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 Precious topsoil can be either washed away or blown away. Trees help prevent both.
Once the protective cover of trees is gone, fine particles of soil simply blow away. Anything that damages soil structure, such as artificial fertilizers, heavy machinery, constant ploughing for arable crops, or the hooves of grazing animals, accelerates soil erosion, which is increasing to a devastating degree in many areas of the world.
Trees reduce topsoil erosion, prevent harmful land pollutants contained in the soil from getting into our waterways, slow down water run-off, and ensure that our groundwater supplies are continually being replenished. For every 5 percent of tree cover added to a community, storm water runoff is reduced by approximately 2 percent.
Research by the U.S. Forest Service shows that in a 1-inch rainstorm over 12 hours, the interception of rain by the canopy of the urban forest in Salt Lake City reduces surface runoff by about 11.3 million gallons, or 17 percent. These values increase as the canopy increases.
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