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Time to make peace with invasive species?

A conversation with climate science director Stephen Jackson about why and where we should tolerate non-native invaders.


Stephen Jackson has a radical idea for saving the Southwest’s Sonoran Desert: In places where it’s already infested with invasive species, it might be best to just leave it alone. Millions of acres of the Sonoran have been overrun by highly flammable South African buffelgrass, a fire-adapted perennial that burns readily and recovers quickly, crowding out native saguaro cactus and shrubs. Land managers can’t restore all those acres, says Jackson, and they shouldn’t even try; taking a triage approach would let them focus more effectively on high-priority areas.

While the idea of letting an invasive grass set parts of Arizona ablaze may inflame some conservation purists, Jackson’s viewpoint is shared by a growing number of ecologists who believe that, in many cases, tolerating so-called “novel ecosystems” flush with invasive species is more realistic than trying to return changing environments to a pre-industrial condition.

Accepting the presence of some invasive species will undoubtedly cause some problems in the long term, says Jackson, director of the Department of the Interior’s Southwest Climate Science Center, an arm of the U.S. Geological Survey. But he and his colleagues contend that trying to completely eradicate many invasive species is not only prohibitively expensive, it’s often not even possible.

HCN contributor Zack Colman recently caught up with Jackson. Below is an interview with Jackson, which has been condensed and edited for clarity.

Stephen Jackson, director of the U.S. Department of the Interior Southwest Climate Science Center, reviews plant materials under a microscope.
Paige Schwahn/ Cronkite News

High Country News: Where did the concept of novel ecosystems come from? 

Stephen Jackson: The general perception that was widely held among conservationists was that the goal was to make things as if humans hadn’t intervened or hadn’t disturbed the system. (Then came) the realization that restoring to the pre-disturbance condition was often difficult to impossible — basically prohibitively expensive in a lot of ecosystems. And then when (you have) persistent invasive species, you can’t always eradicate the invaders. Environmental change also makes it hard to return to previous conditions. The other direction came from paleoecology, my own field, where since the 1960s, we have been discussing and studying ecosystems of the past that have no modern counterpart on the landscape. Some analyses of climate projections for the late 21st century, particularly under scenarios of high greenhouse-gas emissions, show combinations of seasonal temperatures and precipitation that have no counterpart in the 20th century or any time in the past.

HCN: How do those climate projections reinforce the idea of novel ecosystems?

SJ: Climate change is certainly taking us into new realms, into new environmental realizations. We cannot control wildfires of the magnitude that we’ve been seeing. Our species and our society do not have the capacity to control nature on that kind of scale. As we go further into a world of climate change and altered environments, we’re less and less in a position to be able to maintain historical ecosystems. They’re more and more out of sync with the prevailing environment. And then the more intensively we have to manage to maintain those ecosystems in a museum-piece-like context, it’s no longer a natural system; it’s an intensively managed system that’s aspiring to some putatively natural standard that has become an -anachronism.

HCN: Do you feel like you’re fighting an uphill battle? It seems to collide with the wilderness preservation mindset of a lot of the conservation community.

SJ: I was and continue to be passionate about natural areas and natural -processes. But I’ve also come to realize some of the limitations of that whole philosophy.  The whole idea of ecological novelty forces us to confront our most deeply held assumptions and values concerning what we’re trying to accomplish with restoration and conservation.

(Critics say that) if we accept novel ecosystems and work within that framework, then we are prematurely declaring surrender. A more extreme version of that view is a slippery slope argument: By yielding any ground to ecological -novelty, we open the door to all kinds of bad things happening and the manipulation of the process by people who really don’t have the best interests of biodiversity or ecosystem services or humanity in mind. I understand that concern and agree that there is a risk of that happening, but at the same time there are ways that we can manage those risks. The other perspective that’s coming in here is a reluctance to re-examine or let go of the 20th century conservation paradigm, which is to maintain things in as natural and pristine a state as possible or to restore things to as -natural a state as possible.

HCN: Does whether we accept novel ecosystems come down to whether we have enough money to return the land to some kind of pristine state?

SJ: There are certainly extreme cases where restoring to the pre-disturbance condition is impossible —  no matter how much money is spent — because the soil is gone, the toxic metals are bubbling up to the surface. In those cases, we simply have to accept that, live with it, and figure out what we’re going to do with it.

Perhaps it’s true that in particular settings with enough money and with enough commitment in resources we could restore something to a pre-disturbance state, and maintain it there. But it would require continual and sometimes intensive intervention. A large number of managers and decision-makers working in the field have found the principle of novel ecosystems helpful and even liberating, because it allows them a way out of what seems to them to be an impossible situation.

Piles of dug-up buffelgrass wait to be disposed of after an eradication day in Tucson, Arizona. The Friends of Urban Wildlife filled 79 bags with the invasive species.

HCN: In the Sonoran Desert, what is invasive buffelgrass doing to the ecosystem?

SJ: Buffelgrass was brought in partly for mined-land reclamation, partly for livestock grazing. It’s perennial and it’s highly flammable. And that’s very unusual — most of the grasses of the lower Sonoran Desert are annual, and they’re not very flammable. It’s a very effective seed disperser, and it’s very successful in the kind of climate that we have here. So it’s been able to establish itself pretty broadly in many parts of the Sonoran Desert, including in the mountains around Tucson. It’s in Saguaro National Park, it’s in the Coronado National Forest, it’s in some of the (Bureau of Land Management) lands.

One of the threats with buffelgrass is that it is potentially an ecosystem transformer species.  The buffelgrass survives fire, most everything else doesn’t survive, and then the buffelgrass comes back even more aggressively because the competition is gone.

HCN: Are we just going to have to cede the Sonoran Desert to buffelgrass?

SJ: The novel ecosystem that buffelgrass has created in some parts of the Sonoran Desert is an undesirable ecosystem from my point of view. I don’t really see any value in it. Nothing that I or most other people value about the natural world is there in a buffelgrass-dominated ecosystem compared to the beautiful and diverse Sonoran Desert ecosystem. This is a novel ecosystem that in my view should not be embraced.

That said, buffelgrass can be eradicated locally, but it’s a very intensive process. You can dig it up, and as long as you get the underground material, it’s gone. There are campaigns in various places of just going out there and digging it out. That’s actually been very effective within Tucson and some of the urbanized areas. But the labor is immense, and just hauling the bags of buffelgrass out is a huge logistical problem, especially in the backcountry.  It can also be controlled with herbicides, but they’re effective only in the brief period of buffelgrass green-up.  You have to get your ground crews mobilized and helicopters in the air on very short notice, and cover a lot of territory in a narrow time window. It may be impossible to completely eradicate it. But what we can do instead is maintain vigilance and manage it.

HCN: For any novel ecosystem, is there a sort of Ten Commandments for proper management?

SJ: Ecological management and ecological restoration is highly situationally dependent. All management decisions in the real world require a series of trade-offs, and all of them entail direct costs, and all of them entail opportunity costs.

For some parts of the Sonoran Desert, such as Saguaro National Park, that seems to be a fairly easy and straightforward decision: We like Saguaro because it’s this extensive area of beautiful native vegetation that imparts aesthetic values, it imparts ethical values, it imparts cultural values, it imparts economic values through tourism and hiking. To prevent the park from converting over to a mono-specific buffelgrass meadow, resource managers and others have made the decision that it is worth the investment to control buffelgrass.  In other cases, the decision calculus may come out to be different if the invasive species is less likely to have such a transformational effect on the ecosystem. It would be a wonderful world if we had enough resources to go around and do everything we want, but as optimistic as I was in the 1970s after Earth Day, I haven’t lived long enough to see that day yet. And I’m not sure it’s going to come any time soon. In the meantime, we have to use the resources we have as wisely as we can, not letting the perfect interfere with the good.

Zack Colman is the deputy energy and environment editor at the Christian Science Monitor.