Analysis On Growth Process And Response Of Thinning Of Chinese Fir Commercial Forests For Large-diameter Cultivation

This paper analyzes the growth process and stand structure of Chinese fir commercial forest under three kinds of site index, taking the example of Jiangle State-owned forest farm for large-diameter cultivation. We discussed the durations and divisions of sapling stage, fast-growing stage, woody stage and slow-growing stage under the three kinds of site index, as mentioned above. A thinning test was carried out in the Chinese fir stand of site index 18, at the same time, and changes of the average diameter at breast height, average height and stock were analyzed among different thinning intensity, four main conclusions can be drawn as follows from the experimental results:(1) The increment of all the three measurement factors including diameter at breast height, height and volume of site index 16,18,20,respectively, increase as the site index increases. Both the average increment of diameter at breast height and the height arrive at the peak at 12a of the three site index with an amount of 1.04cm,1.19cm and 1.31 cm of diameter at breast height and 0.89cm,1.11 cm and 1.24cm of height, respectively. There is a slightly difference between the ages, fluctuating around 25a, when the average increment and current annual increment of volume intersects, which means the quantitative mature age of Chinese fir is 25a or so.(2)Quadratic polynomial function, exponential function, power function, Logistic function and Richards function were fitted using increment data of diameter at breast height, height and volume, respectively, to select the best model for the growth process of Chinese fir. Results indicated Richards function showed the best performance (R2>0.93).(3)The results showed that the duration and division of sapling stage, fast-growing stage, woody stage and slow-growing stage varied with the site index differed. The duration of Chinese fir in fast-growing stage of site index 16 lasts longer (7-15a) compared with the other. While woody stage lasts long with the site index increases. Finally, Chinese fir begins its slow-growing stage of site index 16,18,20 at 22a,23a and 25a, respectively. Meanwhile, the slow-growing stage begins later as the site index increases.(4)DBH of stand of thinning intensity by 20%,25%,33%,50%has advanced growth after thinning 2 years, the diameter distribution is obviously moving to the right. Diversity of the average DBH of different thinning intensity was significant, sig.=0. There was no significant diversity between the 25% and 33%thinning intensity when the second years. Non-thinning compared to thinning intensity by 50%, diversity of the average height of tree was significant, other thinning intensity is not significant after thinning 1 years. Diversity between the different thinning intensity was significant after thinning 2 years. The Diversity of increment of stock of different thinning intensity was significant.