Dense forests suck up surface and groundwater and dump it into the atmosphere through the process of evapotranspiration. This means that there is less water for other uses.
“There are too many trees in Sierra Nevada forests, say scientists affiliated with the National Science Foundation (NSF) Southern Sierra Critical Zone Observatory (CZO).”
A new study supported by the National Science Foundation published in the journal Ecohydrology (see press release) proclaims “Billions of gallons of water saved by thinning forests.” The study of the Sierra Nevada Mountains in California notes that “excessive evapotranspiration may harm a fragile California water system, especially during prolonged, warm droughts.”
The primary methods of good forest thinning are fire and logging.
Forest Service policy exacerbated sound forest management. Remember Smokey the Bear, “only you can prevent forest fires?” But fire is nature’s way of managing forests. Logging was largely reduced for misguided environmental reasons such as saving the spotted owl.
From the NSF study:
“Forest wildfires are often considered disasters,” said Richard Yuretich, director of NSF’s CZO program, which funded the research. “But fire is part of healthy forest ecosystems. By thinning out trees, fires can reduce water stress in forests and ease water shortages during droughts. And by reducing the water used by plants, more rainfall flows into rivers and accumulates in groundwater.”
Using data from CZO measurement towers and U.S. Geological Survey satellites, researchers found that over the period 1990 to 2008, fire-thinned forests saved 3.7 billion gallons of water annually in California’s Kings River Basin and …17 billion gallons of water annually in the American River Basin — water that would otherwise have been lost through evapotranspiration.
Forest thinning has increased in recent decades in an effort to stave off disastrous wildfires fueled by dense forests. This study shows that restoring forests through mechanical thinning or wildfire can also save California billions of gallons of water each year.
Perhaps we should take guidance from the first land managers in North America, the Indians. In my article “The Pristine Myth” I note the following:
Archaeological and anthropological research during the last 25 years or so, shows that much of what we thought was pristine in the Western Hemisphere, even the Amazon rain forest, is actually human-formed landscape created by the first New World inhabitants, the Indians. It seems that American Indians, from North America, Mexico and South America, were the ultimate land managers, and they transformed the land to suit their needs. They constructed the world’s largest gardens.
American Indians built cities and civilizations, cultivated forests and farms, and developed more than half of the crops grown worldwide today. Indians, rather than subsist passively on what wild nature provided, instead survived by cleverly exploiting their environment. Their principal tool was fire. They did not domesticate animals for meat, but instead used fire to change whole ecosystems to raise deer, elk, and bison.
A new study (“Effects of Climate Variability and Accelerated Forest Thinning on Watershed-Scale Runoff in Southwestern USA Ponderosa Pine Forests” published October 22, 2014) conducted by The Nature Conservancy and Northern Arizona University recommends accelerated forest thinning by mechanical means and controlled burns in central and northern Arizona forests. The study estimates that such thinning will increase runoff by about 20 percent, add to our water supply, and make forests more resilient.