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Preserving Natural Resources During Landscape Construction – Part 2

Silver Falls trees

Last week, I discussed looking for valuable resources on your site prior to construction. Trees, particularly, add value and permanence to the landscape. They are the largest and longest-lived elements of most landscapes, and can be the largest element lost in it during construction. They also require the greatest area of protection to remain, so they take up what could be “usable” space. If trees are going to be kept on a site, they absolutely require protection in order to survive. Too often no protection or wholly inadequate protection is given, and trees will subsequently decline and die.  It can take years for damage to show, so don’t fool yourself if you see a tree still alive after a year or two. Mulch and sod can cover alot, but it doesn’t really fix things. Trees operate on a different time scale than we do, and damage often takes years to fully manifest itself.
  One of the main things to remember about trees are that the part you see above ground is only half the story. While the above-ground portion needs to be protected from careless treatment and machine operators, the damage that occurs to roots is much more likely to kill them.

What not to do: Cutting through roots in the tree’s root plate will compromise its long term stability.

Tree roots usually extend a great distance from the trunk, far past the “dripline”, with the vast majority of roots in the upper 18 inches of soil. In fact, the tiny, hairy absorptive roots that do most of the work obtaining moisture and minerals are usually in the organic-rich top few inches. Imagine each large root as a river that with many tributaries. All of those roots are flowing mineral-laden water in to support the tissue of the whole organism. These roots require soil, certainly, but too much soil can be damaging; they also require moisture and oxygen in the soil, with the ability for moisture and gases to move through the pores in the soil. Besides cutting of roots leading to root loss, fill soil and compaction disrupt roots’ ability and can kill them as well. Depending on soil types, sometimes even a few inches of fill soil can kill roots.
  A more important element to remember for safety is that tree roots are what physically hold trees in the soil. There is a zone around the trunk of larger roots that is especially important for anchorage, called the “root plate”. This area varies by tree, site, and species, but the rule of thumb is that the root plate is roughly going to be in a radius from the edge of the trunk 3 times the trunk diameter at breast height from the edge of the trunk.

Compaction from machinery and material storage should not be allowed around trees which are to remain on the site.

Design in mind- reducing footprint

1. After determining the needs and desires of the client for a particular project (and their desire or willingness to work on saving resources) as well as the community requirements, find the necessary expertise to assess the resources on a site, preferably before building and infrastructure siting, if possible. What existing trees, plants, or resources are desirable, and for what reasons? Will it be possible to integrate them into the new landscape? Will there be any conflicts in the future? Accurate mapping and inclusion in plans is critical to success.

2. Where preservation will occur, make it an integral part of the plan from the beginning, and follow through. In design, consider techniques that either protect resources, or integrate creation of infrastructure conducive to restoration. Post and pier construction and cantilevers minimize soil disturbance (though of course, there are limitations for implementation of those), and vertical construction damages less than horizontal. Structural soils, pervious pavers, soil cells, etc. can provide necessary infrastructure while providing opportunity for environmental benefit. 
 For preservation to work, it has to be a part of the process from start to finish. There has to be either one person or a set chain of people who maintain that consistency. Tree locations and protected root zones should be visible on all relevant project plan sheets. Grading, erosion control, foundation, civil, paving, and landscape plans may all impact tree preservation efforts. Notify all the professionals involved in the project that tree and resource preservation is a design goal. Show the protected trees and root zones on all plans to ensure that they are aware of the trees as they complete their work. Set protection zones, pathways for traffic, layouts and material storage and disposal areas, and limits on concrete or chemical debris disposal and tool washing. And remember that these protections can be written into contract language so there is a legal obligation to follow them, as well as set consequences for failure to follow them.

3. Again, a basic tenet of natural resource preservation is minimization of disturbance. Where soils, roots, and waterways are intact, resources are preserved. Of course, this is difficult on construction sites, so identifying areas that can reasonably be protected in the first place is critical. Remember that it’s not just the footprint of the building and entrance, it’s the utilities, sewer/septic, site grading and drainage, compaction from traffic, material lay down, soil storage, chemical spills, and fires, as well as any other activity that encroaches on trees above or below ground, alters the soil, or alters the drainage patterns on a site. Define areas of disturbance and storage, parking areas, etc. before work begins. Specify the process for initial clearing; removing understory plants with a machine is destructive to soils and roots, and grubbing stumps can damage remaining trees. If understory plants are to be removed, consider using either labor and herbicide, or perhaps a mulching head machine (if away from roots of remaining trees). If stumps must be removed, consider using a stump grinder instead of grubbing. If roots are torn, cut them cleanly and cover them as soon as possible.

4. After defining the protection zone, put up sturdy fencing with signs, and keep it in place throughout. The “critical root zone”  varies from 10 inches to 1.5 feet of radius per inch of trunk diameter as the minimum. This is not always possible. Where traffic and potential compaction may occur, but the roots are still present in the soil, layers of mulch or gravel covered with sheets of plywood or steel can distribute weight more evenly and reduce compaction.

5. Have a plan for post-construction. Irrigation and soil remediation can help trees recover. And remember that while landscaping can help rehabilitate a site, it too can damage roots. Be prepared for some failure, and try to mitigate as soon as possible.


Michael Davie

ISA Board-Certified Master Arborist

Snow Creek Landscaping, LLC



James Urban, Up By the Roots- Healthy Soils and Trees in the Built Environment
Nelda Matheny and James R. Clark, Trees and Development: A Technical Guide to Preservation of Trees During Land Development
Laurence R. Costello and Katherine S. Jones, Reducing Tree and Infrastructure Damage by Tree Roots
The Landscape Below Ground- proceedings from the International Workshop on Tree Root Development in Urban Soils
NC State “Construction and Tree Protection”:

Sample tree protection language:

USFS Urban and Community Foresty:

USFS Itree tools:

Construction Damage Assessment: Trees and Sites, by Kim Coder, Warnell School of Forest Resources:

Preserving Natural Resources During Landscape Construction – Part 1

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In “Green” building, the main emphasis is usually on creating energy-efficient design and using sustainable materials. Other than typical erosion control measures, often not much thought is given to site preservation.
 Natural resources are the existing resources within a landscape, supplied by nature. Plants, animals, soils, water, even microbes are some of the natural resources on any given site before disturbance. The quality of the resources can vary widely from site to site, or even within a site, but don’t discount the value of the resources without investigating what is there. While what looks like a thicket of scrub or a weed patch to the uninformed may be just that,  many times there are a variety of wonderful plants there that can be kept and managed to benefit the site. Often many of the plants on a site are well suited to it, already established, and already adding value to it. Existing soils are usually stable, and nearly always better for plants than disturbed soils, due to fertility, porosity, and fungal and microbial activity. Of course, building projects by their nature have to disturb or destroy some of those resources; trees must be felled, soil must be moved, water must be diverted. This is unavoidable; but it can and should be done in a way to minimize the damage and integrate the project into the landscape.
  The most basic tenet of natural resource preservation is minimization of disturbance. Sites can be cleaned up and somewhat rehabilitated after construction, but even site rehabilitation involves more disturbance. The goal is creating a stable and sustainable environment around buildings, one conducive to human use. Whenever it is feasible, not disturbing parts of a site puts us well on our way to that, and can often make new construction more attractive, seem more established, reduce erosion, and provide habitat and other environmental benefits.


Some of the benefits of trees and natural resources:

Social– Trees and nature create a pleasing environment for us to inhabit. Vegetation can cool surrounding air in the summer, and trees can provide privacy, shade, and shelter. It’s even been shown that patients recover from surgery more quickly in rooms with views of trees.
Aesthetics – At times, the existing plants, trees and water are beautiful. Mature trees can add many aesthetic benefits to a place, and give the landscape a sense of permanence. Sometimes, things may look poor, but consider that it may just require a little work to make it attractive, and it can be possible to have established landscape in those areas immediately, as well as intact soils.
Intact soils – If the soil matrix is intact, soil likely has fertility and horizons— that is, the strata that develop in mature soils. Undisturbed soil absorbs more runoff, and is much less likely to erode. Roots of plants and trees in undisturbed soil hold the soil in place, absorb moisture, and cool temperatures in summer. Some plants can even absorb heavy metals in soils.
Property values – time and again studies have shown that landscaped properties and those with mature trees are more valuable than ones without.
Environmental – the environmental benefits of trees are manifold. They provide shade, habitat, shelter from the elements, improve air quality, moderate temperatures, and on and on. Soil, especially undisturbed forest soil, is not just dirt, it’s a complex interweaving of ecosystems, a balance between fungal, microbial, biotic and abiotic entities.

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Often, taking a look at what plants are growing on a site can give clues as to which plants will thrive in the landscape. Next week, we’ll look at some of the ways to minimize site disturbance.

– Michael Davie

Master Arborist
Natural Resource Manager


Using boulder walls to retain a slope and stones for a patio serve a purpose in the landscape that goes beyond function. Choosing the right materials for the hard elements in a project can make the difference in a landscape that looks complete and authentic versus one that will look dated and unnatural as the years go by. Here are a few photos of projects with nice hardscapes that will stand the test of time and get better with age.

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More Flowering Trees

As spring marches on, every day seems to bring another favorite tree into bloom. I’ve compiled some photos to showcase some of the best flowering trees.

First up, the lovely Serviceberry, Amelanchier canadensis, also known as shadblow. This tree finished blooming a few weeks ago:Serviceberry1


Here is the elegant Silverbell, Halesia diptera. These trees are so pretty with their white bell-shaped flowers:


Halesia detail

Also blooming right now is Aesculus x ‘Fort McNair’. Fort McNair is a hybrid between the Red Buckeye (native) and the European Horse Chestnut.

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And last but not least, the Fringetree, Chionanthus virginicus. I know I’ve said it before, but one of my favorites.


Fringetree detail

As you can see, there is a wealth of trees that are well-suited for our region. Featured here are natives, or partial natives, that can be wonderful assets to your garden.

Dogwoods and Redbuds: Two Favorites


Eastern Redbud


Flowering Dogwood

Little introduction is needed for two common trees that are found in our Appalachian region. Anyone who lives here can’t help but to notice the spectacular displays of the flowering dogwood, Cornus florida, and the eastern redbud, Cercis canadensis. These species of trees are native and are also commonly planted. In order to maintain genetic diversity, it is best to stick with straight species of plants when re-naturalizing disturbed areas, but for a specimen tree in the garden setting, often a cultivar is a better choice.

Cornus florida

Flowering dogwoods are wonderful trees but can suffer from diseases, especially an introduced one called anthracnose. Cornus fl. ‘Applachian Spring is a selection that was introduced as the most disease-resistant cultivar on the market. It has the typical form and habit of a common dogwood, but the white flowers (really just bracts; the true flowers being the small ones that make up the yellow center) are a little larger and creamier in color. It also has excellent red color in the fall accompanied by red berries that birds find irresistible.

Foliage of Cornus florida ‘Appalachian Spring’
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Cercis canadensis var. texensis ‘Oklahoma’

Eastern redbuds look stunning with dogwoods, which bloom around the same time. A fine cultivar to try is Cercis canadensis var. texensis ‘Oklahoma‘. This tree was a favorite of plantsman J.C Raulston, and for good reason. ‘Oklahoma’ has a lusterous leaf and consistent deep purple flower color, with the shape of the tree being generally wider and more compact than the straight species.

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‘Oklahoma’ flowers

If you are looking for special trees to plant in your garden or yard, these are unrivaled in their beauty. Since both are native to our region, they are well-suited to our climate and offer benefits to wildlife as well.
We have dogwoods and redbuds in stock. Give us a call – 828.687.1677