Protect Your Trees, Please!

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We all love trees in our built landscapes, but the odds are against their survival if we don’t follow a few simple rules. Although I’m not a horticulturist or urban forester, I’ve worked with people in those professions in the past and learned a lot from them. I’ve also attended lectures and webinars by renowned arboriculture expert, James Urban, from which I’ve gained valuable knowledge.

I’ve seen countless examples of trees that are improperly sited, planted, and/or maintained, which oftentimes has shortened their life span. Below I’ve listed some guidelines for design, installation, and maintenance that will increase the chances of your new trees thriving to a venerable old age, and keep existing trees healthy as well.

New Trees:

  • Shade trees such as Maples and Oaks should be spaced at least 35 feet on center for healthy crown (canopy) development.
  • Do not specify tree grates or guards. These will girdle (i.e. strangle) trees when their trunks outgrow the size of the grate hole or guard diameter. Better alternatives around the base of the tree are mulched areas, groundcover plantings, pavers on sand setting beds, or porous rubber surfacing, which the tree trunk can push away as it grows.
  • Avoid specifying staking and guying, since the guys are frequently never removed, girdling and killing the tree as it grows. A tree cannot survive if its supply of water and nutrients is completely cut off. (This action occurs in the cambium layer, just beneath the bark.) Trees do not need stakes and guys unless they are planted in extremely windy sites or have abnormally small root balls in comparison to the size of their canopy. In these cases, make absolutely sure that the stakes and especially the guys are removed after the first growing season.
  • Tree roots generally extend at least to the edge of the zone beneath the canopy of the tree, and often beyond that. Don’t limit the root zone to such a small area that the tree becomes stunted. Plan for its future growth where possible.
  • When the budget allows, invest in modular subgrade cells and structural soils to prevent soil compaction where trees are sited in sidewalks, plazas, and other hard-surfaced areas. These allow roots to grow sufficiently beneath paved sites, resulting in much healthier trees than those planted without these systems.
  • The planting hole should be at least twice the diameter of the root ball.
  • If roots are pot-bound (encircling the root ball), they should be unwound and extended out from the root ball as much as possible when planting.
  • The root ball should be set on firm soil so it the ball does not settle. The trunk flare, or collar, needs to be at least 3 inches above surrounding grade.
  • After the root ball is set in the hole, the areas around the root ball should be backfilled with un-amended native soil. Tamp soil in place by hand. Water heavily before mulching, and fill with more native soil where it has settled. Do not place any soil over the root ball.
  • Mulch should be about 3 inches thick, but no mulch should be placed within 6 inches of the trunk.
  • Trees should be watered at least once a week during drought periods for the first two years after installation. This means thoroughly soaking the root ball by hand, and not relying on sprinklers!

Existing Trees:

  • On construction sites, keep construction equipment and any other heavy objects away from the root zones of existing trees. I advise specifying/installing temporary fencing around the root zones for this purpose. Compaction of soil around roots will kill a tree.
  • Do not specify any grading within root zones of existing trees (neither cut nor fill). Cutting will destroy roots; filling will suffocate them.
  • Do not trench though a tree’s root zone, for installation of utilities or any other purpose. As mentioned earlier, this zone often extends beyond the tree’s canopy edge. The small feeder roots near the surface of the soil are just as important to the tree as its larger roots are. Cutting through any roots will often shorten the life of the tree.

All Trees (Old and New):

  • Do not “volcano mulch” around trees (piling mulch high around the trunk). This can lead to rot and decay of the buried part of the trunk, and result in a tree’s death. As noted earlier, mulch should only be about 3” thick, and should not be placed within 6” of the trunk.
  • Keep a mulch or plant bed around trees that are in an open lawn situation, instead of allowing grass to grow to the trunk. Turf adjacent to trees can be an invitation for overzealous weed trimming around the trunk, which can cut through the bark, particularly of young trees. If these cuts completely encircle the tree, this can result in girdling, leading to the tree’s death.
  • If you’re going to hire someone to prune your trees, be sure to hire a certified arborist for this job, not just anyone with a chain saw. Improper pruning can compromise a tree’s health.
  • Do not encircle a tree’s trunk and branches with strings of holiday lights, unless you plan to remove the lights after the winter season or holiday. If the lights are left in place indefinitely, the tree will be girdled as it tries to grow.

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Death by tree ties
 
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Trees outgrowing their grates and guards
 
Photo credits:
Top photo of large tree – Stefan Wernli (obtained from Wikimedia Commons)
All other photos – Alice Webb

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On the Ground – Creative Pavements in Montreal

While visiting Montreal recently, I came across a number of public spaces with attractively-patterned pavement, many combining various types of stone. My favorite was Place d’Armes, which was renovated in recent years, but other fine examples are shown below as well.

Montreal plazas 1
Place d’Armes, in Old Montreal, includes smooth granite pavers in various shades of gray, interspersed with stripes of pinkish cobles. The custom-designed tree gates coordinate well with the coble patterns.

Montreal plazas 2
The cobbles in the streets surrounding Place d’Armes are repeated in random stripes within the perimeter of the plaza.

Montreal plazas 3
The large, central, open area of the Place d’Armes includes gray granite pavers punctuated by these pink ones sporting fleurs-de-lis.

Montreal plazas 4
The renovated Square Dorchester includes pavers with a range of textures. The smoothest ones shine both during day and evening, giving the walkways a glittery appearance.

Montreal plazas 5
Intermittent crosses in the pavement at Square Dorchester, formed with rough-textured pavers, signify the historic use of this space as a burying ground.

Montreal plazas 6
Stripes of colored concrete pavers in various hues and sizes at Place Ville Marie

Montreal plazas 7
Metal drainage grates serve nicely as linear accents in this park next to Montreal’s convention center.

Montreal plazas 8
An attractive pattern of concrete pavers and tree grates

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Strips of white pavers repeat the linear pattern of water jets in the Place des Festivals.

Photos by Alice Webb

Parc Hydro-Quebec

In Montreal’s Quartier des Spectacles, an interesting little park is tucked between two buildings, designed by renowned landscape architect, Claude Cormier. It features a raised metal grill of varying widths that functions as a pedestrian walkway/court, punctuated with Honeylocust trees and star-shaped benches. Native perennials and ground covers are planted in the low-lying areas along the sides of the park. The walkway, essentially one large tree grate, protects the underlying soil from compaction and allows for rainwater infiltration, promoting healthier trees and sustainable stormwater management. In fact, there are no impervious surfaces in this park that are larger than the benches. Appropriately, the park is situated next to the green-roofed Centre for Sustainable Development.

Parc Hydro-Quebec 1
Parc Hydro-Quebec with the Centre for Sustainable Development in the background

Parc Hydro-Quebec 2

Parc Hydro-Quebec 3
Interesting use of pottery shards instead of gravel beneath the walkway

Parc Hydro-Quebec 4

Photos by Alice Webb

Pedestrian Promenades

During my recent travels, I have seen a number of notable walkways along waterfronts, beside city streets, and through urban and suburban parks. Well-designed pedestrian ways have ample width for movement and social interaction, and include visually-unifying elements throughout, such as a continuous paving pattern and repeated furnishings and plantings. These promenades should also be designed to correspond with the character of their surroundings, as well as provide a pleasant and safe experience for pedestrians.

Transit shelter, Portland OR
The transit mall in downtown Portland, Oregon, has wide sidewalks with decorative pavement, beside streets that have traffic lanes reserved for light rail and buses. The walkways include these attractive clear transit shelters.

Streetside boardwalk, Portland OR
A boardwalk runs along NW 10th Avenue in Portland, Oregon for 4 blocks between two parks. It’s unusual to see a wooden walkway along an urban street. This section, which is adjacent to Jameson Square, is wide enough for a double row of trees – a pleasant place to take a stroll.

Streetscape, South Boston MA
Eye-catching pavement pattern along a portion of Northern Avenue, adjacent to the Fan Pier Public Green in South Boston, Massachusetts

Fayetteville St, Raleigh NC
Fayetteville Street in Raleigh, North Carolina, was turned into a pedestrian mall in the 1970s, but the street was added back in 2006 along with these wide sidewalks with decorative planters, benches, lights, and other features. This corridor’s revitalization is reported to be a success in terms of bringing in more business.

Church Street Marketplace, Burlington VT
The Church Street Marketplace, in Burlington, Vermont, has been in place since 1981, and is one of the few continuously successful pedestrian malls in the U.S. This lively promenade is full of retail stores and restaurants with outdoor seating areas.

Park in Clayton MO
This park in Clayton, Missouri, includes a linear lawn space extending between two streets, bordered by two walkways. Seating areas and plantings line the edges of the promenade. Not many people were outside on this cold day in late October.

Streetscape, Clayton MO
A simple but attractive pavement design along a street in Clayton, Missouri

Walnut Street Park, Cary NC
This beautifully-patterned brick walkway winds its way through Walnut Street Park in Cary, North Carolina.

Boardwalk & Promenade, Myrtle Beach SC
This curvilinear promenade runs along part of the ocean in Myrtle Beach, South Carolina. It is surfaced with concrete in contrasting colors and textures.

Waterfront Park, Burlington VT
Waterfront Park in Burlington, Vermont, is bounded by a boardwalk which includes nautical-style lighting, granite bollards, and swinging benches.

Central Park - The Mall, New York City
The Mall in Central Park, New York City, is an example of a historic promenade with lovely old trees.

Photos by Alice Webb