symbiotic invasion

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Both are alien to this city.  Both, invasive. Both stretch their tendrils across vast underground webs, consuming moisture, and nutrients. Yet, they were planted with abandon in the past specifically because they grew so quickly, luxuriantly, in their new domains.

Welcome to the urban landscape of the Norway Maple and the Common Ivy.

Norway Maple
The Norway maple is the dominant tree of urban forests in many North American cities, including Toronto. Due to its tolerance of urban pollution, salt and other stresses it was planted by choice to replace elms destroyed by Dutch Elm Disease in the mid 20th century. Today it is not only the most common planted tree in Toronto parks, yards and streets, but it has also independently invaded Toronto’s remaining natural ecosystems.

Common Ivy
Hedera helix (common ivy, English ivy, European ivy, or just ivy) is a species of flowering plant in the family Araliaceae, native to most of Europe and western Asia. A rampant, clinging evergreen vine, it is a familiar sight in gardens, waste spaces, on house walls, tree trunks and in wild areas across its native habitat. It is labeled as an invasive species in a number of areas where it has been introduced.

When we moved into our home in the summer of ’09, both the Norway Maple and Common Ivy in the front yard had reached maturity. The two were entwined in an embrace that had developed over years. The base of the Maple tree was knotted with inch thick vines wrapped tightly around the trunk, snaking into the top most branches of the tree. Later that summer, flowers developed on the ivy. While a treat for birds, the flowers also attracted nests of hornets adding an element of danger to those allergic to their venom. For the next two years, the two invaders continued their wild-growth dance, spreading above and below, both seemingly healthy and spirited in their symbiotic embrace.

Then one day a representative of the Urban Forestry Services dropped off an official notice telling of an impending tree trimming. The city was concerned that the ivy had reached such proportions that it might be choking the the life from the tree. Or worse, supporting a dead or dying tree that could crack falling to the sidewalk endangering the local pedestrians. It was quite probable this Norway Maple were nearing the end of its urban lifespan, so caution was recommended.

On a balmy autumn day in September two employees from the city mandated arborists arrived at the front yard to begin disentangling the ivy and the tree, a project that would take some five hours to complete. As the sheets of ivy pulled away from the trunk it became clear that, aside from some bark damage the Norway Maple was fine. As the huge swaths of thick limbs were fed into the chipper it was amazing to see the volume of ivy that had grown and clung to the tree for so many years.

With the stripping complete, the tree presented a stark outline against the sky. After all, we had seen it ‘dressed’ in its sinewy evergreen mantle for over two years and the previous owners of the home for a decade or more.
With the limbs trimmed, the ivy removed and chipped, the crew left the leafless, ivy-less Norway Maple to survive the winter, without its thick ivy blanket.

But by early October, a mere two weeks later, little green sprouts of ivy once again were seeking purchase into the bark. The cycle had re-initiated. And the two symbiotic invaders continued their charge ever outward and upward.

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