Managing urban forests for climate resilient cities requires all hands on deck

Background/Question/Methods

Strategies to improve cities’ resilience to climate change are critical as urban areas expand, urban populations grow, and extreme events increase in frequency in a warming world. Tree planting is a prominent strategy for building climate resilient cities, leading to increased investment at municipal through national levels. However, simply adding trees is not enough. The diversity and structure of the urban forest influences ecosystem service delivery to local residents, with strong implications for environmental equity across cities. Ensuring delivery of forest-based ecosystem services is further complicated by the fact that trees are governed by multiple stakeholders, with their own values and preferences. Here, we share ongoing work from two cities, Madison, WI, and Montreal, QC, highlighting the role of urban forests in a changing climate. In Madison, we used sensor technology to show how impervious surfaces and canopy cover interact to influence urban air temperature at fine scales (e.g. 10s to 100s of meters), highlighting the critical role of the urban forest for providing temperature regulating services. We build on this work through community science approaches in Montreal, highlighting the role of land use governance in shaping the patterns of urban forest diversity and structure that drive ecosystem service provision.

Results/Conclusions

In Madison, a custom-developed mobile temperature sensor mounted on a bicycle was used to complement a fixed in situ network of 150 temperature sensors – collecting observations approximately every 5 meters. Mean daytime air temperature differed by 3.5°C between the hottest and coolest parts of the city, with temperature regulation services varying non-linearly with changing tree canopy cover. The most significant cooling occurring in neighbourhoods surpassing ~40% canopy; highlighting challenges to achieving equitable distribution of climate-related ecosystem services across our cities, particularly alongside densification. Results also highlight the importance of an “all hands on deck” approach to urban forest management, with multiple stakeholder contributing to canopy cover. We further investigate the role of land use governance in shaping patterns of urban forest diversity and structure in a subsequent study in Montreal, QC. Our results show that not only are a significant percentage of urban trees on private land, but that trees on residential land differ significantly in diversity (higher species richness, and altered species composition) and structure (shifted towards a smaller size distribution) relative to their public counterparts. Our results emphasize that managing urban forests for climate resilient cities will require working closely with multiple stakeholders across spatial scales.