Identification of Individuals
Attributes that involve counting, particularly density, are subject to error in situations where it is difficult to distinguish discrete individual plants. Problems are most frequently confronted with stoloniferous or rhizomatous grasses, such as black grama (Bouteloua eriopoda) or tobosa (Hilaria mutica) but can also be encountered when mature bunchgrass tussocks break apart. Woody plants that feature multiple stems, such as duned mesquite (Prosopis torreyana) or vegetative propagation, such as aspen (Populus tremuloides) present similar challenges.
In these cases, selection of alternative counting units such as stalks, culms, tillers, or stems, should be based on morphological characteristics of the species and the objectives of the study. Clear ground rules defining the counting unit are needed to reduce personal bias and provide repeatable data among observers and over time.
References and Further Reading
(Note: pdf files require Adobe Acrobat (free) to view)
Bartos, D.L., Brown, J.K., and G.D. Booth. 1994. Twelve years biomass response in aspen communities following fire. Journal of Range Management 47:79-83. (pdf)
Bonham, C.D. 1989. Measurements of terrestrial vegetation. John Wiley Sons, New York, NY. pp 138-140.
Kalmbacher, R.S., Martin, F.G., and J.E. Rechcigl. 1993. Effect of N-P-K fertilization on yield and tiller density of creeping bluestem. Journal of Range Management 46:452-457. (pdf)
Mueller-Dombois, D., and H. Ellenburg. 1974. Aims and methods of vegetation ecology. John Wiley Sons, New York. pp 68-69.