Through conversations with Janet and other LEAF staff, I became really interested in learning more about the outcomes of LEAF planted trees. We decided to focus on a sample of 2,000 trees LEAF planted in the City of Toronto through the full service BYTP program to analyze how many trees are retained five years after planting and how many trees remained in 2022, using a mixed age group. The first five years are important, as this establishment period is often associated with higher mortality because younger trees are more easily stressed. If trees survive the first five years, then there is a good chance they will thrive for decades to come.
A challenge of monitoring backyard trees is getting permission to access every backyard. Instead, we decided to use the publicly available air photos the City of Toronto takes nearly ever year to identify whether trees were retained or removed without needing to access backyards.
Master student Ashlynn Flemming and undergraduate student Pamela Sleightholm spent the summer of 2024 carefully plotting tree planting locations. Using LEAF’s excellent record of siting forms, they clicked through nearly 20 years of air photos, tracking trees from as early as 2005 through to 2022 or the date they disappear from the images. In some cases, we could not determine if a tree was still present because of obstructions like other trees or house shadows blocking the view or poor image quality, but for most trees we easily came to an agreement on its presence or absence from each year’s image.
Based on our image analysis, we found that 83% of trees survived the first 5 years after planting. Our survival rate during establishment is a better than average outcome for residential planning programs in North America, and much better than the retention rate for urban trees in general. The retention rate of our mixed-age sample was lower (60% still present in 2022) as you would expect when it has been up to 26 years since some trees have been planted.
We then compared neighbourhood census and property data with the tree data to explore factors associated with tree retention or removal. The factor that was most strongly associated with tree removal was a change in homeowner. Each time a house was sold, it decreased the likelihood of the tree being present five years after planting and also in 2022.
A very positive finding is that construction activity on a property, including building additions or sheds, was not associated with higher tree loss. Another positive finding was that people who had more trees planted in one order, were more likely to retain trees over the long term.
Together these results suggest LEAF program participants are taking care of their trees– even when there is disruptive construction– but that new homeowners who inherit the tree(s) may not be as inclined to steward or as knowledgeable about tree care.
We also found that trees planted in the spring were slightly less likely to be retained, which highlights the importance of regularly watering young trees during the summer when we are increasingly having stressful periods with very hot and dry conditions.
We believe our findings show the strengths of the Full-Service Backyard Tree Planting Program, leading to higher tree retention than many residential planting programs in other regions. Hopefully the methods we developed – low cost, low tech and not disruptive for homeowners – can be used to assess LEAF planted trees every five or ten years so LEAF can continue to monitor the outcomes of the planting program.
Fleming, A., T.M. Conway, P. Sleightholm, and J. McKay. 2025. Aerial imagery as a tool for monitoring urban tree retention: Applications, strengths and challenges for backyard tree planting programs. Arboriculture & Urban Forestry 51(5): 498-513.
Conway, T.M., A. Fleming, P. Sleightholm, J. McKay. 2025. Keeping trees in the ground: How property management and socio-ecological factors affect retention of trees planted through a backyard planting initiative. Urban Forestry & Urban Greening 129154.
Tenley Conway is a Professor in the Department of Geography, Geomatics and Environment at the University of Toronto, Mississauga and is a LEAF board member. She lives in Bloor West Village and enjoys weekend walks along the Humber River.
LEAF offers a subsidized Backyard Tree Planting Program for private property. The program is supported by the City of Toronto, the Regional Municipality of York, the City of Markham, the Town of Newmarket, the City of Vaughan, the Regional Municipality of Durham, the Town of Ajax, the Municipality of Clarington, the City of Oshawa, the City of Pickering, the Township of Scugog and the Town of Whitby.