Transpiration of Poplar Based Short Rotation Coppice under Drought Stress

This study compares canopy transpiration (T) of two treatments with different levels of water availability calculated using sap flow (SF) measurements based on thermal dissipation (TD) method. The study was conducted in a poplar based short rotation coppice (SRC) plantation in Czech-Moravian highlands during the summer of 2012 (DOY 154-274). There are 3 pairs of experimental plots under research. Each pair comprises a control plot, and a neighboring plot, equipped with a roof system, draining 40% of incoming rain water away (the water reduced plot). Sap flow of 4 trees within the control plots and 4 trees within the water reduced plots was measured. Data from both treatments were scaled up to stand level separately. Then, potential transpiration (Tp) of SRC for the period DOY 154-183) was successfully (R-2=0.89) modeled, as a function of global radiation and vapor pressure deficit (VPD), using the Penman-Monteith formula and a parameterized semi-empirical stomatal conductance model. Finally, canopy transpiration from controls (T-c) and water reduced plots (T-s) were compared with modeled Tp and further analyzed. In the period June-September the mean daily T-c=1.86 mm, T-s=1.38 mm and T-p=2.27 mm; daily maximum occurred on 24 June - T-c=3.75 mm, T-s=2.84 mm and T-p=3.89 mm. The T totals over the study period reached T-c=226 mm, T-s=168 mm and T-p=276 mm. T of both treatments differed depending on actual soil water availability. Our results show that a 40% reduction in throughfall resulted in a 26% reduction in transpiration over the four months study period. Results also confirmed that even a low number of sensors (4+4) can be used for credible estimates of canopy transpiration.