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Periodic annual increment (PAI), is a forestry term that describes the change in the size of a tree between the beginning and ending of a growth period, divided by the number of years that was designated as the growing period (Avery, 339).〔Avery, T.E.,B.E. Harold. 2002 Forest Measurements, fifth edition. New York: McGraw-Hill. 426 p.〕 For sigmoid growth, the graph of PAI increases rapidly and then quickly declines, approaching zero. PAI may go negative if a tree loses volume due to damage or disease. Periodic annual increment is commonly used instead of current annual increment as a basis for computing growth ''per cent''. Growth ''per cent'' indicates the rate of increase with relation to the wood capital required for its production, this is usually based on a single year's growth (Chapman, 315).〔Chapman, H.H.,1921, Forest Mensuration, second edition. New York: Wiley & Sons, Inc.〕 == Equation == Where: Y is the yield (volume, height, DBH, etc.) at times 1 and 2 and T1 represents the year starting the growth period, and T2 is the end year. Example: Say that the growth period is from age 5 to age 10, and the yield (height of the tree), is 14 feet at the beginning of the period and 34 feet at the end. Then: 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「periodic annual increment」の詳細全文を読む スポンサード リンク
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