Investigating street tree decline and mortality in commercial urban spaces revitalized with structural soil cell technology to improve planting and maintenance practices

2016 | Camilo Ordóñez, PhD, Ryerson University, Canada and Co-Investigator Andrew Millward, PhD, Ryerson University, Canada

Trees in downtown commercial areas improve air quality, regulate summer temperatures, and enhance retail activity by improving the aesthetics of streets. However, growing trees in these spaces is usually difficult, given the lack of space, and low soil quality, among other factors. Structural soil cell technology can improve habitat quality for trees in these spaces. This technology was used most recently to plant trees as part of Toronto’s revitalization of both Bloor and Queen’s Quay Streets. These trees faced or are facing subsequent decline and high mortality. There is a lack of research on these landscapes and this technology, so it is unclear why these trees failed. Assessing the factors that contributed to their decline and mortality is necessary to guide future decisions about the use of this technology. This will ensure the success of green infrastructure investments, reduce the costs of tree planting and maintenance, and help companies and cities develop sound guidelines for planting trees in downtown, commercial areas. This research project will analyse already-existing soil and biophysical data from these two sites and use multi-variate regression and contingency analysis techniques to elucidate the factors that have contributed the most to tree decline and mortality. The information emanating form this project will be made accessible to urban forest managers and other stakeholders through research reports, academic publications, workshops, conference presentations, and webinars, and train one Canadian student in contemporary urban forest issues.

Study Results
The Bloor Street Revitalization project in Toronto, Canada, was finalized in 2010 and involved the planting of 133 trees in structural soil cells. These cells are an underground framework that supports the above pavement and contains soil that can support trees. The framework is usually accompanied by a system that can collect and filtrate surface water runoff, while also providing passive irrigation to the tree. The Bloor trees performed poorly and were removed and replaced in 2015. There is limited research on tree performance in soil cells, so it is unclear why this happened. To help solve this problem, this research project collected and analyzed data on tree performance along Bloor Street with the objective of isolating the factors that contributed the most to tree performance. Results of our work indicated that trees that were alive at the time of removal, were in good condition, and showed higher growth, had: 1) lower levels of soil salinity; 2) fewer signs of damage; and 3) only moderate daily exposure to direct sunlight. Based on these results, we have developed guidelines to improve tree performance in structural soil cells that are include in a final technical report. We have also produced three academic publications, trained two Canadian students from Ryerson University, delivered one workshop and two conference presentations, and initiated a second phase of investigation on Queens Quay in Toronto, where soil cell technology has also been used to plant trees, and where early tree growth data points to healthier trees.

Year: 2016

Funding Duration: 1-3 years

Grant Program: Jack Kimmel International Grant

Grant Title: Investigating street tree decline and mortality in commercial urban spaces revitalized with structural soil cell technology to improve planting and maintenance practices

Researcher: Dr. Camilo Ordóñez

Key words:

Peer Reviewed Publications from Grant:

General Audience/Trade Publications:

  • UFRED Ryerson. “De-icing Salts and Street Tree Performance in Structural Soil Cells.” Urban Forest & Ecological Disturbance (UFRED) Group, Ryerson University: Toronto, ON, Canada, 2017. Research project summary.
  • UFRED Ryerson. “Street Tree Decline and Mortality in Commercial Urban Spaces.” Urban Forest & Ecological Disturbance (UFRED) Group, Ryerson University: Toronto, ON, Canada, 2017. Research project summary.
  • UFRED Ryerson (2017). Street tree decline and mortality in structural soil cells: Investigating causes to improve planting and maintenance best practices. Urban Forest & Ecological Disturbance (UFRED) Group, Ryerson University: Toronto, ON, Canada, 32 pp (UFRED Group: Millward, A.; Ordóñez, C., Sabetski, V.)

Professional Presentations:

  • UFRED Ryerson (2017). Street tree decline and mortality in structural soil cells: Investigating causes to improve planting and maintenance best practices: the case of Bloor Street, Toronto,
    Canada. Presentation. 1 March 2017, Toronto, Canada (UFRED Group: Millward, A.; Ordóñez, C., Sabetski, V.) Sabetski, V.; Ordóñez, C.; Millward, A.; Grant, A.; Steenberg, J.; (2017) Socio-ecological dynamics of street tree planting in revitalized commercial urban spaces: the case of Bloor Street, Toronto, Canada. Presentation. Trees in the City: Critical Issues in Urban Forestry, Association of American Geographers (AAG) Annual Meeting, 6–9 April 2017, Boston, USA.
  • Ordóñez, C.; Sabetski, V.; Millward, A.; Grant, A.; Steenberg, J.; (2017) The Hierarchy of Decisions in the Governance of Engineered Greening Projects in Downtown Urban Areas: Presentation. Accepted. Trees in the City, Canadian Association of Geographers (CAG) Annual Meeting, 29 May – 2 April 2017, Toronto, Canada.

For more information on this project, contact the researcher via TREE Fund at treefund@treefund.org.