Specific Guidelines on Sample Unit Shape for Density

The smaller sample units used to determine the density of herbaceous species are conventionally square or slightly rectangular shaped quadrats. In sparse and patchy vegetation, elongated quadrats may reduce sample size requirements, by decreasing the sample variance and improving precision.

When bigger sample units are required to obtain density estimates for larger species, particularly trees and shrubs, an extended belt transect is often selected. A belt transect is favored because it is easy to progress along its length to account for the entire area, while methodically ensuring that plants are neither missed nor counted twice. By contrast, belt transects are rarely used as sample units when measuring other attributes, such as biomass or cover, where most techniques require that the entire quadrat can be assessed from a single viewing.

Also refer to Sample Unit Shape in the Sampling Concepts section.

References and Further Reading

(Note: pdf files require Adobe Acrobat (free) to view)

Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York. pp. 142-148.

Eddleman, L.E., Remmenga, E.E., and R.T. Ward. 1964. An evaluation of plot methods for alpine vegetation. Bulletin of the Torrey Botanical Club. 91:439-450.

Lyon, L.J. 1968. An evaluation of density sampling methods in a shrub community. Journal of Range Management 21:16-20. (pdf)

Mueller-Dombois, D., and H. Ellenburg. 1974. Aims and methods of vegetation ecology. John Wiley Sons, New York. pp. 68-70.