Ornamental invaders are too close for comfort
Written by Eve Beaury, edited by Bethany Bradley
Summary
Many invasive species are expanding into new locations, including the Northeast, with climate change. Previous research by the RISCC leadership team has shown that horticultural trade is one of the primary vectors that could unwittingly facilitate this movement. To assess the extent of this risk, Beaury et al. (2023) compared the distribution of ornamental sales of 89 invasive plants to locations where these species are currently invasive as well as to locations where these species could pose future risk with climate change. The study found substantial evidence that invasive species are sold as ornamentals near existing invasions, including cases in which an invasion was less than 1 kilometer from a plant nursery offering that species for sale. Nearly all of the studied species had at least one nursery offering the species within its current invaded range (estimated using species distribution models). 25 invasive species had at least one nursery located in an area that is not currently suitable for invasion, but could become suitable with climate change. Horticulture therefore presents a major risk of facilitating invasions under current climate as well as seeding future invasions with climate change - including providing propagule pressure to existing invasions, the infilling of species ranges under current climate, and the expansion of species ranges with climate change. To reduce these risks, we need to expand the scale at which we manage introductions from horticultural trade.
Take home points
An easy first step to stop the harm caused by invasive species is to stop planting them in our backyards. Beaury et al. (2023) identified species and locations where we can do a better job at reducing invasive plant spread from horticulture.
The distance between an observed invasion and a nursery selling that species varied from <1km to 4000km, highlighting room for improvement as well as lower risk horticultural introductions.
Some ornamental invasive plants have a particularly high risk of expanding quickly as the climate changes, including tree-of-heaven, callery pear, and other species in RISCC’s ‘Do Not Sell’ Management Challenge
Management implications
The plant nursery industry has expanded its geographic reach to increase invasion risk at distances representative of ‘down-the road’ and across the country. We need to respond by expanding the scale at which we manage invasion risk from horticulture.
It’s never too early to start working with industry partners to prevent the next wave of invasions. Resources like RISCC’s ‘Do Not Sell’ Management Challenge can be used to inform nurseries on species to avoid.
Climate watch lists could also identify species that are particularly likely to expand quickly via horticultural trade.
Related papers
Beaury et al. 2021, Bradley et al. 2023
Keywords
Invasive plant, horticulture, ornamental plant, range expansion