Forest Thinning to Increase Groundwater Recharge

The State of New Mexico’s first approved basin water plan, for the Estancia Basin, recognized the fact that the basin is running out of groundwater. The Estancia Basin Planning Committee proposed thinning trees in the upland forests as one of their major efforts to increase recharge by eliminating transpiration from juniper and pinyon trees. EnviroLogic Inc. was tasked with performing a combined field/modeling study to quantify the increase in recharge associated with thinning. The field site contained contrasting landscapes of a pinyon/juniper forest and an adjacent open meadow. Soil moisture and temperature monitoring in trenches and boreholes were combined with a site weather station that monitored air temperature, precipitation, solar radiation, and wind speed and direction. Continuous monitoring for several years detected no significant response of deep soil moisture to precipitation in either the forest or the meadow. Unsaturated zone modeling based on 100 years of simulated weather combined with soil properties taken from trench and borehole samples indicated no recharge during the simulation period for either the forest or the meadow. In summary, neither the experiment nor the modeling supported the assertion that forest thinning increases groundwater recharge.