Construction, pollution, and invasive species threaten urban forest

By Chantilly Post

The Harbord Village Residents’ Association (HVRA) is updating its neighbourhood tree inventory thanks to the help of environmental scientist James Steenberg.

In 2007, the HVRA implemented NeighbourWoods, a method of quantifying the location, health, and strength of the trees in the village.

“[So far] it’s been great,” said Steenberg. “I can do nothing but applaud the volunteers and the people who’ve worked with this inventory.”

This community-based urban forest program analyzes the species, size, age, and other characteristics of the trees in the community. The comprehensive program requires minimal training to be used effectively, and creates a better understating of the urban forest’s structure and benefits.

Steenberg will also evaluate why, how, and where the urban forestry is most vulnerable, and re-assess the stability of the tree inventory.

Currently pursuing his PhD at Ryerson University, Steenberg uses NeighbourWoods as it is an efficient method for observing the vulnerability of the forest’s ecosystem, as well as for tracking the growth and mortality rates of the area’s trees.

“[There’s] not tons of ice storm damage along the major streets, and people’s front lawns, [where] the trees are doing great,” said Steenberg.

But, according to Steenberg, there is a problem with what he terms the “accidental urban forest,” which is the trees that sprout up in alleyways, parking lots, and along fences. Typically Manitoba Maple or White Mulberry, such trees grow fast, and are often cut down.

“Because [trees] live so long and because they are all around us in the city we tend to think they’re permanent,” said Steenberg.

Unfortunately, that’s a misconception.

The biggest threats to the city’s urban forests are construction, pollution, and invasive species like the Asian long-horned beetle and ash borer. The latter is a green beetle that destroys upwards of 860,000 ash trees on private and public lands throughout Toronto.

Other threats include drought and drainage problems, which can reduce a tree’s life span from 100 to 30 years in an urban environment.

However, “people are becoming more aware of [such threats], and in many neighbourhoods, especially in downtown and older residential neighbourhoods, the urban forests are getting better,” explained Steenberg.

Although trees have a major impact on our ecosystem, they are a very vulnerable kingdom. It is said that a minimum coverage of 30 per cent forestry is required to maintain a sustainable, healthy ecosystem.

Toronto alone has an estimated 10.2 million trees, 4.1 million of which are located on public property, including 3.1 million in the city’s parks, and 600,000 on the city’s streets. In all, the City maintains approximately 40 per cent of its urban canopy.

Steenberg and his crew of volunteers will be maintaining the Harbord Village tree inventory until August.

To conduct a tree inventory in your neighbourhood, please visit www. forestry.utoronto.ca/neighbourwoods/web/.