for clean water and healthy ecosystems, combined with tensions related to water supply or flooding risks, challenge forest hydrologists to predict how changes in a forest will affect the quantity and quality of water to help meet that demand. These challenges are becoming more acute as water demand increases simultaneously with changes in climate, land use, and other processes in forest systems. This report discusses these challenges and provides the scientific basis and context for addressing them using a suite of recommendations for the scientist, the forest or water manager, and the citizenry.


Forests account for 33 percent of all U.S. land area, covering about 750 million acres (300 million hectares) (Powell et al., 1993; Smith et al., 2004). Of this, 57 percent (430 million hectares) are privately owned, and the remainder is public forest. The federal government owns or manages land in all 50 states, with its largest holdings concentrated in 13 western states.

The forest products industry is an important element of the global economy, accounting for approximately $200 billion each year. In the United States, timber harvesting operations produce nearly 400 million cubic meters of wood annually. Forests also provide recreational opportunities and aesthetic values, carbon sequestration and mitigation of some air pollutants, and fish and wildlife habitat. Forest management plans and programs must address fire, drought, insect and diseases, habitat protection, wilderness areas, and recreation. All of these activities can have measurable influences on water supply and quality for municipalities, agriculture, and aquatic ecosystems from the channel to the watershed and landscape scales.

Forests are also efficient, low-maintenance, solar-powered living filters that provide high-quality water supplies that support aquatic ecosystems. Precipitation that comes as rain or snow in forested areas is cycled back to the atmosphere or drains through the soil to streams and aquifers, thereby producing much of the nation’s water supply. In this way, forested areas provide water to 40 percent of all municipalities (Nulty, 2008) or about 180 million people in the United States (

The Forest Reserves Act (1891), the Organic Act (1897), and the Weeks Act (1911) first designated and established management of national forests. Since then, the social, economic, and political changes of the twentieth century, especially after World War II, increased the number, scope, and complexity of laws and regulations that guide the management of public and private forests. In addition to favorable conditions of flow and a continuing supply of timber, the USFS today must manage national forests for multiple objectives. These management responsibilities are sometimes supported and sometimes constrained by an increased understanding of forest- and water-related ecosystem services: natural filtration by vegetation and soils, provision of species habitat, groundwater and streamflow regulation, erosion control, and channel stabilization.

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