Urban Forests and Climate Change

In recent years, cities have increasingly recognized the importance of a healthy urban tree canopy as an essential and valuable part of urban life. There are many compelling reasons why people – and cities – love trees.

Barwinsky notes that there are practical and tangible benefits to a healthy urban tree canopy, including “reduced cooling costs: reduced energy costs all around.” She points out that trees help offset the urban heat island effect, keeping our cities cooler. They also help manage stormwater runoff, reducing demands on drainage infrastructure, and help prevent river bank erosion. [1][2]

Urban forests are an essential asset in dealing with our changing climate.

She also says that there are “a lot of intangible benefits as well, such as helping our psychological well-being, our social well-being, and the social structure of our communities.” Recent research suggests that trees are beneficial to our physical and mental health as well as better community cohesion, and improved quality of life. [2][3]

All of this makes urban forests an essential asset when dealing with our changing climate. In the face of rising heat and the threat of more extreme weather hazards, urban forests and green spaces can improve health and well-being, provide a buffer against heat extremes and dangerous weather events, and promote community resilience, all while helping us save money on costs such as air conditioning and municipal infrastructure. [3]

Unfortunately climate change also poses real challenges to the health of our urban forests. Barwinsky strikes a cautionary note about the seriousness of the threat: “When it’s lost, then people realize what value it had. Let’s not get to that point, where we realize what we’ve lost.”

Urban forests are already difficult to manage: a typical Canadian city is not a friendly place for many tree species, and the most effective urban forestry practices are costly and labour-intensive. Climate change makes these existing challenges worse, but also adds entirely new and troubling problems.

We need only look at the summer of 2018 in Winnipeg to see why. The city experienced 26 days that were 30 °C or warmer, which is the most since 1988 (when there were 34 such hot days). [4][5] Climate projections show that this unusual heat is likely to be the “new normal” in the near future. [6] This will have lasting consequences for trees. Barwinsky says that “there are a number of tree species that are going to suffer. They are going to have a hard time getting through those hot conditions, those dry conditions.”

And yes, it was also a very dry summer. The total precipitation in Winnipeg over June, July, and August was only half the normal amount. [4] Barwinsky clearly sees the effects of drought stress in some local tree species . But she points out that not all impacts will be immediately apparent, since “trees don’t necessarily show the effects of those changes immediately: it can take five years, it can take ten years.”

Other threats can appear suddenly and unexpectedly – damaging insect infestations, for example. The recently introduced emerald ash borer killed off 99% of Toronto’s 850,000+ Ash trees in less than a decade. [7][8] It has now been found in Winnipeg as well. [9] Barwinsky notes that “Where normally some of these invasive pests may not be able to survive our winters, and particularly our growing season, with climate change they might start surviving, and we’re going to have a problem managing them.” Warmer climates allow insects to reproduce and spread more quickly, but warm and dry conditions are also stressful for trees, leaving them with less capacity to defend against pests and infection in the first place. [10]

Urban foresters are rising to the challenge of climate change in part by adjusting their management plans to account for the changing climate. For example, Barwinsky notes that currently “when we plant trees, we water them for the first two years to get them established. After that, they’re on their own. Possibly in the future we may have to water these trees over a longer period of time.” She also reports that the city has embarked on a program of rapid removal of infected trees to address the growing threat of invasive pests.

Changes in mindset are essential when it comes to dealing with climate change.

But protecting the health of urban forests requires long-term planning for resilience as well as short-term crisis management. One of the most challenging aspects of planning for the hazards of climate change is knowing that unpredictable threats (such as the arrival of the ash borer) are likely to arise. Barwinsky says that the best strategy for dealing with the unexpected is to expand the diversity of the urban forest. She notes that in urban forestry “there has always been a tendency to create monocultures of particular tree species that perform really well in an urban environment. But we need to continue to move away from that monoculture mindset.”

Changes in mindset are essential when it comes to dealing with climate change. As Barwinsky says, “The most important thing is that we have to recognize that it’s happening. Recognizing that and getting started on it and knowing we’ve got to change what we’re doing: that’s a big part of it.” Appreciating the impact of climate change on our trees and the value of trees in dealing with climate change is key to taking action in the short term and cultivating resilience in the long term.

This shift in attitude has to include all the stakeholders, politicians, and citizens who benefit from the advantages of urban forests. After all, a majority of Winnipeg’s trees are on private land and thus not in the City Forester’s care. “The City of Winnipeg can’t do it all”, Barwinsky says. “We need partnerships to get the message out and to help people understand what we’re faced with,” she says.

Community groups and residents’ associations have long taken a keen interest in tree health and maintenance, and are an important way for citizens and city staff to collaborate on education and action. Barwinsky’s team also does outreach in schools, and she sees that “there’s a greater awareness with this next generation” about the importance and value of trees. Collective effort and education as well as well-funded and -directed government programs are key to preserving and expanding our much-loved and much-needed urban forests in the face of climate change.

Our cities are much better off when they have healthy, thriving forest canopies. [11] The benefits of trees will only become more valuable in all senses – promoting community resilience, improving health and well-being, and providing economic benefits to private citizens and public budgets – as our climate continues to change. [12]

References

1. Tree Canada. Compendium of Best Urban Forest Management.
2. Food and Agriculture Organization of the United Nations. “Guidelines on urban and peri-urban forestry”
3. Canadian Forest Service and Department of Forestry, UBC. Canadian Forest Service and Department of Forestry, UBC.
4. Winnipeg Free Press. “The long, hot summer: Winnipeg had 26 days of 30 C or more — the most since 1988.”
5. CBC News. “Record setting hot dry summer takes toll on Winnipeg trees”
6. The Climate Atlas of Canada. Winnipeg, MB : Very hot days (+30°C) (RCP 8.5).
7. The Toronto Star. “Bug 1, Tree 0: Most of Toronto’s ash trees expected to die by 2017.”
8. Edward R. Wilson and Sandy M. Smith (Faculty of Forestry, University of Toronto). “All that is Green is not Gold: The Emerald Ash Borer (EAB) Invasion of Toronto’s Urban Forest, Canada”
9. City of Winnipeg. “Emerald Ash Border (EAB)”.
10. Natural Resources Canada. “Climate change: Impacts”
11. Green Infrastructure Ontario Coalition. Urban Forests.
12. Anika Terton. Building a Climate-Resilient City: “Urban ecosystems”