Non-native species become invasive as they adapt to a new environment where they don't experience the predator and parasite loads that they face in the environment where they evolved. In the bell-shaped distribution among plants of a certain species, for example, those that allocate fewer resources (such as chemical defenses) to deter herbivores will have more resources to devote to reproduction or outcompeting native rivals. The gene distribution shifts over several generations species and the plants become increasingly prolific. That's why we often see a lag of several decades before a species explodes and becomes a real pest. To date, many invasive species have become major pests along waterways and riparian areas. I'm concerned that the "California friendly" plant species being promoted now will increasingly swamp our upland habitats later in this century, and we will look back and ask, "How could we have been so stupid?" as we do today for Aurndo, pampas grass, and their ilk.
I should get into this conversation, as I have thoughts on the subject, many of them. I will add more if I have time.
In New Zealand, we have the example of gorse. It's invasive, it's costly, it's altering native habitats, it's costing farmers millions of dollars, it's one of New Zealand's worst weeds, it's displacing native species, it's encouraging fire, it's allowing native forest to regenerate, it saved an endemic insect from extinction... it's complicated.
That's the thing with many non-native, including invasive, species. Most have good and bad points, with how much good and how much bad depending on what they are, where they are and what the values of the person looking at them are. There are species which I'd call invasive in New Zealand which I believe should only be controlled under very limited circumstances, either because they aren't that harmful or because controlling them harms other things (an example would be Cytisus proliferus). There are species which I believe could be controlled to great benefit and minimal harm almost everywhere they occur in New Zealand, such as rats and possums (one rat species should be preserved on some offshore islands for cultural reasons though). But there are such large areas affected that we can't do it all.
This is why decisions about managing invasive species aren't, or shouldn't be, taken lightly. In my experience, most of the people making decisions about invasive species management get the point about prioritising both which species are controlled and where they are controlled, both because of limited resources and because they need to be sure that they are doing more good than harm. However I think that the scientists sometimes lose the nuance in the debate because they aren't having to make difficult management decisions.
Melanie, as always, thank you for your thoughtful and informed comment. You are correct that things with invasives can get complicated. I think some folks get confused as to the distinction between nonnative and invasive. Here, in Southern California, we have LOTS of nonnative species, such as magnolia trees native to the American South and Chinese elms. These don't spread or reproduce or cause problems.
I think that people also get confused with the term invasive. We have palms from the Pacific islands that are invasive but not particularly problematic. If you chop them down, they will go away and not come back. On the other hand, Arundo Donax transforms habitats, taking over, and it is almost impossible to kill. We could compare this to human health and ailments. Acne and high blood pressure are both ailments. Generally, acne is not going to kill you, but you better not think that way about your high blood pressure.
A problem here is that there are dozens of invasives. In conversations about invasives I think this can get overlooked. If you look at any one invasive, it may not seem all that bad, but taken together they can overwhelm landscapes. Here in California we have thousands of hectares in which the coverage of invasives is over 90%.
I’m wondering what you thought of his section on tamarisk? You might have noticed my comment about my coverage of the issue in my book, All the Wild and Lonely Places, back in 2000. At the time, biologists had just discovered the southwest willow flycatcher using tamarisk, and that undermined the contention that it was useless to native species. Mark Jorgensen told me he understood the risk of using glyphosate in wilderness areas and that we might someday learn that it’s more harmful than we knew (and now we do).
When I was writing an early draft of that chapter for an Environmental Studies class, the professor told me I needed to look up the water consumption of natives like cottonwoods and willows in order to support the common claim that tamarisk used more water, but I could never find any studies about that. (They probably existed but very little was online back then.)
The most damning evidence against the tamarisk was obvious: desert washes devoid of cottonwoods and willows, nothing but tamarisk. Do you know about the new treatment for tamarisk that Sam mentioned? I haven’t been able to look it up yet to find out how effective it’s been. Can’t visit those washes because I’m here in Michigan, where we occasionally see a tamarisk but they don’t spread.
Overall I’m skeptical of the claim that invasives are harmless. The wonderful diversity of life on Earth at the present moment is a result of island biogeography at various scales. With everything now interconnected, humans are doing away with the kind of isolation that led to speciation. The result over centuries is likely to be greater homogenization rather than diversity.
I think I should probably have said island biogragraphy is *one* source of the diversity of life, because of course there's species diversification in a given area. Otherwise there wouldn't have been a bunch of different finches for Darwin study.
I think you might agree with the conclusion I came to in the book, that we should manage exotics on a case-by-case basis, and those decisions should be based on science, not prejudice. But human bias will always influence science, a fact I wasn't quite so aware of back then.
Looking forward to it. You don't happen to have more sources for what's going on with tamarisk in the southwest right now, do you? I know that was just one small section of your previous piece, and I'd like to know more. Also, I'm lazy and distracted so haven't tracked them down on my own.
That's a good article! It comes to roughly the same conclusion about tamarisk removal that managers were hoping for when I interviewed them. The best they could hope for was to make space for native species by removing the tamarisk, knowing they'd never get rid of it completely. I'd point out that the areas I was covering weren't affected by western water management. These were desert washes in Anza-Borrego Desert State Park pretty far removed from even groundwater pumping. Mark Jorgensen, the resource manager in charge of the effort, was familiar with the situation on the Colorado and its tributaries and felt that little could be done over there, but he was encouraged by the success they were having in isolated desert washes away from the Colorado watershed. I need to revisit some of these places and see how they look now! (Or maybe I should just ask my friends who still live out there.)
Larry, thanks for your input. Tamarisk is curious. We have a grove of it growing at the entrance to where I work. In the ten years that I've been there, it has not spread or seemed to cause any problem. On the other hand, there are some nearby canyons where constantly spreads.
Anza-Borrego has a number of tamarisk infested places. There is even Tamarisk Grove. People actually go there because of the tamarisk. I believe the big concern there is that the deep roots of the tamarisks are pulling up deep groundwater, which, because of the citrus groves out there now, is already being depleted.
Are the ones where you work the tall kind (60 to 100 feet)? That’s the kind at tamarisk grove, usually planted as a wind break, and they don’t tend to spread. The smaller shrub-sized ones, brought over as ornamentals, are the ones that spread rapidly. I forget the species names, but it’s important to distinguish the two.
"Western water management"? So the only species you're concerned about any negative in real world matriculation is Homosapien? The spadefoot toad, along with the animal kingdom dwellers of precipitation collecting areas of the south west would highly disagree. If they lowered themselves to communicate with us.....
The only dynamic you need to understand concerning Tamarix L. (Tamaricaceae) introduction into the American Southwest is it water usage. There are myriads of other negative impacts on the bio regional Eco also. It has dramatically reduced the populations of the spadefoot toad in the water catching areas of the region.
In short, there are no "less important" strands in the web of life. To contend interrupting in infusing something that is foreign to that regional Eco habitat web is never a positive or neutral thing. Meaning, when you interrupted environment that has achieved stasis, you have damaged it. There's no other verbiage.
To me, the insistence of "non-native species introduction" paradigm being anything else, nothing more than an opinion. A poorly formed one. Arrogant even. We know so little about the Earth's native biosphere. To make such a judgment is a mistake and obtuse. Conceited.
Thank you for this very important counterpoint. Well stated. Invasives are simply not ok - and much different than exotics that do not affect our natural areas.
This was super interesting. Fairly new to the Substack community but like you said i noticed it was really friendly and it’s really inspiring to see people engaged in important ecological conversations like this! I look forward to reading more
I appreciate hearing your perspective Paul, and I agree with you on the great value of the "polite disagreement" culture of Substack. Dedicated stewards of their local landscapes and ecosystems like you are exactly the kind of people I'm excited to talk to about this!
So, impromptu, a few points that spring to mind on my reading of your post.
First, let's clarify our terms. If I understand you correctly, you agree that some nonnative species are harmless or beneficial, but that invasive species are by definition harmful, so it's wrong of me to advocate for them. Okay, but I think the last few decades of research seem to be finding that more and more invasive species are not nearly as harmful as we first thought!
A regular problem with cost estimates of invasive species is that they often factor in the effort of removing them, creating a bit of a "self-fulfilling prophecy" (this "invasive" species is doing well, so they'd cost a lot to remove, so we must remove them because they're so costly!). Biological control agents tend to be cheap to introduce and have a very high success rate, as discussed in the Novak paper I cited in https://sammatey.substack.com/p/the-dawn-of-immigrant-species-biology .
You say, "You might as well tell me that cancer has an upside." Do you then disagree that Australian saltwater crocs and Brazilian jaguars benefiting from wild boars as prey is an upside, at least to some extent? Or Puerto Rican tree frogs living on African tulip trees? Or zebra mussels' filtration effects boosting alewife and salmon populations? Or gorse sheltering young native plants in New Zealand? Or purple loosestrife being correlated with *increased* biodiversity of native plants in North America? If those do count as upsides, and you believe invasives are by definition bad, then do wild boar, African tulip trees, zebra mussels, gorse, and purple loosestrife no longer count as "invasive" for you? Those are 5 of the IUCN's 100 World's Worst "invasive" species! It seems to me that your views are a little self-contradictory here. From my perspective, of the statements (1) these five species are invasive, (2) all invasives are bad, and (3) these five species have some upside for native ecosystems, you can logically agree with any two of them, but not all three at once. Which of these three statements, if any, do you agree or disagree with?
I have another article on this general subject coming on Monday, and would love to hear your thoughts on the examples in there as well! I suspect you'll strongly disagree with me on several points, but I really admire your principled and courteous engagement in this discussion and I hope you feel like continuing it.
Sam, thanks for your thoughtful comments. You’ve obviously thought about this topic and researched it a great deal.
As far as costs of invasives. I’d be willing to say that putting dollar amounts on their damages may overlook a lot of their harms. When invasives cause or contribute to the extirpation of a species, there is no ledger of the dollar amount.
And if there is an invasive disrupting and ecosystem or causing damage to crops or forests, it makes sense to add the cost of removal to the ledger of the full cost of the species. As an example, the cost of tagging would include removing or covering up the graffiti as well as the police work of catching the taggers.
Also, from my experience, removing and controlling invasives here in San Diego, much of that work is done by nonprofits and volunteers, so the costs are pretty low and may support the argument that costs of invasives are underestimated. Where I work, much of invasive removal is done by school groups, and it’s administered through the education department. So in our ledger the costs are under the education department So on the books, there is no cost of conservation or invasive removal. It’s a bookkeeping thing, but once again points up that removal and control costs are probably underestimated for a lot of invasives.
You have a point about some invasives fitting an ecological niche or helping native species in their new environments. And that is a dicey issue. Once an invasive is established and there is a new dynamic, that can be a real judgement call as to how much of the invasive to allow or control to let it help without causing further harm.
From personal experience I sometimes think the benefits can be overestimated. I work in the middle of a wildlife refuge. U.S. Fish and Wildlife were reluctant to allow me to remove a eucalyptus tree, as it provided roosting and nesting sites for herons and other birds. Because it was a pressing safety issue (the tree’s branches were falling into our parking lot.), FWS relented. Well, all the birds just nested in the native trees nearby.
Same with removing invasive sea lavender in our estuary. A very endangered species, bird’s beak, fed on the sea lavender. It was feared that removing the sea lavender would extirpate the bird’s beak. That did not happen. As a matter of fact, with the removal of the sea lavender, the bird’s beak is thriving better than before.
I know these are anecdotes. Take them for what they are worth.
I was talking with a colleague about this conundrum and I suggested that we don’t simply label a species as invasive. We give it an invasive score that acknowledges both the species benefits and harms. So, eucalyptus here in Southern California could get a score of 2/7. The tree scores two points for providing habitat, wood, and shade. The tree gets seven demerits for extirpating all natives around it, being invasive, and being a fire and safety hazard.
Wadaya think? Would this be a step forward in our thinking?
I really appreciate your openness to dialogue and a more nuanced evaluation on this! Not simply labeling a species as "invasive" sounds like a very good step to take, and I applaud you for considering it. I actually discuss eucalyptus trees in today's upcoming article as well - I would give them a net positive score for their boost to momarch butterfly populations.
Oh my goodness. My crew and I were actually working with eucalypti today. In some places they don't present much of a problem, but here, in coastal Southern California, they can sometimes be a nightmare, taking over entire canyons.
Where they take over nothing else grows. It will be a monoculture of eucalyptus that pushes out thousands of species. Eucalyptus trees are not the single cause of the decline of several species here, but their presence contributes to their decline, in particular the Quino checkerspot and Hermes copper butterflies, California gnatcatcher, and the least Bell's vireo, all of them endangered. Dozens of other species suffer as well.
They are dangerous, dropping limbs from time to time. They are also a fire hazard and have exacerbated fire conditions here. Native chaparral will not burn--it is impossible to ignite--for several months of the year. Eucalyptus trees remain tinder throughout the year. Ask anyone involved in fire safety or conservation in Southern California about eucalypti, and they will say, "They shouldn't be here."
Now, they can help Monarch butterflies. Perhaps we could clear the eucalyptus trees where they have proven to be problematic but leave them in the few places where monarchs use them. My friend at work also works at the San Diego Zoo. He told me this morning that he has a class on eucalyptus, as the zoo maintains a grove to provide food for their captive koalas. Maybe we could have groves like this feeding koalas and helping Monarchs.
I should have qualified that my blunt, forward and tactless conversational style is not meant to be confrontational or rude. Obviously, I'm lacking middle-class sensibilities.
Hardy alpine goats are the key to eradicating such large scale environmental ravage. The breed "alpine" a very close to the wild type species which is a wonderful milk producer. Managed in an extreme intentional rotational grazing model, has the possibility of correcting the breach of morality. Along with a someone highly knowledgeable of the process, obviously.
The Sonoran Desert near my home is being invaded by Buffelgrass (Pennisetum ciliare, Cenchrus ciliaris). There is currently no economic loss until there’s a fire with this invasive species as fuel.
We are suffering from 2 or 3. An asian ant that damages concrete; ground elder which blocks root systems and the honey bee competing and distributing disease. We need wild pollenators.
Non-native species become invasive as they adapt to a new environment where they don't experience the predator and parasite loads that they face in the environment where they evolved. In the bell-shaped distribution among plants of a certain species, for example, those that allocate fewer resources (such as chemical defenses) to deter herbivores will have more resources to devote to reproduction or outcompeting native rivals. The gene distribution shifts over several generations species and the plants become increasingly prolific. That's why we often see a lag of several decades before a species explodes and becomes a real pest. To date, many invasive species have become major pests along waterways and riparian areas. I'm concerned that the "California friendly" plant species being promoted now will increasingly swamp our upland habitats later in this century, and we will look back and ask, "How could we have been so stupid?" as we do today for Aurndo, pampas grass, and their ilk.
Yup. A lot of folks don't understand how destructive invasives can be.
I should get into this conversation, as I have thoughts on the subject, many of them. I will add more if I have time.
In New Zealand, we have the example of gorse. It's invasive, it's costly, it's altering native habitats, it's costing farmers millions of dollars, it's one of New Zealand's worst weeds, it's displacing native species, it's encouraging fire, it's allowing native forest to regenerate, it saved an endemic insect from extinction... it's complicated.
That's the thing with many non-native, including invasive, species. Most have good and bad points, with how much good and how much bad depending on what they are, where they are and what the values of the person looking at them are. There are species which I'd call invasive in New Zealand which I believe should only be controlled under very limited circumstances, either because they aren't that harmful or because controlling them harms other things (an example would be Cytisus proliferus). There are species which I believe could be controlled to great benefit and minimal harm almost everywhere they occur in New Zealand, such as rats and possums (one rat species should be preserved on some offshore islands for cultural reasons though). But there are such large areas affected that we can't do it all.
This is why decisions about managing invasive species aren't, or shouldn't be, taken lightly. In my experience, most of the people making decisions about invasive species management get the point about prioritising both which species are controlled and where they are controlled, both because of limited resources and because they need to be sure that they are doing more good than harm. However I think that the scientists sometimes lose the nuance in the debate because they aren't having to make difficult management decisions.
Melanie, as always, thank you for your thoughtful and informed comment. You are correct that things with invasives can get complicated. I think some folks get confused as to the distinction between nonnative and invasive. Here, in Southern California, we have LOTS of nonnative species, such as magnolia trees native to the American South and Chinese elms. These don't spread or reproduce or cause problems.
I think that people also get confused with the term invasive. We have palms from the Pacific islands that are invasive but not particularly problematic. If you chop them down, they will go away and not come back. On the other hand, Arundo Donax transforms habitats, taking over, and it is almost impossible to kill. We could compare this to human health and ailments. Acne and high blood pressure are both ailments. Generally, acne is not going to kill you, but you better not think that way about your high blood pressure.
A problem here is that there are dozens of invasives. In conversations about invasives I think this can get overlooked. If you look at any one invasive, it may not seem all that bad, but taken together they can overwhelm landscapes. Here in California we have thousands of hectares in which the coverage of invasives is over 90%.
I’m wondering what you thought of his section on tamarisk? You might have noticed my comment about my coverage of the issue in my book, All the Wild and Lonely Places, back in 2000. At the time, biologists had just discovered the southwest willow flycatcher using tamarisk, and that undermined the contention that it was useless to native species. Mark Jorgensen told me he understood the risk of using glyphosate in wilderness areas and that we might someday learn that it’s more harmful than we knew (and now we do).
When I was writing an early draft of that chapter for an Environmental Studies class, the professor told me I needed to look up the water consumption of natives like cottonwoods and willows in order to support the common claim that tamarisk used more water, but I could never find any studies about that. (They probably existed but very little was online back then.)
The most damning evidence against the tamarisk was obvious: desert washes devoid of cottonwoods and willows, nothing but tamarisk. Do you know about the new treatment for tamarisk that Sam mentioned? I haven’t been able to look it up yet to find out how effective it’s been. Can’t visit those washes because I’m here in Michigan, where we occasionally see a tamarisk but they don’t spread.
Overall I’m skeptical of the claim that invasives are harmless. The wonderful diversity of life on Earth at the present moment is a result of island biogeography at various scales. With everything now interconnected, humans are doing away with the kind of isolation that led to speciation. The result over centuries is likely to be greater homogenization rather than diversity.
I think I should probably have said island biogragraphy is *one* source of the diversity of life, because of course there's species diversification in a given area. Otherwise there wouldn't have been a bunch of different finches for Darwin study.
I think you'll enjoy (and/or vehemently disagree with!) my next post on these topics!
I think you might agree with the conclusion I came to in the book, that we should manage exotics on a case-by-case basis, and those decisions should be based on science, not prejudice. But human bias will always influence science, a fact I wasn't quite so aware of back then.
Looking forward to it. You don't happen to have more sources for what's going on with tamarisk in the southwest right now, do you? I know that was just one small section of your previous piece, and I'd like to know more. Also, I'm lazy and distracted so haven't tracked them down on my own.
I found this article really good, especially on the history of the the "scapegoating" of tamarisks.
https://cronkitenews.azpbs.org/2018/07/30/non-native-tamarisk-are-demonized-across-the-west-but-are-they-really-the-enemy/
That's a good article! It comes to roughly the same conclusion about tamarisk removal that managers were hoping for when I interviewed them. The best they could hope for was to make space for native species by removing the tamarisk, knowing they'd never get rid of it completely. I'd point out that the areas I was covering weren't affected by western water management. These were desert washes in Anza-Borrego Desert State Park pretty far removed from even groundwater pumping. Mark Jorgensen, the resource manager in charge of the effort, was familiar with the situation on the Colorado and its tributaries and felt that little could be done over there, but he was encouraged by the success they were having in isolated desert washes away from the Colorado watershed. I need to revisit some of these places and see how they look now! (Or maybe I should just ask my friends who still live out there.)
Larry, thanks for your input. Tamarisk is curious. We have a grove of it growing at the entrance to where I work. In the ten years that I've been there, it has not spread or seemed to cause any problem. On the other hand, there are some nearby canyons where constantly spreads.
Anza-Borrego has a number of tamarisk infested places. There is even Tamarisk Grove. People actually go there because of the tamarisk. I believe the big concern there is that the deep roots of the tamarisks are pulling up deep groundwater, which, because of the citrus groves out there now, is already being depleted.
Are the ones where you work the tall kind (60 to 100 feet)? That’s the kind at tamarisk grove, usually planted as a wind break, and they don’t tend to spread. The smaller shrub-sized ones, brought over as ornamentals, are the ones that spread rapidly. I forget the species names, but it’s important to distinguish the two.
"Western water management"? So the only species you're concerned about any negative in real world matriculation is Homosapien? The spadefoot toad, along with the animal kingdom dwellers of precipitation collecting areas of the south west would highly disagree. If they lowered themselves to communicate with us.....
You are citing an opinion piece. Do you have anything that is credible concerning its actual real world affect upon the Eco habitat?
The only dynamic you need to understand concerning Tamarix L. (Tamaricaceae) introduction into the American Southwest is it water usage. There are myriads of other negative impacts on the bio regional Eco also. It has dramatically reduced the populations of the spadefoot toad in the water catching areas of the region.
In short, there are no "less important" strands in the web of life. To contend interrupting in infusing something that is foreign to that regional Eco habitat web is never a positive or neutral thing. Meaning, when you interrupted environment that has achieved stasis, you have damaged it. There's no other verbiage.
To me, the insistence of "non-native species introduction" paradigm being anything else, nothing more than an opinion. A poorly formed one. Arrogant even. We know so little about the Earth's native biosphere. To make such a judgment is a mistake and obtuse. Conceited.
I enjoyed this post. It’s important to remember there is more than one perspective in all matters.
You might enjoy this article I wrote on invasives.
https://x.com/the_earthmonk/status/1819005064884744389?s=46&t=yHhr9CFS49ZimrUMgPJlQw
There are always three versions of the truth
No. Just no.
Thank you for this very important counterpoint. Well stated. Invasives are simply not ok - and much different than exotics that do not affect our natural areas.
Karen, thanks so much. Yes, I think that folks get confused and conflate exotics with invasives.
This was super interesting. Fairly new to the Substack community but like you said i noticed it was really friendly and it’s really inspiring to see people engaged in important ecological conversations like this! I look forward to reading more
I appreciate hearing your perspective Paul, and I agree with you on the great value of the "polite disagreement" culture of Substack. Dedicated stewards of their local landscapes and ecosystems like you are exactly the kind of people I'm excited to talk to about this!
So, impromptu, a few points that spring to mind on my reading of your post.
First, let's clarify our terms. If I understand you correctly, you agree that some nonnative species are harmless or beneficial, but that invasive species are by definition harmful, so it's wrong of me to advocate for them. Okay, but I think the last few decades of research seem to be finding that more and more invasive species are not nearly as harmful as we first thought!
My kudzu source: https://www.smithsonianmag.com/science-nature/true-story-kudzu-vine-ate-south-180956325/ .
A regular problem with cost estimates of invasive species is that they often factor in the effort of removing them, creating a bit of a "self-fulfilling prophecy" (this "invasive" species is doing well, so they'd cost a lot to remove, so we must remove them because they're so costly!). Biological control agents tend to be cheap to introduce and have a very high success rate, as discussed in the Novak paper I cited in https://sammatey.substack.com/p/the-dawn-of-immigrant-species-biology .
You say, "You might as well tell me that cancer has an upside." Do you then disagree that Australian saltwater crocs and Brazilian jaguars benefiting from wild boars as prey is an upside, at least to some extent? Or Puerto Rican tree frogs living on African tulip trees? Or zebra mussels' filtration effects boosting alewife and salmon populations? Or gorse sheltering young native plants in New Zealand? Or purple loosestrife being correlated with *increased* biodiversity of native plants in North America? If those do count as upsides, and you believe invasives are by definition bad, then do wild boar, African tulip trees, zebra mussels, gorse, and purple loosestrife no longer count as "invasive" for you? Those are 5 of the IUCN's 100 World's Worst "invasive" species! It seems to me that your views are a little self-contradictory here. From my perspective, of the statements (1) these five species are invasive, (2) all invasives are bad, and (3) these five species have some upside for native ecosystems, you can logically agree with any two of them, but not all three at once. Which of these three statements, if any, do you agree or disagree with?
I have another article on this general subject coming on Monday, and would love to hear your thoughts on the examples in there as well! I suspect you'll strongly disagree with me on several points, but I really admire your principled and courteous engagement in this discussion and I hope you feel like continuing it.
Sam, thanks for your thoughtful comments. You’ve obviously thought about this topic and researched it a great deal.
As far as costs of invasives. I’d be willing to say that putting dollar amounts on their damages may overlook a lot of their harms. When invasives cause or contribute to the extirpation of a species, there is no ledger of the dollar amount.
And if there is an invasive disrupting and ecosystem or causing damage to crops or forests, it makes sense to add the cost of removal to the ledger of the full cost of the species. As an example, the cost of tagging would include removing or covering up the graffiti as well as the police work of catching the taggers.
Also, from my experience, removing and controlling invasives here in San Diego, much of that work is done by nonprofits and volunteers, so the costs are pretty low and may support the argument that costs of invasives are underestimated. Where I work, much of invasive removal is done by school groups, and it’s administered through the education department. So in our ledger the costs are under the education department So on the books, there is no cost of conservation or invasive removal. It’s a bookkeeping thing, but once again points up that removal and control costs are probably underestimated for a lot of invasives.
You have a point about some invasives fitting an ecological niche or helping native species in their new environments. And that is a dicey issue. Once an invasive is established and there is a new dynamic, that can be a real judgement call as to how much of the invasive to allow or control to let it help without causing further harm.
From personal experience I sometimes think the benefits can be overestimated. I work in the middle of a wildlife refuge. U.S. Fish and Wildlife were reluctant to allow me to remove a eucalyptus tree, as it provided roosting and nesting sites for herons and other birds. Because it was a pressing safety issue (the tree’s branches were falling into our parking lot.), FWS relented. Well, all the birds just nested in the native trees nearby.
Same with removing invasive sea lavender in our estuary. A very endangered species, bird’s beak, fed on the sea lavender. It was feared that removing the sea lavender would extirpate the bird’s beak. That did not happen. As a matter of fact, with the removal of the sea lavender, the bird’s beak is thriving better than before.
I know these are anecdotes. Take them for what they are worth.
I was talking with a colleague about this conundrum and I suggested that we don’t simply label a species as invasive. We give it an invasive score that acknowledges both the species benefits and harms. So, eucalyptus here in Southern California could get a score of 2/7. The tree scores two points for providing habitat, wood, and shade. The tree gets seven demerits for extirpating all natives around it, being invasive, and being a fire and safety hazard.
Wadaya think? Would this be a step forward in our thinking?
I really appreciate your openness to dialogue and a more nuanced evaluation on this! Not simply labeling a species as "invasive" sounds like a very good step to take, and I applaud you for considering it. I actually discuss eucalyptus trees in today's upcoming article as well - I would give them a net positive score for their boost to momarch butterfly populations.
*monarch
Oh my goodness. My crew and I were actually working with eucalypti today. In some places they don't present much of a problem, but here, in coastal Southern California, they can sometimes be a nightmare, taking over entire canyons.
Where they take over nothing else grows. It will be a monoculture of eucalyptus that pushes out thousands of species. Eucalyptus trees are not the single cause of the decline of several species here, but their presence contributes to their decline, in particular the Quino checkerspot and Hermes copper butterflies, California gnatcatcher, and the least Bell's vireo, all of them endangered. Dozens of other species suffer as well.
They are dangerous, dropping limbs from time to time. They are also a fire hazard and have exacerbated fire conditions here. Native chaparral will not burn--it is impossible to ignite--for several months of the year. Eucalyptus trees remain tinder throughout the year. Ask anyone involved in fire safety or conservation in Southern California about eucalypti, and they will say, "They shouldn't be here."
Now, they can help Monarch butterflies. Perhaps we could clear the eucalyptus trees where they have proven to be problematic but leave them in the few places where monarchs use them. My friend at work also works at the San Diego Zoo. He told me this morning that he has a class on eucalyptus, as the zoo maintains a grove to provide food for their captive koalas. Maybe we could have groves like this feeding koalas and helping Monarchs.
I should have qualified that my blunt, forward and tactless conversational style is not meant to be confrontational or rude. Obviously, I'm lacking middle-class sensibilities.
Hardy alpine goats are the key to eradicating such large scale environmental ravage. The breed "alpine" a very close to the wild type species which is a wonderful milk producer. Managed in an extreme intentional rotational grazing model, has the possibility of correcting the breach of morality. Along with a someone highly knowledgeable of the process, obviously.
The Sonoran Desert near my home is being invaded by Buffelgrass (Pennisetum ciliare, Cenchrus ciliaris). There is currently no economic loss until there’s a fire with this invasive species as fuel.
We are suffering from 2 or 3. An asian ant that damages concrete; ground elder which blocks root systems and the honey bee competing and distributing disease. We need wild pollenators.