Recently there was an article published in the journal Science (widely considered one of the most prestigious science journals in the world) by two professors who I knew while I attended college in Pennsylvania (Franklin and Marshall College — Anyone ever heard of it?). I found this article particularly interesting because it explained how the beautiful Pennsylvania scenery that we assume is natural was actually created over the course of three hundred years. Saw mills and dams changed water flow patterns — those pretty streams that flow through the Southeastern PA (and nearby areas) that I grew up in aren’t natural at all.
Of course this is just another thing that we’ve done to make this country different from what it was when people first came here. We’ve also farmed the heck out of the land, built large industrial areas and, on top of that, there’s the issue of global warming (which, for the sake of this post, we’ll assume is caused by humans), increased carbon dioxide in the air, decreased top soil and forest land (mostly because of the farming), and a general increase in soil, water and air pollutants.
So, with all that said, It seems to me that we’ve done a lot of things to change the environment. With all that we’ve done why are we so upset when some plants, which we call “invasive” thrive in these settings? It’s not their fault that they do well in the conditions we’ve created. Sometimes I feel like we’ve built this great big smorgasbord of lutefisk (fish treated with lye — it’s pretty nasty) and then get angry when only people who grew up eating this type of fish come to the party.
I’m not trying to promote invasive plants — And I’ll be the first to admit that this post is oversimplifying the whole question of invasives — Still, it irks me sometimes that we aren’t more concerned about the environment where we plant our greenery rather than the plants themselves who, after all, are just feeding on the smorgasbord that we’ve created.
Jeff, I don’t have any problem with introduced plants that behave themselves, including those that naturalize without displacing natives. But many invasive species become monocultural, which is just as bad as monoculture in conventional agriculture. It reduces biodiversity of plants and animals and certainly does nothing to enhance aesthetics. Consider areas in the South where kudzu, or English ivy in Oregon and Washington, have taken over forests. Both of these were deliberately introduced as ornamental plants. And they do just as well in natural settings – not just those landscapes we’ve created. It’s relatively easy to control these plants in one’s own landscape. But I’ve spent years, literally, controlling Himalayan blackberry, Scots broom, English ivy, and so many other aggressive, deliberately introduced species in restoration sites. The problems associated with aggressive invasive species requires a national, unified awareness – not just a regional one. Invasive species don’t recognize boundaries.
Jeff, thanks for this post. While invasive species are a problem in many parts of the world they are often a symptom. The symptom shows that the local environment is not healthy enough to ward off the invasive species. Removing the invasives (while necessary) does not address the root of the problem – environmental and climactic changes wrought by humanity (arguably the most invasive species).
But the main problem is so huge it seems much eas
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ier to fight the symptoms. It’s easier to get people to volunteer to pull invasive weeds than to change their lifestyles and lobby for improved pollution control measures.
Thanks again for the thought provoking post.
Diana, it’s really not an issue of environmental health. Introduced species are successful in natural environments because those environments do not have the natural pests, predators, diseases, and competitors of the introduced species. That’s how classical biological control started – to deal with invasive species such as tansy ragwort by introducing their natural predator (in this case cinnabar moths). Any landscape is at risk when a new species invades without its natural controls.
Linda, You might be reading a little more into my post than I intended (or I might be reading more into your response…). I basically agree with what you’ve said — there are certainly invasive weeds that can monopolize “wild” areas. However, in cases such as the South and Kudzu, our farming practices created areas where the plant would thrive and outcompete native plants. Likewise, here in MN buckthorn is considered a terrible invasive, but in truly undeveloped land it isn’t nearly as much of a concern as it is on land that was reforested after being farmland or in suburban locations. I agree with you on the national awareness issue — without it we’ll get nowhere.
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Jeff GillmanLinda, I have to disagree with your last post — sometimes it’s an issue of natural enemies — but frequently it’s an issue of environment. Look at Buddleia in the Northeast — It prefers damaged areas. In England Buddleia wasn’t considered a big deal until after the 2nd World War — it was one of the few plants that literally thrived in bombed out buildings. December 10, 2009
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Linda Chalker-ScottI get twitchy when the impact of invasive species is only seen as a problem in developed landscapes. The seeds of invasive species easily find their way into otherwise pristine areas on the boots of hikers, for instance. Tamarisk is taking over the palm oases in the southern California desert at least in part to this unwitting transport. Seeds on the tires of cars and bikes have been linked to invasions in Hawai’i’s forests. Before I moved back to Washington, I lived in Buffalo and researched control mechanisms for zebra mussels, which were introduced to the Great Lakes in ballast water. The economic and environmental impact of these species in this country has been huge. In 20 years this species has spread from Lake St. Clair throughout the country and is making its way to the west. The complacency with which people on this side of the country regard zebra mussels is astounding…December 10, 2009
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Jeff GillmanI absolutely don’t mean to imply that invasive species are only a problem in developed landscapes — all this post was meant to do was to point out that we humans sometimes change the environment so that invasives are more successful than they would otherwise be. December 10, 2009
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Linda Chalker-ScottYou’re entirely correct – invasives generally have a much easier time invading disturbed environments than intact systems. But many, many gardeners do not see a connection between what they do in their yard and what happens to natural areas. The mentality and the behavior has to change – and I think you and I probably agree on that!December 10, 2009
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Holly S.*munching on popcorn and enjoying the great discussion*December 10, 2009
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Ray EckhartThe amount of Japanese Knotweed, Mile-A-Minute Vine, and Japanese Barberry seen along the Appalachian Trail here in South Central PA, Franklin County (not far from F&M in Lancaster, professor) lends credence to Linda’s last point. See also this recent story.
In a paper titled “Forest Roads Facilitate the Spread of Invasive Plants,” published in the August 2009 issue of Invasive Plant Science and Management, Mortensen detailed some eye-opening revelations about the process by which invasive plants advance so quickly.
“Roads can play a profound role in the spread and growth of invasive species by serving as corridors for movement and by providing prime habitat for establishment,” Mortensen explained. “For example, forest managers have reported that the borders of hundreds of miles of forest roads have been invaded by Japanese stiltgrass in a period of less than 10 years.”
December 10, 2009
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Jeff GillmanThanks for that post Ray!December 10, 2009
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Joseph TychonievichRecently I wanted to find out more of the specific ways invasive species damage native landscapes, so I started looking through the literature about the big ones in the area I grew up (loosestrife, buckthorn) and was pretty shocked at the quality of the publications — in virtually every case, researchers demonstrate that the species has moved into wild areas, and stop there, just assuming that means ecological damage. When I could find papers quantifying actual effect on native species, the conclusion was generally: None — unless you are talking about predators and diseases, or isolated ecosystems like islands and lakes.
Made me feel a little like I’d been sold a bill of goods — with so many incredibly significant environmental problems, why are we investing so much time and energy in trying to exterminate purple loosestrife (and the like) which doesn’t seem to actually harm anything? December 10, 2009
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Linda Chalker-ScottIt’s been a while since I looked at the purple loosestrife literature (like 20 years) but when I was teaching Envirionmental Biology at Buffalo State College I used this as a local example of an invasive species. I’d have to go looking to find the original research, but what I remember finding – and discussing – was that loosestrife decreased nesting habitat of waterfowl, who could not swim through the loosestrife thickets. Cattails and other plants, apparently, were wider spaced. Fish diversity also decreased. As I said – I don’t remember the original source, but this is the type of damage that invasives can have. I’ll try to remember to take a look at the literature over the holidays and see if I can find some further information for you.December 10, 2009
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Jeff GillmanJoseph, You’re right that we don’t have enough information on what many invasives do and many people (including myself) make grand over-arching statements on the effects of these plants without sufficient objective data to back them up. I would agree with you that invasives are not at the top of my list of “scariest environmental problems”. That said, check out some of the scientific literature on Norway Maple vs. Sugar Maple on the East Coast. There are places where invasives are doing significant damage. December 10, 2009
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Ray EckhartA starting point for quantifying the impact of invasive species.
Here’s another, specific to Purple Loosestrife.December 10, 2009
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Linda Chalker-ScottThere is also a solid body of scientific literature on the ecological devastation caused by zebra and quagga mussels in freshwater systems. There is a great deal of money available for studying this type of invasive problem from Sea Grant, because of the negative impact on fisheries and other activities associated with water habitat. In contrast, there’s relatively little for studying invasive ornamentals, unless they interfere with food or fiber plants (the only kind of research funded by the USDA). Jeff’s example of the impact on the maple sugar industry might be one such funded study. December 10, 2009
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Linda Chalker-ScottWow, Ray, you’re doing my job for me! Thanks for this great link.December 11, 2009
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MarieGreat discussion. Thank you all!
December 11, 2009
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DebBoy, great discussion. December 11, 2009
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DebIt’s true that plants will grow where conditions welcome them, and we’ve created conditions to welcome many exotic plants that human actions have brought here. Both Linda and Jeff are making great points! One big deal: even stable ecotones are being disrupted by invasives, and the damage extends to organisms other than plants — vertebrates and invertebrates native to a place often get crowded out by the pushy newcomers. Here in MA we have a big problem (well, we have lots of problems with invasives, but I’ll use this one as an example) with garlic mustard, a biennial that thrives in sun or shade and propates profusely by seed. It is allelopathic, and so suppresses the germination and sporulation of other plants and fungi while it takes over an area. The result: monocultural stands that spread quickly and reduce edible habitat for non-plant native inhabitants of the area. Bill Cullina recently wrote a great article for the New England Wild Flower Society about biodiversity and the merits of using native plants ; he coined the terms ‘biopositive’ and ‘bionegative’ in his discussion, which touches on the problems introduced by invasives — it’s worth a read, as it may add even more dimension to this great discussion. Here’s the link:http://www.newenglandwild.org/publications-and-media/articles/the-biodiversity-all-stars.html/December 11, 2009
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Jeff GillmanDeb, That is a very interesting link — I hope that the people following the discussion here check it out!December 11, 2009
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joeneFirst off, thank you all for sharing your lively discussion for home gardeners to read. Second, I don’t see any mention that non-native species support fewer insects than natives and, therefore, decrease the available food for birds and so forth … as Doug Tallamy explains in his book Bringing Nature Home. This is a whole aspect of natives versus non-natives that is little discussed.December 11, 2009
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MrBrownThumbJeff,
Interesting perspective and one I’ve been leaning towards myself. Thanks for giving it a voice. December 11, 2009
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Linda Chalker-ScottJoene, it’s very important to differentiate between nonnatives that are invasive and those that are not. There are many nonnative plant species that take can take the place of extirpated natives, providing food and habitat for animal species that were dependent on the natives. Plus, without nonnatives, many ornamental landscapes would be pretty bleak! The trick is to choose those species whose likelihood of becoming invasive is low. There is a whole body of science behind predicting invasiveness. (Both topics – predicting invasiveness and choosing between natives and nonnatives – are covered in two chapters in a book I’ve edited that is coming out right before Christmas called “Sustainable Landscapes and Gardens: good science, practical application.” More on that when it’s out and ready to go!)December 12, 2009
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joeneLooking forward to reading the book’s release, Linda. Thanks.December 13, 2009
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fireflyOne book that gathers a great deal of research on the effect of invasive plants and other organisms is “Alien Species and Evolution” by George Cox, published 2004 by Island Press.
Covers basic concepts of invasion and evolution, processes of evolutionary change, evolutionary interaction of aliens and natives, and evolutionary consequences.
A fascinating, if somewhat depressing, read.
Here’s a link to the TOC at the publisher’s site:
http://tinyurl.com/ycu7xn9
Linda, I have to disagree with your last post — sometimes it’s an issue of natural enemies — but frequently it’s an issue of environment. Look at Buddleia in the Northeast — It prefers damaged areas. In England Buddleia wasn’t considered a big deal until after the 2nd World War — it was one of the few plants that literally thrived in bombed out buildings.
I get twitchy when the impact of invasive species is only seen as a problem in developed landscapes. The seeds of invasive species easily find their way into otherwise pristine areas on the boots of hikers, for instance. Tamarisk is taking over the palm oases in the southern California desert at least in part to this unwitting transport. Seeds on the tires of cars and bikes have been linked to invasions in Hawai’i’s forests. Before I moved back to Washington, I lived in Buffalo and researched control mechanisms for zebra mussels, which were introduced to the Great Lakes in ballast water. The economic and environmental impact of these species in this country has been huge. In 20 years this species has spread from Lake St. Clair throughout the country and is making its way to the west. The complacency with which people on this side of the country regard zebra mussels is astounding…
I absolutely don’t mean to imply that invasive species are only a problem in developed landscapes — all this post was meant to do was to point out that we humans sometimes change the environment so that invasives are more successful than they would otherwise be.
You’re entirely correct – invasives generally have a much easier time invading disturbed environments than intact systems. But many, many gardeners do not see a connection between what they do in their yard and what happens to natural areas. The mentality and the behavior has to change – and I think you and I probably agree on that!
*munching on popcorn and enjoying the great discussion*
The amount of Japanese Knotweed, Mile-A-Minute Vine, and Japanese Barberry seen along the Appalachian Trail here in South Central PA, Franklin County (not far from F&M in Lancaster, professor) lends credence to Linda’s last point. See also this recent story.
In a paper titled “Forest Roads Facilitate the Spread of Invasive Plants,” published in the August 2009 issue of Invasive Plant Science and Management, Mortensen detailed some eye-opening revelations about the process by which invasive plants advance so quickly.
“Roads can play a profound role in the spread and growth of invasive species by serving as corridors for movement and by providing prime habitat for establishment,” Mortensen explained. “For example, forest managers have reported that the borders of hundreds of miles of forest roads have been invaded by Japanese stiltgrass in a period of less than 10 years.”
In a paper titled “Forest Roads Facilitate the Spread of Invasive Plants,” published in the August 2009 issue of Invasive Plant Science and Management, Mortensen detailed some eye-opening revelations about the process by which invasive plants advance so quickly.
“Roads can play a profound role in the spread and growth of invasive species by serving as corridors for movement and by providing prime habitat for establishment,” Mortensen explained. “For example, forest managers have reported that the borders of hundreds of miles of forest roads have been invaded by Japanese stiltgrass in a period of less than 10 years.”
Thanks for that post Ray!
Recently I wanted to find out more of the specific ways invasive species damage native landscapes, so I started looking through the literature about the big ones in the area I grew up (loosestrife, buckthorn) and was pretty shocked at the quality of the publications — in virtually every case, researchers demonstrate that the species has moved into wild areas, and stop there, just assuming that means ecological damage. When I could find papers quantifying actual effect on native species, the conclusion was generally: None — unless you are talking about predators and diseases, or isolated ecosystems like islands and lakes.
Made me feel a little like I’d been sold a bill of goods — with so many incredibly significant environmental problems, why are we investing so much time and energy in trying to exterminate purple loosestrife (and the like) which doesn’t seem to actually harm anything?
It’s been a while since I looked at the purple loosestrife literature (like 20 years) but when I was teaching Envirionmental Biology at Buffalo State College I used this as a local example of an invasive species. I’d have to go looking to find the original research, but what I remember finding – and discussing – was that loosestrife decreased nesting habitat of waterfowl, who could not swim through the loosestrife thickets. Cattails and other plants, apparently, were wider spaced. Fish diversity also decreased. As I said – I don’t remember the original source, but this is the type of damage that invasives can have. I’ll try to remember to take a look at the literature over the holidays and see if I can find some further information for you.
Joseph, You’re right that we don’t have enough information on what many invasives do and many people (including myself) make grand over-arching statements on the effects of these plants without sufficient objective data to back them up. I would agree with you that invasives are not at the top of my list of “scariest environmental problems”. That said, check out some of the scientific literature on Norway Maple vs. Sugar Maple on the East Coast. There are places where invasives are doing significant damage.
A starting point for quantifying the impact of invasive species.
Here’s another, specific to Purple Loosestrife.
There is also a solid body of scientific literature on the ecological devastation caused by zebra and quagga mussels in freshwater systems. There is a great deal of money available for studying this type of invasive problem from Sea Grant, because of the negative impact on fisheries and other activities associated with water habitat. In contrast, there’s relatively little for studying invasive ornamentals, unless they interfere with food or fiber plants (the only kind of research funded by the USDA). Jeff’s example of the impact on the maple sugar industry might be one such funded study.
Wow, Ray, you’re doing my job for me! Thanks for this great link.
Great discussion. Thank you all!
Boy, great discussion.
It’s true that plants will grow where conditions welcome them, and we’ve created conditions to welcome many exotic plants that human actions have brought here. Both Linda and Jeff are making great points! One big deal: even stable ecotones are being disrupted by invasives, and the damage extends to organisms other than plants — vertebrates and invertebrates native to a place often get crowded out by the pushy newcomers. Here in MA we have a big problem (well, we have lots of problems with invasives, but I’ll use this one as an example) with garlic mustard, a biennial that thrives in sun or shade and propates profusely by seed. It is allelopathic, and so suppresses the germination and sporulation of other plants and fungi while it takes over an area. The result: monocultural stands that spread quickly and reduce edible habitat for non-plant native inhabitants of the area. Bill Cullina recently wrote a great article for the New England Wild Flower Society about biodiversity and the merits of using native plants ; he coined the terms ‘biopositive’ and ‘bionegative’ in his discussion, which touches on the problems introduced by invasives — it’s worth a read, as it may add even more dimension to this great discussion. Here’s the link:http://www.newenglandwild.org/publications-and-media/articles/the-biodiversity-all-stars.html/
Deb, That is a very interesting link — I hope that the people following the discussion here check it out!
First off, thank you all for sharing your lively discussion for home gardeners to read. Second, I don’t see any mention that non-native species support fewer insects than natives and, therefore, decrease the available food for birds and so forth … as Doug Tallamy explains in his book Bringing Nature Home. This is a whole aspect of natives versus non-natives that is little discussed.
Jeff,
Interesting perspective and one I’ve been leaning towards myself. Thanks for giving it a voice.
Joene, it’s very important to differentiate between nonnatives that are invasive and those that are not. There are many nonnative plant species that take can take the place of extirpated natives, providing food and habitat for animal species that were dependent on the natives. Plus, without nonnatives, many ornamental landscapes would be pretty bleak! The trick is to choose those species whose likelihood of becoming invasive is low. There is a whole body of science behind predicting invasiveness. (Both topics – predicting invasiveness and choosing between natives and nonnatives – are covered in two chapters in a book I’ve edited that is coming out right before Christmas called “Sustainable Landscapes and Gardens: good science, practical application.” More on that when it’s out and ready to go!)
Looking forward to reading the book’s release, Linda. Thanks.