黄土高原土壤水分的空间分异及其与林草布局的关系

Relationship between vegetation spatial collocations and soil moisture spatial heterogeneities in the Loess Plateau area

通过大面积的土壤水分深土钻测定(5～10m土深)和相应的植被生长调查,对黄土高原土壤水分的空间分异及其与该区林草布局的关系进行了研究。结果表明,黄土高原的土壤水分具有显著的区域分异和微域分异特征;黄土高原土壤水分的空间分布决定着该区植被类型及其生长状况的空间布局,表现为区域植被的地带性分布及各地带内坡面植被景观的规律性分布;人工林草措施的实施,包括宜林宜草选择、造林技术和选种等环节,必须遵循土壤水分的时空分布规律来区别进行,才能获得植被生态环境的持续健康发展。

Water is the key limit eco-factor for sustaining growth of plants in the Loess Plateau area of China for the arid and semi-arid climate, complicated landforms and the unique soil environment of loess deposition. Referring to the Loess Plateau area, water problem essentially means the soil water issue. The insufficiency of precipitation coupled with the deep loess deposition and the gully-hilly geomorphology results in the soil water spatial heterogeneities in the Loess Plateau area, and then this determines the plants' spatial collocations and their growth by the climate-vegetation laws. This is a key scientific issue for afforesting nowadays in the (fragile) eco-zone of West China area, including the Loess Plateau.In this paper, the soil water spatial heterogeneities of the Loess Plateau were analyzed firstly. The results showed that: 1) Regionally, the spatial distributions of soil water contents and available soil water contents under natural grassland had an increasing trend from north to south similarly, with a mosaic structure like a 'water-rich island' at the south tip which mirrored the consistency between the soil water and the corresponding local ground conditions. 2) Locally, the soil water contents along a slope were affected strongly by slope gradients, slope orientations and sites. The soil moistures of down slope were better comparatively than that of upper slope sites, slow slope better than steep slope, and shadow better than sunny. 3) Vertically, the soil water contents under natural grassland along the soil profile appear increasing from upper to bottom.Then the relations between water spatial differences and vegetation collocations were discussed. The results showed that the complicated soil water spatial differences of the Loess Plateau determined the vegetation spatial collocations consistently: 1) Regionally, the soil water spatial differences determined the vegetation zonal distribution; So, in different vegetation zone, different afforesting measures should be made. 2) Locally, the soil water distributions along a slope affected the vegetation distributions too, especially in the transitional zone from forest zone to pasture zone. 3) To adapt to the soil water spatial distributions, local plants species should be concerned mainly, planting technologies about the standing adjustment or planting density control should be developed, and the sustainable perspective avoiding fast-growth species and environment-dampen measures should be focused, while afforesting.So, the water and vegetation laws should be observed strictly while enforcing the vegetation reconstruction measures in West China region.