Micrometeorological observations above a Japanese red pine forest within the growing season

Abstract

Knowledge of vegetation-atmosphere interactions has great importance in ecological research, and to recognize these effective interactions, the collection and interpretation of micrometeorological data are essential. The main goal of this study was to understand the trends of evapotranspiration (ET) and other micrometeorological parameters within the growing season above a Japanese red pine forest in Japan. To measure ET, the Bowen ratio-energy balance approach was employed. These measurements were used with the Penman-Monteith reference evapotranspiration (ET_0) in order to create crop coefficients (K_c) by the ratio of ET:ET_0. Mean daily ET on the dry and rainy days was found to be 3.22 and 2.11 mm day^{-1}, respectively, which was statistically different. K_c values were inconsistent from day to day and ranged between 0.37 and 1.24, and, in general, were less than unity (average: 0.84, standard error: 0.01). Significant differences in K_c were found between rainy days (wet canopy) and dry days (dry canopy). No remarkable changes were observed between rainy and dry days in the average contribution of latent heat flux, ground heat flux, and sensible heat flux to the energy budget. The data indicated that the Penman-Monteith equation may be useful for estimating the ET from the red pine forest within the growing season, and, in particular, when the rainy and dry days were separated.