Improper Mulching
Mulch can reduce weeds, retain moisture and improve soil. But too much mulch close to the trunk base can damage trees over time. Roots , probably in search of more favorable conditions, can grow up into deeper layers of mulch and proliferate there. This may result in roots encircling the trunk, girdling and ‘choking’ the tree and cutting off its water supply. When mulch is piled up against the trunk moisture builds up and creates conditions favoring wood decay fungi. These conditions can damage or kill the bark or create wounds for the entry of wood decay fungi, which in time, cause tree failure.
Trees should have a turf-free zone around them for best results. Three feet is OK for a young tree and 6 to 10 feet for larger trees. It’s also a good idea to separate competing vegetation (shrubs and trees).