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The spatial structure rationality evaluation and ideal spatial structure of forest ecosystem is an important and difficult problem in forest management at home and abroad.In order to reveal the reasons why the community structure is simple and the stability of ecosystem is poor,and to take the regulation mechanism of structure in Dongting Lake forest,the research is targeted at East,South,West Dongting Lake area including Junshan Island,Longshan,Longhu forest farm on Chishan Island,Minglang mountain,Changde forest farm,Hefu Forest farm and natural secondary forest of Taoyuan County.Utilizing the ecosystem internal balance and homogenizing principle of the ecology,in the forest ecological system(plaque) scale,it analyses the spatial structure of mixed,competed and spatial distribution pattern.And then the heterogeneity goal of optimized stand spatial structure is proposed,which has multiple sub-goals in mixed,competed and spatial distribution pattern.Meanwhile the heterogeneity index of single tree and stand spatial structure is also defined,and the evaluation index,evaluation method and evaluation standard of stand spatial structure heterogeneity is determined.By applying the proposed evaluation method to the Dongting Lake area secondary forest heterogeneity evaluation,the results show that: in the fifteen Dongting Lake wetlands under investigation,the forest stand average homogeneity evaluation index is 0.2517.There are 12 stands in the grade 1 and grade 2 which is accounted for 80%,and only 3 stands in the 3 grade accounted for only 20% in the five grades of homogeneity index.However,it lacks of the grade 4 and grade 5 ideal stand spatial structure in Dongting Lake survey.The evaluation results show that only part of stand spatial structure factors in Dongting Lake Forest meet the standard values.Although there is a certain degree of mixed size between dominant tree species and pioneer species,and there are more obvious differentiation between even-aged and uneven-aged forest stands,it yet shows that: the whole stand appears monolayer,and tree species has little isolation;trees′ distribution pattern appears randomized into uniform distribution status;competition is more obvious between individual trees,and it has low diversity and weak illumination.It illustrates that the Dongting Lake stands as a whole have unconspicuous advantage on spatial structure,growth environment and species dominance and other aspects.Many irrational factors exist in forest structural characteristics including space information,and there is far from ideal spatial structure.According to the different altitudes,forest spatial structure homogeneity characteristics gradually grow from the lake to the hilly land in Dongting Lake wetland.This conclusion reflects the real situation of forest resources in Dongting Lake area,and it has a close relationship with the long-term natural and man-made interference,protection and restoration of fatigue. The proposed forest ecological system space optimization objectives and heterogeneity index prolongate the sustainable forest management.The heterogeneity evaluation method breaks through the traditional analysis method of forest spatial structure.The heterogeneity index comprehensively and realistically describes the characteristics of spatial structure,and also quantifies the goal structure of forest spatial neighborhood relation and optimized spatial structure.The method has both forestry and ecological significance on optimizing and adjusting the existing forest spatial structure of Dongting Lake,on transforming large single plantation which mainly consists poplar and willow,and on restoring the functions of Dongting Lake ecological system,such as nourishing and cherishing water,conserving soil and water,reinforcing dam and so on.At the same time,the proposed method in this paper has provided a new way to establish and express ideal spatial structure for other regional forest management.

Crown size is an important tree variable included in growth and yield models,which are commonly used as decision-support tools in forest management.Crown size is usually described as tree crown width or live crown ratio.Tree crown width and live crown ratio have been found to be a useful measure for tree vigor,and allow one to predict tree growth,mortality and aboveground biomass.In this study,using 103 plots of Cunninghamia lanceolata stand in Huangfengqiao forest farm in Hunan Province as an example,each plot was divided into five classes by stand canopy density(CD) following the rules of CD ≥ 0.8(Type 1),0.7 ≤ CD 0.8(Type 2),0.6 ≤ CD 0.7(Type 3),0.5 ≤ CD 0.6(Type 4),and CD 0.5(Type 5).We analyzed the distribution structure of tree crown width and live crown ratio of each tree for each type,and also analyzed the relationships of tree crown width and diameter at breast height(DBH),live crown ratio and DBH,respectively.In addition,nonlinear mixed effects models approach was used to describe the random effects of canopy density on tree crown width and live crown ratio.The commonly used logistic model with predictors of DBH and mean diameter at breast height in larger trees(MDL) was selected as a based model to construct mixed effects crown width and live crown ratio models.The prediction accuracy of the developed nonlinear mixed effects crown width and live crown ratio models were tested using the validation data.Results showed that: the sizes of tree crown width of five types mainly distributed in the interval from 2.5(m) to 4.0(m),accounting for 65.82%,69.56%,70.79%,58.15% and 53.21%,respectively,and less distributed in the intervals of less than 1.5(m) and more than 5.0(m).The sizes of live crown ratio of five types mainly distributed in the interval from 0.3(m) to 0.7(m),accounting for 65.82%,69.56%,70.79%,58.15% and 53.21%,respectively,and less distributed in the intervals of less than 0.2(m) and more than 0.8(m),and specially,there is almost no distributed for more then 0.9(m).The linear correlation between tree crown width and DBH,and live crown ratio and DBH are very weak.The size of crown width of the tree for Type 5 is the largest and is the smallest for Type 1 under the same DBH.For live crown ratio,on contrary,namely the live crown ratio of the tree for Type 1 is the largest and is the smallest for Type 5 under the same DBH.The developed nonlinear mixed effects crown width and live crown ratio models not only described the effects of canopy density on tree crown width and live crown ratio effectively but also have a high prediction.This article main emphasizes on method researches,the effects of many other stand or tree characteristics,such stand age and stand density,on tree crown width or live crown ratio also can be studied using the nonlinear mixed effect models approach.

Forest spatial structure plays an important role in the health and stability of forests,so studying the spatial structure and analyzing the adjustment strategy of Dongting Lake water conservation forest has very important theoretical and practical significance for the restoration of the Dongting Lake forest ecosystem.This research was based on the theoretical principles that underlie structure-based forest management.We established a forest spatial structure optimization model to study the regulation structure and control strategy of the Dongting Lake water conservation forest using the search features of a particle swarm algorithm,and we combined the multi-objective optimization of water conservation forest spatial structure with the Particle Swarm Optimization(PSO)algorithm.Four important aspects of forest stand spatial structure are species composition,intraspecific and interspecific competition,spatial distribution pattern and vertical structure.A number of measures related to these aspects including the degree of mingling,competition index,uniform angle index,stand layer index,spatial density index and open comparison index were selected as the objective functions for water conservation forest health management and optimization of forest spatial structure.In this paper,the entire stand was mapped to the goals solution space of the particle groups and each individual tree was used as a solution in the PSO space.This was done to translate the stand space optimization problem into an optimization process.A PSO optimization algorithm was used that iteratively improved a fitness function,based on the multi-objective function,to identify the optimum solution to the stand spatial structure model.Based on the output of this model,we developed a business strategy for the target tree space structure unit.Based on an analysis of 10 block fixed sample case studies from Changde Hefu national forest park,Taoyuan Guniu mountain,Huangshi,Longtang and the Shejiaping area to the west of Dongting Lake,the research results show that the space optimization model of water resource conservation forest in Dongting Lake is used for forest spatial structure adjustment.The model output with regards to the target tree and its spatial structure unit as the control object was adjusted in terms of tree species composition,competition regulation,horizontal pattern and layering,using single selective cutting,replanting and other management measures.Comparison of the forest stands before and after optimization adjustment showed that the forest spatial structure indexes were very different.The non-spatial structure,tree diameter,species order and age class distribution index remained unchanged.The degree of health increased significantly while the forest layer index remained unchanged.The other three aspects that contribute to the space structure index improved to different degrees.The optimized structure tended to be healthier and more stable while reducing the top target tree competition pressure.From the overall optimization of the stand structure,the optimization model and algorithm can accurately locate weaknesses in stand spatial relationships.Management measures can significantly improve forest spatial structure,which can promote the positive succession of forest ecological systems,become the theoretical basis,and provide technical support for the restoration of Dongting Lake water forest ecological function and health.The optimization model and algorithm proposed in this paper are superior to traditional forest management for water conservation forest health management,and provide a new application of intelligent information technology to forest spatial management.