At this point, the plant has gone into an irreversible decline. When roots decline and die, so does the plant. Inner Bark Tissue Death Above-ground stem tissue of most trees, shrubs and perennials is morphologically different from roots and must be able to freely exchange oxygen and carbon dioxide. Mulch that is piled onto the trunks decreases gas exchange, with inner bark tissue eventually dying. When the inner bark dies, roots no longer receive the energy produced by the leaves through the process of photosynthesis, and the plant dies.
Most plant diseases require moisture to grow and reproduce.
These lethal trunk diseases are no exception and usually gain entry into the stressed, decaying bark tissue. Once established, these cankers will eventually encircle the tree, killing the inner bark, starving the roots and ultimately killing the plant. Thick mulch layers that are placed against the stem will begin to decay and can produce excessive heat. If trunk flare tissue does not adequately harden before freezing weather arrives, the tissue will die, the roots will starve, and again, the plant will go into decline. The tree needs healthy roots to produce the hormones and chemical growth regulators that allow it to properly prepare for winter weather.