I love my hometown, but I have a bone to pick with a few of its inhabitants -- especially the green ones. It's not the lively Nader supporters of Portland, Ore., that I have hard feelings for, but rather the guileful botanic creepers that go by the common name English ivy. Botanic enemy number one is a luscious green forest dweller, a lazy gardener's groundcover, a symbol of old-world garden sophistication -- and, in Portland, an insidious invasive species. English ivy (Hedera helix, for the botanically savvy) infests more than half of the city's forests, choking out trees, ferns, and …