The Role of Horticulture in Plant Invasions in the Midwestern United States

Premise of research. As the second leading cause of biodiversity loss worldwide, invasive species have been introduced accidentally or intentionally into many locations. To prevent their continued spread, identifying common pathways of introduction is critical, as Sarah Reichard emphasized in her classic 1994 study in which she analyzed 235 woody species considered invasive in the United States at that time and reported that the majority had current or historical uses in horticulture. Methodology. We now update her classic study with a literature review and expand it to herbaceous species by examining the origin of species identified as invasive today but within the Midwestern United States. Pivotal results. Of the 295 invasive species in this region, most introductions were through the ornamental trade, comprising 87.1% of trees and shrubs, 81.0% of vines, and 29.7% of terrestrial and aquatic herbs. We found that 85.5% of 83 invasive tree, shrub, and vine taxa in the Midwestern United States were associated with horticulture, compared with Reichard’s national estimate of 82% of 235 species nationwide. Conclusions. In the 29 years since Reichard’s review, the ornamental pathway continues today to be an avenue for the introduction of some plant species that later become invasive in the Midwestern United States, and, as such, the horticulture field could be effective in helping to reduce future plant invasions.