When determining if a potentially hazardous tree should be felled, a number of factors are taken into consideration including the type of tree, the tree’s structure and branching characteristics and site attributes.
An arborist will look for defects that predispose the tree to an unacceptable risk of failure. This could be a completely dead tree or other issues like dead branches, weak branch attachments, cracks, poor crown architecture, root defects, cankers or wood decay. Consideration will also be given to the species as some like maple, ash, elm and birches as well as conifers are more prone to branch failure. The severity of the issue helps dictate the likelihood of failure.
However, the tree itself is not the only consideration. Soil conditions, slope of the site, prevailing wind direction and other properties of the site also play a role. A tree with only minor defects could pose an unacceptable risk given the site and growing conditions.
Along with that, the potential damage resulting from a failure is also a factor. A tree that falls at a wooded property border is very different than one close to a home, building or area where people could be injured.
Tree felling is a necessary part of arboriculture and should always be undertaken with safety in mind.