| Phoebe Zhennan is a subtropical evergreen broad-leaved tree species,which is a traditional precious tree species in China.It is mainly distributed in the Yangtze River Basin and the south of the region.Its material is straight and complete,texture is beautiful,structure is fine,quality is tough and hard to decay,and its fragrance is not decaying.It has great economic value,known as "gold in wood".However,due to the comprehensive effects of artificial felling,slow growth and natural environment,its distribution has decreased dramatically,and now it is a national second-class rare and endangered species.Hunan Province is one of the main areas of Phoebe Zhennan distribution in China.Its total amount of Phoebe Zhennan resources shows a trend of continuous growth,but its low quality and uneven distribution have not been fundamentally improved.Therefore,to study the growth environment of Phoebe Zhennan secondary forest and the influence of environment on forest productivity,and to master the growth characteristics and growth rules of Phoebe Zhennan secondary forest are the key technologies to give full play to forest productivity,promote sustainable development of forest and realize scientific forest management.Taking Phoebe Zhennan secondary forest as the research object in the national forest inventory sample plots from 1989 to 2014 in Hunan Province,the site types are divided by the environmental factor method,the site quality of each site type is evaluated by the DBH site index,and the optimal model is selected to establish the compatible growth and harvest prediction model of Hunan secondary forest based on the mixed effect.The growth equation of the growth characteristics and growth rules can predict and simulate the growth dynamics of the stand under natural conditions.It provides theoretical basis and scientific guidance for the growth prediction and management decision of Phoebe Zhennan secondary forest in Hunan Province.The main conclusions are as follows:(1)Slope,altitude and aspect are the biggest site factors that affect the growth of Phoebe Zhennan secondary forest in Hunan Province.The study area is divided into five site type communities,15 site type groups and 21 site types.Richards model was used to fit the DBH growth guide curve,40a as the reference age,3cm as the site index interval,and the standard deviation adjustment method was used to develop the DBH site index table of Phoebe Zhennan secondary forest in Hunan Province.The accuracy of the drop point test was 98.96%,and the rate of no jump was 76.47%.The results of site quality evaluation showed that the site quality of most of the secondary nanmu forests in the study area was "good" and "medium",with the site index of 15cm and 12cm,respectively accounting for 49.09%and 47.27%of the total number of secondary nanmu forests.(2)The compatible growth and harvest prediction model proposed by Sullivan and Clutter was established.In order to improve the prediction effect of the model,the sample plot effect was added,and the simultaneous equation system of growth and harvest of Hunan Phoebe Zhennan secondary forest based on the mixed effect was constructed.The determination coefficients(R2=0.968,0.913,0.915)and prediction accuracy(P=99.497%,94.101%,98.707%)of the model were improved,and the average error(Bias=-1.105,-0.132,-3.205)and root mean square error(RMSE=7.637,2.530,14.496)were reduced,indicating that the fitting effect of the mixed effect model is better,and it can predict the growth and harvest status of Hunan Phoebe Zhennan secondary forest more accurately.(3)Five basic models with biological significance were used to construct the rule of the change of the area of the secondary forest of Phoebe Zhennan with the age of the stand.The logistic model had the best fitting effect(R2=0.2410,P=98.8213%,SSE=2986.1492).The site index model was constructed by increasing the site index effect at parameter b1,and the determination coefficient was increased to 0.3312.In order to make the model better reflect the stand under different stand densities.The mixed effect model of the growth of the secondary forest of Phoebe Zhennan in Hunan Province was established by adding the random effect of the stand density grade and the difference of the growth of the sectional area,which further improved the determination coefficient(R2=0.9462)and the prediction accuracy(P=99.9506%),the mean error(ME=0.0342),the absolute value of the mean error(MAE=1.0966),the relative mean error(RME=1.6367%)and the absolute value of the relative mean error(RMAE=0.9462%)decreased by more than 40%,and the distribution range of residual became smaller and more uniform. |
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