高寒嵩草草甸的被动与主动退化分异特征及其发生机理

Character of Passive-Active Degradation Process and Its Mechanism in Alpine Kobresia Meadow

高寒嵩草草甸是广布于青藏高原的地带性植被之一,自1980年代以来,发生退化,形成大面积的"黑土型"次生裸地。目前的研究普遍认为,高寒嵩草草甸的退化是由于过度放牧引起的植被演替和啮齿类动物对草场的破坏所致。而本研究认为,随着持续的超载放牧,高寒嵩草草甸的退化过程可以分为异针茅+羊茅-矮嵩草群落、矮嵩草群落、小嵩草群落和杂类草-黑土型次生裸地的四个演替阶段;其经历了异针茅+羊茅-矮嵩草群落向矮嵩草群落植被的被动退化过程和由小嵩草群落向杂类草-黑土型次生裸地的主动退化过程;其发生的动力分别为放牧作用和嵩草特殊的生物学特性(高地下/地上比)引起的草毡表层极度加厚作用。草毡表层的极度加厚,造成土壤水分渗透速率的降低和土壤-牧草之间水分、营养供求的失调,是导致高寒矮嵩草最终退化的根本原因。同时提出高寒嵩草草甸在被动退化阶段,通过降低放牧强度,灭鼠、封育是可以逆转的,而一旦进入主动退化阶段,草皮的塌陷、斑驳,最终形成"黑土滩"型退化草地,这是不可避免的也是不可逆转的。

The degradation of alpine Kobresia meadow was more and more seriously from 1980s and excessive grazing intensity was the essential reason which leaded the pasture ecosystem degradation.Nowadays,it was thought that vegetation succession which caused by excessive grazing and the rodent lead to the degradation in alpine Kobresia meadow.We think the degradation process of alpine meadow can be divided into four stages such as：Stipa sliena ＋Festuca ovina＋ Kobresia humilis,Kobresia humilis,Kobresia parva and herb-＂black-soil-type＂.With the grazing intensity increasing,the mattic epipedon was incrassated,meanwhile both the saturation ration and soil moisture decreased,moreover the nutrient was used to the roots growth and accumulated into the soil.It was found that Stipa sliena ＋Festuca ovina＋ Kobresia humilis community succeed to Kobresia parva community and the Kobresia humilis community was interim.The degradation mechanism should deepen to excessive grazing and special biological characters of the Kobresia,in the same time the degradation process was detached into passive and active stage.The degenerated pasture could recover by reducing grazing intensity,killing rodent and setting up enclosure in passive stage,however once into active stage it was inevitable and unreversed to form finally ＂black-soil-type＂ meadow.