9.5 Mitigation During Construction

Matching Mitigation to the Damage Pathway

Mitigation is not one treatment applied to every construction site. It is a targeted response to a predicted impact. If roots may be cut, the arborist considers route changes, boring, root-sensitive excavation, clean root pruning when appropriate, and inspection. If soil may be compacted, the response is exclusion first, then ground protection where limited access is unavoidable. If grade may change, the response is preserving original grade near the tree or designing transitions that do not bury the root collar.

Avoidance is usually the best mitigation. Moving a trench outside the protection zone is better than repairing cut roots. Keeping heavy equipment away from rooting soil is better than trying to restore compacted soil later. Still, real projects have constraints. The exam may ask what to recommend when conflict remains. The answer should reduce injury while staying practical.

Root-sensitive excavation may include hand tools or pneumatic excavation where appropriate. The point is to expose roots without tearing them blindly. If roots must be cut, cuts should be clean and evaluated by size and location. Large structural roots near the trunk are not equivalent to small absorbing roots farther away. The arborist should be present for critical operations when root decisions affect preservation success.

Ground protection can include mulch layers, mats, plates, or other load-spreading systems based on site needs. It should be installed before traffic begins and removed when no longer needed. It is a controlled exception, not permission for unlimited use. The traffic route, vehicle type, duration, soil moisture, and inspection frequency matter.

Water management is also mitigation. Construction can interrupt irrigation, compact soil so water runs off, expose roots to drying, or change drainage. Watering should be based on soil moisture and tree need, not a calendar alone. Overwatering compacted or poorly drained soil can worsen oxygen stress. Underwatering exposed roots can speed decline.

Field Response Steps for Root Encounters

1. Stop work in the immediate area long enough to assess the root.
2. Identify root size, location, condition, and likely function.
3. Keep exposed roots from drying while decisions are made.
4. Adjust excavation method or alignment if feasible.
5. Make clean cuts only when root pruning is necessary and appropriate.
6. Document what was found, what was done, and who approved the action.

Scenario: A contractor finds roots while excavating for a sign footing. Pulling the roots with a backhoe is a poor response because tearing increases wounds and removes more tissue than necessary. A better response is to pause, expose the area carefully, evaluate root size and location, and decide whether the footing can move or whether controlled root pruning is acceptable.

Scenario: A crane must cross near a preserved tree for one day. The arborist should not simply allow access because the duration is short. Soil moisture, equipment weight, path width, root location, and ground protection all matter. A defined route with load spreading and inspection may be acceptable when avoidance is impossible, but open traffic inside the protection zone is not.

For the exam, select mitigation that addresses the actual pathway of harm. Fertilizer does not repair torn structural roots. Mulch does not justify burying the trunk flare. Watering does not fix a severed root plate. The best answer controls the source of injury first, then supports recovery.