Do street trees increase the environmental impact of cities?

Image from Brookwood Tree Consulting
Trees are green, right? And green is good, right? So trees must be good, right? How could trees be bad for the environment? Many of us have a sense that we are not on the right path; in our bones we feel the damage we do to this planet really does matter. And often we cling overzealously to charismatic symbols like trees and honeybees, and lose sight of the place of the symbols within the system. Cities are trying to respond to increasing environmental pressures. For example, to reduce dependence on agricultural breadbaskets at risk of climate change-induced droughts, cities are promoting local and urban agriculture. To reduce use of climate-changing fossil fuels, cities are promoting renewable energy. These efforts are distinctly urgent as we head for 410 ppm of atmospheric CO2—remember that 350 ppm gives only a reasonable chance of maintaining a climate conducive to advanced civilization. And trees throw shade on those efforts. We need a Right to Light. There is historical precedent here, and various jurisdictions have Right to Light legislation—usually used to make sure a new building does not shade your windows and turn you into a shivering ball of moss—but cities that want to be leaders need to make sure solar panels and gardens have as many rights as condo towers. Sunshine is the renewable energy that is delivered right to your house every day, right to your vegetable patch and your solar hot water collector.Please do not fall for the ruse that Cascadia’s grey skies make solar unsuitable. Germany has far more installed solar, and far more renewable energy in general—and gets less sun than Cascadia. Before electricity turned every building into a faceless box, architects designed both for daylighting and ventilation. Well-insulated buildings can get a great proportion of their heat and light from sunshine coming in the windows. Unless you have a great big tree in front of you. Street trees are more than just comforting tokens; a dense green canopy that helps us forget the moonscape clearcuts that supply us with paper and lumber. Trees do a lot for our cities; they slow and clean stormwater, they remove air pollutants, they look nice and appeal to our old evolutionary psychology, to name just a few. Urban forestry can also be very profitable. Imagine how delighted furniture builders would be to get their hands on oak and maple and cherry, all from their own neighbourhood. Urban trees should be seen as infrastructure alongside the pipes in the ground and the roads we ride on. But the City of Victoria, where I live, protects certain native species and all very large trees—unless of course you want to put in a driveway, or build an addition on your house. You have no rights if you want to cut trees shading your solar collectors or vegetable patch, but if you want a place to park your Hummer, let the chips fly. The City of Vancouver plans to plant 150,000 new trees, but unless a systems perspective is incorporated, they are planting 150,000 new problems and a forest of lost opportunities. Here is how I think our urban tree system should work: Trees are important habitat for myriad species. They look nice, and humans are hardwired to feel better, and perhaps be healthier when they can see trees. In cities they have the important job of shading asphalt to reduce the urban heat island effect. Trees can also provide tons—or on the scale of a city, tens of thousands of tons—of fruit and nuts. Here are my thoughts on fruit and nut trees. This would mean jobs for urban orchardists, food processors, farmer’s markets and foresters. It would also increase urban resilience to disasters by enhancing food security, and reduce the ecological impact of food transport. And they can do all that on the south side of the street. Let’s keep it simple by imagining a street that runs east-west. Trees planted near the sidewalk on the south side of the street will shade the blacktop, but not the garden on the north side of the street. Not the solar hot water collectors, not the windows that brighten life, not the photovoltaic panels, just the blacktop. That is our infrastructure working for us. This does not mean we will have fewer trees, it just means we will incorporate our Right to Light into urban design. It means we will not plant trees where they will block light and preclude energy harvesting with plants or panels for decades to come. So, as infrastructure, when trees no longer serve the city they should be dug up, dynamited, moved or replaced. I do not think this utilitarian analysis of the trees in our entirely human-shaped urban environments should be extended wholesale to wilder places. We don’t remains slavishly loyal to our old pipes and our leaking sewers. We don’t worry about hurting the feelings of our bridges and sidewalks. When our trees are preventing us from accomplishing other goals—goals much more important than a new parking spot—then it is time for them to move.
Data wormhole for those who enjoy such things: In Canada’s ‘Household Sector’ about 40% of our energy is burned by our cars and 60% is burned by our homes. 60% of that 60% is used for heating our homes and water. So about a third of our total personal energy use is just heating. Of the third of our energy use that goes to heating, about 60% is fossil fuels. -Of the 40% share of electricity, 40% of that actually comes from burning coal and and natural gas. The remaining 60% is hydro and nuclear. And nuclear is not renewable. So actually, a large proportion of the energy that keeps the lights on and keeps us warm is non-renewable. And here is a proposal for a solar hot water system that notes trees are blocking some of the insolation.


  1. A successful peach. Wonderful. I’d not have guessed based on latitude alone. I’ll suppose being next to the house may be significant. In fact one might find it possible to populate the lawns on the north side of the E-W streets with dwarf fruit trees such as peach that could take advantage of the solar reflectance from the house. The dwarf nature not only puts the fruit within easy human reach, but also plays into your wider vision of not blocking solar infrastructure like PV or water heaters. Of course the smaller crown of dwarf tree allows them to be sited closer to the house – enabling the house assist for insolation. I can already see the budding publication of a participatory breeding effort to select peach germplasm for just such an environmental niche. Your children may one day approach a neighbor’s front yard fruit stand and inquire, “Freestone or cling?” [or run their own stand]

    Had not heard of the squirrel hack, but I like it. Likely as close to getting squirrels to pay taxes as anything (though I’m not convinced I’d want to let them vote… so might dial that back a tad).

  2. Brilliant! And so attainable. All you need to do is write up the zoning and force everyone to participate. And why wouldn’t they? Fruit and nuts, solar power, cool streets, this is incredible.

    That ‘force everyone’ crack – sounds sort of snarky coming from the private property guy at SFF, no? But I do actually think this could make a dent. I even think you’ve potentially played the role of Charley in the can parable… kicking the can way down the east-west, tree lined (on the south side) street. But dude, we were playing with that.

    Of course as this all comes together you’ll want to specify how tall the trees can get. Coppicing to maintain optimal heights could be another win-win where the trimmings are used for all sort of benefit. Delivery drivers and rapid responders (fire, police) will immediately know the even vs odd sides of the street due to the tree line always being on the south side (east west streets anyway… half the problem solved).

    Squirrels should love this too. And squirrels are delicious – more urban food system support. What about pine nuts… you’ll want some gymnosperms for diversity (and I’m guessing the evergreens do pretty well in your corner of the planet).

    With the right infrastructure you could enable a vast expanse of apiary culture. Those flowering fruit trees will need bee pollinators – and all the honey would serve as sweetener offsetting corn sugars (though sugar beet growers might wince at this).

    Now, snark and hyperbole aside, being a plant breeder by profession I see this urban frontier as a great prospect. Adapting fruit and nut trees that are not currently found in Victoria (I’m guessing you don’t have peach trees in town… or pecans) would keep several breeders busy for some time.

    So impressive. It makes me wonder whether property values would be higher on the south side (vs. the north) because of the trees. Makes one wonder if there is a behavior researcher about who might model the financial impacts. Hmmmm. 🙂

    • Ha! Your snark was a little muted actually, so I installed a WordPress plug-in to dial it up to 11. 😀

      As a matter of fact, we have a peach tree strangely placed on the east side of the house we rent. After I gave it a good prune we got a couple of dozen peaches last year—but yes, few peaches, almost no apricots here on the Island; they are mostly grown in the hot Okanagan Valley in the interior of BC. Lots of pear, plum and of course apple. There is an edible chestnut across the street, a half dozen walnuts in the backyard, and a nice hazel bush—but all of those are pretty much raided by squirrels.

      I once read about a squirrel prank, but have never been able to find the webpage again, or any proof of the concept. The idea was that you imitate a squirrel den, say with some buried PVC pipe. The squirrels collect the nuts and put them in the den, which you then clean out and take home.

      As pessimistic as I may seem, I actually don’t think we should try to be too prescriptive. The night is dark and full of terrors, but we don’t know which terrors, so I don’t think it is worthwhile to start fighting about which trees will be pollarded in a city that currently does not even allow outdoor fires. My interest is more in trying to break the grip of the Green is Good—all solar panels are always good, all electric cars are always good, all trees are always good, and get us thinking about what sustainability might actually involve.

      I think things like the tree bylaws and fire bans will be quite problematic in the early stages of contraction. Think about the real estate collapse of 2008—there was a very painful and damaging period of time where everyone was trying to pretend it was almost over, that it was going to get better, that we would return to normal.

      Meanwhile the tent cites are forming and people are sleeping in their cars all over.

      I would like to be more prepared for this phase, I think it is crappy enough to lose your house and be living in your car without the municipality and police trying to move you along, making your life even harder.

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