Analysis Of The Ecological Water Use Of Vegetation In Huangfuchuan Watershed

After long-term artificial vegetation construction and comprehensive management of small catchments, soil and water loss has been checked in a certain extent, and the vegetation coverage has increased markedly. But the following question with it is that the ecological water use of the vegetation is also increasing gradually. Thus, the ecological water use should be paid attention especially in the comprehensive harness of the soil and water loss and conversion from cropland to forest in the watershed. In this study, we use remote sensing method to analyze vegetation pattern change owing to the vegetation construction of the watershed during 1987-2003. And we calculate the ecological water use of the main vegetation types and the total watershed with the fieldwork data in 2002. This can provide some scientific gist for proper distribution and sustainable use of local water source and future vegetation construction, comprehensive management of soil erosion and conversion from cropland to forest. The results are as follows:1 There are 6 main types of vegetation, 12 types of community in Huangfuchuan watershed. The main types of vegetation are arbor, shrub, grass land, cropland, sandy vegetation and marsh vegetation. Natural grassland, artificial shrub and cropland dominate the whole watershed, but there also are some bare lands to distribute. The proportions of the area of arboreal forest, artificial shrub, natural grass land, cropland and bare land are 5%, 19%, 38%, 22%, 10% respectively in the entire watershed.2 After 17 years (1987-2003) of artificial vegetation construction, the area of bare land has been decreased markedly, but the area of artificial shrub has been increased noticeably, especially Form. Caragana davazamcii. The area of cropland has a declining trend.3 The differences of community transpiration in Huangfuchuan watershed are distinct, and the order is: dam land> Form. Populns simonii> Form. Salix psammophyla > cropland on the slope > Form. Hippophae rhamnoides subsp. sinensis > Form. Caragana davazamcii >Form. Thymus serpyllum> Form. Stipa bengeana > Form. Pinus tabulaeformis >Form. Artemisia sacrorum - Attemisia giraldii >Form. Artemisia ordosica> Form. Attemisia giraldii.4 The proportions of the area of chestnut soil, loess, aeolian sandy soil and wet soil are 58%, 10%. 15.8%, 13% of the entire watershed respectively. Because of the effect of terrain, soil texture and community transpiration, the difference of all types of soil pondage in the watershed is noticeable.5 The differences among the amount of ecological water use of the main vegetation types on per unit area in Huangfuchuan watershed are notably, and during the growing period, which is strikingly affected by the distribution of the precipitation. On the whole, the ecological water use of artificial vegetation types is higher than the natural ones'. And the community evapotranspiration of the vegetation is the leading effect in the ecological water use.6 The total ecological water use of vegetation in Huangfuchuan watershed is 0.73 billion tons in growing period in 2002. The characteristics of structure of the ecological water use in the watershed are: artificial vegetations use the most amount of the water; the ecological water use of natural vegetations takes arelatively smaller part.7 The characteristics of spatial distribution of the vegetation ecological water use in Huangfuchuan watershed are: the ecological water use of the crops and Form. Populus simonii distributed in the plain areas is relatively higher. And the ecological water use of the grassland on the plateau and the gully vegetation on the slope and the Form. Artemisia ordosica distributed in the sandlot is lower. We can notice from the branches of the Huangfuchuan watershed that ecological water use in Changchuan watershed is higher than that in Nalinchuan watershed. In the southern part of the Huangfuchuan watershed, the ecological water use is relatively higher because of the large area of the cropland.8 Comparing the amount of ecological water use of different vegetation pattern between 1987 and present situation, the ecological water use of artificial shrub increases markedly; but as for cropland, it has a decreasing trend. The change of the ecological water use in per unit of area and the vegetation pattern are the main factors which influence the variation of the structure of the ecological water use in Huangfuchuan watershed.