Range Sites
Range sites are the principal units of rangeland classification that are based on categorizing vegetation according to site potential. Site potential is defined as the capacity of an area to support a distinct species composition and/or total biomass. Range sites act as the primary organizational element to obtain inventory and monitoring information during sampling. Therefore, the vegetation represented by a range site must be sufficiently uniform for the valid interpretation and extrapolation of data for management applications, yet incorporate the inherent variability expected in rangeland landscapes.
The range site concept was developed by the Soil Conservation Service (SCS, now Natural Resources Conservation Service) by adopting ideas previously introduced into forestry science. Other government agencies with land management responsibilities (ie., Bureau of Land Management, and Forest Service) use similar, but not always equivalent, concepts and terms to classify rangelands, such as ecological site, ecological type, or habitat type.
Most important, range site classification is centered on identifying differences in potential productivity, rather than simply categorizing the existing vegetation. A classification based on site potential is more meaningful to planning and management because it encourages the consideration of a wider range of options, rather than being restricted to existing conditions. However, deciding the nature of the potential plant community is also subject to the biases of personal judgement, particularly when the vegetation has been modified under a long tradition of land use.
These differences among range sites reflect the combined influence of environmental factors, including climate (total precipitation, seasonality of precipitation, temperature, frost free days, etc.), soils (soil surface texture, water holding capacity, etc.), topography, and fire. Therefore, common principles of ecological succession are incorporated into the range site concept, by assuming that only one distinctive plant community (the climax community), can evolve under a certain set of environmental conditions.
The importance of soil characteristics and topography on plant growth is well recognized, and these factors are usually included when naming range sites (e.g. Limestone Hills, Sandy Loam Upland, Clayey Bottom, etc.). Soil maps are often adopted as the foundation of range site maps, but extensive field reconnaissance, coupled with sampling of vegetation attributes such as biomass and species composition, must also be followed during the process of delineating range sites within an area. The same range site can occur at different locations across an extensive region, wherever the vegetation is considered to exhibit a similar potential for productivity and species composition.
Comprehensive descriptions have been developed for each range site, based on research, field surveys and professional observation. The description includes climate, topography, soils, potential vegetation, and management interpretations such as carrying capacity and resource value ratings. A major disparity between the various government agencies is that descriptions of the potential plant community are restricted to native species under Natural Resource Conservation Service (NRCS) procedures, whereas other agencies include naturalized introduced plants. This difference has considerable consequences, particularly when using the descriptions as benchmarks of site potential for range condition assessments.
References and Further Reading
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Anderson, E.W. 1983. Ecological site / range site / habitat type: A viewpoint. Rangelands 5:187-188.
de Oliveira, J.G.B. 1979. Characterization of range sites. Ph.D. Dissertation, University of Arizona. pp. 1-105.
Driscoll, R.S. 1984. Classification for stratification, mapping, and data display for range inventories. In: National Research Council/National Academy of Sciences. Developing strategies for rangeland management. Westview Press. pp. 615-626.
Frost, W.E., and E.L. Smith. 1991. Biomass productivity and range condition on range sites in southern Arizona. Journal of Range Management 44:64-66. (pdf)
Leonard, S.G., Staidl, G.J., Gebhardt, K.A., and D.E. Prichard. 1992. Viewpoint: Range site/ecological site information requirements for classification of riverine riparian ecosystems. Journal of Range Management 45:431-435. (pdf)
Mueggler, W.F. 1984. Classification for stratification, mapping, and data display for range inventory: Comments and discussion. In: National Research Council/National Academy of Sciences. Developing strategies for rangeland management. Westview Press. pp. 627-630.
National Research Council. 1994. Rangeland health: New methods to classify, inventory and monitor rangelands. National Academy Press. pp. 66-75, 82-85.
Shiftlet, T.N. 1973. Range sites and soils in the United States. In: D.N. Hyder. (ed.) Arid shrublands. Proceedings of the Third Workshop of the United States/Australia Rangelands Panel. Society for Range Management, Denver, CO. pp. 26-33.
Society for Range Management. 1983. Guidelines and terminology for range inventories and monitoring. Report of the Range Inventory Standardization Committee. Society for Range Management, Denver, CO.
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.
Weixelman, D., Zamudio, D., Zamudio, K., and R. Tausch. 1997. Classifying ecological types and evaluating site degradation. Journal of Range Management 50:315-321.