The sub‐surface flow of water within a watershed is traditionally thought to depend solely on topographic or physical influences, such as slope, soil permeability, and channel density. Though often overlooked, some researchers propose that the role of vegetation and its feedback on subsurface flow could be just as important in some cases. Plants tend to increase subsurface flow by increasing soil conductivity and preferential flow paths. They can also cause it to decline, as plants use subsurface water and nutrients to fuel their growth, drawing it out of the system through evapotranspiration. Both sets of feedbacks affect the downslope availability of water. To capitalize on this idea, Hwang et al. devised a system called the hydrological vegetation gradient (HVG).