3 Common Tree Risks

Most homeowners don’t think about tree risk until something goes wrong. A branch comes down on a fence, a storm drops a limb on a car, or — in the worst cases — a tree fails entirely and causes serious damage or injury. The frustrating truth is that most tree failures are predictable and preventable. The signs are visible well in advance, if you know what to look for.

Here are three of the most common tree risks on residential properties in the Treasure Valley, and what to do about each.

Risk #1: Dead Branches

Dead branches are the most common tree hazard and the most straightforward to address. A branch dies for any number of reasons — shading out by the upper crown, disease, pest damage, drought stress, physical injury — but once it’s dead, its behavior becomes predictable: it will eventually fall.

Dead wood loses moisture and flexibility over time. It becomes brittle and unpredictable. Unlike a healthy branch, which bends and flexes under wind load and distributes stress along its length, a dead branch can snap suddenly, often without the warning that flexing provides. Ice loading in winter is particularly problematic — a dead branch may carry ice weight until it suddenly fails.

What to look for:

• Branches with no leaves during the growing season (or dead leaves that haven’t fallen)
• Peeling or missing bark on branches
• Fungal growth (mushrooms or conks) on branch surfaces
• Branches that feel hollow or sound hollow when tapped

What to do: Have dead branches removed promptly, starting with those positioned over structures, vehicles, walkways, or areas where people spend time. Prioritize size — a 2-inch dead branch falling from 40 feet is a different risk than a 6-inch branch from the same height.

Risk #2: Root Damage

Root problems are the most invisible — and in some ways the most dangerous — of the common tree risks. Roots are out of sight, and root damage rarely produces obvious above-ground symptoms until it’s quite advanced.

Root damage in urban settings has many causes:

Construction and soil compaction are among the most significant. When soil is compacted by heavy equipment, root growth is restricted and gas exchange in the soil is reduced. Trees commonly decline and die in the years following nearby construction, even when their above-ground portions weren’t directly affected.

Grade changes — adding or removing soil around a tree — can be fatal. Even a few inches of added soil over the root zone changes the oxygen and moisture dynamics in ways that kill fine roots. Removing soil can directly sever roots.

Girdling roots occur when roots grow in a circular pattern around the trunk base, eventually constricting the vascular tissue. Trees with girdling roots may look fine for years before suddenly declining or failing at the root crown.

Trenching for utilities, irrigation, or fencing frequently severs large structural roots without anyone considering the consequences for the tree.

What to look for:

• Lean that has developed or worsened over time
• Soil mounding or cracking at the base of the tree
• Exposed root flare on one side, buried on another
• Dieback in the crown above damaged roots
• Mushroom/conk growth at or near the base of the trunk

What to do: If you suspect root damage, have an ISA-certified arborist assess the tree. Soil decompaction, root collar excavation, and careful structural evaluation can help determine the extent of the problem and whether the tree is safe to retain.

Risk #3: Structural Defects

Structural defects are weaknesses in the tree’s architecture that reduce its ability to handle stress loads from wind, ice, or its own weight. Unlike dead branches (which will fall eventually regardless of conditions) or root damage (which affects the tree’s anchor), structural defects in the crown create specific failure points where the tree can split or break under loading.

The most common structural defects include:

Codominant stems with included bark — Two or more stems of similar size competing for dominance, with bark compressed between them at the union. This creates a weak seam that’s prone to splitting. (See our separate article on codominant stems for a full discussion.)

Cracks and splits — Cracks in the trunk or major branches indicate internal stress and often reveal decay. A crack that runs the length of a branch or through the trunk is a serious warning sign.

Decay cavities — Hollows in the trunk or major branches indicate decay. Some level of decay can be tolerated in large, otherwise healthy trees, but extensive decay significantly reduces the tree’s load-bearing capacity.

Cankers — Dead areas in the bark caused by fungal or bacterial infection. Cankers disrupt the vascular system and can structurally weaken branches or trunk sections.

Overextended limbs — Very long, heavy branches with most of their weight concentrated at the end create enormous leverage at their attachment point. A classic example is a large horizontal branch that has grown out far from the trunk, heavily leafed out, over a structure.

What to do: Structural defects should be evaluated by a TRAQ-certified arborist (Tree Risk Assessment Qualification) who can formally assess the likelihood of failure, the consequence if failure occurs, and appropriate mitigation measures — which may include pruning, cabling, or removal.

The Value of Proactive Evaluation

None of these risks require you to become a tree expert. What they do require is knowing that risks exist and getting qualified eyes on your significant trees periodically. An arborist evaluation every 3–5 years for mature trees — or any time you notice a change in a tree — is the most cost-effective form of tree risk management available to homeowners.

The cost of a professional evaluation is a small fraction of the cost of emergency storm damage remediation, insurance claims, or liability resulting from a preventable tree failure.