Phloem cells may die, interfering with the downward movement of food to the roots and eventually lead to root dieback, reduced water uptake, and ultimately tree death. In addition to creating conflicts with the root collar, excessive mulch retains surface water which promotes shallow rooting of trees. Considering our irregular climatic patterns, it is advantageous to promote deep rooting of trees. Deep rooted trees will survive drought stress more readily. Deep rooted trees are less susceptible to wind throw during saturated soil periods.
Secondary pathogens attack the weakened tree.
Phytophthora fungus prospers in areas of high moisture and creates cankers which may girdle the trunk. Stressed trees are the primary target of boring insects. Bores are often blamed for tree decline when in fact the true culprit is an over zealous individual placing excessive mulch around and against his tree. Symptoms of root collar disorders include yellowing foliage, early leaf discoloration and drop, and dieback of the upper crown. Large trees severely declining from root collar disorder should be removed before they become hazardous.