Selection of sites for sampling is a critical consideration when designing rangeland inventory or monitoring schedules. Documentation of site locations, either on maps or with clear written directions, is also an important component of the sampling protocol.
Site selection typically assumes a procedure of selected sampling for either inventory or monitoring programs. After general locations have been identified, further decisions must be made concerning the layout of sample units within the selected sampling area. This next step entails the adoption of a combination of random sampling and systematic sampling approaches.
When undertaking an inventory of an area, it is preferable to establish sampling locations throughout the management unit to ensure a thorough coverage of the site. Sampling efficiency may be obtained by adopting a stratified sampling scheme, often using range sites as the basis of stratification.
In monitoring, it is usually only practical to sample a few areas. Each site should be restricted to relatively uniform areas, such as range sites, to facilitate data collection and guide the degree to which interpretations can be extrapolated beyond the immediate sampling area. Permanently located sites reduce sampling error associated with spatial variation of the attributes so that data can provide a clearer depiction of range trend over time.
The location of sites and sample size depend upon the selection of attributes and their variability within the management unit, the type of management and expected responses, the availability of sampling resources, and the purpose of the inventory or monitoring program. Effective site selection will minimize sampling requirements, enhance statistical accuracy and precision, and ensure that the collected data can be interpreted in a manner relevant to the objectives of the program. Therefore, several different approaches are commonly used to select and classify sampling sites, reflecting the various purposes of inventory or monitoring programs.
References and Further Reading
(Note: pdf files require Adobe Acrobat (free) to view)
Bureau of Land Management. 1996. Sampling vegetation attributes. Interagency Technical Reference, BLM/RS/ST-96/002+1730. pp 3-13.
Larson, L.L., and P.A. Larson. 1987. Use of microsite sampling to reduce inventory sample size. Journal of Range Management 40:378-379. (pdf)
McClaran, M.P., and D.N. Cole. 1993. Packstock in wilderness: Use, impacts, monitoring, and management. General Technical Report INT-301. Intermountain Research Station, United States Department of Agriculture, Forest Service. Ogden, UT. pp 13-14.
Reppert, J.N., Reed, M.J., and P. Zusman. 1962. An allocation plan for range unit sampling. Journal of Range Management 15:190-193. (pdf)
Smith, E.L., and G.B. Ruyle. 1991. Considerations when monitoring rangeland vegetation. G.B. Ruyle. (ed). Some methods for monitoring rangelands and other natural area vegetation. University of Arizona, College of Agriculture, Extension Report 9043. pp 2-4.