A Study Of Water Consumption Regulations Of Main Forestation Trees In Semi-arid Region Of The Loess Plateau

By the measurement method of single-tree water-cycle balance based on the principle of hydrologic balance, the dynamic of soil moisture in forestland and the water consumption of different tree species in the semi-arid region of the Loess Plateau were measured with neutron moisture meter for 2 successive years. The results were as the following:(1) In semi-arid region of the Loess Plateau, the soil moisture contents of forestland and wasteland were low, near to the wilting humidity. In May 2002, soil moisture in 6m layer was 4.99%-5.57%, in May 2003, the soil moisture was 4.65%-6.40%. The influence on soil moisture only took take place within the surface 2m of soil, in 1.8-4.0m layer, there was obvious soil desiccation, and the soil moisture was on the wiltin humidity. The difference of soil moisture in forestland and wasteland was not obvious, and it only took place in surface 2m layer precipitation influenced. In May 2002, the amount of soil water stored in surface 6m of forestland with different tree species and different site was 390mm-433mm, by supplement of plenty of precipitation, the soil water stored was up to 456mm-526mm at the end of October 2003.(2) In semi-arid region of Loess Plateau, the distribution of soil moisture in different forestland and wasteland was studied, soil dry layer was a general regulation. The cause was the long term deficit of water the specific climate leaded to, it was not the consequence of trees growth.(3) Canopy and litter have a important role to decrease the evaporation of the forestland. By measured, in 16 year-old Pinus tabulaeformis forestland, the canopy decreased evaporation of the forestland was up to 104.12mm, in growing season, 2cm thick litter kept from 102.19mm.being evaporated.(4) In semi-arid region of Loess Plateau, the precipitation was up to 600mm, in growing season (May to Oct), 16 year-old P. tabulaeformis artificial forest on South-west slope, the single-tree water consumption was 2178.48kg, on North slope and North-east slope was 1568.96kg. in growing season (June to Oct) in 2002, water consumption was 1412.24kg on north-east slope; 16 year-old Pinus sylvestris var.mongolia on North-east slope, the single-tree water consumption was 1189.60kg in 2003, it was 707.02kg in 2002; 26 year-old Caragana microphylla on south-west slope, the single-tree water consumption was 1049.12kg in 2003, in 2002, it was 865.64kg; 16 year-old Populus alba L. var pyramidalis Beg, the single-tree water consumption was 1384.32kg in 2003. (5) The efficiency of transpiration of P.alba L. var pyramidalis Beg was 3.63, it was the highest; P. tabulaeformis was the second, the efficiency of transpiration was 1.81-2.26; the not cutting C.microphylla was the lowest , it was only 0.36. The efficiency of transpiration of the same tree species changed according to the water condition of different sites. The worse the water condition was, the lower the efficiency of transpiration was.