Preventing Root Damage in Forests and Landscapes

The Root of the Problem

It may not look like it at now, but mud season is right around the corner. In towns and villages, spring involves returning songbirds, blooming flowers, and a birth-frenzy of construction projects fresh off their winter-long gestation.

But "construction damage" does not only apply to human landscapes. In rural areas, maple production often brings tractors into the woods during mud season, and timber harvests may continue even during the period between snow melt, and dry soil conditions.

More often than not, residents and developers are on the same page in protecting mature trees from construction damage.Sadly, a great many tree-preservation efforts fail in the end, but not due to lack of political will or good intentions.

The issue is that bright engineers, architects, landscape designers, and community activists are rarely also experts in tree biology. As an example, those good folks I just mentioned would probably say it would be a problem if a forwarder or cement truck were to clip a tree as it drove by, tearing a huge divot from the trunk.

An arborist would tell you differently. She or he would explain that the real problem is the massive, irreparable, fatal but invisible harm inflicted by that heavy vehicle on the its way past the tree. A glaring wound on its stem would be of no significance whatever, because that tree has been killed. It will take 3 to 7 years for it to “realize” it is dead, however – lethal root damage shows up over time. A tree preservation plan which focuses on guarding trunks from being hit by vehicles is worthless. Construction damage to trees is root damage; there is no other kind.

About 90% of tree roots are in the top 10" (26 cm) of soil, and 98% are in the top 18" (46 cm). A tree’s roots extend, unless there’s an obstacle like a road or building, two to three times the length of its branches. This is a tree’s root zone: a broad, shallow, vulnerable mass of roots.

It’s true that trees such as oaks and walnuts have a taproot when young, but in maturity their root systems look like a pancake, not a carrot. Most of us have seen trees which have been uprooted by a storm, but that monster taproot has yet to be spotted. It’s no coincidence that the flat root system one sees on a windthrown tree is referred to as a root plate.

To survive, roots need to get oxygen directly from soil pores. Compaction from vehicles or equipment operated within the root zone will permanently compress pores and exclude oxygen. Adding soil to the root zone to raise the grade (for instance to lay sod) has the same effect. In these cases, roots slowly suffocate, and trees will eventually show symptoms of decline. In wet soil conditions, he damage potential is much, much greater.

Excavation or trenching activities within a root zone will sever some tree roots, and compact the rest. Root damage may kill a tree outright within a few years, but more commonly there will be a prolonged decline over 5-10 years. Because of this time lag, oftentimes it is secondary, opportunistic agents which get the blame.

It is a fair question to ask how street trees in little concrete squares (tree pits) in the sidewalk survive. Because they are put there when young, they adapt to available root space. In technical parlance they are deemed “unhappy.” If a mature tree with a normal root system suddenly has its roots cut or damaged to the size of a tree pit, it would be termed “dead.”

To preserve trees, one must take preventive action BEFORE the first vehicle or worker arrives. Work with an International Society of Arboriculture (ISA) Certified Arborist to cordon off root zones at least to the drip line or branch length. Even stockpiling material under a tree can cause root damage. If driving close to trees is unavoidable, maintain wood chips at a depth of 8-16" (20-40 cm) in the traffic lane(s) throughout the life of the project.

When excavation within the root zone is necessary, consider directional drilling, which can tunnel below roots. If that is not an option, try to cut roots cleanly, flush with the trench wall. Lay wet burlap over the root ends until it is time to backfill. If over 40% of a tree’s root system is cut, it is better to remove the tree. Damage of that magnitude will lead to future instability.

Mitigating damage after the fact is not as effective, but if that is the case, act quickly. By the time symptoms show up, it will be too late. Hire a Certified Arborist to loosen soil with high-pressure water or air injection. Soil injections of beneficial microbes in solution has been proven valuable.

For more information on avoiding root damage to trees, visit the ISA’s educational pages at, or reach out to your Cornell Cooperative Extension office.

Paul is an Educator for CCE-St. Lawrence, has been an ISA Certified Arborist since 1996, & is a member of the SAF, NY Arborists, & the Canadian Society of Environmental Biologists.

Views: 61


You need to be a member of CornellForestConnect to add comments!

Join CornellForestConnect


Saving the American Chestnut

Started by Stephen Kutney in Woodlot Management Aug 24. 0 Replies

Below is a message from the American Chestnut Foundation on the deregulation of the Darling 58 blight-resistant American chestnut.SteveThe 60-day public comment period is now open and will remain open until Monday, October 19, 2020. Here are two…Continue

Forester recommendations?

Started by Roger Rodriguez in Woodlot Management. Last reply by Kelly Nywening Jul 15. 1 Reply

We are new to forestry ownership and need some advice. We would like to be good stewards of the property and also provide occasional profit of some kind, especially to offset the taxes we pay on the property. I was thinking tree farming (?) as a…Continue

Nitrogen fixing bacteria for Alder trees

Started by Joanne Vaughn in Woodlot Management. Last reply by Joanne Vaughn Jul 11. 14 Replies

I am thinking of starting some alder trees from seed for planting into an area that does not and has not hosted alders.  How can I gain the nitrogen fixing bacteria for inoculation of the roots ?  Continue

How long do brush cutter blades work?

Started by Joanne Vaughn in Woodlot Management. Last reply by Ely McLaughlin Jul 8. 1 Reply

I dunno maybe it's because time flies when it's multiflora rose and buckthorns that are getting whacked. It seems that these blades are needing retirement after 8 or so hours.   Is this typical for this type of material. WIde range of material but…Continue

Tags: cutter, brush

Seeking advice on controlling oriental bittersweet

Started by Kristen Whitbeck in Woodlot Management. Last reply by Lew Ward Apr 15. 2 Replies

A student in my silviculture class is seeking relayed the scenario below. If anyone has any tips or tricks I will gladly pass them along. Thanks in advance!"Oriental bittersweet is choking out my mature white pine trees and my mature apple trees.…Continue

Tags: bittersweet, Oriental

Are Gall's a reason to cull Hickory trees?

Started by Thomas Wilson in Forest Health. Last reply by Ron Goodger Apr 7. 8 Replies

I'll take a photo, but in the meantime....I have a lot of bitternut hickory and some shagbark as well.  I haven't yet noticed any on the shagbark, but about half of the bitternut have gall's.  They get up to about 3 inches in diameter.  Some tree's…Continue

Removal of grass around seedlings in pasture

Started by Joanne Vaughn in Woodlot Management. Last reply by Peter Smallidge Mar 19. 11 Replies

Even after the timely discussion of "green lie" this week, I am still unsure of the best method to eliminate grassy vegetation around the pine, cedar and oak seedlings we are putting in this spring. I feel this is very important because we lost a…Continue

Saving Trees With Tree-Eating Mushrooms

Started by Lew Ward in Forest Health Feb 27. 0 Replies

Saving Trees With Tree-Eating MushroomsControl of Amellaria Shoe-string Rot Fungus



© 2020   Created by Peter Smallidge.   Powered by

Badges  |  Report an Issue  |  Terms of Service