| The growth rules and rational rotation of 9 main cultivated poplar clones were systematically studied through research of quantity mature, process mature and economic mature in conmon cultivation density 4m×6m condition The result showed that growth tendency of height, diameter at chest height(DBH) and volume of the various clones was slow-fast-slow. Logistic equation was applied to fit growth rules of height, DBH and volume of 9 poplar clones at the age of 11, the results showed that the fitting effect is remarkable and correlation coefficient all above 0.90. The growth process of poplar clones were divided into 4 periods, survival period, prophase period, fast-growing period and anaphase period. It had obviously growth rule of slow-fast-slow in latter three periods. The earliest arriving at the fast-growing period was height growth of various clones, DBH followed and volume was the latest. The time of heights and DBH arriving at the fast-growing comer was the same, at about 2nd year. but that of volumes turned to be at 5th-6th year. DBH followed and volume was the latest. DBH arrived the time of the retard period of the growing earliest, height growth followed, and volume was the latest.The result showed that 9 poplar clones still in their blooming period at the age of 7 or 8 years, growth of volume kept increasing in nearly linear, and the mean of volume didn't arrive to its max when intersected with annual growth, poplar clones didn't arrive their period of quantity mature age besides L324 quantity mature age was about 10.5a. Growth curve displays that the rational rotations of poplar clones were about 13-19th years, but not the 7-8th when they were in fast-growing period and could increase unit area volume by increasing density in short-term rational rotation., the years of 9 clones reaching their process mature age were about 12-14. Determining the rational rotation based on the max of net discount, the years of 9 clone's economic mature age were about 10-21 years when they reached the max DBH rotation. The final rational rotation of 9 poplar clones, such as L35,T26,L323,I-102,I-802,L324,T66,I-107,zhonghe-1 were 17,16,14,19,15.5,13,14,15,18years, which result is much higher than that of generally consider 7th-8th year.This article provided the theory basis of intensive cultivation in short rotation, high-yield cultivation and improving forest land productivity by analysis of poplar growth characteristic , discussing of growth rulers and rational rotation.
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