. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. usually validated the application of these mixed design- computation procedures. If the reliability of the estimates is extremely important as might be the case for an inventory that was being disputed in court, a systematic sample such as is described could be modified by includ- ing some sort of randomization process for subsets of the plots to assure multiple random starts within the area of interest. Computations would then follow the procedures for systematic sampling plans as described in
. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. usually validated the application of these mixed design- computation procedures. If the reliability of the estimates is extremely important as might be the case for an inventory that was being disputed in court, a systematic sample such as is described could be modified by includ- ing some sort of randomization process for subsets of the plots to assure multiple random starts within the area of interest. Computations would then follow the procedures for systematic sampling plans as described in Cochran (1977) or other statistical sampling texts. Stratified Sampling— Often the forest is heterogeneous with respect to forest type, maturity, or site class. It may be worthwhile to consider stratified sampling if these character- istics are of interest or if the variance within the categories is more homogeneous than the overall forest In stratified sampling, units of population are grouped together on the basis of similar characteristics. These groups are called strata. Total variance can be reduced by the amount of variance that can be attributed to the difference between the strata. For instance, suppose that a large tract of land had considerable merchantable volume interspersed with recently regenerated stands. Estimates of overall volume and the associated stan- dard errors will be considerably reduced if the forest is partitioned into merchantable and nonmerchantable strata. Stratification may be made after plots are established (post- N ' 0 FEET 5000 Forest Boundary. Figure 15—Mapping of stands around the sample plots showing meas- ^ Conifer ured (*) and Forest average (a) volume (ccf) per acre. Q Hardwood £1 Brush/Open O Field Plot (Initial) 36. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work
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