放牧对荒漠草原狭叶锦鸡儿个体形态和种群增长的影响

Effects of Grazing on Individual Morphology and Population Growth of Caragana stenophylla in Desert Steppe

放牧对草本植物的影响研究很多,但是放牧对草地中灌木个体和种群特征的影响报道很少。本文以内蒙古草原灌丛化的重要灌木狭叶锦鸡儿(Caragana stenophylla Pojark)为研究对象,研究了不同放牧强度对锦鸡儿属灌丛个体形态特性和种群增长特性的影响。研究发现,随着放牧强度的增加,狭叶锦鸡儿灌丛高度、面积和生物量(轻牧下降34.9%、中牧下降66.2%、重牧下降76.4%)大幅下降;放牧导致植株小型化,而高度和面积小型化程度不同。随着放牧强度的增加,狭叶锦鸡儿种群出生率降低,死亡率升高,种群增长率降低,种群密度下降;禁牧和轻牧使种群增长,中牧种群出现衰退现象,重牧导致种群明显衰退,所以荒漠草原应该控制在中度放牧压力以下。

Although many studies examined the effects of grazing on growth of herbaceous plants,few studies addressed the effects of grazing on individuals and populations of shrub plant in grasslands.In order to understand the effects of grazing on the individual development and population dynamics of shrub plants,we studied Caragana stenophylla Pojark,which plays an important role in thicketization in the Inner Mongolian steppe.Specifically,we examined the individual morphological characteristics(including shrub height,shrub area and shrub biomass)and population growth characteristics(including annual population recruitment,annual population mortality,annual population growth,population density)across a grazing gradient.As grazing intensity increased,shrub height,area and biomass of C.stenophylla sharply decreased;shrub biomass decreased by 34.9%,66.2%and 76.4%under the light grazing,moderate grazing and heavy grazing treatments,respectively.The effects of grazing on the shrub height and area did not follow the same pattern.As grazing intensity increased,the annual population recruitment decreased,the annual population mortality increased,and thus the annual population growth and population density decreased;the annual population growth decreased by 55.0%under the light grazing treatment,compared with the no grazing treatment,and showed negative growth values under both moderate grazing and heavy grazing treatments;shrub density decreased by 45.1%,65.1%and 72.0%under the light grazing,moderate grazing and heavy grazing treatments,respectively.We concluded that grazing led to miniaturization of individual size,decreases in population growth rate and population individual numbers of C.stenophylla shrubs in the desert steppe.C.stenophylla population increased under the no grazing and light grazing treatments,declined under the moderate grazing treatment,and sharply declined under the heavy grazing treatment.Our results suggested that to maintain the viability of Caragana populations in the desert steppe,grazing intensity must be controlled below the level of moderate grazing.