Specific Guidelines on Sample Size for Density
Sample size is a critical decision for determining density, because it is a key way to influence the precision of the collected data. Larger sample sizes are required if the collected data has a large sample variance or if the key species occurs in low abundance. In both cases, a greater proportion of the population must be sampled to obtain an accurate and precise measure of density.
Sample Size for Density Sampling
- if the collected data follows a normal distribution, esitmate sample size using either statistical techniques or graphing techniques
- if the collected data follows a Poisson distribution, sample precision is determined by the total number of individuals counted, rather than the number of sample units in the sample
- sampling intensity may be set as an arbitrary percentage of the entire area. (For example, it could be decided to sample 1% or 5% of the site area), and sample number depends on the sample unit size selected.
References and Further Reading
Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. p. 192.
Eddleman, L.E., Remmenga, E.E., and R.T. Ward. 1964. An evaluation of plot methods for alpine vegetation. Bulletin of the Torrey Botanical Club. 91:439-450.
Greig-Smith, P. 1983. Quantitative plant ecology. Blackwell Scientific Publications, Oxford.3rd ed. pp. 26-32.