Specific Guidelines on Sample Unit Size for Biomass

The size of sample units is a critical decision in estimating biomass in order to obtain precise data without spending too much time sampling. If too small, the many empty quadrats will give the collected data a skewed sampling distribution, and infrequent species may be missed. Conversely, if quadrats are too large, sampling becomes time consuming and there is a greater likelihood of sampling errors originating from careless evaluation or boundary decisions.

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

Sample Unit Size for Biomass Sampling

  • increasing quadrat size will reduce the number of emply quadrats, so that collected data assumes a normal distribution.
  • if more than 5% of quadrats are 'empty', increase quadrat size.
  • when sampling involves the use of equipment such as small field scales, ensure that average quadrat biomass is >10 g, to overcome the potential error from insensitive measurement intervals.
  • have quadrats no larger than necessary, to avoid problems associated with careless sampling, boundary decisions, and excessive time requirements.

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, NY. pp 217-226.

Brummer, J.E., Nichols, J.T., Engel, R.K., and K.M. Eskridge. 1994. Efficiency of different quadrat sizes and shapes for sampling standing crop. Journal of Range Management 47:84-89. (pdf)

Papanastasis, V.P. 1977. Optimum size and shape of quadrat for sampling herbage weight in grasslands of northern Greece. Journal of Range Management 30:446-449. (pdf)

Sukhatme, P.V. 1947. The problem of plot size in large-scale yield surveys. Journal of the American Statistical Association 42:297-310.

Van Dyne, G.M., Vogel, W.G., and H.G. Fisser. 1963. Influence of small plot size and shape on range herbage production estimates. Ecology 44:746-759.

Weigert, R.G. 1962. The selection of an optimum quadrat size for sampling the standing crop of grasses and forbs. Ecology 43:125-129.

Wight, J.R. 1967. The sampling unit and its effect on saltbush yield estimates. Journal of Range Management 20:323-325. (pdf)