An assessment of Canada thistle in northern U.S. forests

This publication is part of a series that provides an overview of the presence of invasive plant species monitored on an extensive systematic network of plots measured by the Forest Inventory and Analysis (FIA) program of the USDA Forest Service, Northern Research Station (NRS). Each research note features one of the invasive plants monitored on forested plots by NRS FIA in the 24 states of the Midwestern and Northeastern United States. Canada thistle (Cirsium arvense) is an herbaceous perennial in the Aster family. Since its arrival to North America from Europe in the early 1600s via contaminated crop seed, it has caused considerable impact by displacing native plants and reducing crop and pasture productivity (Czarapata 2005, Kaufman and Kaufman 2007).