呼伦贝尔典型草原群落退化对其物种多样性及生物量的影响

Effects of community degradation of Hulun Buir typical steppe on its species diversity and biomass

采用样带和样地相结合的方法,在呼伦贝尔典型草原划定65个样地,根据群落调查结果,基于群落各层优势种对各样地的群丛进行划分,并首次采用草原群落退化指数(SCDI)对草原群落退化程度进行分级;在此基础上,分析了草原退化程度对物种多样性及生物量的影响。结果显示:依据SCDI值可将呼伦贝尔典型草原群落分为4个等级,即未退化草原(Ⅰ级,0.00<SCDI≤0.40)、轻度退化草原(Ⅱ级,0.40<SCDI≤0.65)、中度退化草原(Ⅲ级,0.65<SCDI<1.00)和重度退化草原(Ⅳ级,SCDI≥1.00);各等级样地的优势种存在一定差异,分别对应5、15、12和12个群丛。随草原退化程度(SCDI值)的增大,草原群落的物种丰富度(S)、Shannon-Wiener指数(H′)、Simpson指数(P)、地上生物量和枯落物生物量均逐渐降低,且在不同等级退化草原群落间存在显著差异,但Pielou指数(J)和地下生物量无显著变化。相关性分析和曲线拟合结果显示:除J值外,SCDI值与物种多样性的其他指标和生物量指标均呈极显著或显著负相关,且这些指标与SCDI值的拟合曲线均为一元二次方程。Ⅰ级退化草原群落的S值、H′值和生物量指标以及Ⅱ级退化草原群落的P值整体均较高,Ⅳ级退化草原群落的S值、H′值、P值、地上生物量和枯落物生物量以及Ⅲ级退化草原群落的地下生物量整体均较低。综合分析结果表明:呼伦贝尔草原退化主要对草原群落的物种多样性、地上生物量和枯落物生物量有较大影响,但对群落物种均匀度和地下生物量无明显影响;气候变化和过度放牧是导致呼伦贝尔草原退化的主要原因。此外,本研究采用SCDI值衡量草原群落退化程度,其定义为群落的相对盖度、相对高度和相对总生物量加权平均值的倒数,该指标消除了因单一指标计算造成的数据误差,是一个衡量草原退化程度的可量化综合指数。

65 sample plots were designated in Hulun Buir typical steppe by a combination method of transect and sample plot,and the association of each sample plot was divided based on dominant species in each layer of community according to community investigation result,and steppe community degradation index(SCDI)was used to grade the steppe community degradation degree for the first time;on the basis,effects of steppe degradation degree on species diversity and biomass were analyzed.The results show that the community of Hulun Buir typical steppe can be divided into 4 grades according to SCDI value,that is,undegraded steppe(gradeⅠ,0.00<SCDI≤0.40),lightly degraded steppe(gradeⅡ,0.40<SCDI≤0.65),moderately degraded steppe(gradeⅢ,0.65<SCDI<1.00),and seriously degraded steppe(gradeⅣ,SCDI≥1.00);there are some differences in dominant species of each grade of sample plots,corresponding to 5,15,12,and 12 associations,respectively.With the increase of steppe degradation degree(SCDI value),species richness(S),Shannon-Wiener index(H′),Simpson index(P),above-ground biomass,and litter biomass of steppe community all gradually decrease,and there are significant differences among degradation steppe communities with different grades,but Pielou index(J)and under-ground biomass have no significant variation.The correlation analysis and curve fitting results show that except for J value,SCDI value shows extremely significant or significant negative correlation with other indexes of species diversity and biomass indexes,and the fitting curves of these indexes with SCDI value are all univariate quadratic equations.S and H′values and biomass indexes of gradeⅠdegraded steppe community,and P value of gradeⅡdegraded steppe community are relatively high in general,and S,H′and P values,above-ground biomass and litter biomass of gradeⅣdegraded steppe community,and under-ground biomass of gradeⅢdegraded steppe community are relatively low in general.The comprehensive analysis result shows that the degradation of Hulun Buir steppe has a great effect on species diversity,above-ground biomass and litter biomass of steppe community,but has no significant effect on community species evenness and under-ground biomass;climatic variation and overgrazing are the main reasons causing degradation of Hulun Buir steppe.In addition,SCDI value is used to evaluate the steppe community degradation degree in this study,and its definition is reciprocal of weighted average of relative coverage,relative height and relative total biomass of community,this index eliminates the data error caused by calculating with single index,and is a measurable comprehensive index for evaluating the degradation degree of steppe.