The Structure And Growth Process Of Chinese Fir Plantation At Different Stand Ages

Forest ecosystem is an important part of terrestrial ecosystem,as it is the basis of improving ecological environment and regulating the balance of terrestrial ecosystem.Plantation is an indispensable component of forest ecosystem,among which plantation of Chinese fir,the main fast-growing timber tree species in the subtropical region of southern China,plays an important role in relieving the pressure of increasing demand for wood and protecting the ecological environment in China.In this paper,the diameter structure and growth process of Chinese fir plantation with different ages in Hunan Province were studied,and the structure and growth traits of Chinese fir plantation were studied systematically.The results are of important theoretical value and practical significance which can offer more accurate prediction on the growth dynamics of Chinese fir plantation and to formulate a scientific and reasonable management plan for Chinese fir plantation in China.The main findings are as follows:?1?Cubic equation y=e₀+e₁x+e₂x²+e₃x³ could effectively fit the cumulative percentage of relative diameter-plant number of Chinese fir plantations at different ages,the fitting effect was the best and the applicability was the strongest,and the equation decision coefficient R2 was more than 0.980.?2 tests were carried out on the theoretical value and actual plant number of each diameter relative to plant at a=0.05 significant levels and all the results were accepted.?2?The normal distribution function could fit the diameter distribution of Chinese fir plantations at different ages,and with the help of the normal distribution function table,the number of theoretical plants can be calculated,and ?2 test was carried out on the actual number of plants and the theoretical number of plants obtained at the significant level of a=0.05.The acceptance rate of fitting test was 89%,but the fitting test of diameter distribution of Chinese fir stand was not accepted for 3a.?3?The characteristics of diameter distribution of Chinese fir plantations at different ages were as follows:the number of trees in the middle part of diameter distribution was the majority,and the number of trees on both sides decreased gradually.With the increase of age,the average DBH also increased,and the median value of DBH distribution moved to the right.Its diameter normal distribution curve shape is similar to mountain shape,and take peak point as symmetry axis,the left and right sides are approximately symmetrical "convex"type.?4?The total increment of DBH,height and volume of Chinese fir increased with the ascent of age.The growth rate of Chinese fir changed from fast to slow and went smoothly gradually.At the 5th year,the successive annual growth of DBH was equal to the average growth.The annual growth and average growth of tree height intersect at 10a-15a,the maximum annual growth of volume appeared at 20a,and there was an intersection between annual growth and average growth of 25a-30a.?5?Richards model,Gompertz model,Logistic model and modified Weibull model were used to fit the growth process of 31a Chinese fir DBH,tree height and volume,and then the optimal model was selected according to the principle of the maximum R2 and the minimum square of residual deviation SSE of the models.The results showed that the Richards model was the best to fit for the three factors.The growth equation of DBH of Chinese fir for 31a was as follows:y=17.18*?1-exp?-0.09*x??^0.984,the expression of tree height growth equation was:y=18.234*?1-exp?-0.084x??^1.460,and the expression of volume growth equation was:y=0.288*?1-exp?-0.065*x??^2.673.?6?The growth process of Chinese fir of the same growth potential at different ages and different growth potentials of the same age was analyzed.The results showed that the growth rate of I dominant wood,? average wood and IV crushed wood decreased with the increase of age.The growth curve of older Chinese fir was similar to "S" type,and the difference between different growth potentials of Chinese fir gradually widened,indicating that the competition was intensified and differentiation degree increased.The growth rate of I dominant wood in the whole growth process was higher than that of ? average wood and ? crushed wood,which reflected the strength of competitive power,indicating that the I dominant wood had obvious advantages in form and life competition.The DBH,height and volume increased with the rising of age,but the growth curve has almost no intersection.There is no transformation phenomenon in the whole growth process,the growth of pressed wood has been restricted,and the survivalcompetitiveness is the weakest.?7?The results showed that with the increase of age,the total biomass of Chinese fir stand increased,and the biomass of the same organ of different ages had great differences,and the biomass of each organ of the same age also had obvious difference.3a and 11a the percentage of biomass of various organs in Chinese fir stand was as follows:stem>leaf>root>branch;In 16a,the biomass of various organs in Chinese fir stand was as follows:stem>root>leaf>branch;21a,25a,26a,29a the biomass of each component of Chinese fir stand was in the order of stem>root>branch>leaf;In 32a,the biomass of Chinese fir stand was as follows:stem>branch>root>leaf;In 100a,the biomass of each organ in Chinese fir stand was in the order of stem>branch>leaf>root,which indicated that the proportion of biomass of each organ changed with the increase of age in the growth process of Chinese fir forest.Biomass concentration was transferred with age.