The United Nations’ International Year of Biodiversity is winding down. Governments gathered in Nagoya, Japan, in October to ponder once again what to do about the so-called “sixth extinction” eradicating species across the planet. One major cause of extinction is the replacement of native species with nonnative ones. Are nonnative species a threat to biodiversity that must be fought at all costs? Or should we acknowledge that in a world where the European honeybee is vital to the agricultural economies of continents to which it is not native, the battle against invasive species is sometimes misguided? To find out, Momentum asked an ecologist who has raised eyebrows by arguing that many invasive species aren’t so bad after all, along with a conservation scientist on the front lines of efforts to eradicate nonnative species.

Mark Davis
Ecologist, Macalester University

We need to be discriminating in what we declare as harm. If we cast too wide a net, then we’re in danger of putting resources, human and monetary, into trying to change aspects of nature that we might be better off just calling change instead of harm. For example, nonnative forest plants are not causing human health problems. In most cases, they’re not causing economic problems. They are just mak­ing the habitats different from the way we knew them when we were growing up.

Nature is always changing. Environments are always a mix of spe­cies that have been there a long time and species that are recent. Get over it, that’s the reality. There is nothing you can do to change that except divert valuable resources away from other efforts.

For a lot of the plant people, you’d think these other species were nuclear or toxic waste. Buckthorn, garlic mustard—these are species that are not going back whether we like it or not. They’re now residents, and they’re going to be residents long into the future. It’s very easy to get people excited about going out and digging up these horrible invasive species. It makes people feel good that they are sort of purify­ing the environment. But natural ecological and evolutionary dynamics argue that over time species of pathogens or insects will take advantage of this newly abundant resource.

Sometimes what we’re looking at is personal preference: We’d like nature to look a certain way. We’re used to certain species around us, and we don’t want to see those species become less abundant. They’re not going extinct in the vast majority of cases.

This notion of wilderness, of pristine environments, is very much a 20th century phenomenon that is dissipating. There is no place on Earth that you can regard as pristine. Humans, in various ways, are affecting all environments around the world.

Josh Donlan
Director, Advanced Conservation Strategies

Some nonnative species are major threats to biodiversity. We have lots of data, lots of examples that some nonnative species are hav­ing devastating impacts. Invasive mammals on islands are one example. The majority of vertebrate extinctions since 1600 have been on islands, and invasive mammals are directly or indirectly responsible for most of those extinctions. When you move to continental areas, the answer gets more variable. There are lots of examples of invasive plants and animals having a significant impact on biodiversity and ecosystem services. And there are lots of invasives where we don’t see impacts. It has to be viewed through a cost-benefit lens and not just black-and-white ‘all invasive species are bad.’

Over the past decade, the ability to remove invasive mammals has been revolutionized by a half-dozen projects around the world, setting a new benchmark for restoring ecosystems. That includes rats, cats and nonnative herbivores. In the Galapagos, 150,000 wild goats were removed from two of the larger islands, islands the size of Rhode Island. We haven’t been as good in developing innovative ways to deal with other invasive species such as plants, which come with a whole different suite of challenges.

Now we are taking some of these approaches and applying them to continental systems potentially. For example, there are beavers in Tierra del Fuego. They were introduced in the 1950s, and they have changed the ecosystem by deforesting 7 million hectares. Now they are coloniz­ing the mainland. It’s very alarming in terms of potential impacts to the ecosystems of southern South America. Now, from a holistic science standpoint the beavers aren’t at the moment causing extinction, nor are they reducing biodiversity overall. It is clear that they are changing riparian areas and changing the ecology of the ecosystem. A feasibility study has concluded it would be possible to remove beavers from the entire area. It’s going to cost lots of money, tens of millions of dollars.

Ultimately, it comes down to really more of a value issue. Does society want a world that is dominated by rats and dandelions, or a world that is diverse and less homogenous than the trajectory we’re currently on?

David Biello is an associate editor at Scientific American focusing on environment and energy. His series on carbon capture and storage won an inaugural Earth Journalism Award last December in Copenhagen.