Dead Limbs and Root Plate Heave Are the Two Watch Signs That Demand An Arborist
Claim: Of all the visible signs that a tree is hazardous, dead limbs over a target (structure, vehicle, walkway) and root plate heave are the two that indicate failure is coming rather than possible. Seeing either of these signs is the trigger to call an ISA-TRAQ arborist immediately — not at the next scheduled inspection.
Mechanism
Trees fail in two distinct ways, and each has one dominant pre-failure sign that a non-specialist can see:
Path 1 — Root plate failure (the whole tree falls) The root plate is the disc of roots, soil, and mycorrhizal mat that anchors the tree against wind and gravity. When it is compromised — by root decay from fungi, by severed major roots from nearby excavation, or by saturation from BC’s wet winters — the anchor loosens before it fails completely. The visible sign is root plate heave: soil lifting, cracking, or displaced in an arc around the base of the tree; roots that used to be buried now exposed; the tree’s lean angle increasing over a season. A new lean on a previously straight tree is the same signal.
Root plate failure is the catastrophic failure mode — the whole tree falls, often at night, often during a storm, with little additional warning. It is the failure most likely to reach a structure.
Path 2 — Structural union failure or dead limb drop (a major branch falls) Dead wood loses the living wood’s ability to flex and absorb wind energy. It becomes brittle. A dead limb larger than about 10 cm in diameter over a structure or walkway is a falling-object risk. The other path is included bark: where two stems grow in a V-shape (rather than a U-shape), bark is trapped at the junction rather than the wood fusing. The bond is mechanical, not structural, and it fails cleanly under ice or snow load.
Fungal conks (shelf-like, bracket-shaped growths on the trunk or at the base) are a warning for either path. The fruiting body is the visible tip; the mycelium is already throughout the wood, actively decomposing it. A conk at the base of a large tree combined with any lean or root heave is a multi-indicator emergency — call an arborist the same day.
The two-level inspection protocol
Owner-level (what you can see from the ground during the seasonal walkover):
- Dead or brown sections in the crown (no leaves, dry grey bark)
- Hanging limbs still connected but at an angle
- Fungal conks or shelf growths anywhere on the trunk or base
- Soil heaving or cracking within 1–2 metres of the trunk base
- V-crotches visible in major stems
- Lean that has visibly changed since the last photo
Arborist-level (what requires a TRAQ assessment — owner cannot diagnose):
- Internal decay extent (resistograph or sonic tomography)
- Root plate integrity below grade
- Cabling or bracing recommendations
- Quantified risk rating (low / moderate / high / extreme) per the ISA TRAQ methodology
Scope
Applies to mature trees near targets — any tree within one-to-two tree-lengths of the house, a parked vehicle, a walkway, or a neighbouring structure.
Does NOT apply to:
- Trees in open space away from any target — a falling tree that hits only ground is a low-consequence event even if the failure likelihood is high
- Young trees (under ~5 m) — structural failure risk is much lower; focus is on establishment
Idea Compass
North: Where this comes from
- trees (Home Systems) — parent component note
- ISA TRAQ (Tree Risk Assessment Qualification) methodology — the industry-standard two-axis risk framework: failure likelihood × consequence of failure
East: Tensions / failure
- The failure mode of the inspection: most dead limbs are NOT over a target, and most leaning trees have been leaning for decades. The skill is distinguishing “been this way for 20 years” (monitor) from “new since last October” (act now). The photo-comparison protocol over years is the key tool.
- Liability: if a hazard sign was visible and no action was taken, an owner may be found liable for damage from a subsequent failure
South: Where this leads
- When-To-Hire-An-ISA-Arborist-vs-A-Tree-Service-In-Metro-Vancouver (Home Systems) — the arborist credential required for the follow-up assessment
- Tree-Permit-Trap — Metro Vancouver Bylaws Protect Trees You Can See From the Street (Home Systems) — once the arborist recommends removal, the permit process starts here
- insurance-warranties (Home Systems) — arborist documentation is the liability defence
West: What’s similar
- electrical-panel (Home Systems) — burning smell at the panel is the equivalent “call a pro today” sign; both are sensory/visible signs of imminent failure where delay has catastrophic downside
- The T&P valve test on a water heater — water-heater (Home Systems) — same logic: a simple owner inspection identifies a specific signal that triggers a pro