Calculating the Number of Plots Required

Sampling Intensity

It is important that the approximate level of reliability is required before beginning an assessment. All available information should be utilised to estimate the number of sample plots required for each forest type. Guidelines may be obtained from previous reconnaissance information in the area itself or similar areas by using the formula given below. In the absence of such information, the following sampling levels may be taken as approximate guidelines.

Sawlog Volume

Approximately 200 acres of sample (approximately 600 x 66 feet radius plots) are required for reliability of + or – 5 %. Approximately 50 acres of sample (approximately 150 x 66 feet radius plots) are required for reliability of + or – 10 %. For reconnaissance level surveys, it has been found that a minimum of 40-50 x 66 feet radius plots is required to give any meaningful estimate.

Pulp Volume

Approximately 60 acres of sample (800 x 33-foot radius plots) are required for reliability of + or – 5 %.

Approximately 15 acres of sample )200 x 33-foot radius plots) are required for reliability of + or – 10 %.

Calculating the Number of Plots Required for a Meaningful Sample

The actual number of plots required may differ from the guidelines according to the quality and variability of the forest being assessed. Sampling requirements during the survey can be reviewed as data becomes available by extracting a sub - sample of say 30-40 plots, compiling the plot volumes by hand from the relevant volume tables and then analysing the results.