Quadratic Mean Diameter (from a Tally)
The QMD reineke-sdi requires, straight from the tally sheet: QMD = sqrt(sum(count x DBH^2) / trees). Enter a diameter tally (one token per tree "12" or per class "12:40") and get the QMD, the arithmetic mean beside it (so the gap is visible), the tree count, and the tallied basal area. QMD is the diameter of the tree of average basal area, always at or above the arithmetic mean - the number a plain average gets wrong. A mensuration helper, not a cruise compilation.
Formula and source
QMD = sqrt( sum(count x diameter^2) / sum(count) ); arithmetic_mean = sum(count x diameter) / sum(count); basal_area_ft2 = 0.005454 x sum(count x diameter^2).
USDA Forest Service forest-mensuration practice (quadratic mean diameter), by name.
Audience
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