Growing tree cover faces more threats
Report says invasive species pose serious threat to quality, resilience of urban forest
The good news is that Toronto’s tree canopy has expanded since 2008, according to a landmark report presented at city hall on Thursday.
The bad news is that invasive species have grown too, and pose a serious threat to the future quality and resilience of Toronto’s urban forest, especially in ravines.
Those were some of the conclusions in the first update of Toronto’s 2008 tree canopy study, presented to the infrastructure and environment committee.
Certain neighbourhoods in the city have fared worse than others, according to the report. In general, the north and wwwest areas of Toronto are losing canopy, wwwhile south and east parts of the city are seeing increases.
Lambton-Baby Point saw a 30 per cent increase in canopy and the canopy increased by about 22 per cent in both Old East York and Runnymede-Bloor Village. The canopy declined 20 per cent or more in Forest Hill North, Dufferin Grove, Kennedy Park, University and a hair under 25 per cent in Playter Estates-Danforth.
“It is of ecological concern when dead spots are allowed to take over areas of this city. Wildlife, birds, bees, butterflies — our taste of nature — needs contiguous green,” said Sue Dexter, representing the Harbord Village Residents’ Association, whose members live in an area experiencing canopy loss.
“The city report said it does not understand why these losses are occurring,” Dexter said. “We need those answers because (they) may signal the need for policy changes.”
The report also found that while To
ronto’s canopy cover increased by 1.3 million trees over the 10 years — despite losses from the 2013 ice storm and infestations of emerald ash borer and Asian long-horned beetles — the overall condition of trees and shrubs has declined. Parks and ravines saw an increase in invasive tree cover from 10 to 14 per cent and an increase in invasive shrub cover from 15 to 32.5 per cent between 2008 and 2018.
Buckthorn was identified as the principal culprit among invasive shrubs. Native to Eurasia, buckthorn was introduced to North America in the 1880s as an ornamental plant and has spread into the wild, altering nitrogen levels in the soil, which discourages the growth of native species.
Ahealthy tree canopy can help mitigate damage from climate change and provide cleaner air.
The committee asked staff to prepare and implement areaspecific action plans to enhance the tree canopy for neighbourhoods that showed significant loss. The matter will be considered by city council on Jan. 29.
Other findings of the report include:
The health and condition of street trees has improved, due to better species selection and maintenance, for a net gain of 12,000 trees. They’re also in better condition. About 74.4 per cent of Toronto’s street trees are in excellent or good condition, compared to 49 per cent in 2008.
The amount of impervious land cover — hard surfaces like concrete that repel rainwater — increased about 892 hectares, or the equivalent of 1,670 football fields over the 10-year period. Construction of single family homes accounted for 349 hectares of that.
Residential housing construction and other development in the city are having detrimental effects on the forest canopy. Construction can result in tree roots being severed and in soil compaction, which restricts root growth.