Certified Arborist
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Hazardous Trees

Diseased Trees Case Study

Example of hazardous treeAnother example of hazardous tree

Trees are hazardous when a failure of one or more of their parts results in property damage and/or personal injury. All trees have the potential to fail. ISA Certified Arborists evaluate individual trees, assesses their potential to fail and recommends appropriate action. Trees can develop diseases, tree blight, broken or cracked limbs and heavy limbs that could fail. Learn more here about what to look for and how a ISA Certified Arborist can help prevent or treat tree care disease.

Signs of a Sick Tree

  • Man-made Wounds
  • Cracks
  • Decay
  • Insect Damage
  • Dead Wood
  • Dead Branches
  • Wilted or Discolored Leaves
  • Mushrooms or Fungi Growing at the Base of Tree
  • Root Problems
  • Conks or Cankers
  • Sawdust at the Base or Root Zone of the Tree
  • Hollow or Decayed Areas in the Tree
  • Cracks in the Trunk or Major Limbs
  • Co-dominant Stems with Included Bark
  • Weak Branch Unions
  • Blight
  • Poor Tree Architecture

Trees add to our enjoyment of outdoor experiences whether it is in forests, parks, or urban landscapes. Too often, we are unaware of the risks associated with defective trees, which can cause personal injury and property damage. Interest in tree management has increased in recent years due to safety and liability concerns resulting from preventable accidents. Recognizing risk in trees and taking proper corrective actions can protect property and save lives. A “hazard tree” is a tree with structural defects, likely to cause failure of all or part of the tree, which could strike a “target.” A target can be a vehicle, building, or a place where people gather such as a park bench, picnic table, street, or backyard. This brochure was created to help home owners and land managers in recognizing hazardous defects in trees and to suggest possible corrective actions. We recommend that corrective actions be undertaken by professional ISA Certified Arborists. Because of the natural variability of trees, the severity of their defects, and the different sites upon which they grow, evaluating trees for hazardous defects can be a complex process. This publication presents guidelines, not absolute rules, for recognizing and correcting hazardous defects. When in doubt, consult an ISA Board Certified Master Arborist.

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