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Will Silva Cells help improve Toronto's urban forest?

Posted by Matthew Harris / August 7, 2010

Silva Cells ExamplesThe city's Official Plan calls for the extension of the city's tree canopy from its current 17% to 30%. One of the major issues limiting the current tree canopy is the difficulty in growing healthy trees along the city's main thoroughfares. Urban trees face several difficulties, but the most intractable issue is the problem of soil compaction. Trees are healthiest when they are planted in uncompacted soil because this allows water, air and nutrients to reach their roots. However, an urban environment requires hard surfaces to support people and vehicles, and hard surfaces naturally compact soil. Silva Cells are a potential solution to this problem.

Silva Cells are rigid frames that support hard surfaces such as asphalt parking lots or sidewalks, but they keep soil loose and provide space for irrigation systems and utilities. They are produced by a company called DeepRoot and were first commercially available in 2007. Although there is not a lot to date on their effectiveness, the makers hope that they help provide trees with a soil environment that largely mimics a natural environment.

This YouTube clip provides some evidence. DeepRoot's Silva Cells were planted two years ago in Vancouver's Olympic Village. Since that time, the trees have seen strong growth, including bud extensions of up to 32 inches. They also look pretty vibrant compared to some of their stunted cousins in Toronto.

The city of Toronto has begun using the Silva Cells in several projects: the Bloor Street Project, and in Waterfront Toronto's Sugar Beach and Sherbourne Common. These projects are serving as pilot projects of the Silva Cells before the city commits to using them on an ongoing basis. The Silva Cells substantially increase the upfront costs of tree planting: for the Bloor Project, they cost $2.5 million. The city staff I spoke to said that integrating their installation into an already complicated planning process that involves working with hydro, water and transportation services is something the city still needs to sort out.

20100807 Silva Cells Bloor Street.jpgBut their benefits extend beyond the simple aesthetics of a tree covered walkway. On the Queensway, the city has installed a test case of the Silva Cells for stormwater treatment. The cells hold a bioretention mix that will help remove some pollutants like heavy metals from stormwater run-off. The cells also retain some of the excess stormwater, which helps prevent it from being washed into the lake. Since the city's beaches can be polluted by stormwater run-off, the Silva Cells have the potential to help improve Lake Ontario's water quality.

Silva Cells ExamplesSilva Cells Bloor Street SouthIn Toronto, future projects for the Silva Cells will include projects in the West Don Lands: installation of some of the cells on Mill Street should begin in a few weeks. They will also be used along the Viva Next rapid bus route. Although it will take a few years to truly see how effective this system will be in improving the life and vitality of Toronto's urban trees, the early results are promising.



Bonk / August 7, 2010 at 01:09 pm
Right on, i'm all for these magic plates in making an alreadly notably green city into a super green one!
Eric26 / August 7, 2010 at 01:26 pm
Toronto's downtown is still very grey, so the more trees the better.
seanm / August 7, 2010 at 02:20 pm
Cost overruns and construction delays notwithstanding, Bloor St. really looks great. Pending success of the Silva Cells, hopefully the city will pass ruling that all developers must make use of them for street tree plantings.

We also need to be harsher on people who grab at and injure young trees. A limb for a limb, for anyone who snaps off branches.
W. K. Lis / August 7, 2010 at 03:37 pm
• Roncesvalles Avenue to get new trees planted using Silva Cells as part of the reconstruction, where available.
* Temperatures forecast and recorded are shade temperatures, add 4° - 8* for full sun. The shade under mature trees help lower the temperature for comfort in summer.
° However, the city does plant dwarf trees, which are actually the same as the non-dwarf trees but grow slower. They will take longer to grow to maturity height.
bob / August 7, 2010 at 03:48 pm
Where were these photos taken?
Matthew Harris / August 7, 2010 at 04:16 pm
bob: all of the photos are of the current Bloor-Yorkville BIA's Bloor Street Project. They are currently installing Silva Cells on the north side of Bloor between Avenue and Bay. I'd recommend checking out the finished portion - it does look very nice.

W.K.Lis: The city plants a variety of trees (the ones on Bloor are mature London Plane trees) but it's true that direct comparisons to Vancouver are difficult, due to that city's longer growing season and different trees being used. But the city has identified premature tree death and stunted growth as a problem.
snowy / August 7, 2010 at 05:48 pm
The pictures of Bloor are nice. Silva cells do cost a frickin fortune, though, I've been investigating them for a project in another city recently.
Ayan T / August 8, 2010 at 01:16 am
Bloor St. is looking great, although the traffic on the road isn't too pretty. I know Silva Cells are also going to be implemented alongside the LRT projects when the medians and sidewalks will have trees planted. The first installations will be for the Sheppard East line
Niklas / August 8, 2010 at 07:22 am
Good, Toronto is such a grey city and could use a lot more trees downtown.. everyone feels better with green around them
Jer / August 8, 2010 at 08:07 am
I am not sure i agree with main thoroughfare sidewalk tree plantings. Even wide sidewalk plantings like Bloor. Trees are not ornaments; they are part of ecosystems. Weak ecosystems such as parks and lawns notwithstanding, we need to develop dense systems with many varieties of green. Poor and infrequent sun in downtown cores with buildings in excess of 6 floors and sunlight hours on the trees less than a few hours daily is unhealthy - and the traffic and pedestrian contact is further damaging. Perhaps some trees survive, but they deserve to more than survive, they deserve to flourish. Would we agree to tie animals to posts along roadways so that we could add a bit of colour and excitement, even if well cared for? - likely not. There is a limit to what type and amount of nature can be transplanted into dense urban areas. Maybe we could get more street art out there, similar to Spadina. There are certainly a lot of starving artists out there looking for work - and it would likely be cheaper in the long run than maintaining and replacing failed trees. Trees on smaller residential streets do better (though there is an insufficient mix of young and old and variety). Its time to stop depending on tiny unhealthy 'acts of nature' as people's only source of wild. Get to park. Get out of the city, weekly.
Matt replying to a comment from Jer / August 8, 2010 at 12:06 pm
How do you propose we "develop dense systems with many varieties of green" in our downtown core? It is impractical. The initiative mentioned in the article do the next best thing.

I am not sure of what kind of plants the city is planting, but there are kinds that do not need hours and hours of direct sunlight to survive.

And street art? I'm all for it, but it cannot bring as much vibrancy to the streetscape as vegetation can. Pedestrians and traffic can do just as much damage to those installations as to planted vegetation.

Personally, I'd rather have reduced heat-island effect, cleaner air, cleaner water and a much more pleasant experience than some pretty picture on the wall, or fancy sculpture for tourists to take photos of.

Janet McKay / August 9, 2010 at 11:29 am
An exciting technology with lots of promise if implemented in the right situations. The important thing is to look at our urban forest as a whole and decide the most important ways to spend limited resources. Let's not forget about the need for preventative maintenance on our large growing street trees in residential areas, protection of our natural areas and ravines from invasive species and soil compaction, and the need for resources to implement and enforce our tree protection bylaws in the face of development and infill. Lining our major arteries with trees has clear benefits. But knowing what other urban forestry programs and services we might be sacrificing in order to undertake these expensive projects would allow for a more enlightened and educated opinion on the issue.
Leda Marritz replying to a comment from snowy / August 9, 2010 at 05:43 pm
I work at Deep Root Partners, the makers of the Silva Cell, and I wanted to chime in quickly.

First off, we are so excited about what is happening in Toronto and the use of the Silva Cell to help bolster green infrastructure in the city.

I know the cost issue causes a lot of people to balk initially, because the Silva Cell is more expensive than other soil delivery systems out there. However, I want to make sure that folks understand that on a cost per cubic meter of soil basis alternatives like Structural Soil or ordinary tree pits are actually almost three times as expensive as Silva Cells:

While the cost of the Silva Cell will typically be shouldered by a municipality or a developer, the value that trees growing in Silva Cells will bring to surrounding homes and businesses is quite significant:

Anyway, I just wanted to speak quickly to those two issues. We are thrilled by Toronto's commitment to creating truly green infrastructure, and we can't wait to watch the trees thrive in the coming years.
Jennifer / August 11, 2010 at 10:24 pm
This is great - a wonderful way of really making a difference in the world through healthy tree growth, stormwater treatment and creation of a beautiful urban environment.
Peter / November 15, 2010 at 03:17 pm
Toronto should consider requiring in it's tree planting specifications a minimum rootable soil volume per tree. One City in California does this. The minimums are 600, 900 and 1200 cubic feet per tree based upon the estimated height of the tree specie at maturity (small, medium and large.) That is one way to get at providing what trees really need to be healthy in an urban environment.
Other Cities: Montreal