EPOW - Ecology Picture of the Week

Explanation:   Behold the killer!  You are standing beneath tall second-growth Douglas-fir trees in Mary S. Young State Park in the town of West Linn, Oregon.  Engulfing the stately trees and much of the ground vegetation, however, is a creeping plague of an exotic species:  English  ivy.  

English ivy is native to Europe, western Asia, and northern Africa ... not North America, and certainly not urban forest parks in western U.S.  English ivy may be somewhat toxic to pets and other animals.  English ivy is termed a noxious weed and vigorous eradication efforts are underway in many locations.  

Another species of ivy that also suffuses plants and parks is German ivy (also called Cape ivy) -- actually, not German at all but a ragwort climber of family Asteraceae from South Africa.  It thrives in both disturbed and pristine areas alike, threatening native plants and entire natural areas.  Although German ivy (Delairea oderata [prev. Senecio mikanioides] of family Asteraceae) is sold as a cultivare, like English ivy it too is a scourge to protected parks.  Its removal from pristine highland forests of Hawai'i ... from California coastlines ... and from other locations is a major task.  Its current distribution includes western United States, Hawaii, South Africa, Spain, New Zealand, southeastern Australia including Tasmania, and elsewhere.  

Exotic English Ivy blanketing the ground.
Click for larger image.

Like English ivy, German ivy spreads easily by wind, sprouts by root and from every leaf node as well as by seed, and outside its native range in South Africa is considered an exotic species.  It greatly resists eradication.  Even pulling by hand often fails, as stems break off, leaving sprouting sources behind.  This is a most undesirable ivy.

Current agricultural research, however, may have found a natural enemy: a fly and a moth from South Africa might serve as natural biological control agents, but research is ongoing.  Meanwhile, beware!  The invaders continue to spread ...