TORONTO INDEEP

摘要

ERIC DAVIES pauses every few minutes to bring binoculars to his eyes, scanning for the quick flash of a migratory warbler. The park we're walking in, the Park Drive Reservation Lands in Toronto's Don River watershed, is not silent-bird sounds abound-yet something seems slightly off For one thing, there's no native understory, and the green that is starting to appear on the forest floor is an invasive plant, garlic mustard. Davies, a PhD candidate in forestry at the University of Toronto, shakes his head, pointing to a tree not yet leafed out He breaks off a small twig, revealing a milky white sap. "See this latex sap? It's completely toxic to insects. This is a Norway maple. They now make up 40 percent of the trees in the ravine. A 1977 study found only 10 percent" Because Norway maples are toxic to insects, Davies explains, migratory birds must now stay twice as long to refuel on their journeys; the Norway maples also make the ground beneath them toxic so that the delicate native understory that used to be here-trillium, hepatica, trout lily, bloodroot, spring beauty, and others-no longer regenerates on its own.