Study On Community Characteristics And The Main Tree Species Spatial Pattern Of Pinus Yunnanensis Var.tenuifolia-Quercus Variabilis Secondary Forest In The Nanpan River Basin

The structure determines the stability and development of the forest community.The forest community is dominated by woody plants.The study of woody population structure can clarify the interspecific association,reveal the potential ecological mechanism of species coexistence and predict the succession dynamics of the community.Pinus yunnanensis var.tenuifolia used to be a typical dominant population in the Nanpan River basin in southwestern China,but decades ago(about 1956-2000)it suffered severe man-made damage,habitats continued to shrink and fragmentation,primary forest disappeared completely,and populations continued to decrease.At present,it is combined with Quercus to form pine-oak mixed forest,and plays important ecological functions such as soil and water conservation and carbon storage in the basin.However,little is known about its community structure.In this study,a typical P.yunnanensis-Quercus variabilis natural secondary forest in Guangxi Yachang Orchidaceae National Nature Reserve was used as the research object,and on the basis of comprehensive investigation,3 permanent plots of 80 m× 80 m,100 m× 60 m,70 m× 80 m were set up.We try to analyze the structural characteristics of the community from non-spatial structure and spatial structure.For non-spatial structure,we mainly analyze the species diversity of the community and the DBH(diameter at breast height)class distribution of the main population.For spatial structure,firstly,the L11(r)function and g11(r)function are used to test the habitat heterogeneity of the plots,and the appropriate null model is selected according to the test results.Next,we use g11(r)function to analyze the spatial distribution of the community and its main populations(DBH?1 cm and numbers of species?20),and use g12(r)function to analyze the spatial correlation of the 6 main populations in each plot.The main results are as follows:(1)Counted with DBH?1 cm,there are 4959 trees in the community,belonging to 27 families,39 genera and 45 species.Among them,there are 1895 trees in plot ?,belonging to 16 families,20 genera and 22 species;1745 trees in plot ?,belonging to 14 families,23 genera and 26 species;1319 trees in plot ?,belonging to 22 families,29 genera and 33 species.Species richness shows plot?<?<?,and the diversity index is ?>?>?.There are 6 common main tree species in the 3 plots:Q.variabilis,P.yunnanensis,Craibiodendron stellatum,Vaccinium bracteatum,Albizia kalkora,Toona ciliata var.pubescens.Among them,Q.variabilis and P.yunnanensis are the dominant species of community.(2)The DBH class distribution of the community is a typical inverted "J"shape,which belongs to the growing type,that is,the young tree is plenty,and the big tree is less.The DBH class distribution of Q.variabilis is similar to the inverted "J" shape,the population is mainly young trees,which belongs to the growing type.The DBH class distribution of P.yunnanensis is Single peak shape,the young trees is lacking,belongs to the recessionary population.V.bracteatum,T.ciliata,C.stellatum belong to the growing type population,A.kalkora is a stable population.The DBH class distribution reflects the characteristics of the early community of succession.(3)The heterogeneity of habitat was not obvious in the community.Q.variabilis belongs to the aggregation distribution in the community,while P.yunnanensis is randomly distributed in the community.The two dominant populations show completely different spatial distribution patterns.In the community,C.stellatum belongs to the aggregation distribution,while A kalkora randomly distributed.V.bracteatum aggregated in plot ?,randomly distributed in plots ? and ?.T.ciliata randomly distributed in plots ? and ?,aggregated in plot ?I.(4)Spatial correlation between populations is complicated.Spatial correlation of the pairs of species changes with the scale,and the same pair is not the same in the different plot.Two dominant tree species Q.variabilis-P.yunnanen.sis have different correlation in the 3 plots.Q.variabilis is negatively correlated with several tree species,such as C.stellatum,T.ciliata,indicating that there is more intense competitive exclusion relationship between Q.variabilis and other tree species.C.stellatum-V.bracteatum,Q.variabilis-A.kalkora are generally positively correlated,show an attracted relationship to each pair of species,indicating that species have similar ecological adaptability,or there is a certain dependence in space.(5)Clear cutting completely destroys forest communities,and in the absence of interference,it also takes a long time to reform a forest again by relying on natural recovery(so far 57a).In the community,there are P.yunnanensis(intolerant conifer),Q.variabilis(deciduous broadleaved species),Schima superba(neutral tree species),Cyclobalanopsis glauca and C.stellatum(evergreen broad-leaved tree species),that can be a proof of the continuity of succession.However,the number of P.yunnanensis and its young trees are far less than Q.variabilis,in the future of species competition and community succession,the declining pioneer tree species P.yunnanensis is likely to withdraw from the community without human intervention,Q.variabilis will continue to occupy the dominant position in the community.