Updated: Jun 3, 2018
So, everywhere I turn in this beautiful area of east TN I see mulch under trees >2" thick up to the and touching the trunk. That's a recipe for disaster. The root-trunk zone is an area in which gas exchange is critical, true of all parts of the tree. Granted the roots can take a lower gas exchange ratio than the leaves. When landscapers do this it's because it has become the aesthetic norm not because it benefits the tree. For mulch to truly, positively impact the surface roots of a tree it should be beyond the drip line of the canopy by 1 - 3 meters. That's were the feeder roots near the surface are growing and most productive. In
addition, having thick mulch at the root/trunk interface is choking the plant literally, which is causing a general malaise that can reduce the plant's immune system responses and make it more susceptible to a plethora of diseases. It's killing your trees slowly and costing you more money as a result. For me, tree-hugging devotee that I am, seeing such mulching sends me into a tizzy of heart-ache.