Reseach On Optimization Of Spatial Structure Of Typical Broad-leaved Forest Stands Around Dongting Lake Area Based On Stand Distribution Pattern

Forest resources not only provide many forest products for us,but also play an irreplaceable role in water conserving,conserving of soils,carbon fixation and oxygen release,purifying the environment,biodiversity conservation,and maintaining regional ecological balance,which have great strategic significance for national and global ecological security.China's subtropics have the most typical broad-leaved forest vegetation in the world.The community structure is complex and diverse,playing an important role in biodiversity conservation and maintaining regional ecological security.However,as a result of human,s long-term business activities such as excessive logging and formation of a large number of over-forests and secondary forests,resulting in reduced distribution area,the existing forest structure is seriously irrational,structural simplification,biodiversity reduction and functional degradation,and other series of ecological problems.How to improve the forest structure,restore and reconstruct the subtropical evergreen broad-leaved forest community by technical means has become an important subject to be studied urgently.This paper takes the broad-leaved forest community of Dongting Lake as the object,based on the investigation and analysis of the typical broad-leaved forest community structure,spatial pattern,updating characteristics and its influencing factors,and analyzes the spatial distribution pattern of forest in various areas,and puts forward a method for evaluating the distribution pattern of forests based on optimal mesh,and then establishes the optimization model of spatial structure.By using the improved intelligent evolutionary algorithm to solve the model,a structural optimization scheme of foreststand spatial structure based on forest distribution pattern is proposed.In order to improve the spatial distribution pattern description and analysis of forest spatial distribution pattern,this paper provides theoretical basis for the reconstruction and restoration of the vegetation of the surrounding Dongting lake and the subtropical broad-leaved forest in south China,the protection of natural forest and the sustainable management.The main research contents and conclusions are as follows:(1)Analysis of forest stand structural characteristics of typical broad-leaved forest types in Dongting Lake area.With Lu Tau state-owned Forest Farm,Yuanjiang Longhu Mountain State-owned forest Farm in Hunan,Dawei MountainNature Reserve in Liuyang Changsha,Dashan Chong State Forest Farm in Changsha,Hunan Dark Cloud nature reserve of broad-leaved forest as the object.The characteristics of forest stand structure,including tree species composition,tree species diversity,forest diameter structure and forest stand vertical structure,are used to analyze the structure of typical natural broad-leaved forests.The results showed that 79.91%of the 1364 broad-leaved forest communities with diameter greater than 5 cm were in the range of 5-20 cm,and the diameter distribution of the stands was inverse J-shaped curve,and the number of trees decreased with the increase of diameter rank.The trees with height less than 10 m were the most,reaching 761 trees,and the height of the trees was higher than that of the mature and over-matures forest stand species.The number of trees over 15m was only 281,and the Simpson index ranged from 0.383 to 0.791.(2)On the basis of analyzing the influence of forest stand density on the growth of forest,based on the average crown radius of forest trees,the ideal forest distribution state of forest stand is constructed,and the ideal method for determining the density of forest stand which is relatively independent from tree canopy and tangent to adjacent wood is proposed.(3)The data of the forest stand of the Longhushan State-owned Forest Farm in Dongting Lake and the Daweishan National Nature Reserve in Hunan Province were used as test and verification data.Based on the simulated data and the actual stand data,compare and analyze the difference between the five methods of the neighboring method,the angular scale method,the Voronoi coefficient of variation,the Ripley's L function,and the double correlation function in the judgment process and mode;from the principle of each research method,the statistical characteristics of each method are discussed.In the experiment,the commonalities and heterogeneities of each method kernel were found.The advantages and disadvantages and adaptability of each method in evaluating the spatial distribution patterns of different areas,different forest stand densities and different aggregation egree plots were studied,so as to select the most suitable forest space.The distribution pattern approach provides a reference and basis.The results of different methods for the spatial distribution pattern of different forest stands with the same stand and the same method were obtained.(4)Combining statistics and computational geometry into forestry and ecology.On the basis of several methods of judging the spatial distribution pattern of trees such as Angle scale,through the analysis of the nodes of the ideal forest distribution grid,the optimal grid construction and the evaluation method of the uniformity of the forest distribution pattern based on the optimal grid--the optimal forest grid degree were proposed,and the optimal mesh degree of forest division in 25 of broad-leaved forests is between 32%and 46%,the spatial distribution pattern uniformity of the broad-leaved forest in Dongting Lake is relatively low,and there are many unreasonable factors.This conclusion is a more realistic reflection of the status of broad-leaved secondary forest resources in five regions.(5)A circular distribution index is constructed for the optimal mesh.A ring distribution index describing the uniformity of adjacent wood around the reference tree is constructed to determine the distribution pattern of forest stand,which is used to depict the spatial distribution pattern of forest trees.After the correlation between the 25 foreststand angle scale and annular distribution index in the study area,parameter R is between-0.509 and-0.985.Correlation analysis shows that the cyclic distribution index and the angular scale have significant correlations in different forest stands.The case analysis and the correlation test with the angular scale show that the circular distribution index model objectively and truly reflects the distribution of forest trees on the horizontal ground.The situation is a pattern analysis index with strong releasability.The calculated results can be expressed by both the mean value and the distribution of a single value,which has strong analytical ability to the spatial structure of complex forests,especially to the analysis of forest spatial distribution pattern and the regulation of spatial structure,and provides a theoretical basis for the quantitative regulation of forest stand spatial structure.(6)Research on forest structure regulation methods based on cyclic distribution index.Based on the evaluation of uniformity distribution pattern and forest stand ring distribution index,the target structure of forest stand space structure optimization was constructed from three aspects:traditional stand structure,stand space structure and stand vertical structure.Based on the idea of structured forest management,a multi-objective adjustment optimization model of foreststand spatial structure including 7 species of mixed species,competition index,circular distribution index,forest index,spatial density,open ratio and size ratio was established.Using the parallel computing ability of intelligent PSO algorithm to search the weak links of the stand space,and the problem of multi-objective spatial planning of forest stand is subtly transformed into the problem of iterative optimization of particle population.The practical application results show that before and after structural regulation,the mixing degree,competition index,annular distribution index,space density index,forest layer index and open ratio of the optimization model are improved,and the forest stability is enhanced.This paper comprehensively summarizes the spatial distribution pattern of natural secondary forests at home and abroad,especially on the basis of the advantages and disadvantages of each parameter.From the two scales of forest and forest stands,the method of comprehensive evaluation of optimal grid stand distribution pattern and forest ring is proposed.The distribution index explains its significance of forestry and ecology,and provides a theoretical basis for evaluating the irrationality of forest spatial characteristics and determining appropriate management measures.It provides ideas and research direction to solve the problem of criterion criteria for spatial distribution of natural forests and explore a new way for the ideal structure of forest management and its expression.