放牧方式对浑善达克沙地榆树疏林退化的影响

浑善达克沙地榆树疏林是分布于草原地带的隐域植被类型,相较周边的典型草原区,其植被更加茂密,乔灌丛生,水草丰美,千百年来一直是牧民的优质冬季牧场。近半个世纪以来,因人类的过度开垦以及不合理的放牧管理,浑善达克沙地植被遭到空前的破坏,沙丘活化,载畜能力降低,生态价值和经济价值严重受损。近年来,随着国家草畜平衡以及禁牧政策的推广落实,放牧的牲畜总量得到一定程度的遏制,然而大面积草场还在继续退化。在牧民对生产生活的基本需求下,牲畜总量不可能无限制的压制。另外,适度的放牧对草原生态系统健康是有益的。因此,如何改良放牧方式,合理利用草场,在保持生态良好的基础上合理发挥草场的畜牧价值,是我们亟待探索的问题。以浑善达克沙地的典型天然植被榆树疏林为例,对不同放牧方式下的植被进行调查,基于沙地特殊的基质和植被特征,探讨适合沙地的放牧利用方式。研究表明,在相似的放牧强度下,把沙地作为冬营地,其榆树种群更新正常,植被覆盖度以及植物种类等均能保持良好,而把沙地作为夏季营地,榆树疏林植被退化严重,具体表现为:(1)榆树种群自然更新受阻;(2)灌木群落大量死亡或消失;(3)草本覆盖度显著降低,植物种类减少,多年生草本比例减少,一、二年生草本比例增加;(4)裸沙面积增加,沙丘趋于活化。本研究认为目前沙地植被的退化主要由不合理的放牧引起,并非气候因素所致。沙地适合于冬季放牧而不适合其他季节放牧。借鉴牧民的传统放牧方式,建议配合周边的典型草原区实行季节性倒场放牧,仅将沙地作为冬季营地使用,既能有效保护沙地植被又能充分发挥其畜牧价值。

Effects of grazing management on the degradation of Ulmus Pumila open forest in Otindag Sandy Land

The Ulmus Pumila open forest in Otintag Sandy Land is a intrazonal vegetation type distributed in the typical steppe belt. Compared to the around typical grassland area, the vegetation is denser, with a large number of trees, shrubs, and swamps. It has been a high quality winter pasture for pastoralists for thousands of years. In the last half century, the vegetation in the Otindag Sandy Land has been severely damaged due to over-exploitation and inappropriate grazing management. More and more sand dunes have been becoming bare, and the their livestock carrying capacity has becoming weaker. The ecological and economic value of Otindag Sandy land was seriously weakened. In recent years, with the national grass-animal balance policy and the grazing prohibition policy have gradually been implemented, the total amount of livestock has been reduced to some extent. However, large areas of the sandy land are still degrading. Considering the basic needs of herders, the total amount of livestock cannot be reduced without limit. In addition, moderate grazing is beneficial to health of the natural ecosystem. Therefore, how to improve the grazing management and how to make rational use of the pasture on the basis of maintaining good ecology are the problems necessary to explore. In this study, the typical natural vegetation of Ulmus Pumila open forest in Otintag Sandy Land was chosen as an example to investigate effects of different grazing utilization methods on vegetation and the suitable grazing utilization methods for sandy land were discussed. Two comparative plots were adjacent, with similar climate background, the geographical environment, and grazing intensity. However, due to different grazing utilization methods, the vegetation status was significantly different. The results showed that in the winter pastoral area, the Ulmus Pumila population reproduction, plant coverage, and number of plant species kept well, while in the summer pastoral area, the vegetation was seriously degraded and the sand dunes tended to flow. The most significant aspects of the vegetation degradation included (1) the natural reproduction of Ulmus Pumila was interrupted. Because of over destruction by livestock, the Ulmus Pumila seedlings died or failed to grow into the normal arbores; (2) a large number of shrub communities have degraded or disappeared; (3) herb coverage, plant species, the perennial herb proportion significantly reduced, and the proportion of annual and biennial herb increased; (4) the area of bare sand increased, and sand dunes tended to be activated. Therefore, we consider that sandy land is suitable for winter grazing and is not suitable for grazing in other seasons. The degradation of Ulmus Pumila open forest were not caused by climatic factor but by unreasonable grazing management. Referring to the traditional herding methods of pastoralists, we propose to implement seasonal inversion grazing in conjunction with the surrounding flat grassland areas, and use the sand land as a winter pastoral area.