Earth and Space News: Downtown Commercial Streetscape Tree Populations in Toronto, Canada

Summary: The May 2018 Arboriculture & Urban Forestry examines why 133 hardy London planetrees did poorly or died by 2015 on Bloor Street, Toronto, Ontario, Canada.

In 2010 and 2011, 134 London planetrees (Platanus x acerifolia) were planted in raised flowerbeds and at-grade pit planters on Toronto's commercial-retail Bloor Street, between Avenue Road and Church Street: Peter Kuitenbrouwer @pkuitenbrouwer, via Twitter July 11, 2014

North American cities aspire to augment downtown commercial streetscape tree populations for environmental benefits, including ambient heat moderation, retail traffic and urban aesthetics, according to Arboriculture & Urban Forestry's May 2018 issue.

The article The Influence of Abiotic Factors on Street-Tree Condition and Mortality in a Commercial-Retail Streetscape broaches below-ground, passive-irrigated, runoff-collected, surface-absorbed, water-infiltrated, tree-growing structural soil cells. Sixty-two dead and 71 alive trees in 2015 confirm previous research conclusions concerning disproportionately high mortality levels for trees close to highly urbanized streets and roadsides. Co-authors Amber Grant, Andrew Millward, Camilo Ordóñez, Vadim Sabetski, James Steenberg and James Urban decry compacted, high-alkaline, high-salt, low-nutrient, low-organic, low-volume, low water-holding, poor-drained tree-unfriendly soils.

Abiotic (non-living) factors in high-density, polluted, summer-heated urban canyons with low circulation, light and precipitation levels and multi-story buildings additionally endanger downtown commercial streetscape tree populations.

Eco-stress, miscare and vandalism fit downtown commercial streetscape tree populations into 5- to 20-year life expectancies instead of the 75-year life cycles that tree-friendly factors favor.

Revitalization of Bloor Street, 2010-2011, in Toronto, Ontario, Canada, gathered 133 urban-tolerant London planetrees (Platanus x acerifolia) into soil cell-interconnected at-grade pit planters and raised beds. Toronto has the 7a plant hardiness zone's undisturbed soils "representative of the Lawrence River soil system, characterized by silt clay soils from glacial and fluvial deposits." The study invoked abiotic factors since the pre-removal inspection of the 133 same-species trees in flower beds and ground-level pits identified no visible diseases or pests.

The aim of poor performance triggers and the objectives of ecological, environmental and performance data join the purpose of abiotic factor-effectuated mortality and dead/poor/fair/good condition ratings.

The study's downtown commercial streetscape tree populations knew elevated sodium, highly alkaline soil pH, human-caused damage, low electrical conductivity, moderate sandy-clay-loam soil compaction and variable sunlight.

Tree decline drivers link climate- and human-induced bark and canopy damage, planting characteristics, soil alkalinity and salinity and, possibly, sunlight-induced heat stress and soil moisture losses. The six co-authors mention Bloor Street's "very low tolerance to ice on the sidewalks, thus the intense use of de-icing agents" and raised soil salinity levels. They note the negative effects of street-level planting site characteristics in that pit planters typically net "significantly higher levels of salts" and mortality than raised beds.

The study's downtown commercial streetscape tree populations observed a soil pH within alkaline ranges, at 7.81 (±0.14), above recommended neutral levels at 6.5 for urban tree-growing.

Direct sunlight early in annual growing seasons and low seasonal sunlight variations prompt a more positive tree performance in Toronto, which pulls 2,066.3-hour yearly sunshine averages.

Peeling bark and tree cracks from physical damage and stress versus intact, unscarred bark, branches and trunks respectively queue up greater versus lesser dead-tree count frequencies. Study limitations reflected replacement- and replanting-deficient historical data, temporal cross-sectionality of soil analysis and unprocessed climatic data, such as heat-stressed bark peel and ice-damaged broken branches. The study's conclusions suggest globally warmed climate change sustaining such severe weather events as freeze-thaw cycles and ice storms that support structural soil cell-unfriendly de-icing salts.

The six-member team turns to tethering alkaline and saline soils, de-icing salts, physical damage, planter type and sunlight exposure to strengthen downtown commercial streetscape tree populations.

Urban forest mortality investigations initiated in 2015's study of commercial streetscape London planetrees on Toronto's Bloor Street continue with research on de-icing salt effects on structural soil cells on Queens Quay Boulevard along Toronto's central waterfront: DTAH @DTAHtoronto, via Twitter Feb. 16, 2018

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

DTAH @DTAHtoronto. 16 February 2018. "We've partnered with @RyersonU's UFRED Group to study how de-icing salt affects urban tree performance in soil cell technology & determine ways to advance best practices for street tree planting." Twitter.
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Available @ https://www.facebook.com/InternationalSocietyofArboriculture/posts/10152096628532557

Kuitenbrouwer, Peter. 5 August 2014. "Three years ago $20M was spent planting London Plane trees along Bloor. Now almost half are dead." The National Post > Posted Toronto. Last updated Jan. 24, 2015.
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Earth and Space News

Sunday, May 27, 2018

Downtown Commercial Streetscape Tree Populations in Toronto, Canada

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