. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. Discussion—As applied by the USDA Forest Service FIA units, the variation among the 10 subplots is not calcu- lated because it has been found to be small compared to the variation between clusters. The values from the sub- plots are simply averaged. It should be noted that the variability of a single cluster may be significantly more than a sample from a single point and the variability is not always insignificant. The cluster sample should not be routinely treated as a single plot as it often i
. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. Discussion—As applied by the USDA Forest Service FIA units, the variation among the 10 subplots is not calcu- lated because it has been found to be small compared to the variation between clusters. The values from the sub- plots are simply averaged. It should be noted that the variability of a single cluster may be significantly more than a sample from a single point and the variability is not always insignificant. The cluster sample should not be routinely treated as a single plot as it often is. For our examples, the results are considered as being from a single plot in further computations. Because the 10 subplots within a cluster are located close to one another, the subplots are frequently similar to each other. The cluster therefore may provide less information than randomly located plots that are truly independent. This reduces the precision of estimates, but cost savings from clustering frequently yield the most cost effective inventories because the total travel time is reduced. The 10-point cluster plot is frequently used in extensive forest inventories and where maps of stands are not available. When the population of interest is highly vari- able, then a sampling system that provides the opportunity for a greater distribution of plots throughout the inventory unit is preferred. The following are some other options for sampling within a stand. When used as a part of a forest inventory, each of the options may be considered a form of cluster sampling. Subjective Sampling Subjective sampling is not recommended in this primer. There may be occasions in which such a sample has been acquired and the analyst must make do with it. Our recommendation is to attempt to relate the sample to a probability sample. Statistical Estimates— Figure 10 shows plot locations based upon extremes observed within the stand (sampling without preconceived bias). Observations yie
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