Wetter conditions amplify simulated deep drainage differences between grasslands and forests in the Post Oak Savanna

Study region: The Post Oak Savanna (POS) ecoregion of Texas, U.S. Study focus: Woody plant encroachment in the POS has been linked to reduced groundwater recharge, but it remains unclear whether the removal of these woody plants may increase groundwater recharge rates. To evaluate differences in recharge under contrasting vegetation covers, we simulated deep drainage at 18 paired grassland–forest sites using Hydrus-1D. The simulations were analyzed to assess spatiotemporal variability in deep drainage between paired sites, with these differences serving as a proxy for potential recharge changes due to woody plant removal. Additionally, simulations were used to identify the influence of precipitation and soil texture on the magnitude of deep drainage differences between grasslands and forests. New hydrological insights for the region: Deep drainage was consistently higher in grasslands, which also showed greater variability, while forests had more uniformly limited deep drainage. The differences in deep drainage between forested and grassland sites were larger in wetter subregions and years, with precipitation playing a stronger role than sand content. Higher precipitation amplified deep drainage increases, and soils with lower sand content promoted stronger responses of deep drainage increases than sandier soils. These findings indicate strong promise for enhancing potential recharge through woody plant removal in the POS, but this potential is limited in the southern subregion where precipitation is low. This highlights the importance of regional differences when prioritizing restoration efforts to support groundwater sustainability.