三江源退化高寒草甸草毡表层剥蚀过程及发生机理的初步研究

Process and Mechanism of Mattic Epipedon Denudation Taking place on Degraded Alpine Meadows in the Three River Source Region

草毡表层是高寒草甸系统分类的诊断层,是高寒草甸稳定性维持的物质基础,而草毡表层剥蚀是三江源区退化高寒草甸的主要表观特征之一。2008年8月,通过对高寒草甸退化状况进行的野外调查发现,退化高寒草甸具有2种不同的剥蚀过程,其发生的动力也不同。其中,位于山间滩地和缓坡地段的高寒草甸,其土壤剥蚀呈现草毡表层极度加厚、老化、死亡、开裂、剥蚀过程,其发生动力是鼠类的挖掘与冻融交替作用,剥蚀发生时地表草皮处于死亡或半死亡状态;而处于陡坡地段退化高寒草甸的剥蚀由于植被的不同,呈现水分对草皮下土壤的潜蚀、倒钩蚀,发生草皮悬空、坍塌,其剥蚀动力为水分冲蚀和重力作用,剥蚀时草毡表层牧草生长良好。放牧压力下高寒草甸草毡表层的加厚是造成其土壤发生剥蚀的主要原因。

The Mattic Epipedon（ME） is a diagnostic layer for alpine meadow taxonomy and the foundational material for maintenance of alpine meadow ecosystem stability.The denudation of ME is one of the main characteristics of alpine meadow degradation in the Three Rivers Source Region.In August 2008,field survey on alpine meadow degradation was conducted and two types of denudation process with different driving mechanisms were found.For the grassland located in mountain bottomlands and gentle sloping field,the ME showed gradually thickening,aging,death,cracking,erosion and the driving force was the effects of excavation by murine and alternate action of freezing-thawing.However,for the grassland located on steep slopes,ME denudation appeared as suffosion erosion and barb erosion below ME,suspending and collapse of ME,and the grass grew well on ME with the driving force from water erosion and gravity action.The main reason for ME denudation could be the extreme thickening under grazing pressure on alpine meadow in the Three Rivers Source Region.