| Stand spatial structure and site conditions are the main factors affecting understory reg eneration.The stand spatial structure of natural forests is relatively complex and easy to co ntrol.Exploring how the stand spatial structure affects understory regeneration of natural fo rests is an important prerequisite for promoting natural forest restoration.In this study,49 t ypical plots of 20m × 30m Quercus natural secondary forest in Hunan were investigated.T he stand spatial structure was described from four aspects:tree species spatial isolation(mi ngling),forest layer difference(forest layer differentiation),forest competition situation(op enness,Hegyi competition index)and forest spatial distribution pattern(aggregation index,angular scale).The regeneration characteristics of Quercus and other saplings were describ ed from two aspects:sapling growth status(average DBH,average height,average crown width)and sapling quantitative characteristics(sapling density).The species diversity of Q uercus and other saplings was described from three aspects:sapling species richness(Marg alef index),sapling species evenness(Pielou index),sapling species diversity(Auclair&G off index,Simpson diversity index).The spatial structure characteristics of five forest types,the regeneration characteristics and species diversity characteristics of Quercus and other s aplings were analyzed and compared.Taking the saplings of Quercus and other tree species as two research objects,Pearson correlation analysis and canonical correlation analysis we re used to explore the single factor correlation between stand spatial structure index and sap ling regeneration index,species diversity index and the overall comprehensive influence,a nd the key stand spatial structure factors were screened out.Based on this,a structural equa tion model was constructed to explore the influence of key stand spatial structure factors on sapling regeneration and species diversity.In order to provide a theoretical basis for the res toration of natural secondary forests and scientific experience management,the main resear ch results are as follows:(1)The general spatial structure characteristics of Quercus natural secondary forest in Hunan are as follows:the degree of forest layer differentiation is general,but it is relativel y dense,the competition of trees for light resources is fierce,and the forest layer type is ma inly multi-layer forest.The stand has a high degree of mixing and the tree species structure is more complex;the community as a whole showed a weak aggregation distribution.(2)The regeneration of young trees in the natural secondary forest of Quercus in Huna n was poor.The regeneration density of Quercus or other young trees in five forest types w as below 500 trees/hm2,but the regeneration density of Quercus young trees was higher th an that of other young trees,and the growth status of Quercus young trees was better.Exce pt for the average crown width of Quercus young trees,there were significant differences in the growth status of young trees among the groups(p<0.05).(3)The species richness,evenness and diversity of saplings of Quercus and other spec ies in natural secondary forest of Quercus in Hunan were higher.There were significant diff erences in species diversity of saplings among different forest types(p<0.05),and the speci es diversity of saplings of other species was more abundant.(4)The two statistical analysis methods of Pearson correlation analysis and structural equation model consistently showed that the stand spatial structure indexes affecting the re generation of Quercus saplings were forest competition factor and forest layer differentiatio n.The influence degree of these two stand spatial structure indexes on the growth of Querc us saplings was ranked as follows:forest competition factor(0.776)>forest layer different iation(0.244),and the influence degree on the density of Quercus saplings was ranked as fo llows:forest competition factor(0.548)>forest layer differentiation(-0.3 1).The main facto r affecting the species diversity of Quercus saplings was forest layer differentiation(0.344).Reasonable regulation of these stand spatial structure factors is conducive to the regenerati on of Quercus saplings.(5)The results of Pearson correlation analysis,canonical correlation analysis and struc tural equation model analysis consistently showed that the stand spatial structure indicators affecting the regeneration and species diversity of other saplings were forest layer different iation and mingling.The order of influence on the growth status of other saplings was:stan d competition factor(0.776)>mingling(-0.137),and the order of influence on the density of Quercus saplings was:mingling(0.375)>stand competition factor(-0.157).The order o f influence on other sapling species richness was:mingling(0.289)>forest layer differenti ation(-0.265).Reasonable regulation of these stand spatial structure factors is conducive to the regeneration of other saplings. |
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