The Magnitude of the Weed Invasion

A detailed examination of verifiable distribution records in INVADERS from 1877 through 1997, shows that prior to 1907, during a period of little regulation of the importation of goods and agricultural commerce, about one hundred exotics per decade were establishing in the five northwest states. During the period of World War I, the Great Depression, and World War II, the number of successful introductions declined to about 40 species per decade. With the expansion of global travel and commerce since the 1960's the number of new introductions is again approaching the pre-twentieth century rate despite the enactment of numerous regulatory mechanisms.

Invasion by decades of five Northwest States

New Exotics in the five Northwest States

Cumulative invasion