Research On The Diversity Pattern And Maintenance Mechanism Of Dacrydium Pectinatum Natural Community On Hainan Island,China

Global climate change and the artificial transformation of ecosystems may lead to the decline of biodiversity and threaten the habitat of species.Exploring the spatial pattern of biodiversity can respond to and solve the potential threat of biodiversity loss by promoting biological conservation activities at the regional scale,such as the design of protected areas and habitat restoration.As one of the terrestrial ecosystems with the richest vegetation and most complex structure,tropical forests play a vital role in maintaining biodiversity and the balance of ecosystems.Dacrydium pectinatum is one of the constructive and dominant species of tropical mountain forests in Hainan Island.The plant community formed by it as an absolute dominant species has extremely high diversity.Therefore,revealing the biogeographic pattern and construction mechanism of the D.pectinatum community has important scientific value for the protection of tropical forest diversity.At present,research on D.pectinatum mainly focuses on population regeneration,population distribution pattern,population seed rain and soil seed bank,population genetic evolution.However,studies on the changes in plant composition and diversity of their communities along different environmental scales and the mechanism of community assembly are still lacking.In this study,68 fixed sample plots of 30m×30m were established in the main distribution areas of D.pectinatum(Bawangling,Diaoluoshan,Jianfengling).We investigated the vegetation and environmental factors of community,aims to analyze the following(1)The age structure and spatial distribution pattern of D.pectinatum population.;(2)the spatial variability of plant composition/diversity of the D.pectinatum community and key environmental driving factors.(3)the diversity characteristics of different vegetation layers in D.pectinatum community and interspecific relationships among dominant populations and their environmental interpretation;(4)the seedling regeneration pattern and its relationship with environmental filtering and negative density dependence;(4)the changes of species and phylogenetic α and β diversity along different spatial scales and the relative effects of niche theory and neutral theory on the process of community assembly.The key findings of this study are as follows:(1)The structure and spatial distribution of D.pectinatum population change with the change of habitat scale.The number of seedlings and saplings in Bawangling and Jianfengling are small,or even missing,which shows a trend of decline;However,Diaoluoshan,which has experienced different logging intensities,its belongs to a growing population.The D.pectinatum population of Diaoluoshan presents a clustered distribution pattern,while Bawangling and Jianfengling are randomly distributed or evenly distributed;D.pectinatum shows a clustered distribution in the juvenile stage,however,the adult and old age stages shift from a convergent distribution to a uniform or random distribution.(2)The plant composition/diversity of the D.pectinatum community formed their own flora characteristics.In Bawangling,Diaoluoshan and Jianfengling,the species of Lauraceae and Symplocos are the most widely distributed,while the distribution of other families and genera is relatively scattered and does not show a specific pattern,which conforms to the general composition of tropical mountain rain forests in Hainan Island,China.Jianfengling has the highest species accumulation rate,the most complex species composition,and the lowest uniformity of species distribution;Bawangling is the second,and Diaoluoshan has the lowest species richness and diversity,but the species distribution is relatively uniform.The diversity of the D.pectinatum community is significantly lower than the tropical rain forests of Southeast Asia,South America,and Central America,but its slightly higher than that of the tropical rain forests of West Africa with less precipitation;it has the vegetation properties and diversity characteristics of some tropical rain forests.The environmental factors within the community change with the spatial scale.Elevation,slope,canopy density,soil organic matter,soil p H,soil total nitrogen,soil available phosphorus and soil available potassium 8 environmental limiting factors have caused the variation of the plant composition and distribution on the spatial scale,and the elevation and is the dominant factor.(3)The analysis of the diversity of different vegetation layers and the interspecific relationship of the D.pectinatum community showed that the arbor layer had the highest diversity,followed by the shrub layer and the herb layer.The diversity of its various vegetation layers is much higher than that of the temperate and subtropical forest communities in the middle and high latitudes,and it shows a clear latitude distribution pattern.The species uniformity of various vegetation layer is low.The arbor species and shrub species in the community are mostly smalldensity populations,and there are few tree species that occupy an absolute dominant position.The dominant populations all show the cluster distribution pattern,but the connection between the populations is low,which indirectly reflects the complex process of competition between the populations and the instability of the community structure.Canopy density,elevation,and aspect are significantly related to the species distribution of each vegetation layer,and the canopy density(light environment)is the dominant factor.(4)On a local scale,the mortality rate of adult trees and seedlings in Bawangling is significantly higher than Jianfengling and Diaoluoshan,and the mortality rate of Diaoluoshan is the lowest;while the adult trees density,total basal area,seedling richness,and seedling density are the highest in Jianfengling and the lowest in Diaoluoshan.On the regional scale,they all show a close decreasing pattern with altitude.We found that variations in geographic location and elevation gradients affected the seedling distribution patterns of the D.pectinatum community,and the seedling survival rates weakened gradually from low latitudes to high latitudes and from low elevations to high elevations.The biotic neighborhoods and multiple key environmental factors(such as the canopy density,elevation,slope,soil organic matter,and soil total nitrogen)had a primary impact on the seedling regeneration.Our study supports conspecific negative density dependence and niche filtering as the general mechanism of natural regeneration of D.pectinatum formations.Both biotic and abiotic factors might affect the survival and growth of seedlings,and their relative importance will vary with environmental gradients and species.(5)The species and phylogenetic α diversity of Jianfengling is significantly higher than that of Bawangling and Diaoluoshan;the phylogenetic structure of Bawangling basically shows an aggregation pattern,while Diaoluoshan and Jianfengling show a scattered pattern.Our study found that the species and phylogenetic α-diversity patterns of the D.pectinatum community showed differences at a local scale,which may be related to the local colonization history and the changes in environmental factors.On a regional scale,two α diversity pattern variations converged,and they decreased as the elevation increased and showed a close relationship with topography,soil,and stand factors.The phylogenetic structure changes from overdispersion to convergence with increasing elevation,which indicates the environmental filtering effect of high-elevation areas.Both environmental distance and geographical distance have a significant impact on species and phylogenetic β diversity variation,but the relative effect of environmental differences is greater than that of geographical distance,indicating that environmental filtering is the key factor affecting β diversity patterns.Combining species-based and phylogenetic-based methods strongly proves the key role played by the habitat filtering hypothesis in the assembly process of the D.pectinatum community.In summary,the spatial pattern of D.pectinatum population is closely related to its own growth and reproduction mechanism,interspecies competition,habitat heterogeneity,and human interference.Competition,topography and soil factors are the direct influencing factors that affect the flora composition,distribution,and community renewal variation of Pinus elliottii community at different environmental scales.Competition,topography and soil factors are the direct influencing factors that affect the flora composition,species distribution and community regeneration variation of the D.pectinatum community at different environmental scales.Based on the population structure,species distribution,community renewal,α and β diversity perspectives,combined with the hypothesis of negative density dependence and habitat filtering,it is possible to better understand the changes and maintenance process of the diversity of D.pectinatum community at different environmental scales.Of course,this is essential for the protection of endangered species,natural regeneration and its response to global climate change.