A review of impacts of forestry on groundwater and implications for forest management

Forestry affects groundwater by diminishing groundwater recharge to as little as a tenth of that under grass or hearthland, largely due to the greater uptake of soil water by trees and the increased water-holding capacity of forest soils. Furthermore, afforestation can lead to a significant reduction in surface runoff, by as much as 20%, mainly due to interception of rainfall by the forest canopy. Reduced streamflow is compensated by enhanced loss of groundwater to effluent streams. Groundwater quality may be affected by enhanced acidification and nitrification processes under forests, due mainly to a significant increase in the organic content of forest soils. The reduced recharge rate under forests means that any deterioration in groundwater quality resulting from afforestation may take a decade or more to become apparent. Implications for forest management are discussed.