Patterns Of Species Diversity And Its Maintenance Machanism In Jiaohe Coniferous And Broad-leaved Mixed Forest,Jilin Province

Based on the large permanent observational studies of coniferous and broad-leaved mixed forest in Jiaohe,Jilin Province,we analyzed the patterns of woody species diversity,variation in compositional and structural components of community assemblage and its determinants,species spatial distribution patterns and species associations.We also analyzed the relative importance of abiotic niche partitioning and negative density dependence for survival across multiple life history stages.We main discussed the roles of ecological mechanisms such as niche differentiation,dispersal limitation and negative density dependence in maintaining species diversity in temperate coniferous and broad-leaved mixed forests.The main findings are as follows:1.The species diversity pattern of woody plants at different successional stages.(1)A total of 29 557(belonging to 17 families,26 genera,and 43 species),55 286(belonging to 17 families,28 genera,and 47 species)and 49 678 individuals(belonging to 17 famlies,30 genera,and 47 species)were recorded in half-mature forest plot(HF),mature forest plot(MF)and old-growth forest plot(OGF),respectively.The mean diameter at breast height(dbh)were 11.61 cm,13.34 cm and 15.25 cm,respectively.The total basal area were 28.19 m2/hm2,31.56 m2/hm2,31.01 m2/hm2,respectively.(2)The index of Shannon-Wiener diversity were 2.460,2.717 and 2.785,respectively.The index of Simpson diversity were 0.886,0.902 and 0.917,respectively.The index of Pielou evenness were 0.654,0.706 and 0.723,respectively.We found that the species diversity increased with successional stages.(3)The beta diversity were 0.314,0.347 and 0.420 in HF,MF and OGF plot,respectively.Like alpha diversity,the beta diversity also increased with successional stages.2.Species diversity and temporal dynamic patterns in seedling layer.(1)A total of 3 128(belonging to 11 families,12 genera,and 18 species),11 470(belonging to 9 families,11 genera,and 17 species)and 5 666 seedlings(belonging to 10 families,11 genera,and 17 species)were recorded in HF,MF and OGF,respectively.(2)On the scale of 1 m2 seedling quadrat,the seedling density of mature forest was higher than that of half-mature forest and old-growth forest.However,the species richness of old-growth forest was higher than that of half-mature forest and mature forest.(3)The alpha diversity of seedlings increased with the successional stages.The beta diversity of seedlings in the late successional stage of community was higher than that in the half-mature forest and mature forest.(4)The number of seedling individuals fluctuated greatly with time in the past five years,and there were significant differences among species.The difference in seedling mortality among years is not obvious,but the birth rate varies greatly from year to year,resulting in a large difference in the net growth rate of seedlings between years.(5)For monthly dynamics,there was no significant difference in species composition between June and July,but a great variation in the seedling composition in August.The death and recruitment pattern of seedlings showed significant differences among species and by month.The mortality rate in June was significantly higher than that in August.The mortality rate of perennial seedlings during the observation period was significantly less than the mortality rate of new seedlings.We also found that the recruitment occurred mostly in June.3.Maintenance mechanism of species diversity based on species spatial distribution patterns and species associations.(1)Segregation and partial overlap were prominent in interspecific association types.Few species pairs showed interspecific mixing.This result shows that individuals tend to gather in the vicinity of conspecific species,exhibiting intraspecific aggregation.(2)The proportion of species showing negative associations(repulsion)was found to be greater than that of positive associations(attraction)at most scales.This is an indication that the individuals of different species tend to be separated in space and that they show negative association with few opportunities for direct interaction between interspecific individuals.Intraspecific aggregation and interspecific segregation were the main spatial structure types in the 30 ha study area.The spatial segregation between different species weakens interspecific competition which may prevent a competitive exclusion of dominant against disadvantaged species and facilitates species coexistence and biodiversity maintenance.4.Variation in compositional and structural components of community assemblage and its determinants.(1)The values of overall beta diversity(BD statistics)and the relative contribution of individual sampling units to beta diversity(LCBD indices)depended on whether the species composition,size structure or both together had been taken into account.(2)The value of compositional-structural beta diversity(BDCOMP-STR)was the largest,followed by traditional compositional beta diversity(BDCOMP);the smallest was the structural beta diversity(BDSTR).(3)The sites with high contributions to beta diversity(LCBD values)varied among structural and compositional components.(4)The explanatory power of the environmental variables and the spatial variables also varied widely with different components of a community.The combination of environmental and spatial variables explained the highest proportion of variation(43.8%)in the compositional component and explained the lowest proportion of variation(25.4%)in the structural component of community assemblage.Both deterministic and stochastic processes are acting to determine community assemblages in terms of species composition and structure in our temperate forest site.Our study highlights the importance of considering the structural component of forest communities,in addition to compositional data,when studying beta diversity.5.Abiotic niche partitioning and negative density dependence across multiple life stages.(1)Both biotic and abiotic neighborhood variables affect individual survival.However,their relative importance varied with life history stages of a tree.The strength of the effect of conspecific tree neighbors decrease along ontogeny,while the roles of the topographic and edaphic variables increase at later life stages.(2)We demonstrated species vary widely in their probability of survival under different environmental conditions,and vary widely in response to differences in neighbor identity and density.(3)Wide variation among species in response to abiotic variables is a necessary requirement for niche differentiation and coexistence via niche partitioning processes.(4)The conspecific NDD and abiotic niche partitioning are major structuring mechanism in Jiaohe forest plot.Finally,our results demonstrated the necessity to incorporate multiple life stages and multiple influence factors when elucidating the maintenance of species diversity in temperate forest.