Friday, January 06, 2017

Forests need thinning to reduce wildfires and allow larger trees to get enough water, experts say

Experts say thickened Western forests need to have their smaller trees cut or burned to reduce the risk of wildfire and allow larger trees to get more water and flourish, reports The Economist. "In the early 1900s, an average forested acre in California supported fewer than 50 or so trees. After a century of efforts to fight wildfires, the average has risen to more than 300 (albeit mostly smaller) trees. The extra fuel turns today’s wildfires into infernos hot enough to devastate the landscape, torching even the big older trees that typically survived fires in the old days. Beyond this, the extra trees are worsening California’s driest ever drought."

David Edelson of The Nature Conservancy says it's "like too many straws in a drink,” the British magazine reports. He said that "as a warmer climate lengthens the growing season, trees’ thirst will only increase. This has led to a push for large numbers of trees to be cut or burned down. Overgrown forests catch more snow and rain on leaves and needles, where wind and sunlight increase the amount of moisture lost to evaporation."

The U.S. Forest Service "thinned 600 square miles of California’s watershed in the year to October, up from 367 the previous year," reports The Economist. "By burning or removing about 40 percent of tree and plant-life in these areas, the Forest Service wants to do more than put extra water in reservoirs. The goal is also to reduce the severity of wildfires and to get water into the bigger trees left standing—more than five years of drought have killed more than 66 million trees in California, aerial surveys show."

"Five times as much forest should be thinned every year, estimates Roger Bales, a hydrologist at the University of California, Merced," the magazine reports. "To find out how much extra water a thinned watershed produces, the university has placed sensors in thinned and control plots in the Stanislaus-Tuolumne Experimental Forest north of Yosemite National Park. Depending on landscape and precipitation, thinned areas shed 10-40 perecnt more water into streams. ... The hope, says Eric Knapp, a Forest Service ecologist, is that a new thinning technique will prove to produce even more water when flow volumes from next spring’s snowmelt are known."

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