中国河西走廊草地农业的基本格局和它的系统相悖─—草原退化的机理初探─—

The Pattern of Agro一grassland Systems and System Discordance in Hexi Corridor of China:The Mechanism of Grassland Degradation

河西走廊的草地资源位于西北荒漠的大背景中，由山地、荒漠和绿洲三个子系统构成，其中荒漠子系统居主导地位，具有先天的脆弱性。它们在人为干预下，在自然生态系统的农业化过程中，发生了山地一绿洲一荒漠组成的耦合农业系统。由于耦合不够完善，它所固有的相悖因素未能有效控制，形成涵有系列相悖因子群的系统相悖。主要表现为时间相悖，空间相悖和种间相悖。三者互相影响，但时间相悖起主导作用，使系统的生态危机加剧。它通常表现为草原退化。对草地农业生态系统的自由能的调控，保持自由能的积累和输出基本相当，是防止草原退化的根本出路。草原退化是草地对于草食动物压迫的对策系统和动物对于草地负荷行为的对策系统的综合反映。放牧程度可以作为草原退化过程的向量系统，但不是草原退化的本质。

The grassland resources in the Hexi Corridor of China are featured by the coexistence with huge desertsand semi一deserts in the same region.The local grassland一desert ecosystem comprises three sub一systems:mountains,oases and deserts,with the last one as a dominant component.The characteristics of local natu-ral conditions and agriculture have been intensively discussed in the literature.In general,it can be saidthat the region is ecologically fragile and there exists a discordance between the sub一systems in couplingproduction activities taking place within them as a whole.The discordance is mainly reflected in an inhar-mony between the local livestock preduction and pasture(sward)development:the livestock exerts a press-ing effect on the pastures through grazing while the latter response to the pressure with a varying adaptive“carrying behaviour”.The inharmony between the two preduction systems can be observed in timing of pro-duction activities,in the“ecological field”and in the population of plants/animals,and it can be regardedas a major factor which has caused degradation in the local grasslands.The process of degradation and itsphasing depend upon the degree of discordance between the sub一systems and on the balance between thegrazing pressure of livestock and the adaptive carrying behaviour of pastures,and,therefore,the degree ofthe system discordance itself can be used as an index to assess the extent of degradation in the local grasslandresources.