. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. (fig. 12). Plots are established at the grid intersections. Once the initial plot is established or the grid is fixed on the area, the remaining design is fixed. For this reason it is not truly a random sample. Traditionally, random sampling formulae have been applied to this type of sample alloca- tion, assuming that a random process is associated with distribution of the forest variates of interest. Experience indicates that in most cases estimates of variance will be conservative. Hence the p
. A primer on stand and forest inventory designs. Forests and forestry Mensuration; Forest surveys. (fig. 12). Plots are established at the grid intersections. Once the initial plot is established or the grid is fixed on the area, the remaining design is fixed. For this reason it is not truly a random sample. Traditionally, random sampling formulae have been applied to this type of sample alloca- tion, assuming that a random process is associated with distribution of the forest variates of interest. Experience indicates that in most cases estimates of variance will be conservative. Hence the practicing forester is usually safe in applying this type of design, unless there is some regular variation in the forest that is correlated with the sample placement. A second consideration is that there is no possibility that a plot once chosen will recur in the sample, hence, this is sampling without replacement. For this example, the field plots are assumed to be 10-point clusters covering an area one acre in size. The within-plot variance is not considered. Statistical Estimates— Assume we want to compute the acreage of lands having a particular wildlife use such as that of the red-spotted, snaileater. To compute the estimate for areas having wildlife use, all plots classed as having evidence of snaileater use in the field are assigned a value of 1 and all other plots are given a value of zero. The results are shown in table 5. N = 15,300/1 = 15,300 possible 1 acre plots, y = (0 + 1 + . . 0)/20 = or 55% of the area shows wildlife 32. 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 Lund, H. Gyde; Thomas, Charles E. (Charles Eugene), 1940-; United States. Forest Service. [Washington, D. C. ?] : U. S. Dept. of Agriculture, Forest Service
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