Evapotranspiration Characteristics Of Natural Secondary White Birch Forest In The Southern Daxing'anling Mountains

Forest evapotranspiration is a vital part of the forest ecosystem's water cycle.In order to study the characteristics of evapotranspiration of secondary white birch forest in semi-arid area,we chose the natural birch birch secondary forest in the Saihanwula Balinyouqi as study object.The evapotranspiration characteristics of natural Betula platyphylla forest in the southern Daxing'anling were studied through transpiration of trees,transpiration of shrubs and herbs,evaporation of soil and litter.At the same time,the meteorological data,the data of the birch sap flow,the data of the vegetation and soil,the data of the potential evapotranspiration(ET0)and the actual evapotranspiration(ET0)were used to build the regression model of potential evapotranspiration and actual evapotranspiration in the National Observatory and Observation Station of the Saihanwula in Inner Mongolia(Referred to as:Saihanwula Forest Ecological Station).The main findings are as follows:(1)The general trends of the change of the flow rate of shrub layer during the growing season were single-peak or multi-peak curved.The diurnal variation of the stem-sap flow rate in May was larger at night than that by day.The stem-sap flow from May to September was 1.84 g · cm-2 · h-1,17.76g·m-2 ·h-1,18.95g· cm-2 · h-1,11.43g·cm-2·h-1,4.54 g · cm-2·h-1 in descending order.In the Sunny days,the stem-sap flow is lager than that in the cloudy days,and the latter is lager than that in rainy days.In the sunny days,the ranking of the stem-sap flow rate by the month is June>August>July>May>September,but the differences between those in the cloudy days or rainy days is not obvious.The stem-sap flow range of a single natural white birch was 0.48?52.76L/d.(2)The total evapotranspiration from May to September of 2016 was 209.29mm.The general trend of evapotranspiration in different months was July>June>August>September>May,the magnitude of those was 60.12mm,55.22mm,44.39mm,27.09mm 22.47mm respectively.In 2016,the transpiration in canopy layer was 73.70%of the total evapotranspiration.The transpiration in shrub layer was 1.00%of the total evapotranspiration.The transpiration in shrub layer was 15.83%of the total evapotranspiration.The transpiration in soil layer and litter layer was 9.48%of the total evapotranspiration.(3)Analyzing the correlation between transpiration and meteorological factors of natural white birch forest,it was concluded that the transpiration rate of natural white birch forest was significant positively correlated with the canopy net radiation,air temperature and wind speed.There was a significant negative correlation between the transpiration rate of natural white birch forest and the air humidity.(4)Based on the calculating the potential evapotranspiration(ET0)of secondary natural white birch forest,we established a regression model between the potential evapotranspiration and actual observed evapotranspiration(ET).At the same time,we made a simulation test using partial dataes.The maximum relative error was 9.43%,the minimum relative error was 0.33%,the average relative error was 4.22%,the result showed the simulation result was good.