Effect of Drought Types on Evapotranspiration and Canopy Conductance in a Pinus sylvestris var. mongolica Plantation in Northeast China

According to soil and atmospheric moisture conditions, drought can be categorized into soil drought, atmospheric drought, and compound drought. The effects of soil drought on evapotranspiration (ET) and canopy conductance (Gc) are extensively investigated in forests, but the responses of ET and Gc to atmospheric drought and compound drought still remain unclear in plantations. Environmental factors and ET were continuously measured in a Pinus sylvestris var. mongolica plantation located in the semi-arid areas of Northeast China during the growing seasons (May–September) in 2020–2024. Compared with non-drought, ET increased by 34.96% under atmospheric drought, and decreased by 23.58% and 28.86% under soil drought and combined drought, respectively. Compared with non-drought, Gc decreased by 29.27%, 15.19%, and 68.74% under atmospheric drought, soil drought, and combined drought, respectively. Different from other three water conditions, relative extractable water (REW) replaced net radiation as the most important influencing factor of ET under combined drought. And vapor pressure deficit (VPD) always had a relatively lower contribution to ET under the four water conditions. Unlike the other three water conditions, the dominant controlling factor of Gc was REW instead of VPD under combined drought. This study proved that different drought types have different effects on ET and Gc. Under warmer and drier climates, management practices such as pruning and thinning should be used to cope with the increasing water stress to ensure the sustainable development of the Pinus sylvestris var. mongolica plantations in the semi-arid areas of Northeast China.