Year-to-year differences in evapotranspiration from understory vegetation and whole ecosystem in an eastern Siberian larch forest

We measured the evapotranspiration from the understory vegetation and the whole ecosystem of a Siberian larch forest on the forest floor and above the forest canopy, respectively, using the eddy-covariance method, and obtained the year-to-year difference in evapotranspiration during the early (from 1st to 10th), middle(11th to 20th) and late (21th to the end) periods of month. The year-to-year differences in evapotranspiration from whole ecosystem and understory vegetation were in the range from -11.0 mm to 9.5 mm and from -2.4 mm to 4.7 mm, respectively. These values explained from 20% to 30% of monthly mean evapotranspiration, and thus significant differences were found in this site. To clarify the factor controlling the year-to-year difference in evapotranspiration, we analyzed the relationships among the year-to-year differences in evapotranspiration, radiative and advective terms of Penman–Monteith equation. As a result, due to the small value of decoupling factor of this forest, the most important factor was the year-to-year difference in the advective term. We found that the difference in vapor pressure deficit resulting in the change of the surface conductance was important for year-to-year difference in the advective term in this site.