The National Research Council report, written by a panel of 14 experts, was requested by the U.S. Bureau of Reclamation, the nation’s largest water wholesaler, and the U.S. Forest Service, which manages 193 million acres of land.
'Meeting water supply needs is becoming more difficult because elevated water demand is occurring simultaneously with changes in climate, human population and development, land use and ownership,' says the report. 'How to manage forests and sustain water supplies will be a primary challenge in the 21st century.'
The panel was chaired by Paul Barten, associate professor of forest resources at the University of Massachusetts-Amherst. He also serves as co-director of the U.S. Forest Service-University of Massachusetts Watershed Exchange and Technology Partnership. Vice Chair Julia Jones is a professor at the Department of Geosciences, Oregon State University.
The report, 'Hydrologic Effects of a Changing Forest Landscape,' explores how better management of forest resources could increase water supplies and quality and identifies future research needs.
The report examines how removing the forest canopy, wildfires, insects, climate change, road networks, and applications of chemicals like fertilizers and fire retardants can affect the water output of a forest.
'Some effects of climate change on forests and water are already evident, and future climate changes are likely to have major effects on forest hydrology,' the report states. 'Direct effects of climate warming on forests and hydrology are being observed, such as changes in the timing of snowmelt runoff and increases in wildfires.'
The authors recommend more research to better predict indirect effects of climate change, including evaluations of how changes in forests and forest management influence hydrologic response.
Forests need abundant water to grow. As such, they occur in areas of high precipitation. The precipitation cycles through plants and soil, and some ends up running into streams that flow to larger bodies of water. By their nature, then, forests are vast processors of freshwater.
A question looming larger as human demand for freshwater grows is - can cutting trees in forested headwaters increase water yield downstream for farm irrigation and community uses without harming the forest ecosystem?
It seems not.
'While it is possible to increase water yield by harvesting timber, water yield increases from vegetation removal are often small and unsustainable, and timber harvest of areas sufficiently large to augment water yield can reduce water quality,' the report says.
'The potential for increasing water yield from forest management is also limited by the fact that increases are less likely in seasons when water demand is high and increases tend to be much smaller in drier years.'
Reducing forest cover also may have a detrimental effect on water quality, the report adds.
While scientists extensively have studied the effects of timbering and of roads on forest hydrology, much less is known about how fire, insect invasions and disease influence water output and quality from a forest, the authors say.
They recommend more research on the subject, and the development and use of 'watershed councils' to engage communities in learning about and protecting the watersheds where they live.
Citizens and communities can influence forest and water management at the local, regional, or watershed level.
Cumulative watershed effects, changes in land ownership and management, changing population and development patterns, and water supply concerns have spurred activity to protect watersheds and water quality from the grassroots, community level, the report points out.
New community-level watershed councils and forest groups are proactive in watershed -based restoration and management.
The report recommends that watershed councils and citizen groups should work within communities and with state and federal agencies to use these councils as vehicles to meet multiple goals of integrated watershed management at the community level. Citizens can participate in watershed councils and help them grow in number and influence over watershed uses at the community level.
Forestry best management practices, or BMPs, can mitigate negative consequences of forest management activities, such as roads and timber harvest, but their effectiveness can be highly site-specific and storm-specific or difficult to quantify, the report points out.
The report's authors recommend that managers should catalogue individual or agency BMP use, design, and goals at the national level and make this information available to the public. They should monitor BMP activities for effectiveness and coordinate analyses of monitoring data for use in an adaptive management framework.
Additionally, managers should design adaptive management approaches for forested watersheds that coordinate management, research, monitoring, and modeling efforts.
The authors advise that, 'Scientists who study forest hydrology, forest and water managers, and citizens who use water in many different ways all need to take action to sustain water resources from forests.'