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Quadratic mean diameter : ウィキペディア英語版 | Quadratic mean diameter In Forestry, Quadratic mean diameter or QMD is a measure of Central tendency which is considered more appropriate than Arithmetic mean for characterizing the group of trees which have been measured. For ''n'' trees, QMD is calculated as:
where is the Diameter at breast height of the ''ith'' tree. Compared to the arithmetic mean, QMD assigns greater weight to larger trees - QMD is always greater than or equal to arithmetic mean for a given set of trees. QMD can be used in timber cruises to estimate the standing volume of timber in a forest, because it has the practical advantage of being directly related to Basal area, which in turn is directly related to volume. QMD can also be calculated as:
where BA is stand basal area, n is the number of trees, and k is a constant based on measurement units - for BA in ft2 and DBH in inches, k=0.005454; for BA in m2 and DBH in cm, k=0.0000785. ==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Quadratic mean diameter」の詳細全文を読む
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