重度放牧对荒漠草原主要植物种间关系及群落稳定性的影响

Effects of heavy grazing on the interspecific relationship of main plant species and community stability in a desert steppe

种间关系是群落演替的表征之一,常由种间联结体现。本文采用方差比率法计算主要物种的总体联结性,以χ2统计量检验为基础,结合使用联结系数、共同出现百分率、Ochiai指数、Dice指数,计算了群落的时间稳定性与物种异步性,研究了无放牧与重度放牧时内蒙古短花针茅荒漠草原群落7个主要物种之间的种间联结性,探讨了重牧对种间关系及群落稳定性的影响。结果表明:(1)对照区主要物种总体呈不显著的负联结,负联结种对占比最大,为33.3%,而重牧区呈显著的正联结,正联结种对占比最大,为57.1%,表明重牧使群落物种间的关系由竞争为主转变为互利为主;(2)重牧区种对间的共同出现百分率、Ochiai指数、Dice指数均下降,表明重牧使主要物种间的关系更加松散;(3)重牧区群落的时间稳定性与物种异步性下降,表明重牧使群落处于相对不稳定状态。重牧对群落稳定性的影响与种间关系的改变密切相关,种间关系越紧密的群落稳定性越强。

Interspecific relationship is a characteristic of community succession,which is often represented by interspecific association.In this study,variance ratio method was used to calculate the overall association of the main plant species.Based onχ2-test,association coefficient,percentage of co-occurrence,Ochiai index,and Dice index,the temporal stability and species asynchrony of plant community were calculated.The interspecific association of seven main species in a Stipa breviflora desert steppe was studied under no grazing and heavy grazing to understand the effects of heavy grazing on the interspecific relationship and community stability.The results showed that:(1)Under no grazing,the overall association was non-significant negative association among the main species.The proportion of negative association pairs(33.3%)was the largest.Under heavy grazing,however,the overall association was significant positive association.The proportion of positive association pairs(57.1%)was the highest.Heavy grazing changed the relationship of main species from competition to mutual facilitation.(2)Co-occurrence percentage,Ochiai index,and Dice index were all decreased under heavy grazing,indicating that the relationship between the main species was looser under heavy grazing than under no grazing.(3)The temporal stability and species asynchrony of the community under heavy grazing areas decreased,indicating that plant community was in a relatively unstable state with heavy grazing.The effects of heavy grazing on community stability were closely related to the change of interspecific relationship.The closer the interspecific relationship was,the more stable the community was.