Why Reforest London wants the city to stop planting invasive trees

Reforest London is calling on the city to stop planting invasive species that are impacting local ecosystems.

The non-profit organization is warning that invasive trees and shrubs could grow and kill native plants in London. The intruders often aggressively use up water, nutrients and sunlight that would otherwise be available to native species.

Dean Sheppard, executive director of Reforest London, said the city needs stricter guidelines surrounding planting invasive trees.

"There's a disconnect between what (the city) is planting and its invasive species management," he said.

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City arborists plant about 5,000 trees every year to keep up with the removal of aging or dying trees and a number of invasive species are among a list of species approved by the city. 

A city list of approved street trees suggested that about 20 per cent are deemed as invasive. 

Jill-Anne Spence, the city's urban forestry manager, said invasive plants have a better chance of surviving in a harsh urban setting such as London.

"We're planting them in rare incidences where no other or very limited types of trees will grow because of harsh environmental conditions," she said.

Spence said the city avoids planting invasive species near conservation areas such as Westminster Ponds. The city plants invasive species along boulevards where they are better able to deal with the limited soil space and harsh chemical sprays.

But Sheppard said planting invasive trees and shrubs can affect the wider ecosystem.

"If you want to have healthy woodland, you need a diverse mix of species and animals that have evolved here together for a long time," he said. "An invasive species disrupts that — it totally crashes that."

In 2014, a city strategy emphasized the management of natural areas to proactively tackle invasive species and enhance native species.

List of city approved invasive trees:

• Hedge Maple
• Amur Maple
• Norway Maple
• Sycamore Maple
• Tatarian Maple
• Horsechestnut
• European Alder
• European Hornbeam
• ​Amur Maackia
• Crab Apple
• Callery Pear
• European Mountain Ash