Point Sampling to Determine Cover

Point sampling is one of the most common approaches to estimate cover of a site, since being conceived by New Zealand pasture scientists, Levy and Madden, in the 1920's. It is based on placing a number of points within an area, and determining the proportion of the points that hit (ie., intercept) vegetation. In this manner, total cover can be calculated as the percentage of hits, relative to the total number of points sampled. Cover of individual species can also be estimated by recording the plant species when intercepted by a point. Species composition is the contribution of hits for each species and is expressed as a percentage of the total number of points where vegetation was recorded as a hit. Ground cover, basal cover, canopy cover, and leaf area index can all be measured by point methods, depending on the ground rules established to guide decisions regarding which species will be recorded when multiple hits are encountered if overlapping canopies are vertically intercepted.

Point Sampling Methods

There are three common point sampling methods used in rangeland inventory or monitoring to determine cover:

Special Considerations for Point Sampling

These critical issues should be considered when designing sampling protocols involving methods of point sampling to determine cover.

References and Further Reading

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Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. pp 11-12, 20-24.

Greig-Smith, P. 1983. Quantitative plant ecology. Academic Press, New York, NY. pp 41-45.

Hofmann, L., and R.E. Ries. 1990. An evaluation of sample adequacy for point analysis of ground cover. Journal of Range Management 43:545-549. (pdf)

Levy, E.B., and E.A. Madden. 1933. The point method of pasture analysis. New Zealand Journal of Agriculture 46:267-279.

Mueller-Dombois, D., and H. Ellenburg. 1974. Aims and methods of vegetation ecology. John Wiley Sons, New York, NY. pp 84-90.