[CANUFNET] Trees and boulevards
james urban
jimtree123 at gmail.com
Sun Oct 10 17:00:38 EDT 2021
To my Canadian Friends:
Stock piling and Reusing soil does maintain a serviceable soil for urban trees. It has been the standard for as long as I have been in the profession. Ecological perfection is not the goal just reasonably good tree growth which we see in these soils. Note that I will not using the term “topsoil”, a highly abused term. I will use organic soil referring to the layer that was harvested from the top of the soil profile and with a higher organic content. 2-3% dry weight is fine for trees and wordy shrubs.
The number one issue is stopping the soil screening process, particularly damaging in the silt soils in southern Ontario. The other issues are how the sub grade is prepared or abused, how the organic soil is spread and how deep and how it is compacted. Too often the sub grade is compacted and or graded with a smooth sub grade surface. Then a thin layer of organic soil maybe 4-6 inches deep is spread to support grass and small shrubs.
Solutions:
Idea one is too spread and or grade the last foot of subsoil with a rough chunky surface. This upper subsoil layer should not be compacted greater than 85-90%. It is difficult to control this idea since the engineers write the grading specification. Spread the unscreened organic soil at least a foot deep and to the depth of the rootball for a distance of at least 15 feet diameter at each tree. Or better, make the entire soil profile of organic soil the depth of the root ball. You can add compost to the surface but don’t overdo it below 4-6” deep. Preventing compaction across the soil profile or loosening what is there in a way that keeps chunks and lumps in all the soil is critical.
STOP using soil mixes! FULL STOP! If you have to buy soil, get it from the supplier’s soil pile of the soil, they collect to use in their soil mixes. Do not worry about the organic soil quality. These soils are all local soils and as-long-as they are brown or dark brown with the minimum soil organic matter and a pH that is appropriate for the plants. In southern Ontario that will be a very high pH 7.5-8.5. The tighter you make the soil spec the more things will get screwed up and go south. The project manager will reject the sample and testing results. I would just call your soil supplier and ask them for test results from their recent soil collections and use the numbers in those soils as the basis for the spec. then widen out the windows of each testing parameter enough to accept just about any soil in southern Ontario. Accept the roots, wood chunks, rocks, and construction debris that will be in that pile. It is the removal of debris that kills the soil. A rebar or chunk or concrete or asphalt never harmed a tree. I have written specifications for all this for Toronto many years ago but not sure how the evolved after that My thinking has evolved on that specification.
Dealing with deep compaction is the most difficult part. Do not use a roto tiller. Tillers never go deep enough and are very damaging to the soil, as bad as the soil screener. Use the “soil profile rebuilding” process developed by Susan Day at UBC in Vancouver for sites where there is soil even compacted subsoils. She has lots of information and specifications for this process. She just digs up the soil profile with a backhoe and drops it back into place. Your soils are organic enough, even your subsoils, that you might not need to add compost but that would be a project-by-project decision.
You might think that this will add to the cost for all that organic soil. Actually, unscreened soils from stockpile is much cheaper per Cubic meter than soil mixes currently being used. And you might say well we would quickly use up all the soil available. If I start with a native soil site there is at least a foot or more of organic soil. Most development projects will cover at least 75% of the site with buildings and paving. If you spread a foot of the soil or even two feet of soil at the end of the project you will the net at 50-75% of the site area with left over organic soil to use on another project. If you can stockpile the initial organic soil on site, the soil cost is free and it is just the installation cost.
This introduces a different type of soil problem, that fact that there is typically not enough space to store the needed soil. The organic soil needs to be harvested at the beginning of the project and re-spread at the very end. Here is where you need the soil supplier. Do not try to have them save your soil for your job. It adds too much complexity for very little or no gain. Work with your supplier and establish a relationship to get what you need when you need it.
Here are my summary recommendations:
1. Where you can design the site grading to preserve existing soil resources in place.
2. If you have the room stockpile existing soil on site.
3. Where possible use soil profile rebuilding to prepare the subgrade and upper soil profile layers.
4. If you need additional organic soil purchase unscreened soil.
5. If the subgrade has been graded and or compacted use soil profile rebuilding (SPR) to prepare the subgrade. Add more organic soil either before you do SPR or after.
6. If there is no soil on site use the same methodology as above only with unscreened imported soils.
7. For soil over structure take all the above principles and use them, but with greater care to get very chunky soils which will drain well. In southern Ontario there is very little sandy loams. You may have to resort to soil mixes to convince the architect that the soil will drain but there are ways to make it work it is just more complex.
8. For storm water management soils, the above ideas do work but we have a long way to go to convince the engineers that unscreened soils will drain fast enough. They actually do! I will leave that political problem to some of the more interested people on this thread.
9. Fight hard to get rid of overly complicated soil spects. There are almost no soils in southern Ontario that will not work. This will take quite a bit of education with government people to move the bar on public projects.
10. Learn more about soil and become proficient on the important parts of soil that should be included in the discussion. Rudimentary soil testing should be at the end of the list. Subgrade conditions, soil samples with the clumps intact, should be the top of the process. Touch, feel, smell the soil at the source supply before you buy it.
Call or email me if you need to discuss further.
Jim Urban, FASLA, ISA
410 693 9053
Jimtree123 at gmail.com
> On Oct 5, 2021, at 1:55 PM, pwassenaer1022--- via CANUFNET <canufnet at list.web.net> wrote:
>
> Not in my experience but perhaps others on this list could indicate if they have seen it in their jurisdictions.
>
> Philip
>
> Philip van Wassenaer, B.SC., MFC
> Urban Forest Innovations Inc.
> 1331 Northaven Drive
> Mississauga ON L5G 4E8
> Tel: (905) 274-1022
> Cell: (647) 221-3046
> Fax: (905) 274-2170
> <image002.jpg>
>
> www.urbanforestinnovations.com <http://www.urbanforestinnovations.com/>
>
>
>
> From: CANUFNET <canufnet-bounces at list.web.net <mailto:canufnet-bounces at list.web.net>> On Behalf Of Naomi Zurcher via CANUFNET
> Sent: October 5, 2021 2:31 AM
> To: Canadian Urban Forest Network <canufnet at list.web.net <mailto:canufnet at list.web.net>>
> Cc: Naomi Zurcher <treerap at sprintmail.com <mailto:treerap at sprintmail.com>>
> Subject: Re: [CANUFNET] Trees and boulevards
>
> Philip - as I had indicated, I thought this should at least be possible with Public Infrastructure projects.
>
> Is it being required for projects on public lands?
>
>
>> On Oct 4, 2021, at 10:37 AM, pwassenaer1022--- via CANUFNET <canufnet at list.web.net <mailto:canufnet at list.web.net>> wrote:
>>
>> Ha ha ha….entirely possible but who will impose that and enforce it on the development community?
>>
>> In my experience the development community has an inordinate amount of sway over municipalities and things related to development. Until that changes, these things will remain “possible” but will not be implemented…
>>
>> Philip
>>
>> From: CANUFNET <canufnet-bounces at list.web.net <mailto:canufnet-bounces at list.web.net>> On Behalf Of Naomi Zurcher via CANUFNET
>> Sent: October 4, 2021 10:08 AM
>> To: Canadian Urban Forest Network <canufnet at list.web.net <mailto:canufnet at list.web.net>>
>> Cc: Naomi Zurcher <treerap at sprintmail.com <mailto:treerap at sprintmail.com>>
>> Subject: Re: [CANUFNET] Trees and boulevards
>>
>> Why can’t municipalities require that any and all construction must remove existing topsoil in lifts and thoughtfully store that topsoil for re-installation on the same site. This should be entirely possible at least on public infrastructure projects.
>>
>>
>>
>>> On Oct 1, 2021, at 1:34 PM, Oliver Reichl via CANUFNET <canufnet at list.web.net <mailto:canufnet at list.web.net>> wrote:
>>>
>>> “Nowadays developers remove all of the precious topsoil from the land before building a new subdivision, then bring back enough topsoil to support the new sod.“
>>>
>>>
>>>
>>> That’s been standard practice in the GTA for decades. Can a municipality regulate soil volumes?
>>>
>>> On Fri, Oct 1, 2021 at 11:12 AM Trevor Thistle via CANUFNET <canufnet at list.web.net <mailto:canufnet at list.web.net>> wrote:
>>>> Hi Ian,
>>>>
>>>> Here in Edmonton I have been working almost exclusively with tree conservation during Neighborhood Renewal (NR) for 13 years. NR is the process of reconstructing all sidewalks, curbs and streets in a neighborhood, as well as adding missing infrastructure.
>>>>
>>>> In our oldest neighborhoods I feel that trees growing in boulevards with separate sidewalks (curb on one side, sidewalk on the other side of the tree) have not really been impacted by the perceived restricted growing area, with the exception of roots literally engulfing curbs or overlapping sidewalks. I believe that the reason for this is that the construction standards that were in place decades ago (between neighborhood establishment and the time the sidewalk was last replaced) allowed for the construction of sidewalks on top of organic soil. So, in most cases, the trees had little challenge accessing soil beyond the boulevard.
>>>>
>>>> However, new construction standards include a gravel base and mechanical compaction under sidewalks. Also, greenfield construction is not what it used to be. Nowadays developers remove all of the precious topsoil from the land before building a new subdivision, then bring back enough topsoil to support the new sod. In these cases, regardless of the sidewalk design (mono or seperate) the trees do not have enough soil volume to support them. We do amend soil volumes with trenches in separate boulevards, but these are trenches in clay with still inadequate soil volumes. So my point is, depending on construction practices and standards, the configuration of the sidewalks in relation to the trees may have less impact on soil growing space than we think.
>>>>
>>>> but I would agree that trees in a more free to grow state, with little or no barriers to quality soil will outperform a tree in restricted growing space, and there will be fewer infrastructure / tree conflicts. This means that we will minimize tree related damages to infrastructure and construction related damages to trees in order to maintain that infrastructure.
>>>>
>>>>
>>>> Trevor Thistle Bsc. Forestry
>>>> Urban Forester | PR-4760AM | Tree Risk Assessment Qualified
>>>> OPEN SPACE OPERATIONS
>>>> CITY OPERATIONS | PARKS AND ROADS SERVICES
>>>>
>>>> 780-944-5577 OFFICE
>>>> 780-913-5893 MOBILE
>>>>
>>>> City of Edmonton <https://www.google.com/maps/search/City+of+Edmonton%C2%A0+12830+58+Street+NW?entry=gmail&source=g>
>>>> 12830 58 Street NW <https://www.google.com/maps/search/City+of+Edmonton%C2%A0+12830+58+Street+NW?entry=gmail&source=g>
>>>>
>>>>
>>>>
>>>>
>>>> On Wed, Sep 29, 2021 at 9:21 AM Ian Wilson via CANUFNET <canufnet at list.web.net <mailto:canufnet at list.web.net>> wrote:
>>>>> All, we are having a bit of an internal debate about standards for local/residential roads and boulevards. My observation is that trees that are planted in a boulevard behind a monolithic sidewalk (sidewalk up against the curb and planting area next to the property) generally do better. They have access to more soil volume in the front yard, they get more water and the boulevard is tidier since the homeowner treats it like part of their yard. Also fewer issues with roots lifting sidewalks. Some of our staff prefer the separated treed boulevard, for various reasons. Note, I’m not talking about busier roads where the trees in boulevards help to form a barrier from traffic.
>>>>>
>>>>> We don’t have a lot of good examples here that directly show a comparison. Does anybody have some photos that might show the performance of trees on one side of the road in a separated boulevard, vs. trees on the other side behind the sidewalk?
>>>>>
>>>>> Below is an example that doesn’t exactly show this, but it does show the value of soil volume, with the trees on the left side being able to access the lawn area behind the sidewalk, vs. the trees in “coffins” on the right. These are lindens planted at the same time.
>>>>>
>>>>>
>>>>> <image003.jpg>
>>>>>
>>>>>
>>>>> Ian Wilson
>>>>> Infrastructure Operations Manager | City of Kelowna
>>>>> 250-469-8842 | iwilson at kelowna.ca <mailto:iwilson at kelowna.ca>
>>>>> Submit a request for service on the go | kelowna.ca <http://kelowna.ca/>
>>>>> I acknowledge that my workplace is located on the traditional, ancestral, unceded territory of the syilx/Okanagan people.
>>>>>
>>>>>
>>>>
>>>>
>>>> The contents of this message and any attachment(s) are confidential, proprietary to the City of Edmonton, and are intended only for the addressed recipient. If you have received this in error, please disregard the contents, inform the sender of the misdirection, and remove it from your system. The copying, dissemination, or distribution of this message, if misdirected, is strictly prohibited.
>>>
>>> --
>>> Oliver K. Reichl, B.E.S.(Hons)
>>> -----------
>>> Sent from my mobile phone.
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