Community Structure And Forest Health Assessment In Natural Restoration Of Maolan Degraded Karst Vegetation

More and more international concerns are aroused today by the environmental problems existing in Karst region,thus restoration and reconstruction of degraded Karst vegetation have become a focus and subject in relating research field.Adopting the concept of space as a substitute for time,in this paper we take communities at different restoration stages in Malan Karst Forest National Nature Reserve in Guizhou province of China as research object,and community investigation,data analysis is carried out in succession.By analyzing species composition,structure,stability and other indexes of the community and its different layers,an assessment of community health and vigor has been evaluated, basic variation rules relating to contributions and status of each community layer in the process of vegetation restoration have been revealed.By analyzing properties of interspecific association,interspecific covariation and spatial distribution pattern of major species in each community layer,relationship between the three properties to community health and vigor is disclosed.Some key findings are as follows:Our research indicates that different factors of community composition and spatial structure diversify in their different rules during the process of vegetation restoration. Community species composition,height and community structure are more and more improvement and complex along with the advancing movement of succession,and when reaching to climax community stage as well as to phase of evergreen deciduous broadleaf forests, community height,composition and function are all at their peak state.Succession trend of community life-form is therophytes→cryptophytes→hemicryptophytes→chamaephytes→phanerophytes,and also existing saltatory types,to climax community major component in constructive layer are chamaephytes and phanerophytes,while subordinated layer is the phanerophyte,and there exists a succession tendency that species of therophytes, cryptophytes,hemicryptophytes,chamaephytes are moving to shady tolerant plant types. In the proceeding of succession,species evenness varies a bit and ecological dominance is at an evident low state in each community layer;species richness,diversity index of arbor and herb layer is with little variation,however,as far as shrub layer concern, this two indexes are improving and the variation is apparent;variation rule of interspecific encounter chance is basically similar to rule of richness and diversity index in each community layer.The whole correlation relating to woody plants(arbor,shrub layer) varies from irrelevance to relevance,and the relevance increasing gradually in the process of succession,while the peak emerges at stageⅥ;but to herbs this trend is on the contrary with whole correlation at stageⅠbeing the most.Interspecific association of major species in each community layer is somewhat weaker,and there exists a little species pairs with correlation in significant or very significant level,variation of major species pairs is also inapparent.Interspecific covariation of species pairs in community is mostly no correlation,and numbers of positive correlation are more than negative correlation. Along with the proceeding of vegetation restoration,interspecific covariation shows a "single-chain→multi-chain→net" developing trend,and to climax stage the covariation from is the most intricated.Diverse degrees of instability are indicated in the whole community and in each layer,which may due to high degree of habitat heterogeneity and fragility in Karst region,strong sensitivity of ecosystem to environment,high extent of species richness,diversity,and even higher rapid species updating rate as comparing to climax community of normal landform.Considering to health index of each community layer,arbor layer displays a rising pattern,while the shrub layer indicates a rising forward and falling afterward pattern, and for herb layer the falling types.Given health index cumulative contribution of each layer to whole community,arbor layer contributes most at stageⅥ,while shrub layer at stageⅢ,Ⅳ,Ⅴ;herb layer at stageⅠ,Ⅱ,it reflects the status variation and replace relationship of each layer in the proceeding of vegetation restoration.There is little or no correlation between community health index and interspecific association,however, given variation trend relating to positive interspecific covariation or positive interspecific covariation in significant level of community dominant species,community health index variation is basically following the same trend,and there exists a certain positive correlation.Contagious distribution has been demonstrated a major pattern in spatial distribution of community dominant species,and negative correlation has been revealed between community health index and dominate species aggregation degree.