Deadwood is tissue on a tree that is non-conducive. It has neither moisture nor sugars moving through it. These tissues can be trunks, stems, limbs, branches, twigs, roots or heartwood. In addition, deadwood acts as brood areas for insects and disease. Dead tissues provide an entry for both parasitic and saprophytic organisms. It is unimpeded, there are no toxins, tannins or any other substances to slow down or stop infection. It allows infections to move directly from dead structures to other structures such as heartwood, which is deadwood. It also allows live structures to be infected with the more aggressive organisms of infection.
Removing deadwood through pruning cycles is part of the practice for normal care in healthy trees. In the case of sick or ill trees, it is imperative to have it removed immediately.