Closest Individual Method
The closest individual method was developed by Cottam and Curtis in the 1950's as a plotless technique to estimate density. It is a straightforward distance method to perform, but provides the most variable and least accurate result. Some other distance methods, such as nearest-neighbor and random-pairs methods, are adaptations that have been developed in an attempt to improve on this original simple method. All these distance methods assume that the key species follow a random spatial pattern, and therefore these methods are sensitive to bias when plants exhibit a more contagious or regular arrangement.
In the closest individual method, a set of points (usually positioned along a transect to traverse the area) is initially selected. At each point the closest plant is identified, and its distance (d) from the point is measured and recorded. At the conclusion of data collection, the sample mean of the distance () between plants for the sample area is calculated.
Mean area (MA) can then be estimated as:
Density (plants/area) is then derived by calculating the inverse of MA (1/MA).
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. 149-152.
Cottam, G., and J.T. Curtis. 1956. The use of distance measures in phytosociological sampling. Ecology 37:451-460.
Laycock, W.A., and C.L. Batchelor. 1975. Comparison of distance-measurement techniques for sampling tussock grassland species in New Zealand. Journal of Range Management 28:235-239. (pdf)
McNeill, L., Kelly, R.D., and D.L. Barnes. 1977. The use of quadrat and plotless methods in the analysis of the tree and shrub component of woodland vegetation. Proceedings of the Grassland Society of Southern Africa 12:109-123.
Oldemeyer, J.L., and W.L. Regelin. 1980. Comparison of nine methods for estimating density of shrubs and saplings in Alaska. Journal of Wildlife Management 44:662-666.