The biomass and its allocation of a five years secondary forest which regenerated after slash and burn in Xishangbanna were estimated based on standard tree regression analysis (for tree )and clear cut method (for shrub? liana? herb and litter).The result shows that the total biomass was 40.6959 t·ha -1 , of which 30.37 t·ha -1 are contributed by tree layer; The biomass of shrub is 3.77 t·ha -1 ,and of the liana and herb are 0.55 t·ha -1 and 0.32 t·ha -1 ,respectively. The biomass of litterfall is 4.48 t·ha -1 ,dead standing tree is 0.21 t·ha -1 . The optimum regression models of different dominant plants and organs of the sample trees of tree layer in the stands were built.
通过为期5年的野外试验,包括6个氮添加量(年氮添加量分别为0、5、10、15、20、50 g m^(-2)a^(-1)),每月进行1次氮添加处理,每个实验处理重复10次,基于物种有无和地上生物量两类数据,分析氮添加对内蒙古草原植物群落的影响.结果显示:内蒙古草原植物群落存在非随机的组配规则,存在4组四物种优势组合.氮添加量的增加会削弱组配过程中确定性驱动力,物种优势组合在氮添加量50 g m^(-2)a^(-1)下最弱.氮添加量对群落组成有显著影响,氮添加量与群落的第一主成分和第二主成分均在0.05水平上显著正相关,相关系数分别是0.367和0.436.随着氮添加量的增加,基于Spearman相关系数的物种互作用网络的节点数(物种丰富度)和连接数(物种互作用数)减少,网络的拓扑结构越来越松散.植物群落耦合性(物种互作用的均值)在氮添加量20 g m^(-2)a^(-1)及以下始终保持在0.7以上.本研究表明氮沉降的增加会弱化植物群落的组配规则,减弱物种互作用,因此必须加强草原氮沉降管理,控制草原氮沉降浓度.(图3表3参44附表1)
