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In other to address the problem of cost, time and precision of research activities in sustainable forest management, a simple random sub-sample S of size n is then taken without replacement from S ′ and the characteristic of interest i y is observed for all i ∈ S . The data used for this work are the records of the measure of the girth and height of teak (Tectona grandis) trees based on a survey (thinning exercise) carried out at the Forestry Research Institute of Nigeria, Ibadan in 2007. The records indicated an estimated total of about 1000 (one thousand) teak trees on this plantation. A first phase sample S' of size 80 was taken with the measures of the girth (in metres) of the tree as auxiliary variable and also a second phase sample (subsample) S of size 40 was taken from the first phase sample S' giving the measure of the height (in metres) of the study variable y. This study shows that the method of two-phase sampling is a powerful and economical technique in survey sampling as it yields a gain in precision in the estimation of population characteristics given specified cost limits as against that of simple random sampling.

Sampling techniques procedures in sustainable forest management; a two-phase sampling approach