Curbside Manners – Respecting the Roots

The author inspects his handiwork while exposing the roots of the street tree that was destined to be saved. All photos courtesy of the author.
The author inspects his handiwork while exposing the roots of the street tree that was destined to be saved. All photos courtesy of the author.

I arrived at the site in a tony section of town with some prior experience. Of all the towns in Massachusetts, Brookline has some of the toughest tree ordinances, which is why I was engaged. A town-owned Norway maple stood in close proximity to a planned driveway. In the vast majority of cases I have worked on, I would have advised to remove and replace. The tree was not unique; in fact, it is on the invasive-species list here. Neither was it especially attractive or healthy.

However, Brookline tree ordinances state: “The town will not remove trees because they drop leaves or acorns, because it has grown too large or shades a private lawn, or because it is not conveniently located. The removal of public shade trees requires a public hearing in front of the Tree Planting Committee and the Tree Warden as prescribed by state law.”

City arborist Tom Brady and the homeowner discuss the tree.

I had worked with Tom Brady, aka “Tompa Bay” Brady, the municipal arborist, before, and knew him to be fair and agreeable, but hardly a pushover. Many a developer or homeowner has tried to give Tom the ole’ “I’ll replace the removed tree with x number of nursery-sized stock.” Tom responds with the simple fact that in terms of cooling, storm-water retention, erosion control, wildlife habitat and a host of other environmental attributes, you simply cannot replace the benefits of a mature tree with 3-inch nursery stock.

It’s hard to argue with that. I grew up in Worcester, where streets were lined with Norway maples, replacements for the American elms that previously had been decimated by Dutch elm disease. Norway maple, the tree du jour, was available and affordable. Figuring, “What could go wrong?” the elm trees were replaced with another monoculture.

Fast forward to 2006, when the Asian longhorned beetle was first discovered in Worcester. Close to 35,000 trees were subsequently removed to contain the outbreak, the vast majority maples. I visited my old hood after the carnage to find the streets, desolate in the summer heat, lined with pathetically small replacement trees. My memories, compromised as they may be, evoked a cool oasis lined with an arching canopy. Folks sat outside, and we kids played in the wide, shaded street. The neighborhood that had felt safe and welcoming now seemed barren and stark.

The roots are fully exposed and ready for fill.

Back in Brookline, closely situated, stately brick homes, from modest to generous in size, grace the curving, tree-lined street. The trees are contained in a classic, narrow planting strip between sidewalk and road, intersected by driveways. Lord knows the variety of insults these trees have endured. That said, the Norway abides. Hundreds line the street, the majority in fair to good condition, enhancing the general positive vibe and feel of the neighborhood.

The majority of people who live in these homes would be unaware that these trees are considered invasive, and would hardly care. The benefits provided are obvious, and their loss would be conspicuous.

The subject tree is located six feet from the edge of the proposed driveway. Preliminary excavation revealed major roots close to the surface running parallel to the street. There would be no cutting of roots.

It took almost a year to obtain all the permits, documents and approvals required to begin work on the driveway. Air-tool and Tyvek suit in tow, I arrived at the site to expose the roots and then determine a course of action. I set up my barriers and began playing in the dirt. The soil blowing into my face and up my nose suggested a loamy-clay mix with a hint of root, and an earthy aroma. It broke into small particles easily when air blasted.

I brought the level up to grade, covering the roots and allowing space for the asphalt.

Tom arrived in the afternoon to inspect the site and discuss a solution. I was anticipating some type of bridge system to span the gap over the roots. It would be somewhat complex, expensive and beyond my expertise. The biggest concern was the immediate impact of heavy equipment that would need to drive over the roots during construction. To my delight, Tom came up with a good, practical solution. A structural soil, made on site, would be used to fill over the roots and covered with a layer of permeable asphalt. A layer of wood chips or temporary bridging would be installed over the area during construction.

The aggregate is mixed on site and filled in by hand, making sure to fill any voids.

Wow. That was simple. I have watched arboricultural tools and techniques explode over my career. Some are innovative and game changing. Others, in my opinion, are over the top and not practical in most situations. A recent webinar on risk assessment featuring Jeremy Barrell, a prominent arborist in the United Kingdom, expressed that view as well. He often will show up for a risk assessment with a hammer, poking device and, most important, decades of experience.

Myriad treatments have been offered for improving tree health. To this day, study after study shows that applying a 3- to 4-inch layer of wood chips over the root zone is still the most effective. Be careful of overthinking. Our big brains are a constant impediment to progress. Common sense is not common.

I slept with ease that evening with a plan in mind. I had researched structural soils and came up with a formula to use. A ratio of 80% crushed stone (3/4 to 1-1/2-inch) to 20% screened loam in dry weight is suggested. The soil should be at least 20% clay to maximize water and nutrient-holding capacity. A tackifier also is suggested to bond the soil to the stone, but was not used here.

Enjoying a morning coffee, I noted that a recently passed kidney stone displayed on my desk resembled a scale model of the compacted aggregate I was planning on using. This obvious sign from the heavens confirmed I was on the right path. Feeling confident, I headed off to the job site with a sparkle in my eye and a spring in my step.

Tom, right, appears to have chosen a tidier career path than myself.
The Omen. A simile of the aggregate in the form of a kidney stone is displayed on my desk.

Timing is everything, and I don’t think it could have been much better. The tree was in dormancy and the soil moist and not yet frozen. The weather was agreeable. Using hand tools and the air tool, I was able to expose the roots more and get underneath them to a solid sub-soil layer. Fortune continued to shine on me as a load of stone suitable for my purposes was already on site. The finely textured loam-clay particles that were a result of the air-tool excavation would be excellent filler.

I mixed the materials in small batches and filled the area gradually, carefully poking and tamping to eliminate air pockets. I brought the level up to grade, covering the roots and allowing space for the asphalt. After cleaning up the site, I took a moment to marvel at the patch of gravel I had created. No one would know the efforts placed into that 8-foot by 6-foot piece of earth to save a lowly street tree.

A simple plan: driveway/root mitigation completed.

I thought of my old neighborhood, its character profoundly altered by the loss of the tree canopy. My character was influenced by those trees as well. Would I have become who I am without them? Maybe, but probably not for the better.

Howard Gaffin, BCMA, RCA and Massachusetts Certified Arborist, is owner of Gaffin Tree & Landscaping, a nine-year TCIA member company located in Rowley, Massachusetts.

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