In the past 15 years research being done at the University of Minnesota has shown that trees growing inlandscape settings are sometimes prone to a growth phenomena now referred to as Stem Girdling Roots (SGR). An SGR is a root or roots that grow around the base of the tree instead of away from the tree. Over time as the stem and roots grow larger, the root will compress the stem like a tourniquet, cutting off the upward movement of water and nutrients to the top of the tree and preventing the transfer of photo-synthates (carbohydrates) from the top of the tree to the root system.
This leads to the decline of tree health, often killing significant portions of the tree (affecting its aesthetic value) or may eventually kill the entire tree depending on the extent of the girdling of the stem. Trees with SGRs are also more prone to being blown over, even in a light wind, as the integrity of the stem and root system is compromised.
A root collar excavation is an exploratory and diagnostic procedure, using compressed air to remove the soil at the base of the tree allowing an Arborist to identify and remove roots with the potential to cause stem girdling before significant damage occurs.
It is a process best done on young trees as a preventive measure than on older trees as a therapeutic process. Therapeutic removal of SGRs is possible, however the success depends on the extent of the compression of the stem and how compromised is the overall health of the tree.