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Title 190-Forestry Inventory Methods Technical Note <br />— TPA is a measure of stand density. Each tree size class has a recommended <br />stocking level that can be expressed as TPA. Determining TPA in point sampling <br />is more complicated than when using fixed plots. The tree tally must be expanded <br />to a per acre basis and diameter classes summed for a total TPA. Again, a <br />programmed worksheet simplifies this process. <br />TPA = # of trees tallied X BAF - BA per tree - total number of plots <br />Where BA per tree = 0.005454 X DBH2 <br />The BA for a 10-inch DBH tree = 0.005454X 102=0.5454 <br />The BAF in the cruise example is 10. <br />Five trees are tallied in the 10-inch DBH class. <br />TPA for 10-inch DBH class = 5 tallied trees X 10 BAF - 0.5454-3 <br />plots = 31 trees per acre <br />If this calculation is carried out for the remaining diameter classes found <br />in the cruise: <br />TPA for 12-inch DBH class = 6X 10=0.7853-3=25 TPA <br />TPA for 14-inch DBH class = 5X10=1.068-3=16 TPA <br />TPA for 16-inch DBH class = 3X10=1.396-3=7 TPA <br />Total = 79 TPA 10-inch DBH and greater <br />o Diameter Distribution Table <br />A diameter distribution table is a useful visual to help with the decision -making <br />process for possible management options. Using a programmed worksheet or <br />applications such as the Forest Vegetation Simulator (FVS), a diameter <br />distribution table can be developed for each stand, broken down by species (see <br />table 2). <br />o Volume of merchantable and nonmerchantable timber and biomass <br />It is possible to develop timber volume estimates using information collected <br />during point sampling; however, the accuracy of a volume estimate depends on <br />attributes such as tree form and defect. Collecting this type of information <br />requires specialized training. In instances where volume estimates are desired, <br />consult an area or State forester. <br />(Technical Note No. 190-FOR-01, Jul 2018) <br />10 <br />