Author: John Barker, OUFC
In 2018, the City of Toronto undertook a comprehensive urban forest assessment with its second canopy study. The project followed on the 2008 study, published as Every Tree Counts, which was revised in 2013. The aim was to update the City’s knowledge of current urban forest conditions, quantify the ecosystem services the urban forest provides, identify opportunities to plant more trees, and measure how Toronto’s urban forest had changed over the course of ten years. The study employed i-Tree Eco, aerial imagery analysis, and remote sensing with work completed by BioForest, KBM Resources Group, Dillon Consulting, and Dalhousie University.
The City had experienced some important events in those ten years – and not all were positive. Emerald ash borer had made its way to Toronto, killing ash trees across the city. An ice storm had passed through, leaving damaged trees in its wake. As a major urban centre, Toronto also experienced its share of development and population growth as well.
Nevertheless, the study revealed that in the past ten years the city’s tree population had grown to 11.5 million trees and its canopy had expanded to cover 28.4-31% of the city. At the same time, total leaf area decreased, which corresponded with a decrease in annual pollution removal and carbon sequestration. Each year, Toronto’s urban forest was estimated to provide about $55 million in annual benefits. The study also found that impervious ground cover increased across the city, which has implications for stormwater management, urban heat island effects, and potential planting space for trees.
Currently, Toronto has 11.5 million trees and its canopy had expanded to cover 28.4-31% of the city.
The study draws attention to the importance of measuring and quantifying the structure of the urban forest and the benefits it provides to urban residents. Canopy studies inform and support municipal urban forestry programs and policy by providing scientific fact-based data on important green infrastructure assets.
Studies such as this also draw attention to the impact destructive agents like invasive species can have on canopy health. However, they also highlight the effect positive influences like conservation initiatives can have on the urban forest. For example, tree protection is an important factor for long-term urban forest conservation. Planting trees alone is not sufficient for growing the urban forest if the existing trees are not managed and protected from destruction. Preserving impervious ground cover is also important for providing suitable tree habitat to ensure a healthy tree canopy for the future.
As our understanding of urban forest benefits increases and urban populations grow, cities across Ontario will benefit greatly from studying their urban forests and applying their knowledge to managing trees for the benefit of future generations.