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Posts Tagged ‘utility trenching’

It was just over a year ago that an ecologist and ISA-Certified Arborist, Lisa Montana, contacted me from AECOM, the global architectural/engineering giant.  She works in New York City, and is involved on projects that require utility trenching under sidewalks and around the roots of adjacent street trees.  When her project sites have contaminated soils, excavation must take place with shovels and bars, the old approach to bare-rooting plants.  On sites with clean soils, the workers use air tools, which let them remove soil and preserve important tree roots.

Lisa kindly sent me some photos of air-tool trenching projects she has overseen, and with my apologies to her for the long delay, I’m posting them here.  Take a look, and note how persistent and vigorous those critical roots are even underneath concrete pavement.

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This one is a 26″ dbh Honey Locust.

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This astonishing root mass belongs to a 28″ dbh Oak.

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These roots come from an enthusiastic 29″ dbh Norway Maple that needs the rooting area in the lawn beyond the sidewalk.

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This final photo shows a 32″ dbh London Plane whose roots are seeking moisture in the bed beyond the fence.

It appears as if each of these trees is reaching underground toward open ground, where adequate moisture and air can be found to sustain them.  I have been mulling over these photos for some time, and especially since Hurricane Sandy, when so many uprooted New York street trees appeared to have root masses that conformed to the bar-like shape of their planting spaces.  I wonder if those root masses had been cut at some point, as is often done for the reconstruction of a sidewalk or for utility work done in a less sensitive way than AECOMM’s methods.

Thanks, Lisa, for sharing these photos, and giving us a peek at what’s going on under some sidewalks.

Location:  New York City

Arborist In Charge:  Lisa Montana, AECOMM

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…and go back to school for a day.  If anyone in the Massachusetts woody-plants world has not seen the latest in tree- and shrub-planting techniques, here’s your chance:  on September 27, Rolf Briggs and Matt Foti will be giving a workshop entitled At The Root:  Air Tools Workshop at the New England Wild Flower Society’s Garden In The Woods.   Matt and Rolf will discuss and show the best techniques for planting trees and shrubs fresh from the nursery (air tools not necessary for this), as well as how to use air tools to trench under trees, decompact soil, and transplant trees.

I have my reasons to promote this workshop (and it’s next-day partner, At The Root: Understanding and Managing Healthy Soils), and they center on the fact that every planting season I find myself coaching laborers on how to deal with the root balls of plants that we’re planting on my job sites.  The boss, not knowing or having taught his laborers the proper planting techniques, usually has priced the work based on a quick  installation (dig the hole, stick the plant in, cover up the root ball, basket, and burlap), and the laborers, knowing only the quick and dirty method, look sideways at me as I show them what I want them to do.  The guys do the work the way I want it, but really, the process would go much more smoothly, and more landscapes would establish and grow in better, if everyone knew , priced, and carried out the work in what are considered the most plant-friendly ways.

Some of the most effective tools available to see what can be considered plant-friendly, and to work in soil crowded with roots, are pneumatic air tools.  I believe that Rolf and Matt will be transplanting a tree bare-root, using air, which will afford workshop attendees a chance to see what a tree’s roots really look like when the soil is blown away.  It’s an experience that can change how anyone working with plants understands how a plant grows and anchors itself, and for that alone this workshop is worth attending.

Watering in a newly planted tree-form Taxus from Weston Nurseries.

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The Massachusetts Arborists Association workshop on September 10, 2009, took place on a sunny, cool day at the Mass. Hort. Society’s headquarters at Elm Bank in Wellesley, MA.

Quite a few arborists and other landscape professionals attended the workshop, which began with slide talks and then moved outside to field demonstrations.

Quite a few arborists and other landscape professionals attended the workshop, which began with slide talks and then moved outside to field demonstrations.

This workshop focused on root issues, with demonstrations of what some of those issues are — conflicts with utility lines, the effects of poor growing and planting practices, decline due to compacted and poor soils, and inappropriate tree locations — and how they may be remedied.

Rolf Briggs and Tree Specialists set up shop at a couple of different stations to show how they use air tools both to decompact soils and to excavate utility trenches near trees.  The demonstrating arborists first discussed protective equipment, and showed what  they use when they employ air tools:  We watched as they put on respirators, helmets with face masks, ear protection, gloves, and either foul weather gear or jumpsuits — all necessary to protect from the great quantities of dust, soil, and stones blowing into the air.

To protect the surrounding area from flying detritus, Mike Hickman of Tree Specialists set up plywood or screen barriers around his work zone.  I’ve seen plain plywood sheets used; the Tree Specialist guys have figured out that hinging several sheets together makes for a sturdier barrier, a good thing if you’re using air tools with any regularity in anything but a wide-open landscape.

Hinged plywood panels keep the dust contained to the area around a trench.

Hinged plywood panels keep the dust contained to the area around a trench.

When it's necessary to dig a trench near a tree, air tools can do the job while preserving the tree's roots.  You can see roots crossing this trench, but plenty of space beneath them for a new conduit or line.  This trench was blown out with an air spade, and rocks and excess loose material after the blowing-out removed by hand.

When it's necessary to dig a trench near a tree, air tools can do the job while preserving the tree's roots. You can see roots crossing this trench, but plenty of space beneath them for a new conduit or line. This trench was blown out with an air spade, and rocks and excess loose material after the blowing-out removed by hand.

The power of compressed air will break up soil move it out of the way; it can also damage roots to some extent, by blowing root bark or feeder roots entirely away.  When using an air tool, experienced operators keep the nozzle moving to limit this kind of damage, and whenever possible (definitely not always possible in trenching work), they direct the air flow parallel to the direction of major root growth, away from the base of the tree.

Note the plywood barrier inside the trench as well, to focus the air blast and prevent soil from blowing into a previously blown-out section.

Note the plywood barrier inside the trench as well, to focus the air blast and prevent soil from blowing into a previously blown-out section.

Blowing out the trench.  This air tool is a new product that uses an auxiliary stream of water to help keep the roots hydrated and the dust down.  Tree Specialists is assessing this new feature.

Blowing out the trench. This air tool is a new product that uses an auxiliary stream of water to help keep the roots hydrated and the dust down. Tree Specialists is assessing this new feature.

After blowing out a utility trench, Tree Specialists simply returns the native soil to the excavated area.  They may add some amendments such as lime or humates, if they have already had soil tests done that indicate the need for such amendments.  And to mulch the area once excavation and backfilling are complete, they have developed a proprietary mix of chipped and composted wood fibers (mainly from tree parts 3″ and less in diameter), twigs, and leaves.  They use this same mix in their soil decompaction process, and note benefits to the trees from its use.

Mike Hickman pointed out that air tools break down soil aggregates and so obliterate soil structure in the area blown out.  This breakdown can be considered a disadvantage of using compressed air for excavation; in Mike’s words, “Destruction of some of the soil aggregates I see as a “con,” but proper horticultural practices such as mulching and site specific amendments effectively mitigate these cons.”

Demonstrating arborist at this station:

Mike Hickman, Tree Specialists, Inc., Holliston, MA

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