Plant Density Estimation by Point-to-Plant and Plant-to-Plant Techniques - A Case Study
by
Warren J. Muller
CSIRO Mathematical and Information Sciences
Coauthors: Ken C. Hodgkinson (CSIRO Sustainable Ecosystems)

A long-term study of the effect of grazing systems on the density of grass and shrubs was commenced in 1996 and is ongoing. Ten sites were selected in the semi-arid pastoral zone of NSW and Queensland where mulga occurs. Within each site three equal areas were selected randomly and the treatments 'no grazing', 'tactical grazing' and 'continuous grazing' were applied.

Density estimation of grass and of shrubs is performed annually in each paddock at each site. The technique described by Batcheler (1971) has been used, in which the distance from each point in a regular grid to the nearest plant, then the distance from that plant to its nearest plant are measured and used to determine plant density. This is one of a number of techniques developed in the 1970s and 1980s to determine plant density (see Barabesi, 2001).

Whilst the method is meant to handle non-random plant distributions, it does not work well in all cases. Experiences gained from using the method and a comparison with some other methods will be presented.

Barabesi, L. (2001) A design-based approach to the estimation of plant density using point-to-plant sampling. Journal of Agricultural, Biological and Environmental Statistics 6, 89-98.

Batcheler, C.L. (1971) Estimation of density from a sample of joint point and nearest-neighbour distances. Ecology 52, 703-709.

Date received: August 19, 2002