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