keeping trees alive in the urban...

Trees and Construction

Jennifer Hitchcock

Keeping Trees Alive in the Urban Forest

Illinois Chapter ISA

Chapter 13

Trees and Construction

Outline:

How are trees damaged during construction

Benefits of saving trees

Function and location of tree roots

The tree protection zone

Tree assessment

Construction impacts to trees

Tree protection techniques

Introduction

Wooded lots or lots with mature trees bring added value to the new home.

It is imperative that a professional/certified Arborist get

involved in the planning/design stage, not after the construction starts.

Construction damage is one of the most common causes

of tree death and decline in urban areas. If trees are damaged most often the tree will not show

symptoms of decline until 3-5 years later.

Damage During Construction

Injury to crown & trunk

Cutting of Roots

Compaction

Smothering of Roots

Exposure to Elements

Damage During Construction

1. Injury to crown & trunk

*Breaking branches

* Damaging the trunks of the tree

Damage During Construction

2. Cutting of Roots Severing of one major root can cause 15-25% loss of root

system CASUES OF INJURY 1. Digging/Trenching 2. Lowering Grade Depending on how many anchoring roots have been cut and the proximity of the cut to the trunk of the tree, there is a

possible hazard potential of tree becoming unstable and falling over.

Trees and Construction

Root damage

Damage During Construction

3. Compaction

Soil compaction reduces the pore space resulting in the reduction of oxygen and accumulation of carbon dioxide and other gases.

Root growth may be diminished.

The ability for the root to absorb water and minerals is decreased.

Water infiltration and movement into the soil is reduced.

Roots ability to grow into the soil is also reduced.

Damage During Construction

4. Smothering of Roots

90% of the fine roots are in the upper few inches of

soil.

Piling soil on the root system smothers roots

Raising the grade smothers the roots in addition to altering the drainage pattern!

Sensitive trees such as oaks cannot withstand the added 2-3” of soil.

Damage During Construction

5. Exposure to Elements

Groupings of trees – removing the outer trees in turn changes the inner trees ecosystem. They are now exposed to wind and direct sunlight.

This can cause breakage and sunscald.

NOTE:

Roots that are exposed in a trench must be covered or will dry out.

Benefits of Saving Trees

Energy savings

Social

Environmental

Economic

Homebuyers will pay more for homes with trees.

Benefits of Saving Trees

Residential Site Features That Increase Market Value

Adjacent streams and ponds 5 to 125%

Natural landscaping 5 to 15%

Views of open space Up to 100%

Saving trees 5 to 25%

Increased Market Value

Decreased Costs

Golf Course & County Club Development

Plan for Tree Protection

Developer

Builders

Certified arborist/ urban forester

Natural resource expert

Civil engineers

Utility engineers

Architect

Landscape architect

Contractors

General

Grading

Landscape

Irrigation

City/county planner

A development team should include:

Tree Protection Plan Example

Elementary School Development

Tree Roots: Activity

Where are tree roots?

Tree Roots: Fact or Fiction?

Do most trees have taproots?

Can roots be as deep as the tree is tall?

Some trees have deep roots close to the trunk, but most

tree roots are concentrated in the upper foot of soil.

Tree Roots: Fact or Fiction?

Do a tree's roots extend only as far as the branches?

Roots can extend up to three times the dripline of the tree.

Tree Roots: Fact or Fiction?

Do tree roots need oxygen to survive?

Tree roots grow best where there is plenty of oxygen, water, and nutrients.

Tree Roots: Fact or Fiction?

Does a tree's entire root system absorb

water and nutrients?

Small diameter roots absorb the most water and nutrients.

Planning & Preservation

The arborist should get involved early in the planning stage:

** Development should occur with doing the least amount of damage to the preserved trees.

1. They can decide what trees should be saved and/or removed.

2. They can provide recommendations on location of structures and utilities

3. They can provide recommendations on auguring vs. trenching.

4. They can provide information on the pre-construction, during construction and post construction care the trees will need.

Communication

Arborists must learn to work with engineers, developers, planners, builders and home owners.

Understand the standards and specifications required of development as it applies to trees on the site.

The Arborists needs to be able to explain and show why and how construction can damage trees!

Be able to document problems and concerns that arise and address them to the appropriate people.

Tree Protection Specifications

The tree preservation plan is a road map to identify the requirements and specifications of tree preservation. The following must be included in the specifications to help ensure the plans success. Tree fence Root pruning Crown pruning Tunneling Details on how structures will be built: Brick vs.

concrete Bridging

The Tree Protection Zone: Dripline Method

Dripline distance × 1.5 = protection zone radius

Dripline distance = protection zone radius

The Tree Protection Zone: Dripline Method

Dripline distance × 1.5 = protection zone radius

Dripline distance = protection zone radius

The Tree Protection Zone: Dripline Method

Dripline distance × 1.5 = protection zone radius

Dripline distance = protection zone radius

The Tree Protection Zone: Trunk Diameter Method

Trunk diameter measured in inches at 54" above soil line × 1 ½ ft per inch = protection zone radius

54"

Which Trees Should Be Saved?

Can big trees be saved?

Big trees can be saved only with appropriate practices.

Tree Assessment

Species

Size

Location

Health

Indicators of Health

Structure

Crown

Age/maturity

Past damage or improper pruning

Insects or diseases

Which Oak Would You Save?

A B

Structural Problems Codominant Stems

A B

Other Structural Problems

Included bark

Trunk openings/decay

Leaning trees

Crown Problems

Crown ratio End weight Dieback

Age and Maturity

Past Damage or Improper Pruning

Broken branch Old wound Topped

Insects or Diseases

Wood-rotting fungi Canker Wood-boring insects

Tree Assessment

Species

Size

Location

Health

Individual

trees

Individual Trees

Were These Trees Worth Saving?

Were These Trees Worth Saving?

To Minimize Damage When Saving Individual Trees

Pre and post construction treatments

Tree Assessment

Species

Size

Location

Health

Individual trees

Groups of trees

Groups of Trees

To Minimize Damage When Saving Groups of Trees

Keep natural areas undisturbed

Leave the understory beneath the canopy

Avoiding Tree Damage During Construction

1. Barriers – Tree fence – the single most important action before construction begins.

Place to drip line of tree or 1’ from trunk for each tree diameter.

Nothing happens within fenced area.

2. Limiting Access

Allow 1 access point for all construction equipment

Define limits of storage

Avoiding Tree Damage During Construction

3. Reducing Compaction

If access is within the drip line, installing a 6-12” layer of mulch over the critical zone will disperse the weight of trucks. In addition to this, plywood can be placed on top of the chips.

Avoiding Tree Damage During Construction

4. Changes in Grade How much root system will be disturbed? Type of species Degree the grade will be changed Soil conditions Surface to be used A. Lowering Grade can be accomplished by: • Terracing in steps • Tree islands Must severe roots cleanly and keep them moist

Avoiding Tree Damage During Construction

B. Raising Grade

Aeration systems and Tree wells

If to be affective must be installed correctly using the appropriate materials and taking into consideration the species of tree affected.

Construction Impacts

Clearing

Compaction

Grading

Soil fills

Pavement installation

Utilities installation

Excavation

Dumping

Spilling

Storage

Water changes

Above ground injury

Construction Impacts: Fact or Fiction?

Is construction damage to trees easily seen?

Damage to trees is more often hidden than seen.

Construction Impacts: Clearing

To Minimize Damage by Clearing

Have tree protection in place before clearing begins

Hand clear trees with chain saw

Leave understory vegetation under trees

Use specialized equipment

Construction Impacts: Compaction

Will parking equipment under a tree affect its survival?

Elephant (50 psi) 2-ton Truck (20 psi) based on 48 sq in per tire

Average person (10 psi) Bulldozer (10 psi)

Most compaction occurs during the first pass of equipment.

Construction Impacts: Compaction

To Minimize Damage by Compaction

12” of mulch in equipment path

Steel plates over mulch

Traffic routes

Construction Impacts: Grading

Does lowering the grade on a site harm tree roots?

Removing as little as 2 inches of soil removes many important roots.

Construction Impacts: Lowering the Grade

Construction Impacts: Grading

Will adding 2 inches of soil over the roots harm a tree?

Adding even small amounts of soil can suffocate roots by cutting off oxygen and water.

Construction Impacts: Raising the Grade

Construction Impacts: Grading

Will building a "tree well" help save a tree from the effects of raising the grade?

A tree well is no guarantee of tree survival.

To Minimize Damage by Grading

Appropriate site design

Maintain grade as far as possible

Root prune at edge of excavation

Channel water away from trees

Add coarsely textured fill

Construction Impacts: Installation of Utilities

To Minimize Damage From Installation of Utilities

Consolidation of utilities

Alter the route

Tunneling/boring

Trench only one side of a tree

Trench work location

Keep root ends moist

Construction Impacts: Pavement Installation

To Minimize Damage From Pavement Installation

Adjust finished grades/utilize natural grades

Select paving that requires the least excavation

Minimize cuts

Use extra reinforcement in concrete

Pervious pavers

Construction Impacts: Excavation

To Minimize Damage From Excavation

Use a stem wall foundation

Reinforce the slab

Thicken the edge of the slab

Avoid continuous footings next to trees

Use pier foundations with grade beams above grade

Excavate by hand

Other Construction Impacts

Dumping

Spilling

Storage

Water changes

To Minimize Damage From Other Construction Impacts

Set specific areas for storage and disposal

Use plastic to prevent spills

Clean up spills immediately

Use pesticides according to the label

Channel water away from trees

Use grass swales

Construction Impacts: Above Ground Injuries

Wounds Improper pruning

To Minimize Damage From Above Ground Injuries

Prune before construction

Fence trees

Prune broken or torn limbs to form clean cuts

Cut away dead or injured bark

Construction Impacts: Fact or Fiction?

If a tree survives construction, will it live?

Trees may die suddenly after construction ends or…

…trees may show a slow decline over a period of years.

Punchlist for Tree Survival

Hire a certified arborist early in the process.

Punchlist for Tree Survival

Inventory trees and select which to save.

Punchlist for Tree Survival

Protect the trees you plan to save.

Punchlist for Tree Survival

Do not allow construction activities in the root protection zone.

Punchlist for Tree Survival

Communicate the tree protection plan.

Punchlist for Tree Survival

Plan for accountability.

Punchlist for Tree Survival

Fines and Penalties for violations

*This can include penalties on a per day basis. *When stop work orders will be issued.

The Arborist should visit the site daily.

A plan should be posted at the site for all to see.

Treatment of Damaged Trees

Use all the tools at your disposal Pruning of broken branches Cabling and Bracing Repairing Damaged Bark/Trunk (bark tracing) Irrigation and Drainage – decide what

measures need to be taken to elevate the problem Mulching

Treatment of Damaged Trees

Aeration of the root zone due to compaction and

increase in grade.

Drilling holes/vertical mulching

2-4” diameter, 1-3’ on center throughout the root zone of the tree. Depth 12” filled with organic material.

Radial Trenching

Trenches are dug in radial pattern throughout root zone

(spokes of a wheel). Begin 4-8’ from trunk of tree.

Treatment of Damaged Trees

Fertilization – Not the first year

Monitoring for Decline and Hazards