Tree Risk Library

Tree failure is rarely random. Most incidents are the result of identifiable structural weaknesses, environmental conditions, or long-term stress that go unnoticed until a storm, soil shift, or load change exposes the problem.

This library explains how and why trees fail, what warning signs matter, and when professional evaluation is recommended. The goal is not alarm, but clarity—so property owners can understand risk before damage occurs.

How Tree Risk Is Evaluated

Tree risk is determined by evaluating three factors:

Probability of failure
Size and severity of potential failure
What the tree could impact if it fails

A tree does not need to be dead to be hazardous. Structural defects, root instability, and site conditions often play a larger role than visual appearance alone.

Common Tree Failure Scenarios

Hidden Structural Defects

Internal decay and hollow trunks
Codominant stems and weak unions
Cracks, seams, and embedded bark

These defects often progress internally and may not be visible without professional assessment.

Root System Failure

Soil saturation after heavy rain
Root damage from construction or trenching
Compacted or unstable soil conditions

Root failure is a leading cause of whole-tree collapse, especially during storms.

Storm and Weather-Related Failure

Wind loading and canopy imbalance
Lightning strikes
Sudden environmental stress

Healthy trees can still fail when environmental forces exceed structural limits.

Proximity and Impact Risk

Trees within falling distance of homes
Overhang above driveways or walkways
Trees near neighboring properties

Risk increases significantly when failure could impact people, structures, or utilities.

Warning Signs Homeowners Should Not Ignore

Sudden or increasing lean
Soil heaving or cracking near the base
Exposed or severed roots
Large dead limbs in the upper canopy
Previous improper pruning or topping
Repeated limb failures

These indicators suggest instability and warrant professional evaluation.

Why Visual Appearance Is Misleading

Leaf density, bark condition, and growth do not reliably indicate structural safety. Many trees maintain normal growth while internal defects progress unnoticed. Arborists assess load distribution, defect severity, species characteristics, and site conditions—not just surface appearance.

When a Professional Tree Risk Assessment Is Recommended

A professional assessment is recommended when:

Trees are close to homes or occupied areas
Property damage or liability is a concern
Storms or construction have altered site conditions
Conflicting opinions exist about trimming versus removal

Written evaluations can also be important for insurance documentation, HOA compliance, and long-term planning.

Using This Library

This library is designed to help property owners understand how arborists evaluate tree risk and why certain trees require closer attention than others. Each topic focuses on education, not sales, and is intended to support informed decision-making.

Information provided for educational purposes. On-site evaluation by a certified arborist is required to assess individual trees.