Hazard Tree Risk Assessment

Hazardous trees can present a serious risk to people and property in the surrounding area, especially in the urban areas. While the identification of hazardous trees should be done by experienced arborists, there are several indicators you may want to examine on trees around your property.

Trunk and Branch Inspection


There are several different types of cracks that can occur in a tree. They can be across the grain, up and down the tree, and between growth rings. They can result from internal decay, the shear force between the tension and compression wood of a leaning tree and the tension of large, heavy limbs pulling apart the wood.


A primary objective of an arborist looking at a decayed tree is to determine if there is enough wood strength remaining to support the structure of the tree. Decay can be obvious as shown by the presence of fruiting bodies, conks, and cavities. But, it can also be hidden with significant wood decay showing only limited outward signs.

Poor Structure

Co-dominant stems, which have the appearance of a V shape, are indicators of weak attachments and more prone to failure. Poor structure can also result from incorrect pruning practices, such as topping, flush cutting, and lion tailing. Limb scars are evidence of previous branch failure and could be predictors for future problems.

Root Structure Problems

When roots are severed cracked, or decayed, there can be significant loss of structural support greatly increasing the risk of tree failure. Trees leaning more than 30 to 40 degrees from vertical or leaning with recent root lifting, cracks, or buckling should be considered high risk.

Crown (Canopy) Inspection


The larger the crown on the tree, the more force that is exerted throughout the canopy. This force is amplified in areas of defects, such as poor branch attachment or decay. Excessive end-weight is very common in uncared for mature oak trees and is a frequent contributor to failure. Pruning to reduce end-weight in combination with thinning can reduce the wind sail effect (force exerted throughout the canopy when the branches “catch” the wind) thereby reducing the failure potential.


Dead or hanging branches left in a tree can be deadly. They can break loose and fall at anytime, which can result in significant damage to people or property below. Limbs sprouting from old topping cuts are considered to have a higher failure potential because of the poor attachment and potential for internal decay. These limbs are called epicormic branches.

Common Defects

Mushrooms, conks, bleeding, excessive sap flow, nesting holes, bee hives, borers, and insect damage are common indicators that problems may be present beneath the surface also increasing failure potential throughout the canopy