I really like that you’re looking for the positives. I think that’s important. And I’ll premise this argument saying that I think you’re doing great work with your newsletter. However, I have to disagree entirely with your post and I think the message is dangerous. It is widely documented, including by the Intergovernmental Panel on Biodiversity and Ecosystem Services (leading experts in biodiversity and ecosystem services that synthesise tens of thousands of peer-reviewed research) that invasive species are one of the five main drivers of biodiversity loss. And I premise this also with the fact I agree there are benefits to be gained from non-native species (note the ‘non-native’, not ‘invasive’ terminology here as it’s rare that an invasive species should be accepted without efforts to eradicate it) among their negative impacts, as shown in this paper: https://doi.org/10.1016/j.tree.2022.08.005.
While you’re not cherry picking example species, as you say, you are cherry picking impacts. i.e. You’re showing the positives but not documenting all the associated negatives of a species. The negative impacts of most of these far outweigh the positives that you are describing. Everything has a tradeoff. Of course there will be benefits of invasive species if you look carefully enough. e.g. If an invasive leads to the local extinction of one native that competes with another, the other native will benefit. So there’s a measurable benefit if you just focus on that. Ecological interactions are complex so you have to consider the whole system. For instance, the tamarisk providing habitat for willow flycatchers is a great co-benefit, but tamarisk also outcompete native cottonwoods in flow-modified rivers of the southwest. Cottonwood gallery forests are keystone ecosystems in the US southwest that are being lost and as a result many dependent species are also being lost. These really are oases in the desert. Tamarisk-based ecosystems are much less diverse.
I agree entirely that we should not be demonising such species. It’s not their fault. In New Zealand, we have a pretty unhealthy relationship with invasive species — they’re like an enemy of the state given the widespread effects they have on our forest ecosystems. Demonising them doesn’t help. But there’s no doubt they are extremely problematic.
Re: The zebra mussel example. Yes, they’re great at filtering the water and this has benefited salmon and salmon fisherman through the mechanism you outline, but they have had widespread impacts on native species, each of which provide fundamentally important ecosystem services in their own way. The resulting ecosystems are much more simple and as a result less resilient to stressors that will no doubt arise as the climate continues to change. If you read the transcript of the article you shared on this, they go on to say: “But does this mean that what this country really needs is more zebra mussel infestations? To paraphrase MacISAAC and every other invasive species experts in the country, heck no. First of all, the extra money these big salmons may be generating is but a speck compared to the billions worth of damage zebra mussels do every single year. Secondly, according to MacISAAC, these mussels produce waste that has been linked to all kinds of problems, including giant blooms of toxic algae.” — there are literally hundreds to thousands of peer-reviewed ecological studies demonstrating the negative consequences of zebra mussels on any number of ecological impacts including individual, population, community and ecosystem-level impacts. And these translate into billions of dollars of financial costs.
I won’t go on for each example, but you get the point.
Re: “I think that based on this, it’s reasonable to “shift our priors” to hold as a default assumption that, at least for non-disease species on continents, we should switch our starting assumption to be that invasive species are probably harmless-to-beneficial, even when widely described as a menace. The burden of proof needs to be on people claiming that newly arrived species are providing harm.” — I’m sorry, but this framing is flat out dangerous. The burden of proof should remain that we should prove they’re not harmful. Finally, I’ll note that this is an area I am actively working in: I am involved in a working group currently quantifying these impacts of invasive species globally, devising new synthetic metrics to do so and applying it to databases of thousands of studies with documented impacts.
Seconding Jonathan's thoughts regarding how the article focused on the small positives without discussing the big negatives. Calling a non-native* species “invasive” is not done unless there is a good reason (actively disrupting the ecosystems) or suspicion (has disrupted similar ecosystems). Non-native species can be benign or beneficial, but they don't cause headaches which is why they are not talked about as often as the invasive troublemakers.
I also want to add that some of the species you listed (kudzu, salt cedar, cane toad) do not seem to be as bad because there are or were management efforts. If kudzu was not removed by farmers and munched by hungry goats decades ago, it would continue to spread its green tendrils throughout the open Southern fields. The same goes with the various control tactics people have been using for cane toad, salt cedar, and many other invasive species. Eradicating invasive species is hard and hardly works, but managing them is possible.
Public perceptions of invasive species can be complicated. Kudzu, salt cedar, and cane toads were deliberate introductions with good intentions before they got out of hand. The three predated invasion biology as an idea, but the consequences from them and others formed the discipline. Invasion biology is a fascinating topic, and I hope these critiques do not dissuade, but encourage you to research more about it!
Sam, I’ve been a big supporter of your work, but I’m 100% with Jonathan on this. I have surveyed, propagated, or otherwise worked with about a dozen endangered species. I have researched on controlling invasives in our Southern California estuaries, with the results of our research being recently published in a scientific journal.
In Southern California invasive eucalypti have completely overtaken some of our canyons. South African iceplant can overwhelm landscapes; restoration efforts are hampered because iceplant so changes the composition of native soils.
In California our most widespread plant community is chaparral, yet we have lost tens of thousands of hectares of this beautiful community and the ecosystems it supports to invasive grasses.
I think perhaps the point is that a re-framing is needed- have we lost tens of thousands of acres due to invasive species? To me it seems far more true that we have lost, and are losing tens of thousands of acres of native species habitat due to development and industry. And for some reason we feel good about vilanizing plants and animals and pouring millions of dollars and rather extreme measures like herbicides and pesticides at that "problem" rather than admitting that what really needs to be done is to stop habitat destruction. I am very familiar with California and the American Southwest where plants like tamarisk and cheat grass get villianized but not very many people are willing to talk about the wholesale sell off of desert habitat to solar farms and mining for EVs. I think our good intentions are misguided, our focus misdirected, and I think perhaps that is on purpose by the people who stand to profit from it in the the short term.
I've always regarded this issue with a skeptical eye and I'm glad you're bringing some research to the table in support of an alternative viewpoint. I think we have to be pragmatic about this. We should always be careful to not deliberately introduce new species into ecosystems not adapted to it but once we find that's happened, we should ask how realistic it is to reverse the introduction, the costs involved and what it is we're actually risking if we don't take action. We shouldn't underestimate nature's ability to adapt and adjust itself, and realize, especially in the case of animal species, these are individual beings with individual lives we're talking about and not molecules of a noxious, inert chemical compound. Thinking in longer time scales than we usually do is also important. There are no more wild and pristine environments left in the world anymore, even if at the macro level that might be one's assumption, at the micro level traces of human influence are all too apparent. We must adjust our thinking and learn to manage things in a more holistic way.
A biologist myself, I've always wondered how solid the scientific claims about invasive and harmful species were. 'Invasiveness' in itself arrises not only with newly introduced species but even with authochtone species when an ecosystem is disturbed.
Living on an island, which is supposedly very prone to damage through introduced species, I don't know of any plant being lost or endangered because of introduced species.
In the case of Lampropeltis californiae, introduced in 1998, there is a logical reduction in local herpetofauna (not endangered), and our local depredators (Buteo buteo) which had significantly vanished because of human activity well before that date, still are learning how to capture these snakes.
But the 'social alarm' is there; like a self fulfilling prophecy every introduced species generates 'action plans', prohibitions and dreadful outlooks. Well, not every introduced species: Opuntia spp., Agave spp. are central part of local folklore and iconography...
I thought this was super neat. Although I don't necessarily support your conclusion, I think it's an important parallel narrative. "Invasive" species have been the case for all of history. Tomatoes could be considered invasive to Italy or potatoes to Ireland. I think we should take it on a case by case basis, but the reminder that balance can take time (and sometimes longer than human beings are alive) is also important. I really enjoyed reading about all these. Felt very hopeful.
I had to zoom in on the tamarisk section because I covered it in my book in 2000. It featured a chapter in which I went on a tamarisk eradication mission in Anza-Borrego but also included the new (at the time) evidence about the willow flycatcher. It’s good to hear that a balance has been achieved. At the time, the park manager I profiled pointed out that no native willows or cottonwoods existed in washes taken over by tamarisks. If there’s now a mix of those species, that’s a good thing.
I appreciate your article. Like a breath of fresh air, with citations and references which everyone may explore. Good example of thinking outside the artificial boxes. Presumably disputers publish their findings too, while this is your space. I am hopeful the perspectives you outlne so well are distributed widely so that "land managers" can learn instead of same old same old. Non-humans don't really need management if left to their natural devices. Humans are the main invasive species. Nature was managing balance before humans appeared and will do so after we cause our own demise. It seems nature's corrections are already underway.
https://www.bloomsbury.com/uk/wolves-at-the-door-9781501366765/. Excellent article, thanks for the sense. Also - watch out for a transfer of metaphor from "invasive species" to racist talk about groups of humans. Linking an excellent study that touches this phenomenon.
Super interesting and important conversation to be had about how we imagine "invasives", and I definitely agree about some of these. I can't get behind Japanese Knotweed being good, though--it forms some of the most densest monocultures I've ever seen, particularly in areas that were previously diverse wetland habitat, at least in eastern MA. I add in the eastern MA part because I do think certain non-natives fall into the "invasive" category in some regions but not in others, leading to aggressive efforts to manage a non-existent problem!
A vexed issue. There may be some benefits from invasive species, but I posit they pale in comparison to the real, comprehensive long term impacts, right across each different ecosystems each invades
No no no. You make invasives sound positively lame, and that is just not true. Invasive is a term not given lightly. We continue to fight kudzu on properties throughout western North Carolina. It is not ok and it is strangling out what little habitat remains that the developers haven't taken. This is a dangerous post and it is not ok.
"In the latest careful sampling, the U.S. Forest Service reports that kudzu occupies, to some degree, about 227,000 acres of forestland, an area about the size of a small county and about one-sixth the size of Atlanta. That’s about one-tenth of 1 percent of the South’s 200 million acres of forest. By way of comparison, the same report estimates that Asian privet had invaded some 3.2 million acres—14 times kudzu’s territory. Invasive roses had covered more than three times as much forestland as kudzu.
And though many sources continue to repeat the unsupported claim that kudzu is spreading at the rate of 150,000 acres a year—an area larger than most major American cities—the Forest Service expects an increase of no more than 2,500 acres a year."
We are bigtime knotweed haters. Using black fabric to try to choke out a big clot that apparently came in soil when the previous owners of our home put in a septic field. It outcompetes everything and is very hard to kill. Some of our efforts: https://x.com/Revkin/status/1564936525296668673
I really like that you’re looking for the positives. I think that’s important. And I’ll premise this argument saying that I think you’re doing great work with your newsletter. However, I have to disagree entirely with your post and I think the message is dangerous. It is widely documented, including by the Intergovernmental Panel on Biodiversity and Ecosystem Services (leading experts in biodiversity and ecosystem services that synthesise tens of thousands of peer-reviewed research) that invasive species are one of the five main drivers of biodiversity loss. And I premise this also with the fact I agree there are benefits to be gained from non-native species (note the ‘non-native’, not ‘invasive’ terminology here as it’s rare that an invasive species should be accepted without efforts to eradicate it) among their negative impacts, as shown in this paper: https://doi.org/10.1016/j.tree.2022.08.005.
While you’re not cherry picking example species, as you say, you are cherry picking impacts. i.e. You’re showing the positives but not documenting all the associated negatives of a species. The negative impacts of most of these far outweigh the positives that you are describing. Everything has a tradeoff. Of course there will be benefits of invasive species if you look carefully enough. e.g. If an invasive leads to the local extinction of one native that competes with another, the other native will benefit. So there’s a measurable benefit if you just focus on that. Ecological interactions are complex so you have to consider the whole system. For instance, the tamarisk providing habitat for willow flycatchers is a great co-benefit, but tamarisk also outcompete native cottonwoods in flow-modified rivers of the southwest. Cottonwood gallery forests are keystone ecosystems in the US southwest that are being lost and as a result many dependent species are also being lost. These really are oases in the desert. Tamarisk-based ecosystems are much less diverse.
I agree entirely that we should not be demonising such species. It’s not their fault. In New Zealand, we have a pretty unhealthy relationship with invasive species — they’re like an enemy of the state given the widespread effects they have on our forest ecosystems. Demonising them doesn’t help. But there’s no doubt they are extremely problematic.
Re: The zebra mussel example. Yes, they’re great at filtering the water and this has benefited salmon and salmon fisherman through the mechanism you outline, but they have had widespread impacts on native species, each of which provide fundamentally important ecosystem services in their own way. The resulting ecosystems are much more simple and as a result less resilient to stressors that will no doubt arise as the climate continues to change. If you read the transcript of the article you shared on this, they go on to say: “But does this mean that what this country really needs is more zebra mussel infestations? To paraphrase MacISAAC and every other invasive species experts in the country, heck no. First of all, the extra money these big salmons may be generating is but a speck compared to the billions worth of damage zebra mussels do every single year. Secondly, according to MacISAAC, these mussels produce waste that has been linked to all kinds of problems, including giant blooms of toxic algae.” — there are literally hundreds to thousands of peer-reviewed ecological studies demonstrating the negative consequences of zebra mussels on any number of ecological impacts including individual, population, community and ecosystem-level impacts. And these translate into billions of dollars of financial costs.
I won’t go on for each example, but you get the point.
Re: “I think that based on this, it’s reasonable to “shift our priors” to hold as a default assumption that, at least for non-disease species on continents, we should switch our starting assumption to be that invasive species are probably harmless-to-beneficial, even when widely described as a menace. The burden of proof needs to be on people claiming that newly arrived species are providing harm.” — I’m sorry, but this framing is flat out dangerous. The burden of proof should remain that we should prove they’re not harmful. Finally, I’ll note that this is an area I am actively working in: I am involved in a working group currently quantifying these impacts of invasive species globally, devising new synthetic metrics to do so and applying it to databases of thousands of studies with documented impacts.
Seconding Jonathan's thoughts regarding how the article focused on the small positives without discussing the big negatives. Calling a non-native* species “invasive” is not done unless there is a good reason (actively disrupting the ecosystems) or suspicion (has disrupted similar ecosystems). Non-native species can be benign or beneficial, but they don't cause headaches which is why they are not talked about as often as the invasive troublemakers.
I also want to add that some of the species you listed (kudzu, salt cedar, cane toad) do not seem to be as bad because there are or were management efforts. If kudzu was not removed by farmers and munched by hungry goats decades ago, it would continue to spread its green tendrils throughout the open Southern fields. The same goes with the various control tactics people have been using for cane toad, salt cedar, and many other invasive species. Eradicating invasive species is hard and hardly works, but managing them is possible.
Public perceptions of invasive species can be complicated. Kudzu, salt cedar, and cane toads were deliberate introductions with good intentions before they got out of hand. The three predated invasion biology as an idea, but the consequences from them and others formed the discipline. Invasion biology is a fascinating topic, and I hope these critiques do not dissuade, but encourage you to research more about it!
*https://www.nps.gov/subjects/invasive/learn.htm#:~:text=It%20is%20often%20thought%20that,native%20species%20that%20do%20harm.
Well put, Mantis!
Sam, I’ve been a big supporter of your work, but I’m 100% with Jonathan on this. I have surveyed, propagated, or otherwise worked with about a dozen endangered species. I have researched on controlling invasives in our Southern California estuaries, with the results of our research being recently published in a scientific journal.
In Southern California invasive eucalypti have completely overtaken some of our canyons. South African iceplant can overwhelm landscapes; restoration efforts are hampered because iceplant so changes the composition of native soils.
In California our most widespread plant community is chaparral, yet we have lost tens of thousands of hectares of this beautiful community and the ecosystems it supports to invasive grasses.
Paul, Mantis, and Jonathan, I appreciate your thoughtful perspectives on this!
I think perhaps the point is that a re-framing is needed- have we lost tens of thousands of acres due to invasive species? To me it seems far more true that we have lost, and are losing tens of thousands of acres of native species habitat due to development and industry. And for some reason we feel good about vilanizing plants and animals and pouring millions of dollars and rather extreme measures like herbicides and pesticides at that "problem" rather than admitting that what really needs to be done is to stop habitat destruction. I am very familiar with California and the American Southwest where plants like tamarisk and cheat grass get villianized but not very many people are willing to talk about the wholesale sell off of desert habitat to solar farms and mining for EVs. I think our good intentions are misguided, our focus misdirected, and I think perhaps that is on purpose by the people who stand to profit from it in the the short term.
I've always regarded this issue with a skeptical eye and I'm glad you're bringing some research to the table in support of an alternative viewpoint. I think we have to be pragmatic about this. We should always be careful to not deliberately introduce new species into ecosystems not adapted to it but once we find that's happened, we should ask how realistic it is to reverse the introduction, the costs involved and what it is we're actually risking if we don't take action. We shouldn't underestimate nature's ability to adapt and adjust itself, and realize, especially in the case of animal species, these are individual beings with individual lives we're talking about and not molecules of a noxious, inert chemical compound. Thinking in longer time scales than we usually do is also important. There are no more wild and pristine environments left in the world anymore, even if at the macro level that might be one's assumption, at the micro level traces of human influence are all too apparent. We must adjust our thinking and learn to manage things in a more holistic way.
I absolutely agree with your comment.
At the macro-level nowhere is untouched by human activity either.
1. Species tend to extend their ranges.
2. Since Life got started on Earth 4.5 billion years ago the general case has been survival of the fittest.
3. We cannot and should not reduce Nature to manicured and curated parks of our favorite species. Life will flow around our barricades.
4. Let Nature take its course come what may. Today's invasives are our great grandchildren's endangered natives.
Great article!
A biologist myself, I've always wondered how solid the scientific claims about invasive and harmful species were. 'Invasiveness' in itself arrises not only with newly introduced species but even with authochtone species when an ecosystem is disturbed.
Living on an island, which is supposedly very prone to damage through introduced species, I don't know of any plant being lost or endangered because of introduced species.
In the case of Lampropeltis californiae, introduced in 1998, there is a logical reduction in local herpetofauna (not endangered), and our local depredators (Buteo buteo) which had significantly vanished because of human activity well before that date, still are learning how to capture these snakes.
But the 'social alarm' is there; like a self fulfilling prophecy every introduced species generates 'action plans', prohibitions and dreadful outlooks. Well, not every introduced species: Opuntia spp., Agave spp. are central part of local folklore and iconography...
I thought this was super neat. Although I don't necessarily support your conclusion, I think it's an important parallel narrative. "Invasive" species have been the case for all of history. Tomatoes could be considered invasive to Italy or potatoes to Ireland. I think we should take it on a case by case basis, but the reminder that balance can take time (and sometimes longer than human beings are alive) is also important. I really enjoyed reading about all these. Felt very hopeful.
Thank you so much!
I had to zoom in on the tamarisk section because I covered it in my book in 2000. It featured a chapter in which I went on a tamarisk eradication mission in Anza-Borrego but also included the new (at the time) evidence about the willow flycatcher. It’s good to hear that a balance has been achieved. At the time, the park manager I profiled pointed out that no native willows or cottonwoods existed in washes taken over by tamarisks. If there’s now a mix of those species, that’s a good thing.
I appreciate your article. Like a breath of fresh air, with citations and references which everyone may explore. Good example of thinking outside the artificial boxes. Presumably disputers publish their findings too, while this is your space. I am hopeful the perspectives you outlne so well are distributed widely so that "land managers" can learn instead of same old same old. Non-humans don't really need management if left to their natural devices. Humans are the main invasive species. Nature was managing balance before humans appeared and will do so after we cause our own demise. It seems nature's corrections are already underway.
https://www.bloomsbury.com/uk/wolves-at-the-door-9781501366765/. Excellent article, thanks for the sense. Also - watch out for a transfer of metaphor from "invasive species" to racist talk about groups of humans. Linking an excellent study that touches this phenomenon.
Excellent point - I plan to discuss this more in upcoming articles!
Super interesting and important conversation to be had about how we imagine "invasives", and I definitely agree about some of these. I can't get behind Japanese Knotweed being good, though--it forms some of the most densest monocultures I've ever seen, particularly in areas that were previously diverse wetland habitat, at least in eastern MA. I add in the eastern MA part because I do think certain non-natives fall into the "invasive" category in some regions but not in others, leading to aggressive efforts to manage a non-existent problem!
A vexed issue. There may be some benefits from invasive species, but I posit they pale in comparison to the real, comprehensive long term impacts, right across each different ecosystems each invades
Couldn't agree more, Rod. Have given a pretty long-winded response here on this point exactly.
Well said Jonathan. Also the narrative of this post contributes enormously to shifting baselines by normalising the impact.
Absolutely!
No no no. You make invasives sound positively lame, and that is just not true. Invasive is a term not given lightly. We continue to fight kudzu on properties throughout western North Carolina. It is not ok and it is strangling out what little habitat remains that the developers haven't taken. This is a dangerous post and it is not ok.
Here's Smithsonian Magazine's take on kudzu:
"In the latest careful sampling, the U.S. Forest Service reports that kudzu occupies, to some degree, about 227,000 acres of forestland, an area about the size of a small county and about one-sixth the size of Atlanta. That’s about one-tenth of 1 percent of the South’s 200 million acres of forest. By way of comparison, the same report estimates that Asian privet had invaded some 3.2 million acres—14 times kudzu’s territory. Invasive roses had covered more than three times as much forestland as kudzu.
And though many sources continue to repeat the unsupported claim that kudzu is spreading at the rate of 150,000 acres a year—an area larger than most major American cities—the Forest Service expects an increase of no more than 2,500 acres a year."
https://www.smithsonianmag.com/science-nature/true-story-kudzu-vine-ate-south-180956325/
These days, kudzu does seem closer to "positively lame" than "strangling out what little habitat remains."
A loss of 2,500 acres a year, when we are losing 2,000 acres of farmland and ranchland every day! It all adds up. So even if kudzu is not taking as much land as it used to, we have less land to lose now. And that statistic comes from https://www.agweb.com/news/business/farmland/surface-pressure-us-losing-farmland-alarming-rate
We are bigtime knotweed haters. Using black fabric to try to choke out a big clot that apparently came in soil when the previous owners of our home put in a septic field. It outcompetes everything and is very hard to kill. Some of our efforts: https://x.com/Revkin/status/1564936525296668673