Thinning effects on Korean pine forest transpiration

Background/Question/Methods This study analyses thinning effects on sap flux density and stand transpiration in Korean pine forest. Transpiration is an important component of terrestrial water cycle and core process of water and energy exchange between air and forested land surface. Transpiration is influenced by microclimatic conditions, like radiation, and vapor pressure deficit, and amount of available water in soil. Forest management, like thinning, could change these conditions, therefore have effect on transpiration. Sap flow was measured during 2 months on 30-year-old moderately thinned (30MT) and unthinned (30C) plots and 50-year-old recently highly-thinned (50HT8), moderately-thinned (50MT8) and highly-thinned one year prior (50HT7) plots with Granier’s thermal dissipation probe method.

Results/Conclusions Mean sap flux density of 30MT plot (5.76 g m^-2s^-1) was higher than 30C plot (3.20 g m^-2s^-1). The response of sap flux density to radiation was very strong, and trees in thinned plot responded to radiation more sensitively than trees in unthinned plot. However stand transpiration of 30MT plot (0.86 mm day^-1) was lower than 30C plot (1.07 mm day^-1). Mean sap flux density of 50HT7, 50HT8 and 50MT8 plots were 5.56 g m^-2s^-1, 5.52 g m^-2s^-1 and 5.56 g m^-2s^-1, respectively.  Highly thinning did not result in significant differences in sap flux density of remaining trees, compared with moderately thinning. Stand transpiration of 50HT7, 50HT8 and 50MT8 were 0.66 mm day^-1, 0.43 mm day^-1 and 0.62 mm day^-1, respectively. These results suggest that thinning increases water use of remaining trees, but thinning intensity above some level do not result in increase of tree water use.