| Evergreen and deciduous broad-leaved mixed forest is the most representative forest vegetation type in subtropical regions of China.It is the zonal vegetation type with the most complex structure and the most abundant biodiversity.It is also one of the typical forest vegetation in the special habitat of karst hills.It plays an important role in maintaining the ecological environment of karst hills.In this karst ecosystem,many studies have been carried out on biodiversity patterns and species coexistence,such as species,functional traits and phylogenetics.However,at the level of life forms,especially for two different life forms(evergreen and deciduous)that are common in evergreen and deciduous broad-leaved mixed forests,there are few similar studies.Evergreen and deciduous tree species are a collection of two species with different phenological traits and life history strategies.Therefore,analyzing the species diversity characteristics of evergreen and deciduous broad-leaved mixed forest,which is the zonal vegetation type in karst habitat,and revealing the formation and maintenance mechanism behind it,not only provides a new perspective for the formation and maintenance mechanism of forest biodiversity in karst ecosystem;at the same time,its research conclusions also help to provide a theoretical basis for the ecological restoration,rocky desertification control and ecological reconstruction of the damaged evergreen and deciduous broad-leaved mixed forest ecosystem in karst mountain.In view of this,this paper takes the 2 hm~2 evergreen and deciduous broad-leaved mixed forest community in karst hills of Guilin as the research object,and adopts the methods of biodiversity analysis,species abundance distribution model and spatial point pattern analysis of dominant species.Taking evergreen tree species and deciduous tree species as controls,the species composition and structure,αdiversity characteristics,species abundance distribution model and spatial point pattern distribution characteristics of the evergreen and deciduous broad-leaved mixed forest community in karst hills were analyzed.The ecological process and mechanism of the formation of this pattern were discussed,and the following conclusions were drawn:(1)After conducting community surveys and statistical analyses,it was found that there were 83 species from 66 genera in 35 families of woody plants with a diameter at breast height(DBH)≥1 cm in the community,totaling 3,784 individuals.Among them,the importance values of evergreen and deciduous species were 47.64%and 52.36%,respectively.The main dominant species were Platyosprion platycarpum,Quercus acutissima,Loropetalum chinense and Quercus glauca.The vertical structure of the community is clear and can be divided into tree and shrub layers.The diameter class structure of the whole community and the two groups of evergreen and deciduous species showed an’inverted J-type’distribution,which belonged to the growth community and species collection.The number of individuals was negatively correlated with the diameter class size.The populations of Loropetalum chinense,Quercus glauca and Platyosprion platycarpum belong to the growth population,and the Quercus acutissima population belongs to the decline population.The speciesαdiversity of the community was spatially uneven.The number of individuals in each quadrat changed the most,followed by Shannon-Wiener index,while Simpson index and Pielou evenness index changed little.At the same time,the speciesαdiversity of different life form plant groups are also different.In conclusion,the evergreen and deciduous broad-leaved mixed forest in the karst rocky mountains of Guilin exhibits rich species composition,mature and stable community,and good regeneration,reflecting the typical characteristics of non-zonal evergreen and deciduous broad-leaved mixed forests in subtropical karst rocky mountain regions.(2)Within the evergreen and deciduous broad-leaved mixed forest of the Guilin karst rocky mountains,the abundance distribution of evergreen and deciduous species within the plots was described using the cumulative empirical distribution function.It was observed that there were no significant differences in the species abundance distribution curves between the two types.Additionally,eight abundance models were fitted to the species abundance distribution of both evergreen and deciduous tree species.The results indicated that the neutral theory model provided the best fit,while the niche theory model showed moderate fit or was rejected.These findings suggest that both the neutral theory and niche theory can explain the coexistence and maintenance of diversity patterns of evergreen and deciduous species.However,the neutral theory appears to play a dominant role,thus validating the ecological niche-neutral continuum hypothesis and suggesting that the community of this mixed forest lies towards the neutral end of the continuum.(3)Within the evergreen and deciduous broad-leaved mixed forest of the Guilin karst rocky mountains,a study was conducted using a zero-model-based point pattern approach to examine the spatial distribution patterns and interspecific associations of four major dominant species within the community.The findings revealed that,despite variations in biological and physiological characteristics as well as life history strategies among the different species,there were certain similarities in their spatial distribution patterns.This suggests that seed dispersal limitations contribute to the aggregated distribution of these four dominant species at small scales.However,due to significant habitat heterogeneity and competitive exclusion,the spatial distribution patterns of these species exhibit randomness or uniformity at larger scales.The spatial association between Loropetalum chinense and Cyclobalanopsis glauca,Quercus acutissima and Platyosprion platycarpum,Cyclobalanopsis glauca and Platyosprion platycarpum,Cyclobalanopsis glauca and Quercus acutissima,Loropetalum chinense and Platyosprion platycarpum were mostly unrelated,and there was an extremely insignificant competitive exclusion or promotion effect among these tree species.The spatial association of Quercus acutissima and Loropetalum chinense was positively correlated at small and medium scales.The demand for environmental resources at small and medium scales was similar or complementary,but it transitioned to no correlation with the increase of scales.(4)The research findings on species abundance distribution patterns,spatial point patterns of dominant species,and their interspecific associations demonstrate that both neutral theory and niche theory play a shared dominant role in the coexistence of evergreen and deciduous species and the maintenance of diversity within the evergreen and deciduous broad-leaved mixed forest of Guilin karst rocky mountains.However,the extent and effects of their dominance vary across different scales.Therefore,the formation and maintenance of community species diversity is the result of multiple theoretical mechanisms,and cannot be explained by a single theory alone.The conclusions of this study also suggest that integrating niche-neutral continuum hypothesis is of practical significance.Through by this analysis,we can gain a more comprehensive understanding of the dynamic changes and internal ecological processes of community species composition,providing a theoretical basis for forestry technicians in forest management planning and targeted ecological restoration methods. |
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