Study On The Community Characteristic Of Main Forest In Laoxiancheng Nature Reserve In Zhouzhi County, Shaanxi

The quadrat sampling method was employed to investigate main forest communitys in Yangjiagou, Zhouzhi Laoxiancheng Nature Reserve, which was to study the characteristics of communitys involved type, species composition, intrasecific and interspecific association, ecological niches. It will be helpful to understand the structure and dynamics of communitys in deep, and also greatly important in theory and applied values on biodiversity conservation and vegetation restoration.Based on the data, classify the forest community by two-way TWINSPAN;combined with plot's conditions to research the community structure in study area.The results showed that the 28 plots in research area can be divided into 9 community types;the order of the community diversity is Pinus armandii > Corylus ferox+Populus purdomii >Ulmus bergmanniana>Quercus serrata var. brevipetiolata>Quercus aliena var.acutiserrata> Populus davidiana+ Betula utilis > Pinus tabulaeformis > Betula albo-sinensis >Quercus spinosa.Analyse the specise structure,community diversity and its changes with the elevations of the gradient on species richness S,Shannon-Weiner index,Simpson Pielou index and evenness index.The results showed that the 9 forest communities have vegetation resource in 243 species,pteridophyte have 4 families 4 genera 4 species,gymnosperm have 2 families 4 genera 5 species,angiosperm have 58 families 151 genera 234 species.Species diversity changes regularly along altitudinal gradients,it shows a rising tendency between 1 525-1 920 m.then it shows a downtrend between 1 920-2 340 m.Based on the use of variance ratio(VR) and the 2×2 contingency table,a series of parameters includingχ2-test,percentage co-oc-currence(PC),and association coefficient(AC) were used to analyze the interspecific associations of 21 tree species,25 shrub species and 27 herb species.The result showed that the interspecific association in tree layer or herb layer were not significantly negative while not significantly positive in shrub layer.The number of species pairs having of highly extremely significantly positive association and significantly positive association is small: 8 in arbor layer,14 in shrub layer and 11 in herb layer.According to PC and AC,the interspecific associations of most species is very weak;Forest communities are in early succession, the structure is imperfect and unstable,many species compete the limited environmental resources cause the competition and rejection.Parameters of niche breadth,niche overlap and niche similarity were calculated to show community characteristics.The result showed that niche breadths of Pinus armandii and Quercus aliena var. acutiserrata were larger than other species,with Levins(Bi) and Hurlbert's(Ba)values being 0.654 and 0.699,and 0.534 and 0.460,Smaller niche breadths were found for Quercus serrata var. brevipetiolata and Ulmus bergmanniana spec ies,with Bi and Ba values being 0.064 and 0.023,0.049 and 0.016,respectively.Both the niche overlap and the niche similarity between Betula platyphylla and Populus purdomii,between Betula utilis and Populus davidiana were larger than other s pecies,with Lij and Lji values being 0.108 and 0.114,0.089 and 0.128,with Cij values being 0.939 and 0.744.There was no plot shared by Quercus spinosa with Quercus serrata var. brevipetiolata, Ulmus bergmanniana , Betula platyphylla , Populus purdomii,Betula utilis, which also occurred between Quercus serrata var.brevipetiolata and Ulmus bergmanniana, Quercus serrata var.brevipetiolata and Populus purdomii, Ulmus bergmanniana and Betula utilis. It means these species pairs have different demands on natural habitat.Overall, the niche proportional similarity and niche overlap index were low, which indicates the competition for environmental resources between species is not fierce and spatial heterogeneity is significant.The forest communities in research area have been disturbed intensely by people and livestock, causing the degradation in community structure and function of ecological system and bio-diversity's reduction, so effective measures should be taken to decrease the artificial interference and damage in community structure and function of ecological system and in the process of vegetation succession, strengthen management in middle and young forests, promote their redevelopment.