Excavated Tree Wells
A common practice
when creating a tree well entails removal of soil around the edges of
the ring. The logic behind this practice likely relates to catching
rainfall in the basin that is created; however, soil removal can damage
tree roots. Most absorptive roots grow within the top 12 inches of the
soil, and this excavation can remove these important roots that are
necessary for a tree’s access to water and minerals (which sort of
defeats the purpose, doesn’t it?). If the tree is larger, most
absorption takes place further from the trunk anyway, and larger roots
can incur damage, increasing the potential for root rot and cutting off
transport of these resources back into the tree.
Also harmful,
the removed soil is often piled back within the tree well or even
against the trunk. This addition of fill has its own set of
consequences, which are described in the section below.
Raised Tree Wells
At the other end of the spectrum from soil removal, building up a tree
ring by creating a border with rocks, bricks, or edging and filling it
with soil (as shown in the photo above) can also adversely affect a
tree. One main function of tree roots is respiration, the exchange of
gases between roots and the atmosphere above ground. Addition of even a
couple of inches of soil on top of a tree’s root system slows the rate
of gas exchange and can ultimately result in stress and even root death.
In addition, fill soil makes water less accessible to roots, and if
piled against the trunk it can lead to rot.