Research On The Spatial Structure Optimization Of Mangrove Ecosystem In Zhangjiang, Guangdong

Fromed through long terms of succession between marine and terrestrial ecosystems, mangrove ecosystem is a special forst ecosystem which have stable system structure and high productivity.As playing an indispensable role in the biodiversity and diaster reduction and prevention, it is a problem needed solving urgently at present for mangrove conservation how to optimize spatial structures, to restore functions, and to exert function for reducing and preventing disasters.Making the mangrove in Zhanjiang, Guangdong as a main research object and collecting data of survey trees and around four adjacent of 17 stands, this paper studied the space channels of managing mangrove ecosystem from two levels which were the stand-level and the landscape-level. The study methods were forest sustainable management theory, system science theory, landscape ecology, forest spatial structure theory, nonlinear time observation data distribution theory and methods, data mining and mathematical statistics, nonlinear multi-objective planning, etc. Starting with the structure-function relationship, this paper studied the mangrove spatial optimizing management plans of spatial structure of Zhanjiang, Guangdong in the forest landscape level, which was to protect the ecological system and forest type diversity, to maintain the integrity and stability of forest landscape. Making a stand as a management unit and analyzing stand structure factors which contain spatial information, this paper researched how to make rational management plans to optimize the spatial structure within the system. The main contents and conclusions were as follows:(1) the heterogeneity index of stand spatial structureAccording to the patch inner heterogeneity theory of landscape ecology, the heterogeneity target of stand spatial structure optimizing management was presented. The study selected seven space structure factors which were respectively the aim species index, uniform angle scale, health index, the size than the number of spatial density index, mixed degree, competition index from the respect of mixed, competition, stand spatial distribution pattern, species status and growth advantage. A homogeneity index that described heterogeneity objectives of forest management was delimited by means of multi-objective planning method.(2) The correlation studies of homogeneity index By applying the rough set theory and gray correlation analysis method, this study had classified and screened space factors related with homogeneity index. By deleting the factors which had nothing to do with the homogeneity index including "open degree," "canopy height", "height" and "crown", the index system was retrenched. The case study indicated that the relation degree and priority order between influencing factors and homogeneity index were:competition index 0.716> mingling 0.686> spatial density index 0.670> the aim species index0.644>uniform angle index 0.638> neighborhood comparison 0.616>health index0.607.(3) Analysis on characteristics of heterogeneity impact factor of mangrove Forest Stand.By analyzing the impact factors of stand heterogeneity and the correlation attribute, this paper found that the mangrove in Zhangjiang had some characteristics as follows:①The differences of height and crown structure were large among different stands and different tree species, and the height and crown were positively correlated with individual diameter and negatively correlated with the density of each species.②Tree species composition was simple and diversity was low. The overall performance was the transition state from doctrine to advantage. The level of its species isolated was low, which was a transitional type between the weak mingling of the moderate mingling. The difference of mingling degree among difference tidal forest was obvious. The differentiation size and the portfolio size were also different significantly.③The distribution patterns were randomly distribution mainly and inclined to be uneven distribution (Mission-shaped distribution).④The competition intensity was not significantly different and decreased with the tree diameter class.⑤The differentiation of tree species state was not significant and the number of dominant species was limited. The differentiation of current tree growth status was not significant and the trees which were dead or damaged by pests and diseases were less relatively.(4) Evaluation of spatial structure homogeneity of mangrove stands.According to the significance of stand homogeneity index, this paper defined a quantitative indicator of assessing spatial structure characteristics of forest stand -the heterogeneity evaluation index of stand. This study divided the mangrove forest into seven different grades. Example of the study area showed that the average heterogeneity evaluation index was less than 0.15 in Zhanjiang Mangrove Stands. In 17 forest stands, there were only four stands that the heterogeneity evaluation was two grades, and the others were one grade, which indicated the whole mangroves stand of Zhanjiang did not have the obvious advantage in the spatial structure, growth conditions and tree species in the state and had big gap to the ideal structure.(5) The establishment and application of spatial structure optimization modeling of mangrove stands.Making stand spatial structure homogeneity index as the objective function and setting 8 indices of stand structure as constraints, the stand space optimization model of mangrove forest was established via two management ways which were selective cutting and replanting respectively. By applying the two optimization models to guide forest management, the spatial structure could be improved significantly, which made spatial structure of mangrove stands transforming to ideal spatial structure. The models were simple and workable.(6) The landscape structure optimization of mangrove forest.The landscape structure-function relationship of mangrove Forest was analyzed. On landscape level, this paper had established the spatial structure optimization model of mangrove landscape, by using factors of forest age structure, the proportion of forest area, forest spatial distribution and so on, which was closely related to landscape functions. According to the model, this paper had proposed the management plans about landscape spatial structure optimization of mangrove forest in Zhanjiang, Guangdong, from the target layer, strategy layer, measures layer and sub-measures layer. On the premise of maintaining landscape diversity, mangrove forest developed in the patterns of "reasonable size", "uneven-aged," "mixed", "patch nested", by adjusting the mangrove area, age structure, and patch space allocation to the various elements.For the first time, this paper had proposed homogeneous objectives of spatial structure optimization, and definited the homogeneity objective quantitative indicators-stand heterogeneity index. By using the heterogeneity index two stand spatial structure optimization models were established, which were selective cutting and stand replanting models,. By analyzing the heterogeneity characteristic of forest stand types and applying example of optimization model, the homogeneity index was correspond to objective reality for evaluating stand spatial structure. With the proposal of quantitative standard of homogeneous objectives, the management about landscape spatial structure optimization of mangrove forest made new breakthrough. The optimization models were easy to operate and could be easily understood, and had a certainly practical value. The landscape spatial structure optimization model was established on the landscape level by the application of four factors which was closely related with mangrove landscape function. Based on the model, the mangrove landscape spatial structure optimizing management plans were proposed, which provided theoretical basis for forest management of mangrove in landscape scale.