Good news! Urban forests are better carbon sinks than we realized!

I like cities.

It took me a while to admit that to myself. Throughout my teens, I lived in rural New Hampshire, and I spent a decent portion of my time doing stuff in the woods. Realizing that I actually do like living in cities was a bit of a blow to my identity. That said, there are ways in which I think city life could be made much, much better.

To begin with, every city I’ve lived in needed a better public transit system. A lot of modern cities are designed around cars, and I’d like to see that end. Ideally I’d want urban car traffic to be as close to zero as possible, not just because the roads have been reclaimed for pedestrians and other purposes, but also because getting around a city should be easier without them. That should include infrastructure to ensure full access for folks with disabilities. Another benefit of better public transit and few if any cars, is a dramatic decrease in urban air pollution, which in turn would mean a dramatic increase in the overall health of the urban population.

Another thing that I think should happen is a concerted effort to pack as much vegetation into cities as possible. I’m exaggerating slightly, but I do think that most urban roads, for example, should be converted into public parks with communal garden space, and/or communal greenhouses. I think this would go a long way toward improving people’s mental health in addition to their physical health. More greenery would also soak up some of the air pollution that can’t be avoided, and pull at least a little CO2 out of the atmosphere.

In fact, when it comes to that last bit, it turns out the news is better than expected:

“We think about forests as big landscapes, but really they are chopped up into all these little segments because of the human world,” says Hutyra, a BU College of Arts & Sciences professor of Earth and environment. Forests get cut into smaller parcels, as chunks are taken down to make space for roads, buildings, agriculture, and solar farms — one of the biggest drivers of forest loss in Massachusetts. These alterations to forests create more areas called forest edges — literally, the trees at the outermost edge of a forest.

It has long been assumed that these forest edges release and store carbon at similar rates as forest interiors, but Hutyra and researchers in her lab at BU have discovered this isn’t true. Soils and trees in temperate forest edges in the Northeast United States are acting differently than those farther away from people. In two recent research papers, Hutyra’s team found edge trees grow faster than their country cousins deep in the forest, and that soil in urban areas can hoard more carbon dioxide than previously thought. Their results can challenge current ideas about conservation and the value of urban forests as more than places for recreation.

Pretty much any scenario in which out civilization survives the next century will see that civilization change radically. In that time line, I’d expect to see us continue becoming an urban species, but also changing what urban life is like. Replacing streets with foot and bike paths and light rail would allow cities to pretty much be parks, and because the goal is an economy that lets need drive production, rather than greed, everyone would have to spend far less of our lives working, so we’d have time for stuff like growing food, and just hanging out.

Honestly, thinking about what cities could be like rekindles my irritation at mortality. If we did things right, cities could become some of the most fascinating ecosystems on the planet, with their own unique wildlife communities and crops. As the quoted article states, rising temperatures could reduce net CO2 uptake, but “greening” urban environments as I describe would also go at least some way toward combatting the urban heat island effect. I think there’s potential there for a feedback loop that actually works in our favor, which would be nice.

The last aspect of this I wanted to look at is the way it would affect more rural areas. Dedicating more of a city’s surface area to growing food would take some pressure off current farmland, especially if there’s a simultaneous effort to do large-scale indoor food production, which means more land can be either returned to wilderness, used for carbon capture and sequestration, or converted into things like food forests for less intensive food production.

Years ago, when I was part of a Quaker climate action group, I wanted to set up a “snowballing” climate fund. The basic idea would be that the New England Quaker community could pool some money, either regionally or at the local level. That money would be used to install things like rooftop solar, geothermal heat pumps, and insulation for the whole community, one house at a time. The money saved or even earned from that energy production would all go back to the fund, and once the whole community had gotten their “refit”, that fund could be turned towards other projects.

I think that responding to climate change could work rather like that hypothetical fund. Some of what we do will have immediate results, and some might take decades or even centuries to fully pay off, but in pretty much all cases, the outcome is the same. Taking action to mitigate or adapt to climate change will make life better, and will make it easier to take more action. We’re in the middle of a massive systemic change that has built up a fair amount of momentum. The upside is that we have the capacity to influence that system in ways that will sap some of that momentum. We’re not just stuck on a scripted march towards doom. Everything we do, year by year, can change our trajectory.

We just have to do it.

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  1. jenorafeuer says

    Here in Toronto the city has an explicit plan to increase the canopy cover for the city up to 40%. This involves literally giving away trees to go in the road allowance stretches of land at the road’s edge (which are technically city property anyway) and discounted programs for backyard tree planting, along with grants for various organizations contingent on them helping with the program. It also involves making lists of what trees would be best for this depending on where in the city you are, and making sure to have a good mix while keeping to mostly local trees.

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