The impacts of tree stand thinning on groundwater recharge in aridland forests

Forest thinning has been used as a management tool to reverse the adverse impacts of decades of fire suppression in the western USA. Research into the impacts of thinning on surface water, soil, and vegetation re-growth have occurred concurrently with the growing popularity of forest thinning; however, its potential impact on groundwater recharge and related springs ecosystems has largely been ignored until recently. This systematic review provides an overview of some of the tools used to measure the influence of forest management on groundwater recharge, including numerical and process based modeling, empirical paired-watershed approaches, and statistical stochastic techniques. A brief discussion of the benefits and drawbacks of each method also is provided. The paper provides a literature review of existing studies of groundwater recharge and forest management from 1971 to 2018. The review of 35 studies indicates a range of results and highlights differences between studies of clear-cut forests versus thinned forests. Forests that were thinned had a greater amount of groundwater recharge than clear-cut forests, indicating that recharge responds positively and more strongly to reduced sublimation and evaporation in partially thinned forests than to clear-cut removal of mature trees. A similar test with forest encroachment studies revealed no differences between forest encroachment and either thinning regime. The number of forest management-groundwater recharge studies has dramatically increased over the last two decades, indicating increased interest in finding tools to increase groundwater yields for societal use in rapidly populating aridland forests. To our knowledge there have been no studies of forest thinning impacts on springs ecosystems, a field of study rich with possibilities for ecologists, hydrologists, rangeland and forestry scientists, and interdisciplinary ecohydrology practitioners.