Specific Guidelines on Sample Unit Shape for Biomass
The shape of sample units is a critical decision in determining biomass in order to obtain accurate and precise estimates of biomass. The smaller sample units used to estimate biomass for herbaceous species are conventionally square or slightly rectangular shaped quadrats. In sparse and patchy vegetation, elongated quadrats may reduce the sample size required to obtain an adequate representation of biomass by decreasing sample variance and improving precision. However, such gains may be counterbalanced by increased errors arising from boundary decisions, and larger confidence intervals during the statistical analysis of biomass data.
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, 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)
Pechanec, J.F., and G. Stewart. 1940. Sagebrush-grass range sampling studies: Size and structure of sampling units. Journal of the American Society of Agronomy 32:669-682.
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.
Wight, J.R. 1967. The sampling unit and its effect on saltbush yield estimates. Journal of Range Management 20:323-325. (pdf)