Tree Protection During Construction: Study Guide

You can kill a 100-year-old oak in 15 minutes with a bulldozer. The damage (compaction/root severing) often doesn't show up for 3-5 years, which the ISA calls the "Mortality Spiral."

The Critical Zones

1. Critical Root Zone (CRZ): The absolute minimum volume of roots a tree needs to survive.
2. Tree Protection Zone (TPZ): The area you actually fence off.
   • The Rule of Thumb: 1 foot of radius for every 1 inch of DBH (Diameter at Breast Height).
   • Example: A 20-inch diameter tree needs a fence at a 20-foot radius (40-foot diameter circle).

Types of construction Damage

1. Root Severing: Digging trenches for utilities.
   • Mitigation: Tunneling / Boring under the roots instead of trenching through them.
2. Soil Compaction: Heavy machinery crushing macropores.
   • Mitigation: Use thick mulch (6-12 inches) or steel plates/plywood where machines must drive.
3. Grade Changes:
   • Fill (Adding Soil): Suffocates roots. (Fix: Aeration systems / Tree wells).
   • Cut (Removing Soil): Removes roots. (Fix: Retaining walls).

The Process

1. Inventory: What trees are worth saving? (Don't save a dying tree).
2. Plan: Draw the TPZ on the site map.
3. Fencing: Install before any machinery arrives. It must be fixed (chain link), not easy to move (snow fence).
4. Monitor: The arborist must visit the site regularly to ensure the fence hasn't been moved.

Summary

The best protection is a fence. If you can keep the machines away from the roots, the tree will survive.