Enhancing the positive effects of ecological water conservancy engineering on desert riparian forest growth in an arid basin

In arid areas, ecological water conservancy engineering influences vegetation growth by altering river flooding dynamics in addition to the depths of groundwater. However, few studies have explored how to develop the optimal floodwater and groundwater regulation strategies that take into account both ecological water supply and vegetation growth. Therefore, the aim of the present study was to propose the suitable regulation strategies by revealing that the plant growth responses to hydrological variation (i.e., the flooding and groundwater depth). Based on two growth indicators (i.e., the time-integrated normalized difference vegetation index (TINDVI) for plant canopy growth and the tree-ring chronology for trunk growth) in the middle reaches of the Tarim River, and water consumption, water discharge from ecological sluices for flooding, and groundwater depth data, after the implementation of an scheme in ecological water conservancy engineering, the ecological water transport efficiency, tree-ring chronology in Populus euphratica, and TINDVI improved by 12.4%, 5.6% and 4.2%, respectively. Notably, the tree-ring chronology increased with a decrease in water consumption. Due to a significant correlation between tree-ring chronology and TINDVI, the tree-ring chronology could be used to reconstruct the canopy growth in the case of the unavailability of monitoring data. There were significant correlations between TINDVI and groundwater depth in June-October, between tree-ring chronology and groundwater depth in October, and between water discharge from ecological sluices and vegetation growth in September. In addition, there were high correlation and sensitivity between trunk growth and water discharge (compared to groundwater depth), and between canopy growth and groundwater depth (compared to water discharge). Based on the above results, potentially sustainable groundwater depths (-2.3 to -3.7 m) and discharge water quantities (3.53-5.90 x 10(8) m(3)) and regimes were proposed that could further promote the vegetation growth.