The Water Consumption Regularity Of Typical Forest Vegetation In Loess Region Of Western Shanxi Province Northern China

Water consumption regularity of forest vegetation is the foundation and core of the studies about forest vegetation on hydrological processes influencing mechanism. Relying on national forest ecosystem research station, the typical loess area of Caijiachuan Watershed, Jixian County, Shanxi Province of northern China was taken as the study area. In order to quantitative reveal levels of transpiration and evaporation intensity and their relationship with environmental factors, the water consumption of Pinus tabuliformis, Robinia pseudoacacia and the Populus davidiana&Quercus liaotungensis secondary forest typical forest and related environmental factors were monitored in this region. Then the effects of forest vegetation structure on vegetation characteristics and environmental factors of water consumption were analyzed. The results showed that:1.The soil moisture, surface vegetation and soil temperature had significant effects on soil evaporation. Soil moisture contented varies with changes in rainfall, which directly affect the regular of soil evaportation. There was a highly significant linear relationship between soil moisture in0-20cm soil and soil evaporation. The relationship between soil moisture in20-60cm and soil evaportation was more significant. So soil evaporation could be calculated by using0～60cm soil moisture measurement. When soil moisture was above16%level, the vegetation did not inhibit soil evaporation because physiological vegetation water consumption has been met. After all factor linear regression analysis, the contribution rate of soil moisture on soil evaporation was35.2%, temperature64.8%.2. There was a significant linear relationship between forest water consumption and soil moisture, rainfall, tree crown and tree age. The contribution rate of soil moisture on tree transpiration was43.6%, tree age36.4%, rainfall14.8%, tree crown5.2%.Rainfall affected soil moisture directly,which increased transpiration by the root transporting water into the atmosphere.Due to the growth needs, young forest demanded more water than the mature forest. So with the transpiration would decline by the age growing.3.The water outputs in the study area, which accouted more than96.13%rainfall, was mainly composed by vegetation transpiration,soil evaporation and a small amount of runoff.In this paper,there was an error analysis between the water balance result and measured forest vegetation transpiration and soil evaporation,The maximum error was less than5%.There was a significant linear relationship among evapotranspiration and rainfall, temperature, solar radjation, soil moisture. The contribution rate on evapotranspiration were26.5%,42.7%,2.3%and28.5%.In conclusion, the variation of soil moisture plays the main role in forest water consumption. Forest vegetation satisfies its water needs firstly while the soil moisture is low. To reduce the local forest water consumption, it is better to select the tree species according to their water needs and soil moisture before planting.