Lei Ouyang, Ping Zhao, Yuqing Huang, Guangyan Ni, Xiuhua Zhao, Guangsheng Zhou, Liwei Zhu
Quantifying tree transpiration at a stand scale is important for understanding the hydrological impact of Eucalyptus plantations on the local water yield and water balance. In this study, we aimed to explore the seasonal and monthly changes in stand transpiration, its response to climatic factors, and hydrological impacts of a 5-year-old Eucalyptus urophylla × Eucalyptus grandis plantation in Guangxi Province, Southern China. Stand-scale transpiration (Et) and potential evapotranspiration (ETo) were determined, and seasonal sensitivity of daily Et to vapour pressure deficit was analysed by using the monitored sap flux of the E. urophylla × E. grandis plantation and the associated environmental factors during a 2-year experimental period from June 2012 to May 2014. The results showed that the monthly Et values in the wet seasons were higher than those in the dry seasons, and a temporal Et difference was observed between the 2 years of the experiment. Generally, within a whole experimental year, the highest water consumption mainly occurred from May to August, accounting for more than 40% of the annual total, and the lowest transpiration values (approximately 10 mm) mainly occurred from January to March. This monthly variation would be partly attributed to the difference of climatic factors. Clear seasonal variations were also observed for the ETo values, the Et/ETo and the Et/P (precipitation) ratios, and the dryness index (DI, ETo/P). Compared to the wet seasons, higher ETo and DI (>1) values occurred in the dry seasons. Moreover, the linear relationships between the daily stand-scale transpiration and vapour pressure deficit for the selected months (representing spring, summer, autumn, and winter) suggest weak stomatal control of eucalypt trees. In consideration of the short rotation practices (5–7 years), the non-conservative character of water use of eucalypt plantation, as well as the ratios of Et/ETo, Et/P, and DI, we suggested that Eucalyptus plantations in Guangxi Province might pose a potential threat to catchment water yield and management in this region. The findings of this study will assist in managing the increasing hydrological and water resource concerns related to the rapid expansion of Eucalyptus plantations in Southern China.
