Long-Term Eddy Covariance Monitoring of Evapotranspiration and Its Environmental Factors in a Temperate Mixed Forest in Northeast China

摘要

On the basis of eddy covariance measurements, the results of three years (2005-2007) of direct evapotranspiration (ET) measurements over a mixed temperate forest in Northeast China are presented. The diurnal and seasonal variations in ET and its main driving factors were analyzed. Annual ET values for the forest were 437,506, and 632 mm in 2005, 2006, and 2007, respectively. The contribution of ET during the dormant season was not negligible, ranging from 17 to 23% of the annual ET for the study years. On an annual course, the increase in ET is associated with the increasing air temperature (T_a) and plant growth in late April and early May, peaking in July or August with monthly mean rates of 2.9 mm day~(-1) (July 2005), 3.4 mm day~(-1) (July 2006), and 3.8 mm day~(-1) (August 2007). Priestley-Taylor parameter α also varied seasonally, with its minimum and maximum values occurring in the dormant and growth seasons, respectively. During the growth season, the values of α were generally between 0.6 and 0.9, indicating that the vapor pressure deficit was the main factor affecting ET. In addition, canopy conductance (g_c) also drove the ecosystem ET. Our results show no significant soil water stress in the growth season at the study site. On an annual basis, the ratio of ET to precipitation was 74.3%, indicating that ET was the main water-loss component of water balance in the temperate forests of Northern China.