Construction zones can be dangerous places, for trees as well as humans. Trees cannot protect themselves with hard hats, so it’s up to the homeowner to make sure nothing occurs to injure a tree’s health in work zones. Read on for tips for protecting trees from construction damage.
Did you build your home near mature trees to take advantage of their beauty and aesthetics? You are not alone. Many trees take decades to develop the strong deep roots and attractive canopies they attain at maturity.
Unfortunately, the trees you want near your home are at risk during construction. Preventing tree damage in work zones is a matter of planning carefully and working closely with your contractor.
Trees are at risk when construction work goes on around them. They can suffer many different types of injury. Use these tips to help prevent this damage.
The equipment used during construction can easily injury a tree’s trunk and branches. It can tear into the bark, snap branches and open wounds in the trunk, allowing in pests and diseases.
You can and should emphasize to the contractor your intention to ensure tree protection during construction. In addition, you’ll need to take action to enforce this mandate. Erect sturdy fencing around each and every tree. Place it as far out from the trunk as possible and tell construction personnel to stay out of the fenced areas and to keep all construction materials out.
The tree’s roots are also at risk when work includes digging and grading. Roots can extend out three times as many feet as the tree is tall. When construction crews sever a tree’s roots close to the trunk, it can kill they tree. It also limits the tree’s ability to stand upright in winds and storms.
Tell your contractor and crew that the fenced areas are out of bounds for digging, trenching and every other type of soil disturbance.
Trees require porous soil for good root development. Ideally, the soil will have at least 50% pore space for air and irrigation. When heavy construction equipment passes over a tree’s root area, it compacts soil dramatically. This means that the root growth becomes inhibited, so water cannot penetrate as easily and the roots get less oxygen.
Adding soil may seem less dangerous, but it, too, can be fatal to the tree roots. Since most of the fine roots that absorb water and minerals are near the soil surface, adding a few inches of soil smothers these important roots. It can also result in the death of larger, deeper roots.
The key to protecting tree roots in construction zones is constant vigilance. Make sure the workers know that no additional soil can be added to the fenced areas protecting the trees.
Protecting trees from construction damage also pertains to tree removal. When one tree is removed from your backyard, the remaining trees suffer. Trees are plants that thrive in a community. Forest trees grow tall and straight, producing high canopies. Trees in a group protect each other from winds and scorching sun. When you isolate a tree by removing neighboring trees, the remaining trees are exposed to the elements.
Protecting trees from construction damage includes forbidding the removal of trees without your permission. Plan around existing trees rather than removing any of them when at all possible.
Maintenance, growth and enhancement of the urban forest are important goals of the City. Considering tree protection in the initial stages of construction planning may mean the difference between preserving a healthy tree and having to remove it. Plans created with tree protection in mind help protect the City’s urban forest.
All construction related applications must include a Tree Protection Plan that shows details of tree protection, prepared in conjunction with an arborist report or in consultation with an arborist, when protected trees are in proximity to the proposed work. If the full minimum tree protection zone cannot be provided, a permit to injure the tree must be obtained.
Tree Protection Zones are the minimum required distances where tree protection is to be put in place so that no construction activity of any kind will take place inside the Tree Protection Zone.
A permit to injure a tree under a City Tree Protection By-law is not required if a full tree protection zone is provided.
Please note that the size of a Tree Protection Zone depends on the Tree Protection By-law that applies to a specific area. The Tree Protection Zones for trees located in areas protected under Ravine and Natural Feature Protection By-law are greater and afford greater protection to trees growing in these environmentally sensitive and significant environments.
Table 1 – Tree Protection Zones as they relate to trees protected under Private Tree By-law and Ravine and Natural Feature Protection By-law.
|Trunk Diameter |
|Minimum Protection Distances Required 2 |
City-owned and Private Trees
|Minimum Protection Distances Required |
Trees in Areas Protected by the Ravine and Natural Feature Protection By-law
|3 or 1.2m|
|10cm – 29cm||1.8m||The drip line or 3.6m|
|30 4 cm – 40cm||2.4m||The drip line or 4.8m|
|41cm – 50cm||3.0m||The drip line or 6.0m|
|51cm – 60cm||3.6m||The drip line or 7.2m|
|61cm – 70cm||4.2m||The drip line or 8.4m|
|71cm – 80cm||4.8m||The drip line or 9.6m|
|81cm – 90cm||5.4m||The drip line or 10.8m|
|91cm – 100cm||6.0m||The drip line or 12.0m|
|>100cm||6cm protection for each 1cm diameter||12cm protection for each 1cm diameter or the drip line|
Tree Protection Plan is required for all construction related applications when protected trees are in proximity of the proposed work, to include the following:
Tree Protection Plan must be prepared in conjunction with an arborist report or in consultation with an arborist. Prior to commencing with any demolition or construction activity it is important that an arborist determines the location, species, size and condition of trees on the property and surrounding properties.
Significant trees on private property are protected under Municipal Code, Chapter 813, Article lll known as the Private Tree By-law.
The Private Tree By-law was adopted to preserve significant trees on private property in the City, to assist in sustaining the urban forest in the city and to educate individuals with respect to tree protection measures and alternatives to tree injury and destruction.
If you wish to injure or destroy (remove) a protected tree you must obtain a permit under Private Tree By-law.
All trees situated on City streets are protected under the City of Toronto Municipal Code Chapter 813, Article ll, also known as Street Tree Protection By-law. No objects shall be attached to a tree, including decorative lights without the prior written approval of the General Manager of Parks, Forestry and Recreation.
Tree protection policies and specifications have been developed to protect and preserve city trees. Anyone failing to adhere to the tree protection policies and specifications will be financially responsible for any resulting damage to trees and may be charged under the provisions of the applicable City of Toronto tree by-law.
Urban Forestry maintains City trees in accordance with City standards at no cost to residents. The service delivery may take up to 8 months as clearing hazards after a storm is the highest priority.
If an owner of a private property that is located adjacent to the City tree wishes to have the required work completed sooner than scheduled, they may apply for permission to have an arborist complete the work at their cost.
Permission is required for any tree maintenance work, including minor pruning, tree planting and integrated pest management. Fax the complete application to Urban Forestry Data Management Centre, at 416-392-1915.
Permission may be applied for using this application form and providing all required information, including (but not limited to) the following:
If you are in the process of obtaining a Permit to Injure or Remove a tree under Street Tree Bylaw, Municipal Code, Chapter 813, II, the Permission would not be required, however, you would still be required to complete the Agreement for Arborists Retained by Private Property Owners to Undertake Work on City Trees and the Certificate of Insurance. You will submit these documents to the Planner in Tree Protection and Plan Review section of Urban Forestry that is reviewing your permit application
Trees situated on City parkland are protected under the Parks By-law. This bylaw prohibits and regulates certain activities occurring either on or adjacent to City parkland which may impact existing trees.
If your property is located either entirely or partially within a ravine protected area, you may be required to apply to the City for a permit prior to undertaking any work that includes the injury or removal of a tree, placing or dumping fill or refuse, or altering the existing grade of land.
The Ravine and Natural Feature Protection By-law protects public and private natural areas that are vulnerable to degradation due to removal of trees, changes in grade or lack of management.
Regulation of the injury and destruction of trees on both City and privately owned land. Below are tree related By-Laws which are currently in effect within the City of Toronto.
Ensuring that the City of Toronto achieves it’s goal in the area of urban forestry management of a sustainable urban forest.
To complete your application, the following documents are required.
To prevent damage and potential loss of trees, it is recommended to develop a Tree Protection Plan or a Tree Preservation Plan any time construction or demolition activities (including site access to the site) occur within 5 metres of a City tree.
Please reference the below Step-by-Step Guide for best management practices to follow.
Tree preservation and protection is a critical first step in construction and demolition project planning. Plan ahead! Call 311 to speak to an employee from the City's Urban Forestry team to learn more.
The big Brood X cicadas are expected to emerge this May 2021
Periodical cicadas: You probably remember seeing these giant insects in 2004, with their black bodies, bulgy red eyes, and see-through wings, shedding their skin and clumsily flying through the air. And you likely heard them making noises at night while you were trying to fall asleep.
Every 13 to 17 years, periodical cicadas emerge in the various regions of the United States and can cause temporary and lasting damage to trees. This year, Brood X will be crowding the Northern Virginia, DC Metro area.
2017’s Surprise Emergence:
In 2017, we were all surprised by the Brood X cicadas that plagued our area. Most individuals didn’t expect them, as they typically make their emergence every 17 years and had come four years early.
Well, it’s finally 2021, the year for Brood X. So, what can you expect?
Here’s the good news: cicadas won’t bite or sting you. It has also been predicted that suburban areas with recent construction are less likely to experience a massive emergence.
Here’s the bad news: when these insects do crowd your area, the female cicadas will likely leave damage on your trees.
To help you prepare, we’ve put together a guide on periodical cicadas. We’ll discuss their life cycle, how they might damage your trees, which trees are at risk, and what you can do to mitigate the effects.
Unlike annual cicadas who only spend two years underground, periodical cicadas live underground for their first 17 years, feeding on tree roots and developing into mature nymphs. At just the right soil temperature (
64ºF), adult cicadas come above ground to shed their exoskeletons and mate. Then come the loud mating calls we are all familiar with.
About 10 days after you first hear the cicada chorus, the females begin laying their eggs, which is when the tree damage comes in.
Female cicadas rip into the branches of trees to lay their eggs under the tree’s bark. Within about a month, females lay up to 400 eggs in 40 to 50 pockets under the bark of trees.
Trees may experience damage during the egg laying process, as the female cicada lays her eggs under the tree or branch bark. Laying eggs in this manner commonly causes the stem beyond the egg pockets to die. This tends to result in broken branch ends and wilted leaves: signs that flagging has occurred.
When a tree goes through this type of repeated damage, it can become stressed. Due to the stress and ripped open tree bark, the tree becomes more susceptible to disease and insect attacks.
Younger Trees: The bug may bring slightly more risk to younger trees, especially if they are ornamental fruit trees. Female cicadas are more drawn to smaller trees, as they are more driven to lay their eggs on their branches.
Older Trees: Mature, established trees are stronger and are easily able to recover from the loss of branch ends.
Fortunately, overall, the tree bug bears little damage on a landscape. The issues the insect presents are mainly cosmetic and should cause little to no worry.
As the damage cicadas leave on trees is mainly cosmetic and poses little overall risk, these flying insects are not considered pests and do not kill trees. They come for the sole purpose to reproduce and are gone within a few weeks.
Still, you may want to be on the look-out to make sure your trees are safe from the emergence this year.
Here are the trees most susceptible to cicada damage:
Preferred host trees: elm, chestnut, ash, maple, and oak.
Small or ornamental trees: Small, young trees, especially those 4 feet and under, have the highest risk of dying from cicada damage. In these cases, the tree usually cannot sustain itself after it’s had the majority of its branches killed off by cicadas laying eggs.
NOT healthy trees over 6 feet tall: Healthy, older trees will not be significantly affected by cicadas laying eggs however, they can become stressed and might develop insect or disease complications because of the wounds left behind by the cicadas.
While you can’t entirely get rid of cicadas, you can try protecting your landscape from them.
Hold off on planting new trees: If you’ve been wanting to add new trees to your landscape, we recommend waiting until after cicada season, in the fall, as younger trees are most vulnerable to damage.
Netting For Small, Newly Planted Trees: If you have a newly planted tree that is under four feet tall, you can try to protect your tree with netting. To apply, drape the netting over your tree and fasten it securely around the trunk. When done properly, you can potentially prevent bugs from crawling up from underneath it.
Note: Netting is known to fly off trees and might lead to foliar diseases if left on too long. If netting is used, we recommend leaving it on only during the egg-laying period (the only period the tree is really susceptible to damage).
Don’t Attack Them With Pesticides:
Pesticides do not effectively manage cicadas. On top of that, as an environmentally friendly company, we don’t recommend pesticides as they are not eco-friendly. Pesticides rid your tree of beneficial insects that prevent your tree from harmful insects and diseases.
Give Them Some Extra TLC After Cicada Season:
Bio-stimulants: Biostimulants are often the #1 recommendation our Certified Arborists give to homeowners. They’re the all-natural, organic multivitamin for your plants that can help bolster your trees’ overall health by making sure their roots have all the nutrients they need. Naturally, they are apart of our annual Canopy Protection Program, also known as our total tree & shrub care program.
Post-Cicada Pruning: Removing the deadwood created by cicadas will help your tree look better and stay healthy. Also, pruning within 6-7 weeks after they lay eggs (before they hatch) will reduce the population in your landscape. This helps make the next emergence easier to manage.
Keep Them Hydrated: In order to recover and not contract any other diseases, make sure your tree doesn’t experience any additional stress from drought. Be sure to keep them watered throughout the hot days of spring, summer, and early fall. Check out our watering tips.
Editors Note: This post was originally published in May 2017 and has been updated for accuracy and comprehensiveness.
Damage to trees occurs directly from physical wounding or indirectly through change of environment around the tree.
Careless movement of construction equipment causes wounds to tree trunks and root collars, the area of the tree at ground line where the roots begin to spread out. A healthy tree is capable of sealing off small wounds, localizing injury. However, large wounds and those on stressed trees will not readily seal off, allowing decay to begin.
Improper pruning to create clearance for construction equipment and tree removal techniques are other sources of physical injury to branches and trunks. As trees are removed for placement of a new building or driveway, they may scrape bark off trunks or break branches of trees that are to be saved. These wounds serve as entry points for diseases. Improper pruning leaves branch stubs that die and begin to decay. Make clean cuts with a sharp pruning saw just outside the swollen branch collar.
Below ground, root damage is common from excavation and grade changes. Roots may be torn by improper excavation, opening wounds for disease organisms to enter. Fine, absorbing roots are lost by topsoil removal, putting the tree under stress. Structural support is lost by trenching too close to major roots, creating a potential hazard. Bruising or crushing of roots by heavy equipment may not be apparent from above ground.
Soil compaction is a serious problem on many construction sites. Even when care is taken to avoid trunk and branch injury from equipment, trees may be damaged by equipment driving over root systems. The weight of the equipment compacts soil, reducing air space in the root zone. Limited oxygen availability to roots is also a problem when soil is stockpiled at the base of trees or paving is put over existing roots.
Excessive thinning of tree stands or removal of underbrush causes increased exposure to sun, wind and heat. Sunscald may develop on trees previously acclimated to shade. Increased wind and heat exposure increases moisture stress.
Also, moisture stress may develop from grade changes that lower the water table or divert drainage patterns away from the site. On the other hand, excess soil moisture may develop from grade changes, as well. A rise in the water table, puddling from improper grading, or an increase in water flow through the area will decrease the amount of oxygen in the root zone and lead to tree decline.
Adding fill soil or cutting away excess soil alters the environment around tree roots. Hauling in fill reduces oxygen to the roots. Adding as little as 1 or 2 inches of heavy clay soil on top of the existing grade may damage sensitive trees such as oaks. The soil profile and soil pH are also altered. Topsoil is often more acidic than excavated subsoils spread on the surface. Trees adapted to growing in acidic topsoil will be stressed when forced to develop new roots in soil of a different pH and texture. Ability of roots to take up many micronutrients is reduced in high pH soils, leading to decreased growth rate and yellowing leaves. Construction material buried on-site also often raises soil pH.
Symptoms of damage
Symptoms of construction damage to trees appear over a period of several months to several years after the damage occurs. Because of the delay in development of symptoms, it is often difficult for people to understand the relationship between the earlier injury and the current symptoms.
The first symptoms to develop may be a slight wilting or shedding of a few leaves at the time of construction. Fall coloration often develops early and leaves drop prematurely. In later years, leaf size and shoot growth may be reduced. Twigs and branches die, and in the case of conifers, excessive needle drop occurs. General growth of the tree is slowed and resistance to diseases and insects is weakened.
Diagnosing compaction or root smothering damage can be difficult because it may take five to seven years for symptoms to appear. The speed and severity of symptom development depends on the amount of damage, the species of tree and soil type.
Deciding which trees to save
The first step in deciding which trees to save is to accurately mark out placement of proposed buildings, driveways, parking areas and utility routes. After marking these features, stand back to look over the site. A small shift in the position of the building, a change in driveway location, or altering the proposed utility line could make the difference between saving or cutting a valuable tree.
After deciding on building placement, prioritize trees for saving. Trees directly in the way of construction undesirable, weedy tree species trees already in a state of decline or structurally hazardous trees should be marked for removal. If in doubt, consult a trained arborist, horticulturist, forester or nursery person to determine tree condition.
Next, determine which trees can be saved with little or no protection. Desirable trees located away from construction or traffic areas will survive if reasonable care is taken.
The final group of trees to examine are those that may survive construction, but only if proper measures are taken. Examine them more closely to determine if one of the techniques described below will effectively minimize damage. If severe damage is likely, it will be less expensive to remove the tree before construction begins than afterward.
Control traffic around trees
Tree roots are not mirror images of the tree top. Roots are concentrated in the top 12 to 18 inches of soil and spread two to three times the width of branches (see Figure 1). Protecting roots within the dripline of the tree is most critical, but damage to roots outside the dripline on only one side of the tree may remove one-third or more of the tree's roots (see Figure 2).
|Figure 1. Tree roots are not mirror images of the top branch structure (lower figure). While some trees do have deep tap roots, most do not. Roots spread to where soil conditions provide adequate moisture, aeration and nutrients. Typically, about 85 percent of a tree's roots are within the top 18 inches of soil (upper figure).|
|Figure 2. Roots typically spread out from two to three times the width of the branches. However, the essential roots are usually considered to be within the dripline, which is the area underneath the tree's branches.|
Erect a fence at the dripline or farther out, if possible, to prevent damage from excavation, soil compaction or stockpiling of soil over roots. It is easier to save groups of trees than individual ones. Build a fence around the dripline of the outside trees to keep construction machinery away from the grove. Remove protective fences only after all construction work is done, including final grading and smoothing of the site.
Carefully remove unwanted trees
Be careful removing unwanted trees. A tree being removed might fall on and injure one of the trees you plan to save. If possible, remove unwanted trees when none of the trees have leaves. When trees are in full leaf, sudden removal of nearby trees is a shock and can cause sunburn to other trees.
Make clean cuts
Clean cuts to roots seal off quickly and help prevent entry of disease-causing organisms. Ragged, rough wounds from dull or improper equipment allow decay to progress to the rest of the tree. Sharply cut ends promote a flush of new roots, helping the tree recover from injury. Bulldozers tend to tear roots apart, leaving wounds that will not seal readily. Trenchers and backhoes make cleaner cuts through the soil. When cutting roots larger than 2 inches in diameter, use a pruning saw to make a smooth cut.
Do not automatically prune the top of a tree that has been root pruned. As long as moisture is not limiting, leaves in the crown of the tree manufacture food to help roots grow and recover from being cut. Prune out only weak or dead branches.
Tunnel rather than trench
Trenching near a tree kills a large portion of the tree's roots. Tunneling under the tree does virtually no damage. Since most roots live in the top 18 inches of soil, a tunnel 2 feet deep often does little damage. However, placing the tunnel 3 to 4 feet deep is safer.
It is best to tunnel at least 1 to 2 feet away from the tree's center to avoid a tap root (see Figure 3). For trees under 6 inches in diameter at breast height, trenching should come no closer than the dripline of the tree. See Table 1 for larger trees.
|Figure 3. Trenching near a tree can kill almost half its roots. A tunnel in the same place will do virtually no damage to the tree.|
Table 1. Minimum distance to trench trees. (Adapted from Municipal Foresters of Northeastern Illinois guidelines.)
Tree diameter at breast height
Minimum distance from tree to start tunneling
Please note: This older article by our former faculty member remains available on our site for archival purposes. Some information contained in it may be outdated.
Saving trees makes sense. It improves profit margins, builder reputation and sales. Careful planning, solid communication and a basic understanding of what keeps trees growing will make customers happy for a lifetime.
By Paul Fisette and Dennis Ryan – © 2002
Smart landscaping is the easiest way to increase value and speed the sale of a home. Bank America Mortgage found 84% of the real estate agents they surveyed think that naturally wooded lots are 20% more salable. NAHB researchers report 89% of the homeowners they polled want builders to leave as many trees as possible on their house lots. In another study, NAHB learned that 43% of the homeowners queried actually paid up to $3,000 more for the treed lots they built on. And 27% spent over $5,000 more for a naturally wooded site. Trees have market appeal and improve a home’s performance.
Trees can reduce a home’s energy bill. Strategically placed trees keep homes cooler during summer and warmer in winter. We measured the temperature of a brown-colored roof on a hot July afternoon. Its sunstruck surface was 140 degrees. The surface in the shade of a leafy oak was 50 degrees lower! Leaves give off water vapor, cooling the surrounding air as it evaporates. The combination of shading and evapotranspiration greatly improve a home’s natural ability to stay cool. The EPA figures it’s possible to reduce mechanical cooling by up to 50% with a thoughtful landscaping plan. It is important to shade the east and west sides of a home. The sun angle is lower and more direct on these sides. Shade the cooling equipment too. Air conditioners run more efficiently when they are cool. This single detail can save 10% on your cooling bill. As an extra bonus shading improves durability. Directs sun bleaches color from painted surfaces. It ages building materials like plastics, wood, and asphalt roof shingles.
A carefully positioned windbreak lowers the winter heating load by 20% in some cases. Early settlers apparently knew this. But the concept seems lost on a generation of builders who control the winter chill with blankets of insulation and the force of central heating. A screen of evergreens can passively reduce air infiltration and protect walls from heat-scrubbing winds. Don’t block south-facing windows that provide solar gain. Even deciduous trees that shed their leaves block 50% of the solar gain with their branches. Tree plantings provide an environmental bonus. Lowering a home’s energy requirement reduces the amount of pollutants exhausted up your chimney and utility smokestacks.
Preserving native plantings reflects an environmentally sensitive approach to development. Trees and the underlying vegetation intercept and absorb runoff from storm water, reducing erosion and siltation. They filter pollutants like lawn fertilizers, pesticides and other chemicals present in the landscape. Tree plantings buffer road noise and mask sounds from neighbors. They improve privacy and screen unsightly views. Builders that preserve trees are regarded as environmental stewards. Potential homeowners, regulators, municipal officials, and media recognize the effort. These projects sell faster because they are set apart from the competition as healthy and friendly. In a recent study of 1200 households, more than 70% of the respondents said, “Trees make you feel good!”
The evidence supporting tree preservation is overwhelming, yet builders continue to strip the sites they build on. Many builders like working with a clean slate. They want unrestricted access to all parts of the site and prefer to plant new tress later in the project. Sadly, the few builders who save trees, loose them to a slow but predictable death. Trees often look perfectly healthy 3 or 4 years after construction. However, unintentional construction damage has them marked for the chipper. When a tree finally looks sick it’s too late. Include tree preservation in your construction Master Plan. It pays huge dividends through improved curb appeal, enhanced reputation, and wider profit margins. Site development that preserves trees requires careful planning and thoughtful communication between all the members of the construction team. First, you must understand what a tree needs to remain healthy.
The most obvious injuries to trees are made to trunks and branches. Dangling branches are pruned and bark injury is trimmed with a limited degree of success. But damage to roots is lethal. The resulting death is unsuspected. Valuable trees often die several years after the project is complete. Homeowners mistakenly think their favorite tree has a disease. There is no association made between a thinning crown and the long-forgotten construction project.
There’s a stiff penalty for unintended damage. It costs10 times more to remove a tree near a house compared to the same tree on an open lot. A recent project I worked on is a perfect example. A builder in Denver was asked to preserve a 50 year-old Chinese elm. His clients loved the tree. The tree stood 25 feet from the new home’s southwest corner. Its wide-sweeping branches provided the homeowners with free air conditioning and a beautiful landscape environment – for four years! The tree died, became a hazard, and cost $2,500 to remove from the congested urban lot. The homeowners replanted a 15-foot tree at an installed cost of $500. The case was arbitrated and the parties split the cost. But the process was painful and damage completely avoidable. Tree preservation programs must be thoughtful, involve a certified arborist and be a central element in the original design process.
Serious construction damage is almost always root damage. People don’t understand where root systems are located or how sensitive they are to construction activity. Root networks are shallow, limited to the top 18 inches of soil. The one deep root, the taproot, only provides stability. All other roots provide the nutrients and moisture required by the plant. Roots extend well beyond the drip line of a tree. They extend in a radius that equals 2 times the height of the tree. So feeder roots for a 20-foot tree extend 40 feet from the tree stem. The very fine feeder roots grow like branches. They extend further every year. As the crown of a tree grows and expands, the roots must grow to supply the extra food and water required to support new growth.
There are 3 construction activities that kill most trees. Builders cut roots when they trench or dig near the dripline of a tree. Digging cellar holes, septic systems or even grading a lot will cut roots and kill trees. When roots are eliminated, the tree is not able to draw the water and nutrients it needs. The tree becomes dehydrated and starts to die at the top of the tree crown.
Soil is compacted when trucks and heavy equipment drive over the root zone. Stockpiling lumber, building materials, loam, or excavation soil over the root zone also compacts the soil, smothering the roots. Everyone thinks trees breathe in carbon dioxide and give off oxygen. The only part of the tree that does that is the green leaves during photosynthesis. Other living cells take in oxygen for respiration to convert stored sugars and starches into energy (food). The byproduct is carbon dioxide. So if you compact the soil or lay a driveway over the roots, you cut the supply of oxygen and carbon dioxide can’t escape. It’s just like putting a plastic bag over your head.
When you change the grade around a tree you cut into the root system, add soil, remove soil, or undermine part of a tree’s anchoring system. Excavation fill is often spread over the site. This raises the grade and smothers the roots. If you lower the grade, you expose roots. A good guide is to maintain the root flare at the bottom of the tree. Do not bury the trunk flare. Some professionals claim you can add 2 or 3 inches of well-draining topsoil to an older, well-established tree and get away with it. My experience shows it’s best not to add any soil around trees.
|Alter grade||Loss of structural support, dehydration and suffocation|
Unfortunately, removing all the roots from one side of a tree is a common practice. Trenching, excavating, and driveway grading create “wind-throw” problems. Wooded lots are frequently cleared to leave little islands of trees in the median of a 2-sided driveway. These trees are doomed. Soil compaction, root smothering and wind-thrown trees are inevitable. Unstable trees are lawsuits waiting to happen.
As trees die, people notice they are infested with disease or insects and think this is the cause of death. This is a secondary problem. The real problem is root damage. Cut enough roots and this will effect food production. The tree will weaken and the secondary organisms finish it off.
Effective tree preservation must be integrated with the project design and land development process. Hire a certified arborist that works with residential construction projects and knows what builders are up against. A construction project is no place for an idealistic theorist. The arborist must be familiar with the roles played by members of the project team and become a central member of the team. They must understand the design concept and walk the site before any plans are drawn. The arborist will help lay out the site and communicate appropriate information at critical times during the project.
A professional arborist knows:
Successful development requires careful planning. Tree preservation is an important part of a project’s master plan. It should be contemplated at the very first stage of the process, before any work is done on the site. There are several key elements that guide an effective tree preservation plan:
o Identify trees suitable for preservation
This step provides the most critical information. Here, the arborist creates a Tree Stand Delineation, which describes the quantity and quality of existing trees on the site. Key team members walk over the property during this phase. Brainstorming and visualization is encouraged to stir the imagination and build enthusiasm in the project. Valuable trees are tagged, numbered and referenced on the site plan. This should be done when there is a general understanding of the project goals, but before a conceptual plan is final. This allows the delineation to influence the placement of roads, driveways, buildings, drainage, scenic vistas, wildlife corridors, and guide the very ambiance of the development. Only trees that have a strong potential for sustained long-term growth are selected. A rating chart can be developed to indicate the characteristics of tress listed in the inventory. Remember, the site these trees are used to growing on will be drastically changed, so a projected view of the landscape must be considered. Characteristics such as species, size and health of the trees are noted. Any work that must be done before the lot is cleared and graded is planned at this time.
o Define tree protection zones, recognizing impacts of planned development
Protection zones are the areas located directly around the trees you want to save. Root zones are critical areas. Root zones are depicted as little circles around each tree shown on the landscape overlay or site map. These areas are off limits! No construction activity can occur in these zones. That means grading, digging, storing of materials and all traffic is prohibited in these areas. The size of the zone depends on the health, age and species of the trees you are trying to protect. A healthy tree will probably survive if at least 60% of its roots remain unaffected by construction. The rule of thumb is to hold all work outside a tree’s dripline. However, some trees need more protection. Trees that lean have roots that extend far in a direction opposite of the lean. Narrow trees like Lombardy poplars, some cedars and tightly grouped trees (like those on a forested lot) have roots that run far beyond the dripline. A better rule is to allow 1 foot of protective radius for every 1 inch of trunk diameter.
It is the arborists’ job to minimize damage to valuable trees. All construction activity is referenced on the working drawings and specifications. The trees that could be affected are included in the construction documents and discussed at project meetings. Details regarding the impact should be included in each section of the design plan.
o Outline protective measures and develop specifications
With the relevant information delineated on the site map designers can now locate the building, driveway, utilities, and develop the grading plan. If an overlay sheet is used, it can be colored to show where construction will impact protected zones. If destructive site development can not be modified, these overlay warnings may indicate which trees must be removed. Better now than after the building is constructed. A good site plan will show permitted parking, storage, washouts and other areas critical to the preservation plan.
Materials and methods required to control damage must be clearly described in the construction documents. Include an enforcement or penalty clause in the specifications. Complicated details should be illustrated on the working drawings. Prescriptions are part of the construction documents that are forwarded to the conservation commission, building department and subcontractors who will bid on part of the project. During this stage, hold a meeting with the owner, foremen, subcontractors, and others who will work on the site. Make it clear that preservation is important on this job, requiring everyone to work together.
Typical Protective Measures
o Field inspection and administration
Critical decisions are made during the design phase, but follow-through makes or breaks a project. You must verify that field workers are following the preservation plan. Tree preservation is unusual for many workers. Some may think the extra care required is a bunch of baloney. Keep a watchful eye. Surveyors, well diggers, excavators and truck drivers are usually first to arrive on site. Meet them as they pull in. Instruct them not to wash down equipment near desired trees. Trees are sensitive to chemicals and washing out a concrete truck affects the pH of the soil. Petroleum washed from equipment also hurts. Calcium chloride is often used to keep down dust. Be careful. Salt is toxic. It draws water from plants and seals the soil’s surface, smothering roots.
Verify that all workers understand their role. And be sure the required protective measures are implemented at the appropriate time during the work schedule. The arborist can be hired to oversee field implementation, but the most effective policy is to have the arborist advise a fully invested site supervisor.
The site supervisor should clearly mark the location of each tree being saved on the site. Erect signs that mark storage and clean-out areas. Install protective fencing before any work begins. It should be rugged, like an anchor fence or one built using 2x4s. The fence must be conspicuous. It must be high enough to be seen by operators of heavy equipment, so those workers won’t run over it. Snow fencing is not good enough. Hay bales should be used to protect wooded areas and individual root zones from silt and run off. And a professional should be hired to perform some important tree-care work before building begins.
Many handbooks recommend tree wells as a system used to change the grade around an existing tree. I don’t like them. You can build a stone wall and hold an elevated level of soil back away from the tree trunk, but the rest of the root zone is buried and suffocated. To do it right you must construct a radiating network that provides air and water to the entire root system. Proper tree well construction is incredibly expensive and impractical in most cases. You are better off working with the existing contour of the land if at all possible.
The cost of hiring the arborist depends on the house and scope of project. The service can run from a couple hundred dollars for a plan review and site visit to a couple thousand for a full consulting service. Given the numerous benefits afforded by professional tree preservation, hiring a certified arborist is a sound investment.
National Arborist Association, 3 Perimeter Rd., Unit 1, Manchester, NH 03103
International Society of Arboriculture, P.O. Box 3129, Champaign, IL 61826
American Society of Consulting Arborists, 15245 Shady Grove Rd., Suite 130, Rockville, MD 301-947-0483 www.asca/consultants.org
Trees and Development: A Technical Guide to Preservation of Trees During Land Development by Nelda Matheny & James Clark, International Society of Aboriculture.
Trees & Building Sites, by Gary Watson and Dan Neely, International Society of Arboriculture.
Building Greener Neighborhoods: Trees as Part of the Plan 2nd Edition, by Jack Petit, Debra L. Bassert, and Cheryl Kollin, National Association of Home Builders Press and American Forests.