Higher canopy transpiration rates induced dieback in poplar (Populus × xiaozhuanica) plantations in a semiarid sandy region of Northeast China

•Daily canopy transpiration averaged 1.2 and 1.5 mm d−1 in 2018 and 2019, respectively.•Canopy transpiration was more controlled by radiation than by vapor pressure deficit.•Trees used deep soil water and groundwater to maintain higher canopy transpiration.•Total canopy transpiration was 184.1 and 235.9 mm during 2018 and 2019, respectively.•Plantation was vulnerable to dieback during drought years with decline in water level.