses because many different compositions of vegetation could all provide an equivalent level of soil protection. Newer proposals to evaluate resource status, such as site conservation ratings or rangeland health initiatives, consider soil factors as range condition criteria in an attempt to correct this deficiency.
e. Poorly reflects management objectives - range condition was originally developed to evaluate the impact of livestock grazing, based on the assumption that highest forage biomass was found on areas in near-climax species composition, and that excessive grazing pressure caused vegetation to undesirably depart from climax. In fact, some early proposals that suggested alternative approaches to evaluate range condition were strongly livestock oriented, and focused on relating current forage biomass to potential forage production for a site. However, the connection between climax vegetation and management goals are less explicit when considering nonnative species (discussed above) and multiple use objectives. For example, 'excellent' condition rangeland may not offer adequate habitat for certain wildlife species. Contemporary concepts, such as desired plant communities or resource value ratings, attempt to evaluate management goals separately from the direct assessment of potential species composition for a site.
f. Interpretation of condition labels - the terms excellent, good, fair, and poor are linked to emotive interpretations, often unrelated to the stability, diversity and productivity of the current vegetation. Several agencies have replaced these terms with low seral, mid seral, high seral, and potential natural to emphasize the ecological context of range condition, but interpretation is still open to criticism by those who believe that the climax vegetation must be the exclusive management goal. In many cases, a better understanding of the effect of current land use practices on rangeland resources is realized by highlighting range trends or similarities to the desired plant community, rather than solely being based on climax species composition.
g. Unable to isolate the effects of grazing from other factors - vegetation and species composition vary between locations and over time in response to diversity of factors (including site variability, fire regimes, climatic conditions, etc.), yet range condition and range trend are commonly interpreted using the assumption that the impact of livestock grazing is primary.
References and Further Reading
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Dyksterhuis, E.J. 1949. Condition and management of rangeland based on quantitative ecology. Journal of Range Management 2:104-115. (pdf)
Ellison, L. 1949. The ecological basis for judging condition and trend on mountain rangeland. Journal of Forestry 47:785-795.
Friedel, M.H. 1991. Range condition assessment and the concept of thresholds: A viewpoint. Journal of Range Management 44:422-426. (pdf)
Frost, W.E., and E.L. Smith. 1991. Biomass productivity and range condition on range sites in southern Arizona. Journal of Range Management 44:64-67. (pdf)
Goebel, C.J., and C.W. Cook. 1960. Effect of range condition on plant vigor, production and nutritive value of forage. Journal of Range Management 13:307-313. (pdf)
Humphrey, R.R. 1949. Field comments on the range condition method of forage survey. Journal of Range Management 2:1-10. (pdf)
Joyce, L.A. 1993. The life cycle of the range condition concept. Journal of Range Management 46:132-138. (pdf)
Lauenroth, W.K., and W. A. Laycock. (eds). 1989. Secondary succession and the evaluation of range condition. Westview Press, Denver, CO. pp. 163.
Laycock, W.A. 1991. Stable states and thresholds of range condition on North American rangelands: A viewpoint. Journal of Range Management 44:427-433. (pdf)
Mosely, J.C., Bunting, S.C., and M. Hironaka. 1986. Determining range condition from frequency data in mountain meadows of central Idaho. Journal of Range Management 39:561-565. (pdf)
National Research Council. 1994. Rangeland health: New methods to classify, inventory and monitor rangelands. National Academy Press. pp. 75-81.
Pamo, E.T., Pieper, R.D., and R.F. Beck. 1991. Range condition analysis: comparison of two methods in southern New Mexico grasslands. Journal of Range Management 44:374-378. (pdf)
Pieper, R.D., and R.F. Beck. 1990. Range condition from an ecological perspective: Modification to recognize multiple use objectives. Journal of Range Management 43:550-552. (pdf)
Scarnecchia, D.L. 1991. Review of "Secondary succession and the evaluation of range condition". Journal of Range Management 44:525. (pdf)
Soil Conservation Service. 1976. National range handbook. United States Department of Agriculture.
Task Group on Unity in Concepts and Terminology. 1995. New concepts for assessment of range condition. Journal of Range Management 48:271-282.
Tiedeman, J.A., Beck, R., and R.V. Ecret. 1991. Dependence of standing crop on range condition rating in New Mexico. Journal of Range Management 44:602-605. (pdf)
Tueller, PT., and W.H. Blackburn. 1974. Condition and trend of the big sagebush/needle-and-thread habitat type in Nevada. Journal of Range Management 27:36-40. (pdf)
Westoby, M., Walker, B., and I. Noy-Meir. 1989. Opportunistic management for rangelands not at equilibrium. Journal of Range Management 42:266-274. (pdf)
Wilson, A.D., and G.J. Tupper. 1982. Concepts and factors applicable to the measurement of range condition. Journal of Range Management 35:684-689. (pdf)
Workman, J.P. 1995. The value of increased forage from improved rangeland condition. Rangelands 17:46-48.