Responses of stem sap flow to meteorological factors and water evaporation at different time scales over Quercus variabilis plantation

Stem sap flow of 30-year-old Quercus variabilis individual trees in the rocky mountain areas of the North China was measured by thermal dissipation probe (TDP) during the growing seasons from 2006 to 2008. The responses of Quercus variabilis sap flow to meteorological factors and water evaporation at different time scales were analyzed. The purposes of the study were to establish model between sap flow and water evaporation at long-time scale and to provide theoretical basis for establishing water saving and drought resistance model. The results showed that: (1) During the growing seasons (from April to September), sap flow had positive correlation with solar radiation, air temperature, and vapor pressure deficit. However, the correlation between sap flow and wind speed was unremarkable. Determination coefficients at 10 min, 1 h, 1 day, 10-day, one month scales were 0.388, 0.482, 0.539, 0.654 and 0.812, respectively. It was proved that the longer time scale was, the more significant correlation was found betw