Tree Protection During Construction

Why this matters

Construction is the leading cause of mature tree death in residential and commercial development. The damage doesn't appear immediately; trees typically show stress symptoms 2-5 years after the construction disturbance and may die within 5-10 years. The damage is preventable with proper Tree Protection Zone (TPZ) management during construction. A tree service company that consults on construction projects becomes a critical part of the project team - and often saves the customer's mature trees (which represent significant property value).

Why construction damages trees

The damage occurs primarily underground:

1. Root system compression: equipment driving over the root zone
2. Root system severance: trenching, foundation excavation
3. Soil compaction: pedestrian and vehicle traffic
4. Soil grade changes: filling or cutting around the trunk
5. Soil contamination: oil, fuel, concrete washout
6. Mechanical trunk damage: equipment contact
7. Canopy damage: branches broken by equipment

The customer may not see the damage; the tree's stress reveals over years.

The Tree Protection Zone (TPZ)

The TPZ is the area around the tree that must be protected:

A common rule: 1 foot of TPZ radius for every inch of trunk diameter. Larger trees + valuable specimens get larger TPZs.

The TPZ should be:

1. Marked physically (fencing, ribbon)
2. Communicated to all contractors
3. Monitored throughout construction
4. Treated as exclusion zone (no traffic, no storage, no work)

TPZ marking

Physical marking options:

The fencing should be:

• 4+ feet tall (visible to equipment operators)
• Bright color (orange standard)
• Maintained throughout the project
• Repaired if damaged

Allowed activities within TPZ

What can be done within the TPZ:

• Walking
• Light hand tools (shovel, rake)
• Brief equipment passes (foot traffic level)
• Approved work with arborist supervision

Forbidden:

• Heavy equipment (trucks, excavators, lifts)
• Equipment storage
• Material storage
• Soil grade changes
• Trenching
• Concrete washout
• Pesticide / petroleum spills
• Excessive foot traffic

Pre-construction inventory

Before the project starts, document:

1. Each significant tree (location, species, size, condition)
2. Each tree's TPZ boundary
3. Photo documentation of each tree
4. Site map with TPZs marked
5. Construction plan overlay showing proximity

This baseline is the reference point if disputes arise.

Working within the TPZ when unavoidable

Some construction REQUIRES work within the TPZ:

Each mitigation has cost; the value of the tree must justify.

Root pruning

When roots MUST be cut:

1. Clean cuts only: sharp tools; smooth cut surface
2. Identify the root: hand-dig if uncertain
3. Cut beyond the major buttress roots: don't cut the major structural roots
4. Treat the cut: paint with wound sealant (rare in modern practice; usually just clean cut)
5. Water + fertilize the tree: support recovery
6. Monitor for 2-3 years: declining tree indicates the damage was severe

Specific procedures per ISA Best Management Practices for Root Protection.

Grade changes

Soil grade changes (filling or cutting):

Adding soil: smothers the root zone

• 2-4 inches: typically tolerated by most species
• 4-12 inches: significant risk; species-dependent
• Over 12 inches: high risk; tree well or other mitigation required

Cutting soil: exposes roots

• 6-12 inches removed: stress; recovery possible
• 12-24 inches: severe stress
• More: usually fatal

For unavoidable grade changes:

• Tree well: retaining wall around the trunk maintains original grade locally
• Slope away from the trunk: gradual transition to new grade
• Permeable cover: maintains some root function

Pre-emptive pruning

Before construction:

• Remove dead and damaged branches
• Light reduction pruning to reduce wind load (trees already stressed)
• Branches likely to be damaged by equipment

This pre-emptive work reduces post-construction failure.

Post-construction care

After construction is complete:

1. Watering: provide regular irrigation for the first 2-3 years
2. Mulch: add quality mulch around the trunk (NOT volcano-mulched)
3. Fertilizer: balanced fertilizer to support recovery
4. Soil treatment: address any compaction (radial trenching with high-pressure air for advanced cases)
5. Monitoring: annual inspection for stress signs

Recognizing stress

Signs that construction-damaged trees are declining:

1. Crown thinning: progressive over years
2. Leaf drop earlier than normal: stress response
3. Slow regrowth in spring
4. Branch dieback: top-down progression
5. Epicormic shoots: vigorous shoots from the trunk
6. Decreased leaf size
7. Insect / disease activity: stressed trees more susceptible

If multiple signs appear over 2-5 years, the tree is likely failing. Decision to remove vs. attempt rescue depends on the specific situation.

Documentation for the project

For each tree near construction:

1. Pre-construction condition (photo + assessment)
2. TPZ boundary (mapped)
3. Approved variations from TPZ
4. Post-construction inspection
5. Annual monitoring photos
6. Customer file note

Working with the project team

Roles in construction tree protection:

References

• ISA Best Management Practices for Tree Protection in Construction
• ANSI A300 (Part 5) - Management of Trees and Shrubs in Construction Sites
• ANSI Z133 (Safety Requirements)
• IBC + IRC (building codes; tree protection sometimes referenced)
• Local tree preservation ordinances
• Manuall internal: Tree Risk Assessment, Declining Tree Diagnosis, Tree Pruning Service