The Grand Lie of Urban Forestry
Urban forestry has lots of useful information to offer, but there is a big lie at the heart of the majority of the work of urban forestry which threatens to discredit the entire discipline if anybody will call their hand on it. It’s the Root Zone Myth.
As with any myth, there is some kernel of embedded truth. In the case of the Root Zone Myth, it’s the fact that, left alone in a field, a tree’s roots will spread about as far as its drip line, which is the outer limit of its leaves. So if the tree’s limbs and leaves were 40 feet in diameter, its root system would be, too. Now, the urban foresters are saying that’s not good enough; a tree’s root system actually extends 2-1/2 times as far as the drip line. So for that tree with a 40-foot canopy, the roots actually extend to a 100-foot diameter.