Step Point Method
The step point method, an approach based on point sampling to determine cover, was developed by Evans and Love in the 1950's. To implement this procedure, the observer uses a mark placed on the tip of their boot (often a pin or a notch) as the sampling point. Hits are recorded by identifying whatever falls directly beneath the mark along a paced transect. A distance of 5 paces is commonly recommended between sampling points, although the primary goal is an interval that ensures independence between consecutive observations and rarely includes the same plant. The pace-transect is considered the sample unit, and summarized data from several transects are required for statistical analysis of cover data to compare differences among years or sites.
According to the objectives of the study, either ground cover, basal cover or canopy cover can be determined by this method. Sometimes the step point method is used to estimate leaf area index by recording several strata in the vegetation, which requires the observer to identify hits within the herbage layer, as well as viewing directly upwards from the boot tip to determine overstory cover. Species composition is also obtained from step point data, although the technique is sometimes modified to include a composition tally if sparse cover precludes the collection of sufficient data to provide an accurate sample of the species present. In these situations, the species occurring closest to the sampling point is recorded as additional information whenever bare ground is hit.
The step point method is regularly used for rangeland inventory or monitoring purposes because it is easy to learn and rapid to employ, allowing large areas to be quickly described. In homogenous vegetation types, 300-500 points provide an adequate sample; but many more are usually required to estimate the cover of less common species. Also, undesirably large variability often occurs among observers, caused by bias associated with point size and foot placement. Some modifications, including a pointed rod that extends beyond the toe and the wheel point apparatus, have been developed in an attempt to overcome the biases arising from subjective pacing. Nonetheless, in all situations the best results are obtained from the step point method in open grassland communities because maintaining the transect bearing and ensuring objective point placement becomes a challenge in rugged, shrubby, or cactus-dominated areas.
References and Further Reading
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Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. pp 121-123.
Bureau of Land Management. 1996. Sampling vegetation attributes. Interagency Technical Reference, B.M./RS/ST-96/002+1730. pp 70-77.
Evans, R.A., and R.M. Love. 1957. The step-point method of sampling: A practical tool in range research. Journal of Range Management 10:208-212. (pdf)
Owensby, C.E. 1973. Modified step-point system for botanical composition and basal cover estimates. Journal of Range Management 26:302-303. (pdf)
Tidmarsh, C.E.M., and C.M. Havenga. 1955. The wheel-point method of survey and measurement of semi-open grasslands and Karoo vegetation in South Africa. Botanical Survey South Africa, Memoir 29. 49 pp.