" Poison ivy is a native not only to the American wilderness but to the wilderness of halfway places that grow up around every new housing development and shopping center, highway and train track. Such wilderness is the shadow cast by our collective progress. Studies have shown that poison ivy is especially sensitive to the levels of carbon dioxide in our air. The higher the concentration, the more vigorous the plant, and the more virulent its poison. Since the 1960s, the poison in poison ivy has doubled its strength.4 "

― Christie Purifoy , Placemaker: Cultivating Places of Comfort, Beauty, and Peace