Study On Water Conservation Of Forest Ecosystem In The Upper Reaches Of Yangtze River

Forest ecosystem is a kind of terrestrial ecosystems which has the most wildly distribution, the most complex structure and the richest types. Composing of the flourish canopy layer, loose litter layer and thick soil layer, the forest ecosystem has an ideal capacity to hold and store atmospheric precipitation, and so that the atmospheric precipitation can be redistribute and regulated effectively by its specific water retention capacity. The effects of forest ecosystem's multifunction become more and more important to us as the forest resources lasting reducing and being destroyed, especially after the flood disaster in 1998, the water retention function of forest ecosystems in the upper Yangtze River has been concerned unprecedented.We took the upper Yangtze River region as study areas, and divided them into 21 evaluating units according to their forest types, and built up the evaluating units'index system. Through literature survey and field sampling and experiment, we obtained the index data from the canopy, litter and soil layers of each forest type, and built up the upper Yangtze River forests'water retention database. By using GIS software such as Arcgis, we evaluated the intercepting, holding and storing water capacity of each certain grid (500m×500m), and then studied each water retention capacity of forest sub-ecosystem and the comprehensive water retention in the whole upper Yangtze River region. The results of study express:(1) Among comprehensive water retention capacity of forest ecosystem, water retentions in soil and litter layers account for the most proportion. Soil non-capillary porosity plays the key role in the determination of water retention capacity of ecosystem. The total comprehensive water retentions of forest ecosystems in the upper Yangtze River region are 324.12×108t. Of each forest vegetation type in the upper Yangtze River region, the canopy layer's average one-off maximal precipitation interception is 1.07mm and the total interception is 3.97×108t, accounting for 1.22% of the total comprehensive water retentions; the litter layer's average one-off maximal precipitation interception is 2.00mm and the total water retentions are 7.55×108t, accounting for 2.33%; the soil layer's average water retention capacity is 80.38mm and the total water retentions are 312.62×108t, accounting for 96.45%.(2) Among all the forest vegetation types, the subtropical mountain fir forest has the maximal comprehensive water retention capacity which is 146.60mm, the second one is subtropical mountain spruce forest 132.41mm and the minimum is temperate-subtropical deciduous broad-leaved poplar-birch forest 21.37mm. According to the total comprehensive water retentions, the evergreen needle-leaved shrub land is the strongest one 78.35×108t, the second one is evergreen broad-leaved shrub land 61.52×108t and the last one is subtropical mountain deciduous pine forest 0.28×108t.(3) The spatial distribution expression for forest vegetation water retention capacity is: Mingjiang River, Hengduan mountainous, north mountainous of Sichuan Basin are strongest, next is plateau mountainous in Sichuan Southwest, and the Jialingjiang River, Wujiang River are comparatively weak.