Study On Water Balance Of Different-aged Pinus Sylvestris Var.Mongolica Artificial Forests In Sandy Area

Pinus sylvestris var.mongolica is widely used as a main tree species in the construction of protective plantations since 1950's.Zhanggutai Sandy Land is located in the southeast of Horqin Sandy Land which is in the semiarid area of China,with scarce precipitation water input,strong evaporation.Trees grew rapidly in the early stage of introduction and then declined in many sandy land areas.The unbalance of water use for afforestation,caused by increasing transpiration demand compare to the natural distribution area,was considered to be the main reason for degradation.In order to explore the influence of plantation period towards the soil moisture in 10,20,35,50,60 aged of Mongolian pine plantations were chosen as the research object and compared with the wild grass ground for the first time,located in Zhanggutai area.We also applied portable soil profile fast moisture analyzer and SPSS16.0 approach to study Soil moisture dynamics and water balance of Mongolian pine trees.The main conclusions were as follow: 1)Throughout the growing season the average soil water content of 10-year P.sylvestris var.mongolica artificial forest was the lowest and the highest was the 50-year artificial forest,in planted P.sylvestris var.mongolica of different stand age(10-year,20-year,35-year,50-year and 60-year)with different stand densities(883,850,400,267 and 400 trees per hectare);2)For the vertical variation,the soil water content of soil surface was higher,with the soil moisture content of 10-year,20-year and 35-year Mongolian pine plantations decreased obviously and the soil moisture content in 50-year and 60-year planted P.sylvestris var.mongolica decreased less obviously as the soil depth increased;3)The soil moisture of surface which had significant difference between 35-year planted and other planted was the highest in different stand age Mongolian pine trees.The differences between 10-year and 50-year,10-year and 60-year,20-year and 60-year Mongolian pine trees in soil moisture of surface were significantly;4)The soil moisture of root zone in different stand age Mongolian pine trees had significant difference between 10-year and 35-year planted,20-year and 35-year planted,10-year and 50-year planted,10-year and 60-year planted,20-year and 50-year planted,20-year and 60-year planted;5)While the soil moisture content at the bottom of the soil had extremely significant difference but 50-year and 60-year planted;6)The soil water cycling of Mongolian pine trees,20-year,35-year,50-year and 60-year planted were positive balance.While 10-year trees was a negative balance,because income of soil water was lower than expenditure.Therefore,planted P.sylvestris var.mongolica might need to be lumbered to decrease plant number to keep its stability with the age of stand increased.