The Effect Of Microclimate Elements On Different Models Of Returning Farmland To Forests Or Grass

Ansai is settled in the loess plateau area and is one of the typical regions which are needed to return farmland to forests and pastures. The problems about what and how big influence did the project of rehabilitation of vegetation on this area have always being the focus of pubic interest. Climatic variation is evident characteristic index to rehabilitation of vegetation and the evaluation of the effect of climate is an important research contents.This article adopted parallel contrast in fixed time in the open country. Analyzing the main climate factors, such as air temperature (AT), relative humidity (RH), soil temperature (ST), wind speed of the different models, including mixed forest, shrubbery, grassland and uncovered land, the result showed as followed:1.Daily variation of the air temperature have the same regulation :all go up first and lower gradually, to assume asymmetric curve .Relatively mixed forest have the lowest air temperature while uncovered land have the tallest. The test of the significance of difference shows the difference of air temperature at the height of 150cm was not significant2. The maximal value of the 0 cm ground temperature of this four models occurred at 14:00. Daily range value was uncovered land>grassland>mixed forest> shrubbery. The test of the significance of difference shows the difference of 0cm ground temperature was significant, the differences between mixed forest and uncovered land, shrubbery and uncovered land were big while the differences between grassland and uncovered land, mixed forest and shrubbery were smaller.3. There was a close correlation for 0cm ground temperature and 150cm air temperature between forest land, grass land and uncovered land by correlation analysis.4. The trend of the season variation of air temperature was basically similar .The yearly range value of uncovered land is the biggest, while the mixed forest and shrubbery is smaller. In the transformation process from spring to autumn, the air temperature is uncovered land >grassland >shrubbery >mixed forest; In the transformation process from autumn to winter, the air temperature is shrubbery>mixed forest >grass land> uncovered land.5. The season variation of ground showed, the yearly range value of uncovered land was the biggest and the shrubbery was the smallest. In spring, the ground temperature was uncovered land > grassland > mixed forest > shrubbery; in winter was shrubbery > mixed forest > grassland > uncovered land.6. Daily variation of the air relative humidity showed, the air relative humidity of mixed forest and shrubbery was much bigger than the uncovered land, The test of the significance of difference showed the difference of air relative humidity was significant,and the difference between mixed forest and uncovered land,shrubbery and uncovered land was much more significant at 0.01 lever ;The difference between grassland and uncovered land, mixed forest and shrubbery were smaller. In summer, forest have the biggest air relative humidity, in spring, autumn and winter grassland have the biggest, the uncovered land have the lowest all the year round.7. Different modes had significant difference in lowing the wind speed. The speed of shrubbery and mixed forest was much more lower than the uncovered land, the whole tendency was mixed forest> shrubbery >grassland>uncovered land, forest's effect of lowing wind speed was 3～4 times grassland. The wind speed showed the largest daily range on grassland and uncovered land while forest and shrubbery the smallest. In each season, mixed forest, shrubbery and grassland lowed a lot compared to uncovered land and mixed forest and shrubbery have the significant effect.8. The intensity of illumination differed greatly between mixed forest and shrubbery in different seasons, while there were little differences between grassland and uncovered land neither at a day nor different seasons. During the flourishing leaf stage, the intensity of illumination of mixed forest and shrubbery were much lower than the grassland and uncovered land because of the countercheck of wood's hat. During the defoliate stage, there were little difference between mixed forest,shrubbery,grassland and uncovered land.In conclusion, all different models had obvious effects on the climatic elements on every day and in different seasons. In spring and summer, mixed forest and shrubbery had strong effect on air temperature, air relative humidity and wind speed, they showed these characteristics such as lower air temperature, higher air relative humidity, lower wind speed and less intensity of illumination; all the climatic elements of grassland were in the midst, so it did not have significant effect on adjusting climate; comparing with other models, the uncovered land embodied the properties such as higher temperature, higher air relative humidity, strong illumination and strong speed all year around.