Trees commonly suffer when the grade is set too high against their root flare or root collar. This can occur when trees are planted at the wrong elevation or when trees subside due to improper compaction below the root ball when they are planted. Alternatively, root collars can be buried over time due to the accumulation of mulch or soil around the tree.
Whatever the cause, harm to the tree from grade set above the root collar can be long lasting and should be remediated through root collar excavation (RCX) with an AirSpade. Symptoms of this condition include rot or infection of bark at the base of the trunk, growth of roots that are too high relative to the natural root flare, and girdling roots, which constrict the root flare and tree trunk. Girdling can also occur on urban sites, where roots have limited room to grow or have encountered compacted or anaerobic soil conditions, causing roots to heave around the collar. Use of an AirSpade allows tree root collars and girdling roots to be excavated with minimal damage to the tree. Once uncovered, a certified arborist can easily identify roots that need to be removed or trained.
RCX often impacts a relatively small area of disturbance around the root flare. If grade is being removed, the limit of disturbance must extend far enough to allow appropriate drainage away from the tree. Once turf and other plant material are removed from the work area, the arborist can begin excavation, holding the AirSpade at a 45° angle, continuously working the tool back and forth at 1 to 2 feet per second, until the natural root flare is exposed. The arborist can then perform root pruning, removing any roots that are wrapping the tree or have grown too high in elevation. Sometimes it’s possible to excavate under roots that are grown too high, and train them down into the new finished grade. Soil is then returned to the excavated roots and grade is re-established at the appropriate elevation. RCX is not typically considered a method for soil augmentation; however, like other AirSpade applications, it can be combined with other techniques depending on the project goals and tree health-care needs. Finally, organic mulch (often wood chips are preferable) is applied to the surface in a layer 2-4 inches (5-10 cm) thick.
To learn more about performing air-spading procedures, tree health care and preservation, see the full Arbor Technical Applications Bulletin.