How to Protect Trees BEFORE Clearing Your Land: Step-by-Step

Having a plan to protect trees BEFORE you start clearing your land is ESSENTIAL!  By the time you’ve broken ground, it’s already too late.

If your excavation and building team don’t know how to protect trees properly, then you can pretty much kiss any trees close to the construction site goodbye.  

Even worse, you can assume that any tree with a Critical Root Zone that has been damaged or compacted will die slowly, sometimes over the course of several years.  Dropping heavy limbs as the tree’s health and stability fail.

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Putting your house at risk and creating an expensive and dangerous problem that could have been avoided.

​In this seventh post of the Regenerative Design series, I offer step-by-step instructions for developing a regenerative plan for protecting the trees on your property.  Of course, saving the trees will only work if you also save the soil…which will be discussed in our next blog.  

Image: North Carolina Urban Forest Council

What is the Critical Root Zone?

The Critical Root Zone (CRZ) is the area around the base of the tree where the essential root mass must remain intact and healthy if the tree is to survive.  The CRZ varies by tree species, age, location, and other growing conditions.  This makes it difficult to determine exactly how much area around your tree needs to remain untouched if the tree is to survive.

Techniques for calculating CRZ:
1. CRZ = Dripline

• For a healthy mature tree that has a typical growth pattern, the Critical Root Zone can be assumed to be equivalent to the dripline.  The dripline is the furthest extent that water would drip off the outer leaves of the tree’s canopy.  This assumption would NOT be correct for trees that are newly planted, stressed, leaning, or have a narrow crown.

2. CRZ = 1.5ft x DBH

• Perhaps a more accurate way to calculate CRZ is an area with a radius of 1.5 feet for every inch in trunk diameter at breast height (DBH).  DBH is the standard tree measurement used by professionals with breast height at 4.5ft.  This means you would measure the diameter of the tree at 4.5ft and multiply this by 1.5ft to determine the radius (not the diameter) of the Critical Root Zone for that tree.
• Ex. A tree with a DBH of 10 inches has a CRZ radius of 15 ft (10 x 1.5 ft).  Keep in mind, while the radius of the CRZ is 15ft, the diameter of the entire CRZ is 30 ft.

3. CRZ = What Your Arborist Tells You

• An arborist well-versed in tree protection (like our friends at Preservation Arborists in Asheville) will be able to tell you exactly what the CRZ needs to be depending on the unique variables of each tree.
• Hiring an arborist to work as a team with your home designer will be your best bet for saving the trees your home will be designed to take full advantage of.  ​

The time to call the arborist is before equipment arrives, before someone without tree knowledge or training assures you they will work around the tree and keep it safe, that "It'll be fine!" Take it from the story “How a Tree is Killed.” It’s not fine at all.”
– Chardin Detrich – Preservation Arborists of Asheville, NC

Learn the tangible benefits of saving trees HERE

What You NEED to Know About Roots

A common misconception is that roots mirror the tree’s crown underground.  This is false.  And can lead to gross miscalculations of where critical roots can be found once excavation has begun.

According to Colorado State University most tree roots are located in the top 6 to 24 inches of the soil and occupy an area two to four times the diameter of the tree crown.  

Roots grow where water, minerals, and oxygen are found in the soil.  Because oxygen is usually located in the upper surface layer of soil, the largest concentration of feeder roots (the roots responsible for nourishing the tree) exist close to the surface.  Even a shallow excavation or cut will inhibit the tree’s ability to nourish itself. 
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The thick woody structural roots that hold the tree up are found close to the trunk and within the top 2-3 ft of the soil.  Removal or damage to these structural roots can render the tree hazardous.

What You NEED to Know about Mother Trees and the Mycorrhizal Network

Trees are not solitary organisms.  They live in community.  Dr. Suzanne Simard discovered that trees are connected to one another underground through a mycorrhizal network.  Mycorrhizae means “fungus-root” and is a symbiotic relationship between the roots of trees and fungi.  Trees use the mycorrhizal network to send and receive chemical messages to one another.  Dr. Simard coined the term Wood Wide Web to explain the communication between trees that is much like the Internet. 

Mother Trees are typically the oldest and tallest trees in a forest.  They have the largest mycorrhizal networks with the most connections to other trees.  Through the mycorrhizal network they share nutrients and vital survival techniques learned over the course of their long lives.  Because of the interconnected nature of an ecosystem, all species of the forest rely on these intricate communications and exchanges between trees and the mycorrhizae.  This means that when a Mother Tree is removed it has the most devastating impact on all species around it.

Keep in mind that when excavating your property, you’re not only removing soil and plant life, you’re also disrupting the mycorrhizal network that all trees and species in an ecosystem depend on.

Image: Texas A&M Forest Service

Techniques for Protecting Trees

Tree Protection Zones (TPZ)
Tree Protection Zones (TPZ) are areas where construction activities are prohibited.  They include the Critical Root Zone and/or beyond.

• Work with an arborist to designate TPZs for each tree to be saved.
• Clearly mark the TPZs on a survey before your home is designed.  
• Work with a designer who knows how to maximize your views and natural daylighting with existing trees remaining in place.
• Construct sturdy, semi-permanent, and highly visible tree protection barriers at least 4’ tall.
• Post warning signs for the duration of construction activities. 
• Check on TPZs throughout construction to make sure they have not been violated.

Image: Boulder tree well to save specimen White Oak - Outdoor Landscaping & Grading Company, Inc.

Tree Well
​Grade changes are common when excavating a site to build.  However, trees do not survive significant grade changes without special consideration.  Raising the soil level on top of the root structure is the most serious grade change.  According to Fielder Tree Service, as little as 4 inches of soil placed over the root system can kill some species.

Tree wells are constructed around the base of the tree to maintain the original grade while soil is used to fill in the outside of the well.

In the event, a tree’s root system has already been buried, a well will need to be carefully and slowly dug around the base of the tree to return to the original grade so the tree can breathe again (as seen above).

• Consult with your arborist and builder to determine the diameter and depth required for the well’s retaining wall.
• Assure your arborist knows how to design a well that maintains good air circulation and drainage.
• Make sure the tree requiring the well is clearly marked and communicated to the building team the preservation plan for this tree.
• Work with your designer to find creative solutions for incorporating a tree well into the beauty of your landscape and outdoor living spaces.

Image: Bartlett Tree Experts

Tree Island
Tree islands are areas where the original grade has been maintained around the tree while the grade has decreased or been cut away around the “island.”  ​

Image: Mississippi State University

Terrace
A terrace can be used to maintain the original grade around the base of a tree while drastically changing the grade on a steep slope above and below the grade of the tree.

Image: Dry stacked tree well around rescued White Oak - Preservation Arborists of Asheville, NC

Dry-Stack
Dry-stacking is a method of constructing retaining walls without concrete products.  Concrete (including blocks or pavers, not just mortar) lowers the pH of the surrounding soil.  Mycorrhizal connections (mentioned above) begin to break down in soils with a pH of around 8.  Portland cement, the most common type of cement in general use around the world, has a pH of around 13.5 and has a significant impact on the surrounding soil and mycorrhiza.

Image: Bartlett Tree Experts

Tunnel: Don’t Trench
Trenching is a standard way in which utilities are delivered to a home. However, trenching in Critical Root Zones can sever the roots required to keep the tree stable and healthy.  Tunneling through the soil at a depth greater than 18 inches, below the majority of the roots, will minimize damage.

Image: Semi-permanent fencing around Tree Protection Zone - Preservation Arborists of Asheville, NC

Best Management Practices for Tree Protection

1. Plan and budget for tree conservation as part of the development process.
2. Employ the services of an arborist as part of your team of professionals required to get the job done the right way.
3. Check with zoning and building departments (and protective covenants, if they exist) to see if there are any restrictions or permits required to taking down trees.  Most lakes have a mandatory buffer in which trees cannot be removed.  Some states and counties require trees of a certain size to remain untouched.
4. Plan for protecting trees on adjacent properties with Critical Root Zones, trunks, and crowns that extend into your property.
5. Evaluate soil health and incorporate soil remediation into Tree Protection Plan and budget.
6. Determine areas suitable for future tree planting so soils can be preserved during and after construction.
7. Evaluate existing trees and select trees that will be conserved and protected based upon their location, species, health, and benefits.
8. Work with an arborist to determine if a large tree is a Mother Tree that contributes significantly to the health of all other trees, soil, and plants around it.  DO NOT remove healthy Mother Trees!
9. Conserve and protect trees in groupings to keep the “forest” structure intact.  Trees are not solitary organisms.
10. Create a contract to be signed by your builder clearly stating which trees are to be conserved.  This contract should also clearly detail how each tree is to be protected.  Not all trees are protected the same way.
11. Establish substantial penalties for tree damage and non-compliance with tree protection contract.

Hire the Right Team

Most excavation contractors are accustomed to clearing as large an area as possible.  This makes it easy for equipment access, storage of materials, and space to store backfill.  Saving trees is not the first thing on an excavator’s mind.

Contractors cannot be expected to prioritize tree preservation unless explicitly told, educated, and asked to sign a contract.  A Tree Protection Plan should be created by consulting with an arborist and should be included as part of the plan set.

You will also need to have a conversation with the crew about how the land will be cleared.  The fastest and cheapest method is with a bulldozer.  However, this standard method is the most likely to damage root systems and remove the precious topsoil needed for a healthy yard.  Clearing the land by hand with a chainsaw is more expensive and time-consuming, however it will protect the trees you intend to save.  While the initial costs may appear high, preventing damage to trees is always cheaper and more effective than trying to mitigate damage afterward.

5 Hidden Costs to Avoid When Clearing Your Lot for Home Construction

Make sure you hire an excavator and a builder who understand your concerns and have experience successfully saving trees during home construction.  Ask your builder to follow the steps offered in the Tree Protection Best Management Practices for Contractors and Builders.

And be sure to communicate clearly to your home designer that tree preservation is important to you.  Discuss your desires to save trees BEFORE any design concepts are drawn.

Allow a Tree Preservation Plan to take root
at the beginning of your home design process.

Where There are Trees There is Soil

Most of the damage to trees occurs from soil compaction.  It’s not possible to talk about saving trees without discussing soil conservation.

According to our arborist friend, Chardin Detrich of Preservation Arborists in Asheville, NC, “the first pass of large equipment does most of the compaction, so even one trip alone will damage the tree. The soil will eventually turn anaerobic, and most of the major fungal infections that kill trees in urban environments thrive in anaerobic conditions.”

As stated in our last blog 5 Hidden Costs to Avoid When Clearing Your Lot for Home Construction, soil compaction leads to a myriad of expensive and devastating effects on your entire yard, not just your trees.

Join us next time for a shift in perspective about soils.  I explain what they are, what they aren’t, and why it’s imperative that you protect them on your property.

I intend you and your yard enjoy the benefits of beauty and value that tree preservation will provide for years to come.

Inspired by you,

Jenny Pippin, CPBD, FAIBD, CGP
Pippin Home Designs

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