As part of the natural growing process, a tree may "give up" on the odd limb for no apparent reason (there is often an underlying cause, even if not readily apparent!), or where a limb becomes damaged through storms or by vehicles, it can become diseased and begin the process of die-back. Additionally, badly pruned stumps may also become deadwood and crossing branches that rub in the wind are often the root cause of subsequent disease in a branch.

For conservation reasons, not all dead wood is bad: It provides a habitat for "Saproxylic organisms" (bugs and beasties that feed on dead or dying wood to most of us) which become the meal of choice for Woodpeckers and other creatures. It is necessary to strike a balance when deadwooding: if it is safe to do so, leave some deadwood in a tree for bio diversity, but at the same time assess whether leaving the dead wood is unsafe, or likely to have a longer term detrimental effect on the health of the tree. A thick long branch that has deadwood at it's end is less likely to cause a tree poor health, unlike a short stub near to the trunk which will allow disease into the trunk through the inability for the tree to complete its natural CODIT (Compartmentalisation Of Decay In Trees) process.

When deadwooding, we would normally climb into the crown of the tree and make a systematic check for different types of deadwood and assess whether it is unsafe and remove, cut out crossing branches, trim stumps back to the branch collar to permit the CODIT process and subsequent callusing over of the wound, and if reasonable to do so, leave some dead wood for the insects that birds will then feed on.

Deadwooding is usually done at the same time as Crown Cleaning.