[CANUFNET] Materials for base of trees

[Alex Satel - UFI]

Taylor - here are a few references you might find useful:


  *   London Tree Officers Association - Surface materials around trees in hard landscapes

https://www.ltoa.org.uk/surface-materials-around-trees-document/file


  *   City of Toronto - Tree Planting Solutions in Hard Boulevard Surfaces: Best Practices Manual (Sec. 5.1, starting page 34)

https://issuu.com/dtah/docs/iii-iv_best-practices-manual_append


  *   Trees & Design Action Group (TDAG): Trees in Hard Landscapes: A Guide for Delivery (Sec. 2.6.2, starting page 66, PDF file)
https://www.tdag.org.uk/uploads/4/2/8/0/4280686/tdag_tihl.pdf

All things being equal (in terms of soil quality/volume, drainage/irrigation, etc.), I think the best solution is almost always going to be an open planter, with a raised curb and even foundation planting or a small fence if necessary (great examples of this in downtown Chicago, for instance... large open planters with short fences that keep people and dogs out<https://maps.app.goo.gl/UJQ62BMKru4RavTv6>). This helps keep compaction and soil pollution down and provides the largest area for water to infiltrate (especially in combination with passive irrigation, assuming it's correctly designed, maintained, and not super salt-laden). However, this typology takes up a lot of real estate and is not  always acceptable due to accessibility considerations and cost. These planters can also pose a tripping hazard for the vision- or attention-impaired, interfere with parking, etc. etc.

In those really tight high pedestrian traffic hardscape areas, I think resin-bound aggregate often seems to be a good solution, although it too has its downsides (cost, clogging if not maintained, complexity, limited flexibility for tree growth, heating up, encourages people to go right up to the tree, etc.)

Contrary to what seems to be the prevailing sentiment, I think good old-fashioned tree grates can also work if they are correctly installed, routinely inspected, and maintained (enlarged and/or reset) when required. However, they can also pose a serious tripping hazard, so inspection and maintenance are key. There are also heavy-duty rubber alternatives that look like the traditional iron grates but are more flexible, though I don't know how well they perform; never really seen one in action as far as I know.

Another potentially interesting solution was installed on Roncesvalles Ave. in Toronto maybe 10 or 12 years ago, and that is a combination tree grate and tree guard<https://maps.app.goo.gl/DA9nEHBh2JeZNmeR9>. These trees are planted in a precast pavement bridge situation<http://treecanada.ca/wp-content/uploads/2017/10/CUFC-2014-19-James-Urban-Toronto%E2%80%99s-Pioneering-Standards-for-Trees-in-Hard-Boulevards.pdf> (see slide 13), and many of them are really thriving (though some have died... probably ones without much soil volume). The nice thing about the tree guards here is they have kept bikes away from the stems and people further back from based of the tree, but the time has come that many of the tree guards need to be removed to accommodate stem growth. Many of the tree grates are also lifted, again causing tripping hazards (especially once the guards are removed and people start walking over the grates rather than skirting around them). These grates probably need to be removed and backfilled with something - maybe a good place for the resin-bound aggregate? Mulch could work too, but the lip of the concrete planter edge would, again, probably be a tripping hazard. But not bad for 12 years essentially maintenance-free. Obviously this was a hugely costly streetscape reconstruction, but I think the lessons learned can apply to smaller retrofit situations as well.

We also worked with a municipality a little while ago that was trying bonded pulverized rubber mulch rings<https://www.canadiantire.ca/en/pdp/tree-mulch-ring-recycled-rubber-24-in-0591837p.html> around the base of hardscape trees. In my humble opinion they looked absolutely terrible but apparently they helped keep the weeds and trampling down. <https://www.canadiantire.ca/en/pdp/tree-mulch-ring-recycled-rubber-24-in-0591837p.0591837.html> They were also using plain shredded rubber mulch in some planters and openings, but were having similar issues as with natural mulch after heavy rains... not good to have chunks of rubber all over your sidewalks and gutters after a rainstorm.

Honestly, it seems like we haven't quite figured out the perfect solution to this one yet - for every upside to any approach there seems to be an accompanying drawback. Keep us posted if you try something new that works for you!

Best of luck in your search, apologies for the long-winded response, and have a nice weekend.

Alex

Alexander Satel, MFC
Urban forestry and arboricultural consultant
ISA Certified Arborist ON-1353A
ISA Tree Risk Assessment Qualified (TRAQ)

Urban Forest Innovations, Inc.
Mississauga, ON
T: (905) 274-1022
asatel at ufis.ca<mailto:asatel at ufis.ca>
urbanforestinnovations.com<http://www.urbanforestinnovations.com/>
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From: CANUFNET <canufnet-bounces at list.web.net> On Behalf Of Taylor Morris via CANUFNET
Sent: Friday, April 26, 2024 2:51 PM
To: canufnet at list.web.net
Cc: Taylor Morris <morrist at portcoquitlam.ca>
Subject: [CANUFNET] Materials for base of trees

Hello Canufnet!

I am currently exploring alternative materials to place around the base of trees that are surrounded by sidewalks/paving. Typically we use crushed rock and compact it in order to minimize tripping hazards. We are interested in finding other options to mitigate some compaction and provide better drainage for the trees. We've experimented with mulch, but have encountered challenges with its longevity, particularly due to heavy rainfall in the Pacific Northwest.

I'm reaching out to inquire if anyone in the community has experience with using pour-in-place rubber or molded rubber as an alternative solution?

Any insights or recommendations on materials or techniques would be greatly appreciated.

Thanks in advance!

Taylor Morris City of Port Coquitlam Urban Forestry Tree Technician morrist at portcoquitlam.ca<mailto:morrist at portcoquitlam.ca>

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