10.4 Tree Analysis and Obvious Defects

Inspecting the Tree from Roots to Crown

Tree analysis focuses on the tree itself. Within the assigned assessment level, the arborist observes roots, root collar, trunk, scaffold branches, crown, foliage, deadwood, and signs of decay or stress. The exam asks which defect is most concerning, what should be inspected next, or what recommendation fits a finding.

Obvious defects are conditions that can be seen or reasonably detected during the assessment: dead branches, hanging broken limbs, cracks, splits, cavities, decay indicators, weak unions, included bark, cankers, root-plate movement, severed roots, girdling roots, basal wounds, and fungal fruiting bodies. The presence of a defect is only the beginning. Its significance depends on size, location, target, load, species response, and extent.

Reading Decay: the Strength-Loss Idea

The exam expects awareness that wood loss to decay or a cavity reduces strength, and that a useful rule of thumb in the literature is the ratio of remaining sound wood shell thickness (t) to stem radius (R). A widely cited guideline flags concern when the sound shell is thin relative to radius — often when t/R falls below roughly one third, or when an open cavity removes a large arc of the cross-section — but the BMP stresses that this is a screening cue, not a verdict.

Species, load, lean, taper, and the presence of an open versus closed cavity all modify the conclusion, and confirming internal extent usually requires advanced assessment such as resistance drilling or sonic tomography.

Crown and Root Collar Cautions

Crown condition gives clues but not the whole story. Sparse foliage, dieback, small leaves, or epicormic sprouts may reflect root stress, drought, pests, disease, or age. Critically, a full green crown does not prove structural soundness — a tree can carry healthy leaves while hiding a stem crack, a weak union, or a compromised root plate.

The root collar deserves deliberate attention because soil or mulch piled against the trunk can hide decay, wounds, girdling roots, or buried flare. Fungal fruiting bodies on the buttress roots or lower trunk can indicate active decay; species and location of the fungus matter. The exam does not demand laboratory certainty — it demands that you recognize basal decay indicators as important and potentially grounds for further assessment or mitigation.

Defect Interpretation Questions

1. What part of the tree contains the defect?
2. Is the defect active, recent, expanding, or long-standing?
3. How large is the defective part and what load does it carry?
4. What target is within striking distance, and at what occupancy?
5. Does the current assessment level provide enough information?
6. What action reduces risk without exceeding the arborist's scope?

Scenario: A co-dominant stem shows included bark with a crack extending below the union, directly over a driveway. The concern is not merely imperfect form. Crack plus weak union plus load plus target raises the likelihood of failure and the consequences together. Reasonable recommendations include restricting access, reducing end-weight where appropriate, evaluating a support system, advanced assessment, or whole-tree removal when findings justify it.

Scenario: A trunk cavity appears on an old tree in a rare-occupancy corner of a property. The correct answer is neither automatic panic nor automatic dismissal. Weigh the cavity size, remaining sound wood, species' compartmentalization, targets, occupancy, and whether advanced assessment is needed, then match the recommendation to the actual risk.

Weak Unions, Cracks, and Deadwood in Detail

Included bark forms when bark is trapped between two stems or a stem and a branch as they grow, preventing the strong wood-to-wood connection of a normal branch collar. The result is a union that can split under wind, ice, or its own end-weight, and the risk climbs with branch size, the steepness of the union angle, and the length of the lever arm beyond it. A co-dominant pair with included bark over a target is a common high-stakes exam item.

Cracks demand attention to direction and behavior. A vertical crack aligned with the grain on a sound stem differs from a crack that spirals, opens and closes as the limb moves, or extends from a union or wound into the stem. Two cracks on opposite sides of a stem can signal an internal shear plane and a much higher failure likelihood than either crack alone. Deadwood is graded by size and height: a large dead scaffold over a frequent-occupancy entrance is urgent, whereas scattered fine twigs over a rare-occupancy area are routine. Note also that deadwood retains hazard even on an otherwise vigorous, healthy-looking tree.

Finally, weigh the target and load together with the defect. The same six-inch dead limb is a low concern reaching over an unused fence line and a high concern reaching directly over a doorway, because the consequence and likelihood of impact differ even though the defect is identical. For study, avoid defect-flashcard thinking. A crack is not always the same risk and a cavity is not always the same outcome. Exam success comes from linking defect, load, target, consequence, and scope into one defensible likelihood judgment rather than reacting to the defect label by itself.