The root collar is part of the tree’s trunk and requires the movement of oxygen and carbon dioxide in and out of the phloem (inner bark) to survive. Planting too deep or adding excess soil or mulch on the root collar can inhibit this gas exchange and kill phloem cells, interfering with the downward movement of food (photosynthate) to the roots. Eventually this can lead to root dieback, reduced water uptake and possibly tree death. Trees and shrubs with buried root collars may decline and are more susceptible to attack by secondary pests. It is best to treat the situation as soon as it is discovered by means of a root collar excavation. Other actions such as fertilizing and proper mulching will promote tree health thus improving chances for recovery.