Balancing Risk and Resilience: A New NE CASC Study Helps Demystify Managed Relocation

Many native plants in the U.S. cannot possibly move themselves fast enough to avoid climate-change driven extinction. If these native plants are going to have any chance of surviving into the future, they’ll need human help to move into adjacent areas, a process known as “managed relocation.” And yet, there’s no guarantee that a plant will thrive in a new area. Moreover, movement of introduced plants, albeit over much larger distances, is exactly how the problem of invasive species began—think of kudzu-choked forests, wetlands taken over by purple loosestrife or fields ringed by Japanese honeysuckle. Thanks to new research from NE CASC researchers Thomas Nuhfer and Bethany Bradley, we now have a detailed sense of which plant characteristics will help ensure successful relocation while minimizing the risk that the plant causes unwanted ecological harm.

“We know that, because of climate, native species need to move,” says Thomas Nuhfer, lead author of the paper that appeared recently in Global Change Biology and a NE CASC graduate fellow at UMass Amherst. “But many of the people working to manage invasive plant species have real concerns about unwittingly contributing to the problem if we start moving native species around.”

“We’ve made the mistake of introducing invasive species so many times in the past, and we don’t want to keep making that mistake” says Bethany Bradley,  NE CASC university codirector and the paper’s senior author. “But in a changing climate, doing nothing might do even more harm.”

So how to help plants move successfully without risking them causing harm?

“We often use specific plant characteristics—like how quickly a plant grows, how long it flowers or whether its seeds can be spread by the wind—to determine its risk of becoming invasive,” says Nuhfer. “But these are also traits that could help a native species to survive in a new environment.”

To disentangle which traits could lead to success and which to ecological disaster, Nuhfer and Bradley surveyed a wide variety of papers from restoration and invasion ecology, as well as the plant risk assessments and frameworks that managers in the field often use. What they found is that the same traits help plants to establish themselves in a new location, whether they are invasive species or relocation candidates.  However, as plants try to spread and particularly in the impact they have on their new ecologies, the traits for invasives and successful relocation diverge widely.

What this means is that a specific trait, like a high metabolic rate, is helpful when a plant is trying to establish itself, regardless of if the species is native or invasive. However, there are certain traits, like having a large size, that predispose a plant not only to establishing successfully, but spreading wildly and leaving an outsized impact on its new environment.

Additionally, there are some traits, like toxicity, which can help identify poor native species candidates for relocation - traits that don’t really help the plants establish, but do help them spread or cause harm.

This suggests that there are certain traits associated with invasiveness, especially those that aid in establishing a plant in a new place, that we should actually be looking for in native species to ensure their survival. Instead of filtering out those traits, risk assessments should focus on traits like having water dispersed seeds or toxicity, which don’t help plants establish much but do help them spread and cause harm.

“Many of the current risk assessments that managers are using in the field are so risk-averse as to guarantee that managed relocation will fail,” says Bradley.

“And if the relocation fails,” adds Nuhfer, “then we’ve wasted all sorts of resources and haven’t helped native plants persist.”