Research Into Several Key Problems Existing In Vegetation Construction In Loess Plateau

Eco-environmental construction is a major problem concerning realizing sustainable development of society and economy. Because the Loess Plateau is well-known for serious soil erosion, soil and water conservation has been valued highly for a long time, but so far its eco-environmental construction don't achieve the desired results as a whole, in which anti-erosive vegetation regarded as great substance is still the weakest link. In the new historical stage when the strategy for developing west China is being implemented, in order to get material results in vegetation construction, long-term pratices of construction of forest and grass vegetation in the Loess Plateau have to be examined.From the point of view of generalized vegetation including crops, through widely collecting data and field investigations the paper takes combination of analysis with synthesis or induction with deduction to deal with basic key problems existing in vegetation construction in this region, such as bases, techniques and patterns of vegetation construction, soil desiccation by vegetation, landscape ecological construction.At first, the relations between vegetation structures and their controlling soil erosion are discussed. The results show that magnitude of plant community coverage or canopy closure isn't certainly the adequate condition of an anti-erosive effective community because the community function of soil and water conservation is related to height of coverage layer as well as community coverage or canopy closure. High coverage layer is unfavorable to soil and water conservation by vegetation. Developing degree (coverage or thickness) of coverage layer close to ground is the adequate and necessary condition of anti-erosive effective communities, so coverage close to ground is also the ultimate essential characteristic more common for them. It is important to form coverage close to ground for soil and water conservation by vegetation, and it is a key to soil and water conservation by vegetation to promote development of coverage layer close to ground or pay close attention to changes of it.Based on the above conclusions about anti-erosive vegetation structure, the paper expounds the implication of anti-erosive vegetation by pointing out the fault of its current definitions, and it is considered that anti-erosive vegetation should aim at protecting soil from erosion and fixing active sands in the eroded areas, ground space fully occupied by plants, in general with close structure, especially with outstanding coverage close to ground by organic matter (litter and/or biomass). The further analyses indicate that anti-erosive vegetation should be natural well developed or near natural, and it would be different not only in structure, but also in succession, management, etc., from artificialvegetation taking economical value as only a target. According to this, through discussing the problem about waste slopes it is thought that shrub and/or grass slopes should be distinguished from real waste slopes.In order to construct vegetation in line with local conditions, in addition the paper analyzes the viewpoints relevant to vegetation properties of the Loess Plateau along with regional differentiation of bio-climatic conditions and vegetation zonality. It is shown that the Loess Plateau might be regionalized into different vegetation zones of forest and steppe. It couldn't be believed that zonal environment don't be possessed in the Loess Plateau. So far as the north demarcation line of the forest zone is called the forest line, the north demarcation line of the forest-steppe zone should be called the tree line. Vegetation construction shouldn't be confined to such a land use pattern as "the 28-word general plan" put forward by Zhu Xianmo. The objective reality of thin woods and sparse shrubberies in the forest-steppe zone cannot be ignored.After expounding the bases of vegetation construction, the paper discusses the techniques and patterns of vegetation construction. It is shown that typical plants for soil and wate...