Rangeland Inventory, Monitoring, and Evaluation:
Extensive areas are often covered in range inventory or monitoring programs, making it impractical to count every plant or to traverse every meter of land. Therefore, a sample is collected to obtain a subset of data that is assumed to represent the entire site, or population.
If rangeland vegetation was homogeneous, designing a sampling regime would be fairly straightforward. For example, only a few samples would be needed to obtain an accurate description of a well-manicured lawn. However, rangelands are typically characterized by a diverse assemblage of plant species, some of which are abundant while others may be very rare. Plants are also distributed in a variety of spatial patterns, that may be expressed at several different scales in the landscape. In fact, any factor that affects germination, establishment or mortality will influence the spatial arrangement of plants, including soil type, aspect, water redistribution patterns, grazing distribution (eg., location of fences and water), and wildlife impacts (eg., kangaroo rat mounds). Rangeland plant communities also exhibit considerable temporal variation, so that the presence and abundance of a species may fluctuate markedly between seasons and years.
Designing effective sampling regimes to accommodate this inherent variability is the real challenge of rangeland inventory or monitoring programs. It is the step that determines the efficiency of sampling, the value of the data, and which statistical models may be applied during data analysis.
References and Further Reading
Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Son, New York, NY. pp 1-18.
Cochran, W.G. 1977. Sampling techniques. John Wiley Sons, New York, NY.
Cook, C.W., and J. Stubbendieck. (eds). 1986. Range research: Basic problems and techniques. Society for Range Management, Denver, CO. pp 216-250.