|
|
|
| Study on the evapotranspiration of forest and vegetation in dryland |
| Wang Yanhui, Xiong Wei, Yu Pengtao, Shen Zhenxi, Guo Mingchun, Guan Wei, Ma Changming, Ye Bing, Guo Hao |
| The Research Institute of Forest Ecology, Environment and Protection, The Chinese Academy of Forestry, 100091, Beijing, China |
|
|
|
|
Abstract The studies on evapotranspiration (ET) of forest and vegetation carried out in recent years in the dry areas in Liupan Mountain of Ningxia and Yanqing of Beijing were summarized. As soil water limited ecosystem, the ET of slope vegetation, regardless trees or shrubs or grasses, is always the biggest component in water budget, and transpiration (T) is the biggest component in ET. The order of ET is generally as high- arbor- forest > small-arbor-forest > shrub > natural grassland, but artificial grassland > natural grassland. According to water-yield function, slope vegetation can be classified: natural grassland and shrub as water-yielding vegetation; small-arbor-forest as water-balancing vegetation; high-arbor forest and artificial grassland as water-consuming vegetation. Density is not a determinative factor for slope ET, its function is more on regulating the value of T and the ratio of T/ET. Although ET will be generally reduced with decreasing density, but not in the same magnitude and not in linear, and different vegetations react differently. It shows a tendency that the ET-reducing effect by decreasing density tends to be weaker from igh-arbor, small-arbor to shrub. The function of ET-reducing by decreasing density is limited. More strict comparisons and theoretical researches are required for evaluating the ET-reduction effect by decreasing density, the availability of decreasing density as a measure of reducing ET, and for searching the effective range of density regulation. The LAI and leaves biomass may be better indicators than density for estimating and evaluating water consumption of vegetation, since it is more biological based. From the viewpoint of establishing slope vegetation with characters of water-saving, more stability, high efficiency and multifunction in dry regions, it is sure to say that the ET of grassland and shrub is lower then forest. The savanna-like forest or sparse forest with shrubs is more suitable for water-yielding and for vegetation stability. For a better small watershed management, the theoretical and technical research on an optimal spatial allocation of different vegetation based on the spatial heterogeneity of soil water carrying capacity should be further carried out, in order to meet the needs of water-yield, soil protection, water retention, stable vegetation simultaneously.
|
|
Received: 28 November 2005
|
|
|
|
|
|
|
