芦芽山寒温性针叶林冠层下植被beta多样性格局及其成因

摘要

Ecologists have long been enthusiastic about alpha diversity in montane regions;however,the elevational patterns of beta diversity and underlying crucial processes are still rarely studied.Niche and neutral processes are known to be two key factors in shaping species composition in a community.Although it could be difficult to test independently because of covariability,these two factors could produce competing predictions concerning the pattern of beta diversity between communities with environmental divergence and geographic distance.Our goal was to discover the patterns of species turnover among sites in temperate montane forests,and determine to what extent environmental filtering and limitation of dispersal affect the processes of species assembly.Additionally,we tried to pinpoint the main factors associated with niche filtering,which dominantly control the local floristic composition of the understory.We investigated the coniferous forest communities along the elevational gradient of Luya Mountain,documenting all species encountered and environmental conditions in 1720 m × 30 m plots.For all pairwise sites,we calculated the Simpson's beta dissimilarity (beta-sim) of species composition and the Euclidean distances of independent variables (elevational,geographical,and environmental) for shrubs and herbs.The Mantel test and its partial version were adopted to analyze data,respectively.Linear trends of beta-sim against all ‘distances’ were obtained by ordinary least square regression.Furthermore,we employed canonical correspondence analysis (CCA) to demonstrate the relationship between species composition and the significant habitat descriptors selected through the Monte Carlo permutation test.The results showed that the turnover of herbaceous species between adjacent sampling sites exhibited a decreasing pattern along the elevational gradient,whereas the pattern of shrubs was irregular.For both shrubs and herbs,beta-sim increased significantly with both elevational and geographical distances,except the environmental distance.After controlling the influence of elevation by the partial Mantel test,the significant correlation between beta-sim and geographic distance was still maintained,but not vice versa.Results of CCA suggested that environmental factors together explained 74.4％ of variance in understory species composition,and more specifically,litter thickness,slope,stem density,and basal area were indicated as key factors at the local scale.Nevertheless,there was no significant correlation between community structure and edaphic variables.We therefore concluded that environmental filtering and limitation of dispersal might jointly regulate the patterns of species beta diversity in the understory of boreal coniferous forest within Luya Mountain,with dispersal limitation playing a more important role in community assembly.%群落构建机制是生态学的中心议题之一.对山地植被beta多样性格局及其成因的探究有助于加深对此问题的认识.以芦芽山寒温性针叶林群落冠层下植被为研究对象,结合野外调查与室内实验获取的详细数据,运用Mantel检验、普通最小二乘回归和典范对应分析(CCA)等统计方法,探讨了林下植被的beta多样性格局及其成因,结果显示:(1)沿海拔梯度相邻群落间草本层物种周转率呈现递减格局,而灌木层变化规律不明显;(2)灌、草层beta多样性与海拔差异、地理距离呈显著正相关关系,而与局地环境异质性关系不显著.控制海拔作用后发现,灌、草层beta多样性与地理距离关系依然显著,而当消除地理距离的线性影响后,beta多样性与海拔关系也变得不显著(3) CCA模型中,环境因子共解释了物种组成变异的74.4％,其中,海拔、坡度、凋落物厚度、乔木密度与总干面积对林下灌、草植被物种组成具有显著影响,但土壤因子的作用未见显著.综上,生境筛滤与扩散限制共同主导了芦芽山寒温性针叶林冠层下群落构建过程,但扩散限制的影响强于生境筛滤作用.