Forests Yield Bulk Of Nation’S Water

Study predicts shortages, making forested watershed crucial

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In a nation beset by predicted shortages of fresh water, the ability of America’s national forests to produce fresh water may prove their most important asset, according to a national study of watersheds.

The nation’s forests filter some two-thirds of the nation’s fresh water, making them key to coping with water shortages of the future, concluded the researchers from Oregon State University.

Rim Country currently gets all of its water from wells sustained mostly by rainfall on Forest Service land. The proposed Blue Ridge pipeline will eventually double Payson’s water supply, but it also gets all its water from snow and rain falling on the small watershed that drains into Blue Ridge — one of the most productive watersheds in the entire state.

The Oregon State University researchers cited population growth, the development of rural areas and the impact of global warming in predicting future water shortages.

Another study on the development of rural areas next to national forests by the USDA Forest Service’s Pacific Northwest Research Station underscored the point.

That study said the nation’s 193 million acres of national forest land harbor one-third of the nation’s endangered and threatened species and accommodate some 205 million human visitors annually.

But the housing density on 22 million acres of private land within 10 miles of a national forest boundary will increase significantly in the next 20 years, according to the study.

The watershed study stressed the impact of both mushrooming rural development and the climate models suggesting that the seemingly inexorable rise in global temperatures in the past century will lead to more long, severe droughts — like the 10-year drought that cut the average annual rainfall in Rim Country in half until the near-normal rainfall totals of the past two years.

That drought caused a dramatic drop in well levels in Payson, a sharp reduction in stream flows in the East Verde and elsewhere and beetle infestations that killed millions of trees across Rim Country.

The amount of water that a forest produces relies on a sometimes-delicate balance, the researchers concluded.

Normally, healthy forests produce layers of soil that absorb rainfall, prevent rapid runoff and release the water from storms and snow pack gradually into streams. However, the plants of the forest also absorb water — especially in thick, overgrown forests like those that have spread across millions of acres of Rim Country in recent decades.

The study concluded that logging can increase the flow of water into streams and the water table, by removing many of the trees that would otherwise soak up the water. However, such an increase in the amount of water available is temporary —and quickly overcome by the often great volume of plants that spring up once the shade of the big, mature trees has vanished.

“Because forests can release slightly more water for a decade or so following a timber harvest, it has been suggested that forests could be managed to increase water supplies in some areas,” said Julie Jones, a professor of geosciences at Oregon State University.

“But we’ve learned that such increases don’t last very long and often don’t provide water when you need it most.”

Among the key conclusions of the watershed report:

• Forests cover one-third of the nation’s land area and filter two-thirds of the nation’s drinking water, which means their most important “output” is water.

• Water demand continues to grow as the population increases, but forest acreage continues to decline. Those declines will likely accelerate due to climate change, disease epidemics and fire.

• Healthy forests benefit humans by controlling water yield, peak flows, low flows, sediment levels, water chemistry and quality.

• The acreage affected by wildfires had increased dramatically in the past decade, but chemicals used to fight fires can affect aquatic ecosystems and damp soils.

• Urbanization constitutes to pose the greatest threat to forested watersheds.

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