Gardeners should care about sprawl

photo of residential native plant garden

A car trip between Hamilton and Toronto presents the Golden Horseshoe at its very worst. Crammed with people and industry, the area is home to almost half of Canada’s population. It’s the country’s economic leader, supporting an entourage of snout houses, malls, highways, parking lots and, of course, cars. But the smoggy smear of industrial capitalism obscures an ecological treasure, a patchwork of forests and grasslands, significant and fragile habitats that are home to most of Canada’s threatened plant and animal species.

The southern part of Ontario’s Mixedwood Plain (known as the Carolinian Life Zone) is the country’s smallest ecological zone, comprising only 0.25% of Canada’s landmass yet providing habitat for over 40% of its plant species and probably an equally large proportion of animals, including insects. As well, much of the region (74%) is farmland. Virtually none of the original forest survives, though, and what is left is severely degraded and fragmented. Michael Oldham, in his 2017 technical report listing of all 2545 of Ontario’s vascular plants, puts it mildly: “Essential ecological processes needed for healthy soils, clean water and clean air have in many areas been severely compromised1.”

map of Carolinian Life Zone showing natural core areas
The Big Picture: Natural Cores and Connectors in Canada’s Carolinian Life Zone. caroliniancanada.ca/

That it’s crucially important to save and regenerate these remnants is obvious to all but the most short-sighted, greed-driven developers and speculators. They are few but powerful—and premier Ford fits snugly in their collective pocket. The relentless push to “develop” all land not already paved, embodied in Ford’s Bill 232, has energized environmentalists and spawned a resistance movement that includes, well, almost everyone. Ford’s pro-sprawl legislation has it’s own sordid back story involving grift, handshakes, and election promises, but while that drama festers, let’s turn to our own backyards and look at how sprawl affects gardens.

First, though, a bit of gentle scolding: if you haven’t yet realized the magnitude of the threat posed by sprawl, well, now’s the time to pick a side. If you enjoy breathing fresh air, drinking clean water, and being outdoors on a sunny afternoon in July, you should already have signed a petition or attended one of the many anti-sprawl protests that continue to regularly attract big crowds.

photo of two dogs with anti-sprawl messages on hand-written cards

But let’s say you’re simply bored or not interested in this political stuff and you just want to grow veggies and flowers in your yard. Here’s how sprawl affects you.

Sprawl is a huge contributor to carbon dioxide (CO2) emissions for many reasons but let’s start with its main victim: soil. Currently, soils remove about 25 percent of the world’s fossil fuel emissions each year. While farmed land, especially under traditional or industrial agricultural practices, sequesters less carbon than land with undisturbed or well-managed soils, the benefits of leaving it undeveloped still outweigh any other land use options except restoration3.

Sprawl creates neighbourhoods that are entirely car dependent. Each household has at least one car (more likely two or three) each spewing greenhouse gases, requiring roads, parking, and the continued production of more cars. Electric vehicles (EVs) will not save the day—the green reputation of EVs disregards the environmental impact of producing them. Not only do mines and manufacturing take their toll, EVs are just the latest guilt-massage for rich, fawning devotees of car culture. A typical EV increases household energy (electricity) use by one-third—and Ford will meet the increased demand with gas plants. Regardless of the hype around EVs and the high cost of gas, the best-selling vehicles are still trucks, SUVs, and crossovers, which together with minivans accounted for 77.3% of U.S. auto sales in 20214. The popularity of these bloated road-bullies persists.

All that toxic tailpipe particulate doesn’t just waft upwards into the forget-o-sphere. It lands on our plants. Before they were bulldozed to make room for McMansions, trees used to remove air pollutants by trapping particulate matter in their leaves, needles and bark. Trees, like soils, are huge carbon sinks5. It’s possible to actually calculate the value in sequestered CO2 based on where you live and the size/species of the trees in your neighbourhood6.

Trees and vegetation also mitigate the urban heat-island effect7. They lower surface and air temperatures by providing shade and through evapotranspiration. Shaded surfaces, for example, may be 11–25°C cooler than the peak temperatures of unshaded materials. Evapotranspiration, alone or in combination with shading, can help reduce peak summer temperatures by 1–5°C. This affects you even if you live several kilometers from the former forest. All that heat now enters the local atmosphere where it changes wind and rain patterns. Your garden grew up in conditions far different than the those it will face as we chip away at the greenbelt.

photo of residential native plant garden
Jamie Hunter’s native plant garden in Dundas Ontario, received a Monarch Award in 2022. http://www.monarchawardshamilton.ca

The consequences of sprawl, in essence, are those of climate change. We are already experiencing unprecedented “weird weather”: rapid and drastic shifts in temperature; longer and more frequent periods of drought; more record-setting extremes in temperature and precipitation; and storms that are more extreme, more frequent, and longer lasting. The annual rainfall may not change but it is more likely to come all at once, at the wrong time of year.

The crushing effects of heat waves are mitigated by wise land use. Put simply, less green space equals more (and hotter) heat waves8. We will become twilight people, tending our gardens when it is cool enough to venture outdoors. We’ll be irrigating more often, just to keep plants alive. We’ll see our beloved trees suffer and decline for lack of soil moisture. Species will have to endure conditions they’ve never before experienced in their evolutionary history. With warmer winters and longer summers, the life cycles of all organisms are distrupted. As the interconnected web of life comes apart, strand by strand, insects and diseases will lose their natural checks and balances, forcing us to manage processes that used to happen naturally 9.

photo of toronto suburbs, taken from plane, 2012
Toronto suburbs, 2012. Photo: Angelina Earley via Flickr. CC BY-ND 2.0

Rising levels of CO2 in the atmosphere drive an increase in plant photosynthesis known as the carbon fertilization effect. Research has found that between 1982 and 2020 global plant photosynthesis grew 12 percent which, for some plants resulted in more growth, both above and below ground. But climate change is also expected to bring more combined heat waves and droughts, which would likely offset any benefits from the carbon fertilization effect10.

If you’re a backyard vegetable grower, your yields may increase with elevated CO2. At the same time, however, nutrient levels drop. In one study, protein concentrations in potato tubers decreased by 10 to 15 percent.

Plants respond to increased levels of atmospheric CO2 by thickening their leaves, by up to one third11. This changes the ratio of surface area to mass in the leaf and alters plant activities like photosynthesis, gas exchange, evaporative cooling, and sugar storage. All of these are happening from May through October in our yards and gardens. The result, to put it simply, is a disruption of normal ecological function in response to unprecedented environmental stress. Will insects still be able to use their host plants? Will food plants turn bitter? Will they be perpetually stunted? Will they lose the subtle pheromone and electromagnetic cues that allow them to interact with other organisms.

All plants respond to heat stress12. Tomatoes, for example, fail to produce viable pollen. As well, seed germination fails because soil temperatures and moisture levels are far outside the range the plant evolved in. So if you’re wondering why so many of your plants did not produce viable seed this year, it could be the late-season heat and drought.

Climate change brings not only extremes in heat and drought, but also extreme rain and snowfall. All climate models predict that droughts will be longer, hotter, and more frequent, while rain storms will be less frequent but more extreme, both in the rate and total amount of rainfall. The resulting stress on plants is already evident: increased soil erosion that washes away seedlings, extended periods of soil saturation that suffocates plant roots, and stunted plant growth.

We gardeners are outdoors a lot. Our creativity and love of nature are lavished on our land, to make it beautiful, useful, and ecologically functional. But because the cities and towns where we live are growing outward— replacing soil and plants with buildings and pavement and worsening the effects of climate change—we need to garden differently.

The easiest change is to reduce expectations. In light of the new climate reality, being a “good gardener” will count for less. The more challenging change is the garden makeover. We need to increase plant diversity and species richness by adding native plants, trees, and creating naturalized areas to better support the web of life and mitigate losses. Needless to say, we need to stop removing trees and stop building impermeable hardscape features such as pools and patios. And, if our gardens are small, we can do our best to protect them from the worst of what’s coming.

As we witness the devastation of climate change in our own back yards, let us consider the practical, realistic options available to us. It is unlikely that we will shut down globalized industrial agriculture or manufacturing any time soon. There is no global-scale CO2 removal technology on the horizon. There are no new planets currently available.

But we can take action locally to keep things from getting worse in the short term—by opposing sprawl. If we care about our gardens, if we want them to exist at all, we need to protect the green spaces around our cities, keep them intact. With each new suburb, each new chunk cut from greenbelts everywhere, our cities suffer. Our gardens suffer. We suffer.

Of course it’s true that, compared to the human suffering from famine, water shortages, cataclysmic storms, and the ensuing breakdown of civil society, gardens are pretty low priority. But we are privileged to live in a rich country, insulated from (or blind to) the looming, horrific decades to come. We hold tight to the old dreams and passions. If we love our gardens we cannot help but love this planet.

poster for Dec 4 rally from SSHO
Activism in Hamilton Ontario https://www.ssho.ca/
Dec. 4 rally poster with logos of supporting organizations

Resources and further reading

1. Michael Oldham’s research report “List of the Vascular Plants of Ontario’s Carolinan zone” https://www.researchgate.net/publication/317731067_List_of_the_Vascular_Plants_of_Ontario’s_Carolinian_Zone_Ecoregion_7E

2. Text of Ontario Bill 23: https://www.ola.org/en/legislative-business/bills/parliament-43/session-1/bill-23 and information about Ontario’s greenbelt: https://www.ontario.ca/page/ontarios-greenbelt

3. The role of soil in carbon sequestration: https://news.climate.columbia.edu/2018/02/21/can-soil-help-combat-climate-change

4. The continuing popularity of big vehicles: https://www.forbes.com/wheels/news/best-selling-cars-suvs-pickups-2021/

5. Urban forests and climate change: https://treecanada.ca/resources/canadian-urban-forest-compendium/21-air-quality-climate-change-and-urban-forests/

6. Tree carbon calculator: https://www.fs.usda.gov/ccrc/tool/cufr-tree-carbon-calculator-ctcc

7. How vegetation and trees reduce heat-island effect: https://www.epa.gov/heatislands/using-trees-and-vegetation-reduce-heat-islands

8. Land use affects temperatures during heat waves: “We found that the cumulative hours of extreme heat waves increased significantly with the proportion of urban land and decreased significantly with the proportion of forested land and water. This research provided important information for alleviating extreme heat waves in cities and for rational land planning.” https://econpapers.repec.org/article/gamjlands/v_3a11_3ay_3a2022_3ai_3a10_3ap_3a1786-_3ad_3a941440.htm

9. Insects and ecosystem collapse: https://www.theguardian.com/environment/2019/feb/10/plummeting-insect-numbers-threaten-collapse-of-nature

10. How climate change will affect plants: https://news.climate.columbia.edu/2022/01/27/how-climate-change-will-affect-plants/

11. High CO2 thickens plant leaves: https://www.washington.edu/news/2018/10/01/thick-leaves-high-co2/

12. The impact of heat waves on plants and ecosystems: https://www.canr.msu.edu/news/investigating-the-impact-of-heatwaves-on-natural-and-agricultural-ecosystems
Decrease in nutritional value of crops:
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2486.2007.01511.x

13. How extreme rain events affect plants. The study’s focus is on grasslands, but the citation list is worth reading: https://link.springer.com/article/10.1007/s00442-019-04476-z#ref-CR29

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