Species Diversity Pattern And Maintenance Mechanism Of Mixed Evergreen Deciduous Broad-leaved Forest In Karst Hills Of Guilin,southwest China

Species diversity is the way in which biodiversity is expressed at the species level,and the maintenance mechanism of species diversity is also one of the core contents of community ecology research.This study is located in the northeastern of Guilin City,Guangxi Zhuang Autonomous Region,southwest China.It is a typical Karst hills landform,the karst development is strong,the landscape is complex,and the ecology is fragile,if the vegetation is easily degraded and difficult to restore if damaged.evergreen and deciduous broad-leaved forest is a type of forest vegetation between evergreen broad-leaved forest and deciduous broad-leaved forest.Mixed evergreen and deciduous broad-leaved forest of Guilin is a type of forest vegetation between evergreen broad-leaved forest and deciduous broad-leaved forest formed under special site conditions in the subtropical Karst hills area.It plays an important role in preventing rocky desertification in karst areas,regulating and storing epikarst zones,carbon reservoirs and other ecological functions.In recent years,it has attracted more and more attention from academic circles and government departments.Therefore,exploring the forest species diversity pattern in this Karst hills area and revealing the formation and maintenance mechanism behind the species diversity pattern has important theoretical value for the protection of forest biodiversity in Karst hills.This paper takes the 2 hm~2mixed evergreen and deciduous broad-leaved mixed forest as the research object in Xiaoshui Village,Lingchuan County,Guilin City.By investigating species,topographical factors,and measuring basic data such as soil nutrients and functional traits,systematically analyze species abundance patterns,species diversity patterns,functional trait variation and functional diversity patterns,and explore Guilin Karst hills evergreen and deciduous broad-leaved mixed forest Species diversity pattern and maintenance mechanism.The results show that:(1)The number of evergreen species in the canopy layer,lower tree layer and shrub layer is greater than the number of deciduous species.The difference between the number of evergreen species and the number of deciduous species in the canopy layer→lower tree layer→shrub layer gradually increases(That is,there are 25 species and 24 species,38species and 35 species,49 species and 41 species of evergreen and deciduous leaves in the canopy layer,lower tree layer and shrub layer,respectively).From the perspective of species-abundance curve and species-area curve,the number of species and individuals of evergreen tree species is greater than that of deciduous tree species at different sampling scales.As the scale increases,the proportion of rare species also increases.(2)For evergreen+deciduous species,only the Broken-stick model and the Niche preemption model are accepted at small scales,while only the Broken-stick model is accepted at medium and large scales.All models(Broken-stick model,Zipf model,Zipf-Mandelbrot model,Lognormal model,Metacommunity zero-sun multinomial distribution model,Volkol model and Niche preemption model)of evergreen tree species are acceptable on small scales,but only Broken-stick model on medium and large scales are accepted.For deciduous tree species,the Broken-stick model and Zipf model were rejected on the small scale,while only the Broken-stick model and Zipf-Mandelbrot were accepted on the medium and large scales.(3)We use the TWINSPAN classification method combined with DCA sorting to classify the community data,and as a result,the 50 sample data are divided into 3communities,ie communityⅠ,communityⅡand communityⅢ.(4)The largest change inαdiversity of different squares is the number of individuals,with a coefficient of variation of 49.9%,and the Simpson index and Pielou index have the smallest variation,with a coefficient of variation of 5.9%.The coefficient of variation of species number,Inverse·Simpson index and Shannon-Wiener index were 22.7%,28.9%and 9.8%,respectively.(5)We compare theαdiversity of the three communities and the results show Shannon-winener index,Simpson index,Pielou index and Inverse·Simpson index communityⅡwas significantly larger than communityⅠand communityⅢ(P<0.05),and have the same changing law,ie communityⅡ>community>communityⅢ.The number of species individuals is that communityⅢis significantly larger than communityⅠand communityⅡ(P<0.05),and its changing trend is communityⅢ>communityⅡ>communityⅠ.The number of species was significantly larger in communityⅠand communityⅡthan in communityⅢ(P<0.05),and the change trend was communityⅠ>communityⅡ>communityⅢ.(6)The CCA ranking of topographic factors and species-samples found that disturbance and elevation have a very significant impact on species distribution(P<0.01),slope,thick soil,and rock exposure rate have significant effects on species distribution(P<0.05).(7)We use chlorophyll content,leaf thickness,leaf area,specific leaf area,leaf dry matter content and wood density to analyze intra-and inter-species variation.We found that the difference in chlorophyll content and wood density intra-and inter-species variation was not obvious.The variation of leaf thickness,leaf area,and specific leaf area mainly comes from inter-species,while the variation of leaf dry matter content mainly comes from intra-species.(8)We compared the functional traits of the three communities.The results showed that the chlorophyll content and leaf thickness of community II were significantly larger than those of community I and community III(P<0.05),and they had the same changing trend,ie community II>communityⅠ>communityⅢ.The wood density is significantly smaller than that of communityⅢand communityⅡand communityⅠ(P<0.05),and its changing trend was communityⅡ>community>communityⅢ.The leaf area(LA)is that the communityⅢand the communityⅡare significantly larger than the communityⅠ(P<0.05),the change trend is communityⅢ>communityⅡ>communityⅠ.The specific leaf area(SLA)of communityⅡis significantly smaller than that of communityⅠand communityⅢ(P<0.05),and the change trend is communityⅢ>communityⅠ>communityⅡ.Leaf dry matter content is that communityⅢis significantly smaller than communityⅠand communityⅡ(P<0.05),and the trend of change is communityⅡ>communityⅠ>communityⅢ.(9)We have compared the plant functional diversity indexes of three communities.We found that the change trend of functional divergence index was communityⅢ>communityⅡ>communityⅠ,but the difference between the three communities was not significant(P>0.05).The functional dispersion index and the evenness index were that the communityⅢis significantly larger than the communityⅠand the communityⅡ,and the change trend is communityⅢ>communityⅡ>communityⅠ.It is that the functional richness index of communityⅠwas significantly greater than that of communityⅡand communityⅢ,and the change trend is communityⅠ>communityⅢ>communityⅡ.