Tree Mortality And Species Coexistence In A Typical Mixed Broadleaved-Korean Pine (Pinus Koraiensis) Forest

In forests,tree mortality is a complex ecological process and can shape forest structure and stands dynamics and their successional trajectories,create gaps for recruitment and contribute to tree species coexistence.Understanding the mechanisms that maintain species diversity is a central goal of community ecology.The typical mixed broadleaved-Korean pine(Pinus koraiensis)forest is the dominant vegetation type in the region in terms of species composition and stand structure in Xiaoxing'an Mountains,Northeast China.Studying tree mortality and species coexistence is helpful for improving our understanding of biodiversity maintaining mechanisms in this old-growth temperate forest.Key questions:1)How does stablizing mechanism(e.g.,negative density dependence,NDD)affect tree mortality dynamic?2)What are the relationships between tree mortality-growth/recruitment trade-offs among species and species coexistence mechanisms(i.e.,stablizing and equalizing mechanisms)?3)How do species coexistence mechanisms improve tree mortality dynamic modelling?(1)We used generalized linear mixed-effects model(GLMM)and likelihood ratio test(LRT)to determine the effects of biotic neighborhood variables on tree survival and tested NDD.Our results showed that the effects of neighbourhood variables on tree survival varied among species in a 9 ha mixed broadleaved-Korean pine old-growth temperate forest dynamics plot in Northeast China.However,the results depended on the neighbourhood radius.The neighbourhood radius affected detection of variation in neighbourhood effects among species.The model had the lowest Akaike's information criterion(AIC)value when variable neighborhood radius was used.Species leaf habit may explain these variations in the effects of neighbourhood on tree survival.The effect of conspecific density on survival varied more widely among species than that of the average phylogenetic dissimilarity of heterospecific neighbors,regardless of the neighbourhood radius(i.e.,fixed-5 m,fixed-10 m and variable radii).Overall,our results indicate that NDD in the stabilizing mechanism is one of important mechanisms for maintaining biodiversity in this temperate forest.(2)We used geographically weighted generalized linear model(GWGLM)and geographical variability test(GVT)to determine the effects of habitat heterogeneity on tree mortality.Our results showed that the effects of topography on tree mortality varied over space in this plot.However,the results depended on spatial scale.The spatial scale affected detection of spatial variation in the effects of topography.Shade and drought tolerance may explain these variations in the effects of topographic on tree mortality.Moreover,the effect of elevation varied more widely over space than those of convexity and hillshade at any quadrat scale(i.e.,5m×5m,10m×10m and 20 m × 20 m).(3)We used GLMM and other statistical methods to determine the responses of tree mortality and growth to local variables(i.e.,biotic neighborhood and topographic factors)and tested the relationship between tree mortality and growth.Our results showed that there is a significant trade-off between tree mortality and growth among species in this plot,especially for small trees,resulting in niche partitioning and fitness convergence among species.The responses of tree mortality and growth to local variables slightly different in this plot.There are significant NDD mortality and growth effects,especially for small trees in this plot.Topographic variables have similar effect on both tree mortality and growth.Stablizing and equalizing mechanisms may contribute to species coexistence and maintaining biodiversity in this forest.(4)We used Poisson,negative binomial(NB),zero-inflated Poisson(ZIP)and zero-inflated negative binomial(ZINB)regressions to determine the responses of tree mortality and recruitment to local variables and tested the relationship between tree mortality and recruitment among species.Our results showed there is a significant trade-off between tree mortality and recruitment among species in this plot,resulting in niche partitioning and fitness convergence among species.The tree mortality and recruitment trade-off may contribute to species coexistence,however still need further study.The responses of tree mortality and recruitment to local variables obviously different in this plot.This is a significant NDD recruitment effect,but not mortality,at sub-quadrat(5 m × 5 m)and standard-quadrat(10m × 10 m)scales in this plot.Elevation had a significantly positive effect on tree recruitment and a significantly negative effect on tree mortality at any quadrat scales.(5)We developed an improved tree mortality process-based model based on previous classical models and species coexistence mechanisms using C Sharp programming language under Microsoft Visual Studio integrated development environment and evaluated its performance under a 9 ha forest dynamics plot(FDP)in a temperate old-growth Chinese forest.We simulated the dynamics pattern of tree mortality from 2005 to 2015 in the particular temperate forest using this mortality model.The Area Under the receiver operating characteristic Curve(AUC)value is 0.624±0.002(Meann±SD).Previous research results in this plot support these simulation results via verification and validation tests.Our findings highlight that the process-based tree mortality modelling approach integrated with FDP and species coexistence mechanisms is useful for improving understanding of the spatiotemporal dynamics pattern of tree mortality at fine scale for ecologists.