Ecosystem services of the forest

A past column discussed how various land uses can negatively impact streams. This column looks at why forests — managed and unmanaged — are important to maintaining a clean and dependable water supply. With concerns of rising population and increasing demand for dependable supplies of clean water in Macon County and in cities that rely on water from the mountains, the importance of forests will certainly only increase.

The movement of water through forested and non-forested slopes can be very different. Rain that falls on a forest takes many different paths. Some raindrops never hit the ground because they are intercepted by the tree canopy and evaporate back into the air. The rain reaching the forest floor is filtered and cleansed by the soil as it trickles down to become part of the groundwater or to emerge as streamflow. The rest, about 30 percent of rainfall, is used by the trees and returned to the air by a process called transpiration. In contrast, rain that falls on non-forested surfaces has one of two pathways: filtering into the soil or flowing down the mountainside as surface runoff. Highly compacted or impervious surfaces (like asphalt) result in most of the rainfall flowing along the surface, carrying with it eroded soil and other materials.

On compacted soils without a vegetative cover, raindrops can dislodge bits of sediment when they strike the ground, which then flow down the hill with the rest of the water that cannot be absorbed by the soil. This sediment is one of the major causes of murky streams and can add significant costs to water treatment. It can also increase wear in hydroelectric turbines like the ones in the dam at Lake Emory, with increased maintenance costs being passed on to power customers and taxpayers.

Forests are also important for providing dependable water supplies. The deep and porous forest soils of the mountains act as a sponge that holds water and slowly recharges groundwater and provides stable streamflow.

Soils that are compacted hold less water, and hence, water flows through (or over) the soil more quickly. This means that more water runs down the mountainside faster, potentially increasing flood risk and decreasing groundwater recharge. The excess water often flows too fast to be captured by reservoirs of efficiently used by water treatment facilities. As more and more groundwater and surface water are required to meet growing water demands, maintaining the soil’s ability to absorb and filter water will be critical for ensuring reliable water supplies. Fortunately, researchers at Coweeta have developed well-tested guidelines for proper forest management and road design that can minimize many of these impacts. As a result, forest management can provide landowners with revenue and still protect water resources. Many of these same guidelines are applicable to other activities such as partial forest removal and road building for housing.


This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.


Original Citation: The Coweeta Listening Project. Franklin Press. Column on "Science, Public Policy, Community." Page B4. July 1, 2011.