Hazard Trees

First, some definitions:

Hazard tree

A tree with a risk of failure and resulting damage to people or property that exceeds the risk tolerance of the responsible manager.

Tree failure

Mechanical failure of some part of the tree or its interface with the soil that results in branches, tops, or the entire tree falling.

Tree risk

The likelihood of property damage or personal injury from a hazard tree. Tree risk incorporates the potential for failure, the frequency and duration of target presence, and the value of the target.

Tree defect

A tree condition that increases the likelihood of failure. Defects may be caused by structural flaws associated with the way a tree grew, mechanical damage from wind or being struck by large objects, and very commonly by root diseases, stem decays, and cankers. Defects vary in severity.


People, structures, or property that may be struck and damaged by a hazard tree or part of one.

Hazard tree management

Actively reducing risk from hazard trees with a program that includes tree inspection and mitigation, balancing risk against the benefits that trees provide. Sometimes called “tree risk management”.

Aside: Hazard vs. Risk

Properly, hazard is something that can cause loss or harm; risk is the likelihood that a hazard will actually cause loss or harm (so every hazard has a level of risk associated with it). Thus, when we categorize the severity of hazards, and incorporate the target into the rating, technically it would best be considered a risk rating. Still, it is not strictly incorrect to call it a hazard rating, the traditional term.

Hazard tree management

Hazard tree management is important primarily in developed areas with trees:

  • landscaping around homes, other buildings
  • street trees
  • urban parks
  • campgrounds and other developed recreation sites
  • railroad and highway rights of way
  • utility rights of way

Hazard tree management is all about risk reduction. Tree risk incorporates not just the condition of the tree, but also the potential target. So risk is:

  • potential for tree failure, plus
  • potential for serious loss should the tree fail, which includes:
    • potential for hitting and damaging target, including the frequency and duration of target presence within striking distance
    • value of target

Hazard tree management balances risk against the benefits of maintaining large, beautiful trees on the site (see a separate page devoted to management programs). If not for that balance, we would eliminate risk entirely by removing all trees in developed sites.

Of course, trees fail naturally, and it is not a serious problem unless people, structures, or property are close enough to be hit. Tree failures can and do cause tragic accidents in undeveloped forests, such as backcountry trails, but that is considered to be a risk that people accept when they visit a forest.  In general, managers have no duty to make undeveloped forests safe, nor is it feasible.

Legal issues

This information is provided for general education but has not been checked by a lawyer and should not be considered legal advice, nor should it be relied upon in making management decisions.

Traditionally, a property owner has three levels of responsibility to visitors:

  1. Trespasser: enters without special consent or privilege, without payment or license. Not necessarily illegal. We owe them lowest duty of care, essentially just to not set traps.
  2. Licensee: Has permission or consent, express or implied, to go on land for own purpose. Applies in general to visitors to public land.
  3. Invitee: Someone who pays a fee or is otherwise specifically invited for recreation or business purposes. Highest duty of care, must assure reasonable care has been used to prepare premises and make them safe for user. Must inspect and then remove or warn of known hazards, generally exercising reasonable care to protect user.

Most states use a prudent-person test for the duty of reasonable care owed to people who enter. What would a prudent person do?

Property owners have a general duty to visitors to use reasonable care to keep the premises safe and to guard or warn the visitor from any hidden danger or defect that is discoverable using due care (such as inspection by qualified hazard tree inspectors) and presents a reasonably foreseeable risk of harm.


If owners do not comply with their duty, they may be liable for resulting damages. Lawsuits up to $60,000,000 for serious injury or death are not uncommon. A property owner is negligent and liable if a claimant can prove that:

  1. The owner had a duty to the claimant; and
  2. The owner breached his duty; and
  3. The owner’s breach was the cause of the claimant’s injury or property damage.

In a lawsuit involving tree failure, two fundamental groups of questions come up:

  1. Was the manager negligent? Was there an inspection system? Was it prudent and performed to customary standards? Was it documented?
  2. Was this particular tree inspected? Documented? Could the cause for failure have been detected in a reasonable and prudent inspection?

“Act of God” is not as good a defense as you might think. The same questions will be asked, and if there was detectable defect and no/poor inspection, the manager may still be held liable.

US Federal Government

The US Federal government once had sovereign immunity that exempted it from such lawsuits, but that is now largely waived by the Federal Tort Claims Act of 1946 (28 U.S. Code §1346(b), §2671 et seq.).  An exception is the discretionary function exception (28 U.S.C. §2680(a)), when the government can show that the claim is based on a federal employee or agency performing, or not performing, a discretionary function or duty.  Discretionary function is not well defined, and courts have interpreted it variously ​[1]​.

Federal employees are not individually liable except when acting outside the scope of their employment according to the Federal Employees Liability Reform and Tort Compensation Act of 1988 (the Westfall Act; 28 U.S.C § 2679(c,d)). In such a case, the Department of Justice essentially steps in and replaces the employee as defendant. Attorney General Barr of the United States claimed he could use the Westfall Act to protect then-President Trump from a lawsuit related to his alleged sexual assault of a woman before becoming President, so you know the Dept. of Justice can stretch the Act pretty far when they want to!

More about hazard trees on forestpathology.org

  1. 1.
    Hackman AM. 1997. The discretionary function exception to the Federal Tort Claims Act: How much is enough? Campbell Law Review 19(2):411–446 <https://scholarship.law.campbell.edu/clr/vol19/iss2/6/>.