Agenda - Environmental Policy Board - 07/19/2021

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Title 190-Forestry Inventory Methods Technical Note o A low -intensity inventory is usually adequate for developing a forest management plan. The specific number of plots needed will vary, even for a low -intensity inventory. A stand that is relatively homogeneous in species composition and tree age can be represented with fewer plots, but as variability increases, so does the number of plots needed to provide adequate estimates of stand parameters. o Table 1 offers minimum recommendations based on published sources and typical usage, but the optimal number of plots varies by forest type and other stand characteristics. Table 1: Recommended Minimum Number of Plots for Low -Intensity Forest Inventory in Stands of Various Sizes Acres Minimum # of plots 10 or less 3 11-20 6 21-40 10 41-150 15 >150 1 plot/10 acres o The minimum guideline of three plots for stands of 10 acres or less follows USDA - Forest Service (2015), which notes this recommendation is for homogenous stands. Other sources recommend a larger number of plots (e.g., Wenger 1984). Stand variability will determine the number of plots needed. Consult an area or State forester for recommendations on optimal numbers of plots to use in your location. o For situations where a known level of statistical reliability is desired, refer to methods for determining the number of plots needed to provide an acceptable sampling error. See, for example, the "Number of Plots" discussion in chapter 2 of the FSVeg Common Stand Exam User Guide, Version: 2.12.6. (USDA -Forest Service 2015). • Selecting Plot Locations o Plot locations are chosen without bias, so that all forested acres are equally represented in the sample. One way to locate plots is by using systematic sampling, which involves developing a parallel line pattern on a map with the plots evenly spaced along lines (fig. 2). Orienting the lines north -south or east -west makes it easier to establish on the ground, but other orientations may be used, such as aligning with a slope gradient. Make sure the sampling design places plots far enough away from property lines so that all the "in" trees are in the stand of interest. Plot locations can be preloaded into a device that uses spatial data (e.g., a data recorder, GPS navigation system, etc.). Alternatively, the distance between plots can be paced; in this case, bias will be reduced by stopping at the correctly paced distance even if the location is inconvenient. (Technical Note No. 190-FOR-01, Jul 2018) 5