Construction Trauma can Topple Trees

Coping with construction is the most challenging obstacle many trees will face in their lives. Given enough time to adapt, trees are extraordinary organisms that can withstand many environmental stresses; however, the rapid environmental changes wrought by construction occur too quickly for many trees to survive.

While some trees’ health may decline within days of construction-related stress, others seem to take the damage in stride.

Unfortunately, this is not always an accurate reflection of such a tree’s health, and many of these stoic specimens die a few years after construction takes place.

The only way to prevent large-scale tree losses during construction is by understanding the biology of trees and the types of stress that construction projects create. With adequate foresight and planning, many of these loses can be prevented. Additionally, by understanding which trees are unlikely to survive a given project, you can focus your conservation efforts where they are most effective.

Soil Compaction, Grade Changes and Root Health

A sample of soil is comprised of minerals, organic matter, innumerable microscopic organisms and small voids, called pores by botanists, geologists and others interested in such matters. Some of these pores hold water, while other pores contain air. These pores are very important for trees.

While the large roots flaring out from the trunks of trees anchor them to the ground, they do not absorb significant amounts of water or air. Trees leave this job to their many fine roots, located further from the trunk.

The problem occurs when construction activities compact the soil. This destroys the pores in the soil, preventing the trees from absorbing water and air. Additionally, if compacted enough, the tree’s roots can become trapped and unable to grow in a normal manner.

Many different construction activities compact the soil, such as preparing the foundation of the building, or simply the heavy vehicle traffic associated with construction projects. Even if efforts to prevent compacting the soil are taken, grade changes can just as easily doom trees.

The fine absorbing roots of trees primarily reside in the upper 12 inches of the soil. They penetrate this type of soil well, and are able to provide the tree with resources from a relatively wide area. However, when additional soil is placed over tree roots, it reduces their ability to survive. Grade lowering efforts often sever roots, which is as traumatic and destructive as it sounds.

Mechanical Trauma and Bark Damage

Perhaps the simplest and most obvious form of damage trees suffer from construction projects is mechanical damage to the trunk or major limbs.

Whether heavy equipment snaps part of a tree’s lower limbs, or laborers using hand tools rip large portions of bark from a tree’s trunk, the tree’s primary defense mechanism – the bark – is compromised, opening the tree up to a variety of pests and pathogens. If the cambium layer is affected, the wounds may be serious enough to kill the tree.

Some trees are more resilient than others are in the face of such indignities. Those trees with thick bark are better able to recover from damage to the trunk or major limbs than those with thin bark are.

With adequate tree protection zones in place, such damage is less likely to occur.

Sudden Succession

Trees that grow in the open often develop broad crowns and root systems that help them to withstand strong winds. Over time, many of these trees even produce wood in places that improves their ability to withstand the prevailing winds. However, trees that grow in forests — or where competition limits the spread of their canopy and roots — are more susceptible to windthrow.

Living inside the forest, this is rarely a problem, as the nearby trees partially block the wind. However, when trees along the edge of the forest are removed, it exposes the trees behind them.

These newly exposed trees are now at increased risk of failing, perpetuating the pattern of exposure and failure. In addition to increasing their susceptibility to blowing over, these formerly shaded trees may develop sunscald.

Preventative Steps

When considering any construction project that will take place near trees, you should secure the services of a skilled arborist to assess your trees and develop a tree protection plan. In many jurisdictions, such a plan is required before construction begins.

The arborist will help devise tree protection zones, consider the potential effects grade changes and predict how the trees will respond to changes in wind and water flow. Your arborist may also investigate the health of your existing trees to determine which measures – if any – are appropriate. For instance, trees may require supplemental watering or fertilization, prior to the onset of construction.

Dead branches should be pruned for safety’s sake, and structural pruning may be required to ensure the tree has the greatest chances of surviving the construction. Mulching is usually a good standard practice, but during construction activities, exceptionally thick mulch layers may be warranted.

Critical Condition: Protect the Roots to Protect Your Trees

tree rootsA tree’s fate is largely tied to the health of its roots and the state of the surrounding soil. Unfortunately for many homeowners and arborists, the bulk of the tree’s roots are out of view. Without taking drastic or invasive investigative steps, the health of the tree’s roots must be inferred, rather than directly observed.

Accordingly, the best way to protect your tree is to protect enough of the tree’s roots to sustain it through any damage. With luck, the tree will survive the trauma, generate new roots and thrive for years to come.

The Basics

Roots perform four key functions for trees. Drawing water from the ground is among their most important duties, but roots also absorb essential minerals from the soil. Roots support the weighty trunk, branches and canopy; serve as a conduit for the transport of different substances; and store energy for future use.

When roots sustain damage, the leaves often wilt or drop prematurely. This reduces the amount of water and minerals that can travel up the tree, and it reduces the amount of food that the tree can produce. If enough of a tree’s roots suffer damage or disease, death is all but certain.

Just as a tree’s branches do not all perform the same functions; a tree’s roots delegate different tasks to different portions of the root system. While the large, woody roots at the base of the trunk help stabilize the tree and serve as a shared conduit for the transfer of water and minerals, the fine, white roots absorb most of the tree’s water and minerals.

The Damage Done

A variety of traumatic events can compromise a tree’s roots, but construction damage is one of the most common culprits. Heavy vehicles and foundation work cause soil compaction, which damages roots and alters the soil structure. Grade changes are also damaging — raising the grade buries the tree’s roots too deeply, while lowering the grade exposes the roots, which can lead to further damage and decay.

Trenches dug for utility lines may cut large swaths of a tree’s root system, and landscaping equipment may slice through surface roots. Even if the tree is capable of coping with the reduced water and mineral uptake caused by such events, it is more likely to fail in high winds.

Because few treatments can help repair damaged roots, preemptive strategies are of paramount importance.

Critical Root Zone

Not all root damage is deadly. Trees can survive with some portion of their existing roots – they do not need the entire network. Over time, trees recover from root damage by generating more roots. However, some portion – a critical portion – of these roots is necessary for the tree’s survival.

Tree care professionals call this portion of roots the tree’s critical root zone. Although the tree’s entire root system may extend two to three times farther from the tree than the critical root zone does, this area must be protected at all costs.

Measurable Maps

Different authorities calculate the critical root zone of a tree in different ways. A 1991 study by Patricia Lindsey and Nina Bassuk, published in the Journal of Arboriculture, recommends allowing 2 cubic feet of root zone space for each 1 square foot of canopy spread. (Bassuk, 1991) This usually translates to a circle with a radius of about 1.5 times the radius of the drip line.

Another formula in common use requires 1-foot of critical root radius for every 1-inch of diameter at breast height (4.5 feet above the ground). In other words, a 6-inch thick tree requires a critical root radius of 6 feet. Other tree professionals recommend allowing 1.25 feet for each inch of trunk diameter.

The critical root zone varies with species, site and soil conditions, so determining the critical root radius of a tree accurately requires extensive knowledge and experience. However, by using the formulae above, you can determine the general size of a given tree’s critical root zone.


Bassuk, P. L. (1991). Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers. Journal of Arboriculture.

tree root care

Tree Root Care

The Morton Arboretum states that over 80% of all landscape problems originate underground. With this in mind, it is safe to say that root problems become tree problems. The structure of a tree root system is comprised of large perennial roots and smaller, shorter-lived feeder roots. Perennial tree roots are woody and grow horizontally, primarily in the top 6 to 24 inches of soil. Rarely do they grow deeper than 3 feet. These roots anchor the tree, store food and water, and conduct water and nutrients into the tree. Feeder roots are significantly smaller, usually only 1/16th in diameter, but make up the majority of the root system’s surface area. Because feeder roots do most of the water and mineral absorption, these roots grow predominantly upward and outward from the large perennial roots near the soil surface. Feeder roots die and are replaced regularly. Typically, the entire root system of large and small roots occupy an area underground that is two to four times the diameter of the tree’s crown.

Roots are damage in many ways. The first is soil compaction. This damages feeder roots limiting the nutrient and water-absorbing capacity of a tree. Symptoms of soil compaction appear in the tree canopy as unhealthy foliage, yellowing, and branch dieback. Compaction of the soil is common in construction projects due to heavy construction equipment. One way of protecting trees during the construction process is placing protective fencing around the dripline of the tree’s canopy.

A second problem for roots is changing the soil depth. Avoid placing soil on top of the roots. If root depth increases by as little as 2 to 4 inches, oxygen and water availability is significantly affected.

Lastly, improper watering, both under- and over watering, leads to an unhealthy root system. Over watering reduces oxygen and under watering leads to poor root growth. As you can see, any change in soil condition, water supply, or oxygen supply can be very detrimental to the tree. Healthy roots means healthy tree.

Sherman Oaks Tree Root Damage

The Sherman Oaks Neighborhood Council’s Government Affairs Committee and the Neighborhood Services Committee held a joint meeting to discuss sidewalk repair in the area and what position Sherman Oaks Neighborhood Council (SONC) will take when they present the issue to the City Council. Under discussion was the possibility of shifting responsibility for sidewalk repair and liability from the city to property owners. Sidewalks that are uplifted and damaged due to tree root incursion were at issue. Area residents were encouraged to attend the meeting so they could give feedback on the issues.

“This is an important issue for residents in Sherman Oaks as the area has many miles of sidewalks in need of repair and the cost to individual property owners could be in the thousands of dollars,” read a statement from SONC.

Tree roots can also be destructive by cracking and lifting a home’s foundations, driveways or walls. Evergreen Arborists Consultants, Inc. has expert witness experience with property damage and personal injury cases. We have deposition and trial experience working for plaintiff and defense cases on behalf of individuals, insurance companies, and public agencies. Please call us today for a consultation.

Evergreen Arborists Consultants, Inc. are a Los Angeles certified arborist, tree experts, and tree specialists who provide arboriculture and tree expert advice to Beverly Hills, Brentwood,  West Hollywood, Santa Monica, Malibu, Palos Verdes, Encino, Pasadena, and Sherman Oaks. We specialize in conducting detailed investigations and providing independent analysis, as well as expert witness testimony in support of litigation. Please call us today for a consultation.

Roots Cause House to Sink – Is the City Responsible?

A retired couple in Ottawa, Canada, says the city is partially responsible for the damage done to their home from an Emerald Ash tree in their front yard. The roots of the tree have encroached on the foundation of the house, causing significant structural damage. The couple contends that because the city has maintained the tree by trimming it regularly, they should be partially responsible for the damage it has done to the foundation.

The couple’s front of the house has sunk three feet into the ground, which means that they couldn’t even open their front door. “There was a great ‘bang,’ I thought for sure it was an earthquake,” said the homeowner when the front of the house sank. The house also had cracked walls and floors that have heaved.

The city sent a letter to the homeowners in July stating that the city isn’t liable for damages caused by the tree. “The tree in question was located wholly within the private property line and therefore belong to the resident, not the city,” said a city spokeswoman. She also explained that the city only maintained the tree to keep overhanging branches close to the road in check.

The couple has spent over $90,000 to fix the damages t their house, including $1000 to uproot the tree. A civil suit against the city has not been filed yet, but a forestry contractor who works for the city says the city may be partially responsible for the damages done by the tree.


Tree Roots Damage May Cause Plumbing Problems

Plumbing and underground building foundations may be slowly sustaining damage from tree root systems in the landscape. Roots can burrow into minute cracks in pipes and foundations, but not all trees and shrubs have root systems that are as likely to cause problems. Many problems can be avoided if the tree or shrub is given enough unobstructed room underground to grow out.

There are a few trees and shrubs that have special habitat needs, which will reduce the impact they have on pipes and foundations if these needs are addressed. The weeping willow is one. It needs a very rich and moist habitat and will aggressively seek this out if it isn’t planted in a spot that meets these needs. Magnolia trees have very strong rope-like roots that grow close to the surface and can cause foundation and pipe damage. Poplar trees have an extremely invasive root system, and their roots are able to grow two to three times the height of the tree. Birch trees also have a root system that grows two to three times the height of the tree.



Will LA Homeowners be Responsible for Sidewalks?

The Los Angeles City Council is considering shifting all responsibility of sidewalk care to property owners. Currently, the city takes care of the tree roots, which is considered the biggest problem, while the property owner takes care of the sidewalk. The proposal would also make the homeowner legally liable for any trip-and-fall claims from sidewalk damage. The City Council is also considering more inspections of sidewalks to issue citations and order repairs.

Homeowners and homeowner associations have opposed the policy change. This opposition, along with the inability of council committees to take action, has kept the proposal from passing. “We are celebrating our sixth anniversary of motions and all we are doing is asking the same questions,” said Councilman Bernard Parks, Budget and Finance Chair. “We have spent $100 million to build 500 miles of sidewalk and they are in worse shape than ever before.”

Federal funding originally was used by the city to take care of the tree root damage, but this funding has been used up. The city has been taking responsibility for the tree root damage since 1973, but now the city is strapped for cash. There are 4,700 miles of the 11,000 miles in the city that are labeled as being in poor shape. The estimate to repair damaged sidewalks is $1.2-1.5 billion. The city also pays $4-6 million in liability claims every year.

Other options being discussed by the city council include creating sidewalk assessment districts (where homeowners vote to pay the city sidewalk maintenance); and certifying sidewalks as safe when property is sold, utilities are connected, or when building permits are issued.


Lititz Borough to use Root Containing Device for Planting?

A new method for containing shade tree roots is being considered for use in planting trees in Lititz Borough, Pennsylvania. The new method is called the StrataCell and was developed in Australia by Citygreen in 2009. The StrataCell is a plastic interlocking device that is intended to keep roots from spreading outward and lifting sidewalks, roads, and driveways. Their Shade Tree Commission presented the borough council with this idea. During the presentation, the borough was told that a Citygreen representative would be willing to come to Lititz to help with installation of the interlocking devices for a pilot program. The only concern is that the cost of installation is unknown.

There is one home in the borough that has already decided to use the StrataCell in a pilot program. Residents will be able to see the new device in use, where it is being used to plant a shade tree near the sidewalk. Engineers have calculated that this device will support pedestrian and pavement traffic loads while providing more space for the extensive root growth of large canopy trees. This device has two tiers that lock together and form a framework that offers vertical and lateral strength.

So far, few municipalities have started using this device. “Mostly it is being used by developers. But I see uses for programs like our Shade Tree Commission.” Said George Biemesderfer. “It’s not cheap, but it’s a good alternative.”


Armillaria Root Rot

Armillaria root rot, Armillaria mellea, is often correlated with oaks and other hardwoods throughout California. The disease, which is a root fungus, attacks trees that are often found in urban landscapes as a result of excessive moisture in the soil. This is typically caused by overwatering in the landscape induced by excess irrigation and not allowing proper time for the roots to soak up the water and let the soil dry out. When too much moisture is in the soil, an anaerobic (oxygen free) environment is created. As a result, roots become starved to death by not having any oxygen in the soil. The roots eventually are not able to absorb water and will begin to die- off over time.

Some of the symptoms associated with armillaria root rot can be thinning of the canopy, dieback in the branches, oozing of fluid near the base of the trunk and mushrooms (fruiting bodies) at or near the base of the trunk. Thinning of the canopy occurs when leaves begin to fall prematurely at the ends of branches and no new growth occurs. The tree will appear to have a less dense canopy over a period of time. Dieback in the branches occurs when branches begin to experience discoloration and drying; they will have very little (if any) leaves attached to the branch. When oozing occurs at the base of the trunk, a dark thick liquid substance excretes from the bark, which gives the appearance that the tree is bleeding. Mushrooms are fruiting bodies that indicate that there is more than likely decay at or near the location of the mushrooms. They resemble the appearance of culinary fungi mushrooms commercially grown and purchased at the grocery store but are not edible.

Other factors that contribute to the disease can be compaction of the soil that is experienced during construction activity around or near the tree. Equipment that is stored near the tree can compact the soil due to the weight of the machinery. Equipment used for excavation can also damage trees by severing or crushing roots, even if only minimal disruption has occurred. Adding fill, dirt, to existing soil around or at the base of tree is not recommended as well because the added soil can increase weight and decrease oxygen in the soil where the roots lay causing unfavorable growing conditions for roots.

Once the tree is infected with the disease, it is more than likely the tree will decline over a period of time and in some cases lead to death or failure of the tree. Areas prone to high winds may cause the tree to topple over and fall. At this time, there are no cures for this disease; one of the mitigations for this disease is to check the soil and irrigation for prolonged periods of watering. This can be accomplished by reducing the amount of sprinkler run time for the area that waters the tree. When planning a landscape project, it is best advised to not plant oak trees in a lawn. Oak trees do not have the same watering requirements as turf so if possible redesign the landscape to incorporate oak trees outside the turf area.