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Resilient urban vegetation is the new organic


Wednesday, February 28th, 2018

Expectations were high and the room was full as Ryerson University was graced with a panel of experts for an evening session appropriately titled “Promoting the Health and Resilience of Urban Vegetation”.
Landscape Design Event February 2018-FINAL (1)-page-001

The city is a novel ecosystem

Host Sam Benvie opened the panel discussion by talking about resilience of urban vegetation in the context of climate change, urban intensification and species decline. My favourite line was Sam describing the urban environment as a “novel ecosystem, at best a couple thousand years old”. more on this later but a solid opener delivered in a very off the cuff way.

Michael Ormston-Holloway loves trees

First up Michael Ormston-Holloway from the Planning Partnership who has a LOT of letters after  his name:  BSc, MSc P, GDHort, MLA, ASLA, ISA Certified Arborist. Ormston-Holloway started out contrasting tree death in a forest vs tree death in the city. Including some shots of delivery trucks backing into street trees and other horrors. The general point of which was to make the case that tree death in the city does not come with the benefits that accrue in a typical forest setting. Ormston-Holloway then moved very quickly through some slick looking slides.

My take home from Ormston-Holloway was the need for more diversity in street trees, specifying larger volumes of soils to grow larger trees and the mega economic return on investment of mature trees. My favourite moment was Ormston-Holloway advocating consideration of Leaf Area Index (LAI) as a criteria for tree selection in urban projects. Basically LAI measures density of tree foliage. I wasn’t clear if Ormston-Holloway was advocating for higher or lower densities but it is something we consider in our plant selection choices for the understory layer. Also it is a key component in modelling larger scale systems analysis so that’s a thing.

As it happens Ormsten-Holloway is working on a project at the Ryerson Campus. The project is currently in phase 1 and there is a questionnaire you can fill out about how you use the space. Ormsten-Holloway best line of the night was “trees are infrastructure”. Pretty good stuff.

The impermeable soil problem

Dylan Young, a project manager at Sustainable Technologies Evaluation at the Toronto and Region Conservation Authority was the next speaker. Young started off challenging the traditional model of permeable vs impermeable surfaces.

impermeable soil photoPhoto by arpent nourricier

Young’s argument is surplus runoff is not only due to hard surfaces but also from soils that are compacted, stripped of topsoil and have low percolation rates (there is a further discussion of this in the Peter Del Tredici video) . According to Young if we implemented improved best practices for soil management during our projects it would be win-win for property owner, regulator and developers (so I guess technically that makes it win-win-win).

Young then provided examples of how to reverse the effect of compaction on site by fracturing, tilling, ripping and trenching. Typically in the downtown urban core we often have a mature tree on the property and we need to take tree root injury into consideration when trying to restore soil health after a major renovation (in other words the above strategies might not work in tight quarters).

Soil amendments contradict plant selection strategy

The talk from Young about amending soil and compost standards, left me thinking about how we often remove soil from site and bring in new soil and how that conflicts with the practice of selecting plants based on existing site conditions, or as Sam Benvie puts it “soil and plants are one”. Boom. Sidenote Peter Del Tredici in the video below refers to site prep as a modern form of glaciation that leaves compacted glacial till in its wake.

Ecological references are a great model for plant selection

Stefan Weber ran through some of his research and knowledge around locally rare plants that are not readily available in the trade. Stefan is working on his PhD at McMaster University while still working at St. Williams Nursery and is a co-founder of Ontario Plant Restoration Alliance (OPRA).

Believe it or not the fact that Stefan is using goats to eliminate Buckthorn was not the highlight for me (but its still pretty awesome). It wasn’t when Weber introduced his regional seed strategy ideas and showed slides of regionally rare plants like Lupinus perennis (Sundial Lupine) that have been removed from the species at risk list due to efforts to reestablish it. 

lupinus perennis photoLupinus perennis Photo by wackybadger

It was during question period, Weber was asked about what to do in clay soil situations and again about degraded urban soils later on. That is when Stefan starting dropping bombs about ecological references (my absolute favourite thing and a very useful tool in the toolbox).

On the clay question Weber sited 16 mile creek in the escarpment as good reference as its has steep bluffs of clay soils. Plants grow happily in that heavy clay including Acer nigrum (Black Maple), Tilia americana (Basswood),  Ameclanchier spp. (serviceberry) and Hamamelis virginiana (Witchhazel).

black maple photoAcer Nigrum Photo by F. D. Richards

Weber continued providing understory options such as Mertensia virginiana (Virginia Bluebells), Carex grayi (Mace Sedge) and Carex lupulina (Hop Sedge).

virginia blue bells photoMertensia virginiana Photo by FritzFlohrReynolds

carex grayi photoCarex grayi Photo by son_gismo

carex lupulina photoCarex Lupulina Photo by quinn.anya

And when the questions turned to poor soils Stefan was not fazed, firing back with alvar references saying “I don’t know why we don’t grow Chinquapin Oak more in Toronto”. Yes it was good times.

quercus muehlenbergii photoQuercus muehlenbergii Photo by Nicholas_T

Weeds provide important ecological services

Another great moment was the question “what is the value of spontaneous plants in the city”. If you remember back to Sam Benvie referencing the city as a novel ecosystem. Valuing ecosystem services from “weeds” in degraded urban landscape regardless of provenance was popularized by Peter Del Tredici. The video below fleshes out a lot of the ideas presented here at Ryerson and is well worth your while.

It was a great feeling to hear enthusiasm for spontaneous plants (further proof that we are not alone in considering the value of “weeds”). Of course the response from Weber was equally good. “Weeds provide all kinds of habitat in cities and restoring the urban environment is like undressing a salad, but there are many alvar plants that would do well, so lets consider using them too”. Huge.

City inspector told to delay inspection for 10 yrs

We had an inspector from the city of Toronto tasked with releasing funds to developers after a project is complete. His question “what can I tell the developers to do?” To which Michael Ormston-Holloway responded “can you delay your inspection for 10 yrs?”. Chuckles in the audience and a cackle from yours truly. It underscores the point that as Sam Benvie puts it “plants come from the nursery juiced” and take a while to die…

“Seedbanks are memory” – Sam Benvie

Towards the end of the session Benvie asked the panel “what about seed banks?” To which Dean Young responded “we took a different approach at Corktown commons where the landcare was done with a view to enhancing the seed bank”. Not bad, Not bad.

And there you have it folks, we retired to the Imperial Pub for the meeting after the meeting and our lively discussion continued in an impromtu “shop talk”. The following is a few threads of discussions had and overheard:

Is moss evil? (definite no)

The value of moss on a green roof and sedum mats vs. perennial polyculture:


Native plants offer lawn alternatives

Muhlenbergia mexicana “They shipped me the wrong grass, and I got a spreader that works great in full sun” Steve Smith from Urban Forest Associates.

Ecoman is experimenting with Juncus tenuis (Path Rush) in the garden stay tuned!

juncus tenuis photo
                                                                  Juncus Tenuis Photo by Matt Lavin

The potential for Danthonia spicata as a turfgrass (A topic I am covering in Philly blew my mind part 2 stay tuned).

Restoration contracts might ruin your business

The difficulty in bidding for restoration contracts where site conditions are not optimal and the amazing Gavin Miller at TRCA who knows everything about plant ID.

Deep dive of the week

A study of plants that occur in alvars of canada. Lots of plants from that study would do well here in Toronto. Lots of others might be tough to find in the trade. Nurseries will respond if we ask for these plants!













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