Plant nurseries are the primary pathway for introducing invasive species

Research from the University of Massachusetts Amherst has revealed a startling link between plant nurseries and the spread of invasive species, particularly in a warming climate.

The research, which consists of two papers, offers the most comprehensive mapping to date of how 144 common invasive plant species are expected to respond to climate change in the eastern United States.

Focus of the research

Led by Bethany Bradley, a professor of Environmental Conservation, the UMass Amherst team meticulously analyzed data from 14 invasive species databases. 

Professor Bradley noted that managers have very few resources to control invasions, so there isn’t time to waste focusing on species unlikely to become invasive in a given area. “But the question of what will become invasive and where has been surprisingly tricky to answer.”

“If we can proactively identify these species and the regions they are most likely to become abundant in as the climate warms, then we can head-off a major ecological threat before it’s too late,” said study co-author Annette Evans.

Hotspots of invasive species 

Concentrating on the eastern United States, the team identified current “hotspots” of invasive species abundance. These hotspots, notably around the Great Lakes, mid-Atlantic, and the northeastern coasts of Florida and Georgia, are fertile grounds for over 30 different invasive plants.

Using advanced modeling, the researchers projected the future spread of these species with 2°C of warming. 

Key insights

The team discovered that most species would likely shift their ranges northeastward by an average of 213 kilometers. 

In some areas, this shift could lead to the proliferation of up to 21 new plant species, exacerbating the effects of 40 currently abundant invasives. However, 62% of these species might see a decrease in suitable habitats in the eastern United States.

Primary pathway 

The second part of the study, led by Evelyn M. Beaury, a postdoctoral researcher at Princeton, highlights the significant role of commercial nurseries in the spread of invasive species. 

The study found that nurseries are the primary pathway for introducing invasive plants, with over 80% of the species studied being sold in nurseries.

“When people think of how invasive plant species spread, they might assume species are moving because of birds or the wind dispersing seeds,” said Beaury. “But commercial nurseries that sell hundreds of different invasives are actually the primary pathway of invasive plant introduction.”

Valuable data

The research also revealed a concerning proximity of nursery sales to invasion sites. Approximately 55% of invasive species were sold within 21 kilometers of an observed invasion, implying that local gardening practices might inadvertently contribute to the spread of these species.

“But there’s good news here,” said Beaury. “This is the first time that we have real numbers to show the connection between plant nursery sales and the spread of invasive species – including invasions that occur down the street from nurseries, as well as across state borders.” 

“Now that we have the data, we have an incredible opportunity to be proactive, to work with the industry, consumers and plant managers to think more critically about how our gardens impact U.S. ecosystems.”

Study implications 

The study provides a list of 24 commonly sold invasive plants that are likely to become more problematic with climate change in the northeast, suggesting native alternatives to these species.

“These two papers together make it pretty clear that not only are we facilitating current invasions through the ornamental plant trade, but we are also facilitating future climate-driven invasion,” said Bradley, “But with these papers, maps and watchlists, we can pinpoint which species are most worrisome where, both now and in the coming decades. These are important new tools in invasive plant managers’ toolboxes.”

The study is published in the journal Diversity and Distributions.

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