| Understanding the characteristics of plant communities and their relationship with environmental factors is important for the conservation and sustainable use of community biodiversity and the ecological functions of communities.In this paper,Quercus serrata communities in the core water source area of Danjiangkou Reservoir at the foot of the southern part of the Furniu Mountains were taken as the object of study,and Q.serrata communities were investigated using the typical sample plot survey method.The effects of environmental factors on species composition were analyzed using redundancy analysis(RDA);multiple linear stepwise regression analysis was used to explore the relationship between species diversity and environmental factors;the effects of stand density on species composition and diversity were also analyzed,and principal component analysis(PCA)was applied to score different density stands based on soil physicochemical properties and species diversity,and the main results were as follows:(1)The southern foothills of the Fu Niu Mountain Q.serrata community is rich in species composition,a total of 44 families and 88 genera of 127 species,the number of species more than five species of the family mainly Rosaceae,Asteraceae,Liliaceae,Labiatae,Leguminosae,Erythrinaceae,Chitinidae and Buttercup family.Stratification statistics show that there are 31 species in the tree layer,Q.serrata is absolutely dominant,Quercus variabilis is the second dominant species;shrub layer has a total of 73 species,including 31 species of tree seedlings,shrubs 42 species,rhododendron and Q.serrata seedlings as the dominant species;herb layer has a total of 50 species,Carex lanceolata as a single dominant species.Cluster analysis showed that the 30 samples of the Q.serrata community could be divided into three clusters: Ⅰ Q.serrata + Carpinus turczaninowii-Melampyrum roseum.Ⅱ Q.serrata + Quercus variabilis-Forsythia suspensa-Carex lanceolata,and Ⅲ Q.serrata-Rhododendron simsii-Carex lanceolata.From the diameter level,the tree density of all three clusters was greatest at the low diameter level(DBH <3cm),and decreased sharply with increasing diameter level.The species diversity of the three clusters was as follows: species richness,Cluster III > Cluster I > Cluster II,while Simpson dominance index,Shannon-Wiener index and Pielou evenness index were all basically as follows Cluster I > Cluster III = Cluster II,but the differences among different clusters were small.(2)For Q.serrata community as a whole,the environmental factors affecting species composition were mainly shrub cover,elevation,soil total phosphorus content,slope,total potassium content and litter thickness,with six environmental factors explaining37.70% of the variation in species composition;for the tree layer,four environmental factors explained significantly the species composition of the tree layer,with elevation explaining the most,followed by slope direction,total phosphorus content and shrub cover,with four environmental factors explaining 35.89% of the variation in species composition;followed by slope direction,total phosphorus content and shrub cover.p H,total phosphorus content,elevation,and soil bulk,which explained 30.1% of the variation in species composition.The overall species diversity of Q.serrata community was mainly influenced by elevation,herbaceous cover,soil saturated water content,and effective phosphorus and total potassium content.Habitats with higher elevation,lower herbaceous cover,lower saturated water content,and poorer effective phosphorus and total potassium content had higher species diversity.In terms of stratification,species diversity in the tree layer was mainly influenced by slope direction,thickness of deadfall,shrub cover,herbaceous cover,saturated water content of soil,alkaline nitrogen and total phosphorus content,species diversity in the shrub layer was mainly influenced by slope,depression,herbaceous cover,total porosity,organic matter and total phosphorus content,and species diversity in the herb layer was mainly influenced by saturated water content of soil and effective phosphorus content.(3)There were differences in species composition of Q.serrata communities at different stand densities,and the number of families,genera and species in tree,shrub and grass layers fluctuated with increasing stand densities,and all had maximum or larger values at density C.With the increase of stand density,there were some differences in the dominant species in each stratum.At each stand density,Q.serrata and its renewed seedlings were dominant in the tree layer and shrub layer,respectively;Carex lanceolata was absolutely dominant in the herbaceous layer at each stand density.The species richness indexes of tree,shrub and herbaceous layers showed a bimodal trend of increasing,then decreasing and then increasing with increasing stand density,with peaks at densities C and E.The Simpson dominance index,Shannon-Wiener diversity index and Pielou evenness index of tree and herbaceous layers were not significantly different with stand density(P>0.05).While the Shannon-Wiener index and the species richness index of the shrub layer showed similar trends,with the Shannon-Wiener index being significantly higher at densities C and E than at density A.The differences between the other stand densities were not significant.The effect of stand density on total soil porosity,saturated water content,organic matter,total phosphorus,effective phosphorus,total potassium and effective potassium content was significant(P<0.05).With the increase of stand density,soil physical and chemical properties showed a trend of increasing and then decreasing,with larger values of all nutrients at the intermediate density C.Correlation analysis showed that soil saturated water content was the main environmental factor affecting species richness in the tree layer;total soil porosity,saturated water content,p H,total nitrogen content and effective potassium content were the main environmental factors affecting species richness,Simpson dominance index and Shannon-Wiener index in the shrub layer;species richness and Shannon-Wiener index in the herb layer were mainly influenced by the saturated water content and effective potassium content of the soil.The comprehensive evaluation of different density stands of Q.serrata community based on species diversity and soil physicochemical properties showed that stand density C had the highest comprehensive score and density D also had a high score;therefore,maintaining Q.serrata community at densities C and D was most beneficial to the development of the community. |
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