Intro

Most tree failures don't happen without warning. The branch that comes down in a windstorm, the tree that splits during a Santa Ana event, the root system that buckles a sidewalk — these events almost always have precursors. Signs that were there weeks, months, or sometimes years before the failure occurred.

This post is a practical guide to the warning signs of a hazardous tree — what to look for, what it might mean, and when to call a certified arborist.

Why This Matters for Property Managers & HOA Boards

In commercial, municipal, and HOA settings the legal standard for tree-related liability is whether the property owner knew or should have known about a hazardous condition and failed to act. Visible warning signs on a tree create a duty to investigate. You don't need to diagnose disease or calculate failure loads — you need to recognize the signals that say "this tree needs a professional assessment" and act on them promptly.

Above the Ground: Canopy & Branch Warning Signs

Dead or Dying Branches

Dead wood loses the flexibility of living wood — becoming brittle and unpredictable under wind load or rain. A large dead branch above a walkway, parking area, or structure is a liability event waiting to happen.

Look for: Branches with no leaves during growing season, peeling or missing bark, hanging or partially attached branches.

Cracks and Splits in Major Branches or the Main Trunk

A visible crack in a major branch or the main trunk means structural integrity has already been compromised. Cracks where two major branches meet — called included bark — are particularly dangerous and have a high probability of failure under load.

Look for: Visible cracks along major branches, cracks at branch-to-trunk attachment points, any crack that appears to have grown or widened recently.

Unusual Lean

A lean that has developed or accelerated recently — particularly toward a structure or high-traffic area — warrants immediate professional assessment. It can indicate root failure, soil instability, or structural imbalance.

Look for: A lean that has noticeably changed over a season, soil heaving on the opposite side of the lean, any tree leaning after a significant wind event.

Trunk Warning Signs

Cavities and Hollow Sections A cavity is a visible sign of internal decay. The visible opening is often smaller than the internal hollow it represents — a six-inch entrance can conceal three feet of internal decay. Visible cavities always warrant professional assessment.

Look for: Any opening or hollow section in the trunk, soft or discolored wood inside the cavity, woodpecker activity which often indicates internal pest activity.

Fungal Growth at the Base

Fungal fruiting bodies at ground level almost always indicate advanced decay in the root system or lower trunk — decay that has been progressing for years before becoming visible. This is one of the most serious warning signs on this list.

Look for: Mushrooms growing from soil near the root flare, shelf-like conks attached to the lower trunk, any recurring fungal growth in the same location.

Unusual Bark Conditions

Abnormal bark conditions can indicate disease, pest activity, or physical damage requiring closer examination.

Look for: Sunken or discolored areas called cankers, small round exit holes indicating wood-boring beetle activity, oozing sap from the bark surface, bark that sounds hollow when tapped.

Root Zone Warning Signs

Root problems are the most dangerous category of tree hazard because they're the least visible. A tree with a severely compromised root system can maintain a full healthy canopy right up until the moment it fails.

Look for:

• Soil heaving or cracking near the base — may indicate the root system is failing and the tree is beginning to tip

• Damaged or cut surface roots from construction activity or vehicle traffic

• Girdling roots — roots growing in a circular pattern around the trunk that compress and weaken the base over time

• Recent construction activity within the canopy drip line — soil compaction alone can significantly compromise root function

When to Call a Certified Arborist

Call immediately:

• Visible crack or split in a major branch or trunk

• Fungal growth at the base of the trunk

• Sudden or significant lean toward a structure

• Hanging or partially attached branch over an occupied area

• Any storm damage

Schedule within 30 days:

• Dead branches in the upper canopy

• Any cavity or hollow section in the trunk

• Unusual bark conditions

• Soil heaving near the root flare

• Trees in high-traffic areas not assessed in over two years

The Cost of Waiting

A professional tree risk assessment costs far less than the first hour of cleanup after a tree failure — and significantly less than the legal defense in a liability case. The warning signs in this post are visible to anyone walking a property with this knowledge. The barrier between knowing these signs and acting on them is simply the decision to take tree hazard seriously before something forces that decision for you.