| The Greater Khingan Mountains Forest Region in Inner Mongolia is a national forest ecology function zone with the most concentrated forest,the largest area,the most important ecological status,and the highest latitude among the four key state-owned forest areas in China.Larix gmelini is the main dominant tree species in the forest area.How to manage the Larix gmelini forest scientifically and give full play to the ecology functions of the forest area in the Greater Khingan Mountains Forest Region is the main aim of the forest area.The forest growth and yield model is a set of equations that describe forest trees or stands growth dynamics.It can help understand the structure and function of forest ecosystem,predict the development of forest stands,and lay a theoretical foundation for scientific forest management.In this study,based on the data collected from sample plots from the 6th(2003),7th(2008),8th(2013)and 9th(2018)Chinese National Forest Inventory in Inner Mongolia Autonomous Region,north China,the Larix gmelini forest is researched.One is based on 142 sample plots of Larix gmelini plantation,using Reineke natural sparse equation to develop a density control chart.Based on the density control chart,the parameters of stands which reach the target diameter such as age,dominant height,volume and total yield under the conditions of the same density and different thinning measures are simulated and then the optimal management plan is determined.The second is to develop the variable transition model and the fixed parameter transition matrix model of the tree species using data collected from 667 natural forest sample plots of Larix gmelini from the 2013 and 2018 Chinese National Forest Inventory in Inner Mongolia Autonomous Region,north China.Then,applying the developed models to predict the number of advanced forest stands in the next five years and stand parameters in nearly one hundred years.Third,the linear mixed-effects individual-tree growth models for main tree species are developed using data collected from 626 natural forest sample plots from the 2013 and 2018 Chinese National Forest Inventory in Inner Mongolia Autonomous Region,north China.In addition,the variance functions and autocorrelation structures are applied to describe within-plot heteroscedasticity and autocorrelation.Finally,the optimal mixed-effects model is determined based on the Akaike information criterion(AIC),Bayesian information criterion(BIC),log-likelihood(Loglik)and the likelihood ratio test(LRT).The main conclusions of this study are as follows:Based on 142 sample plots of Larix gmelini plantations,sample plots with fully stocking percent were selected.Using reduced major axis regression,the renike self-thinning equation was constructed.According to the initial density of Larix gmelini,the upper limit equation of optimal density,the lower limit equation and the closed canopy line were constructed.Based on the data,the dominant height model,volume model and carbon storage model were fitted as the auxiliary equations of the density control chart.The total yield and average yield of stand under different densities and different measures were simulated by using the yield prediction model.It was found that reasonable management and thinning measures could improve the yield of stand.Based on the 667 natural forest sample plots of Larix gmelinii,the tree species are divided into four types: birch,soft broad-leaved species,hard broad-leaved species,and Larix gmelinii,and the growth model,recruitmen model and mortality model were developed.The developed models have good explanatory and predictive ability.The short-term and long-term prediction of the forest stand were made through the developed model.The results of the short-term prediction are basically the same as the theoretical value,and the long-term prediction was in line with to the theoretical value.In addition,the transition matrix model established by using the fixed-parameter average method is likely to produce higher prediction results than the actual value when predicting the actual forest stand structure,while the variable parameter transition matrix model method that takes into account the forest stand status is consistent with the theoretical value.Based on the 626 natural forest sample plots of Larix gmelinii,the tree species are divided into three types: birch,oaks,and Larix gmelinii,and the basal area increment models were developed.Using sample plot as a random effect,the AIC and BIC reduced,and the Log Lik increased.It is found that the results of different combinations of random effects while considering all independent variables and the intercept in the basic model are better than the basic model for the three tree species.The general positive-definite matrix was selected for the optimal random effects variance–covariance structures.Considering the heteroscedasticity of the basic model,exponential function,power function and constant plus power function can all correct the heteroscedasticity of the model to a certain extent.In model prediction and evaluation,the mixed-effects model that considers sample plot as a random effect outperformed the basic model,which significantly improved the accuracy of prediction.Compared with the basic model developed using least square method,the mixed-effect model considering the hierarchical structure significantly improved the performance of the model,and the developed model has certain biological significance and statistical reliability. |
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