On several observations in Texas, a few of us are getting tangled up in definitions (and subsequent annotations) of the term “invasive”. I’d like to open the discussion up and seek some formal context on these terms. I would assert that, ecologically speaking (and not necessarily from a legal or regulatory standpoint), that the concept of an “invasive” plant species may at times be applied to certain native as well as non-native species in a given region. Others have pointed out that “invasive” explicitly applies to species not native to a region.
I’d like to hear other opinions, particularly accompanied by references, citations, or other published guidance. Thanks in advance.
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This paper might be a good place to start:
Valéry, L., Fritz, H., Lefeuvre, J. C., & Simberloff, D. (2009). Invasive species can also be native…. Trends in Ecology & Evolution, 24(11), 585.
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in my personal opinion, I strongly disagree. Proponents of that view are ignoring the important point that in addition to being native to a specified region, any given species will also be ‘native’ to particular habitat or soil types. Thus, a species could be native to a particular region, but invade different habitat types and have detrimental effects when eg facilitated by human impacts.
A good example to illustrate my point is an Australian species, specifically in the state of NSW. Cupaniopsis anacardioides is a smallish tree species that is pretty common along the NSW coast all the way down past Sydney. The NSW flora states its habitat preferences as “littoral rainforest and scrub near the sea and along estuaries”. This is its ‘normal’ habitat, and it’s quite a common species in it.
Recently, this species has become increasingly popular as a planting choice at shopping centres, outside hardware stores, etc. It has big orange fruits which attract birds; you can see where this is leading. In the bushland reserve I survey near my house, which is certainly not littoral rainforest or scrub, this species is now popping up everywhere in the woodland there due to bird dispersal.
The reserve is in NSW and in Sydney. Cupaniopsis anacardioides is native to NSW and to Sydney. But is it invasive in the reserve? In my opinion, absolutely; it’s competing with other plants for resources, taking up light, etc., in a habitat type which it has historically never been present in (or at least in exceptionally small numbers). This is not a one off case, and this species is increasingly being observed as invading drier and more inland bushland sites in Sydney due to dispersal from plantings. I guess you could argue that birds could have dispersed the tree from its rainforest habitat into my drier woodland naturally anyway, but the human plantings have greatly accelerated/facilitated this process.
Another important element in this entire discussion is scale. You say native/not native to a ‘region’, but what scale are we talking about? At a country level, there are many completely unambiguous examples of Australian species that are native to one part of the country, but a highly invasive and impactful weed in others, including many species native to the east coast that are invasive on the west coast, and vice versa. But Australia is a very big place, so maybe state is a more realistic level? Same thing still applies. Acacia baileyana is certainly native to NSW, yet it’s an invasive weed in most parts of NSW! Why? Because it’s actually only native to a very small area of NSW, anywhere outside that its presence has been dictated by (originally) garden escapes (very popular cultivated plant) and then prolific self-seeding from those in natural bushland.
Another interesting example is Leptospermum laevigatum. According to the Victorian flora, it is “Common on sandy coastal foreshores and dunes from c. Anglesea eastward (where native); introduced and naturalised on some western Victorian coasts (e.g. Port Fairy, Portland).”
I have a good mate who lives in Anglesea, and he tells me that in some areas there, this species has become hugely invasive. It was originally planted as a dune stabiliser decades ago at or just westwards of the accepted westernmost edge of its ‘natural’ distribution, and then has gone nuts, and in some dune systems, has completely taken over to the detriment of all other species and has formed vast monotypic stands that exclude everything else. So this is an example of something that is not only in the same region to which it is native, but even in the exact same habitat type to which it is native, which has become invasive.
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I’ve always gone off of:
Endemic- Naturally found there and only there
Native- Naturally found there
Introduced- From somewhere else
Invasive- From somewhere else and causing ecological damage
Naturalized- From somewhere else but not causing any environmental damage
Good terms from other people:
Pioneer Species- Native that quickly inhabits new territory (Not an aggressive native)
Aggressive Native- Native that perpetuates ecological damage from invasives
Archeophyte- Introduced pre-Columbus (Europe)
Neophyte- Introduced post-Columbus (Europe)
They’re really basic definitions, but they work.
(I’m gonna keep editing this to include terms from other people)
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is good.
I have learnt to recognise
https://www.inaturalist.org/taxa/585823-Felicia-echinata
Yes it is indigenous. But bling flowers and garden escapee.
Comes from much further up the coast!
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In Europe, Introduced is split on two subgroups: archeophytes were brought before Columbus (e.g. buckwheat which came in the middle ages), neophytes after that. This probably won’t work on other continents.
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This paper has some good discussion about this exact topic.
Regarding natives and invasives they say:
Invasion biology defines being introduced by humans as a fundamental characteristic of invasive species, which differentiates this process from colonization that occurs naturally. Thus, the process of categorizing species as ‘invasive’ or ‘native’ is often difficult. When species were introduced in historical or prehistoric times, it is challenging to categorize them as exotic or native. For example, at least 157 plant species were introduced to Britain by humans between approximately 4000 BC and 500 years ago (Preston, Pearman, & Hall, 2004), and these species have been variously classified as native and/or exotic, depending on the authors (Willis & Birks, 2006).
Carthey & Banks (2012) argued that evolutionary theory predicts that alien predators cannot remain eternally novel; prey species must either become extinct or adapt to the new threat. As local enemies lose their naiveté and coexistence becomes possible, an introduced species must eventually become native. These authors discussed the example of the dingo (Canis lupus dingo), which was introduced to Australia approximately 4000 years ago, although its native status remains disputed.
Chew & Hamilton (2011) analysed the concept of biotic nativeness and were categorical when diagnosing the ‘native’ adjective as ‘uninformative, even deceptive’ (p. 44). Thompson & Davis (2011) took a different approach for the same problem when they suggested that with continual global changes in nutrients, climate, and disturbance regimes, all species can be considered to be inhabiting novel environments and, therefore, distinctions between native and non-native species are becoming even less ecologically meaningful.
In the modern, human-dominated landscape, an increasingly sharp distinction exists between ‘winner’ and ‘loser’ species, and this distinction may have little association with native or alien status (Thompson & Davis, 2011). Rare, restricted species are disappearing, while the common, widespread species are becoming even more abundant and widely dispersed. This phenomenon has been referred to as the homogenization or cosmopolitanization of the global biota (Brown & Sax, 2004).
Another point that I really like about this paper is their critique of including negative impacts in the definition of invasive species. It doesn’t really make sense, in part because it’s circular like they mention, but also many species have not been documented to have negative effects because their ecology has never been studied, and labeling them as not invasive reflects more of our understanding of their ecology than their actual ecology.
Invasion biologists tend to view any environmental changes produced by non-native species as being harmful. Marcelo H. Cassini Sagoff (2005) suggested that if one defines any significant change caused by a non-native species as having negative impact, the statement that non-native species harm ecosystems represents a tautology. Larson, Kueffer, & Zi (2013) proposed that the term ‘impact’ could simply be replaced with the term ‘change’ or ‘effect’. Facing difficulties evaluating negative impacts, some invasion biologists have proposed that the impact of a species should not be considered at all in the definition of invasiveness (Daehler, 2001; Blackburn, Pyšek, & Bacher, 2011). By contrast, Davis & Thompson (2001) argued that there are compelling conceptual and practical reasons for impact to be included in the defining criteria of an invading species.
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Thank you for that new knowledge! I will keep that in mind for the future :)
If Colombus is the cut-off point I would think that this should work just as well for other continents, especially in the Americas since the Columbian Exchange went into two directions. Equivalent Europan arrivals with similar results are found all across the Pacific, sub-saharan Africa, Australasia, so what makes you say this wouldn’t work?
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Your list doesn’t cover a native that is causing ecological damage. Is a term needed or do you feel that natives just don’t cause damage, that the changes they cause never constitute damage?
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Did American First nations or Australian Aborigines travel to other continents and brought plants from there? Maybe Vikings brought something to the east coast during the middle ages, but I don’t know. If not, there should be no archeophytes there.
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In these cases, the point is more that they travelled from other places to arrive in North America and Australia (not to mention all the other Pacific islands) and any plants they brought with them from mainland Asia would be archeophytes under that definition
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Scientists have been arguing about what the term “invasive” means for >25 years, and I don’t think that any consensus is coming soon. When I review/edit papers in Invasion Biology (my field), I just make sure that the authors define how they are using “invasive” or any related terms in their paper so that ambiguity is minimized.
In general, I think that the most common use of invasive is for a species that is not native to a region. I do see “invasive” occasionally used for native organisms that often take over disturbed habitats. I understand the motivation behind describing these as “invasive” based on how they function, but I don’t use that term to describe them because it leads to confusion. I think that there are often better, more specific terms to use anyways - disturbance specialist, colonizer, monoculture, etc.
Ultimately, the goal of using words to to communicate ideas. So I would suggest not getting too hung up on specific terminology and focusing on communicating meaning clearly. That may vary depending on the audience, but defining how we are using a term that has multiple current uses is generaly good practice.
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I’ve heard the term aggressive used for natives that have similar characteristics as invasive counterparts (e.g., the tendency of some plants to create large monocultures by outcompeting other natives). In my opinion, most typically, aggressive organisms only perpetuate ecological damage rather than being the source of the damage (e.g., a disturbed field never returns to it’s former biodiversity, in part, due to competition from aggressive natives; raccoons have an outsized impact on shorebird nests because coastal human development has boosted raccoon populations in coastal areas, in addition to directly hindering many shorebird populations).
Linguistically, I think it makes sense for “invasive” to refer specifically to nonnatives considering “invasion” means an incursion or intrusion by an outside force into another’s domain.
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Refinements are possible: for example the distinction between exotic invasive (arriving from abroad + successfully established + now taking much space) and invasive (now taking much space, e.g. following local disturbance). ‘Envahissant’ vs. ‘envahisseur’ if you pardon my French.
There may be grey areas due to semantic issues, knowledge gaps, or complicated histories. I recently stumbled upon a weird case: an introduced population of a (once-)native plant species that behaves invasively in a peculiar location.
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Yes, I understand your reasoning now, but like @bugbaer pointed out the pacific islands provide an excellent example of how new species tend to be brought in by first and subsequent arrivals of humans, whether intentional or not. Whenever humans travel long distances go they tend to carry at least some of their food sources with them, as well as some non-food domestic species (e.g. dogs to the Americas). There is even evidence, albeit controversial, of some exchange of crops (yams) domestic animals (chickens) and human genetics between Polynesia and South America.
Even if we exclude first human arrivals and pre-historic exchanges, there would still be something to be said for archeophytes on other continents. If buckwheat arrived to Europe from Asia along trade routes, surely there were crops moving the opposite direction as well. Some trade routes across and around the Sahara existed too, so there are likely archeotypes to be found in Sub-Saharan Africa. Even within continents major pre-columbian introductions into new ecosystems have taken place (e.g. Maize from Mexico into the US, Colombia, and Peru by 5000 BCE).
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Yes, that is my impression, too. There are native plants on noxious weed lists, but those labels pretty much only apply to them in an agricultural or garden setting.
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I’ve just had a long chat with my (Italian) ecologist husband about just this concept and we both agree that the word “invasive” can be applied to either native or non-native species which act invasively in a particular context. Certainly some (but definitely not all) species non-native to a particular geographical location, whether large or small, can be invasive. Here in Italy, Ailanthus altissima, native to China, is an excellent example of a non-native invasive, as is the South African Senecio inaequidens. And so far all seems clear. BUT things start to get interesting when you consider NATIVE invasives… in other words, species autochthonous to a particular geographical area/habitat, which for some reason start behaving in an invasive fashion.
As has been mentioned above, this may well be due to man’s intervention and in this case it is generally not a good thing. But sometimes there are natural (or semi-natural) causes, such as climate change, where a species already present in a certain habitat starts acting as an invasive when more favoured by the changing conditions than other “fussier” species. For example, in the Italian Apennines where I live, some grassland areas at an altitude of about 1900/2000m are being “invaded” by Trifolium pratense, previously present but relatively rare, but which is now taking precedence over the once dominant but less adaptable Trifolium thalii. Whether we like it or not, this is nature’s way of adapting and I personally don’t believe we have sufficient understanding of the dynamics underway to decide whether in the long run it is a “good” or a “bad” thing. Only time will tell.
Other examples of native invasives are the many species (such as Rubus spp.) which rapidly invade and colonise a cleared area in a forest caused, for instance, by a natural event such as an avalanche, to then gradually disappear again as part of the natural succession which would lead in time to reconstitution of a new area of forest. Here the invading being done is definitely a good thing and an essential step in a natural process.
So yes, I do believe when we talk about invasive species, we should specify in what sense we use the word, given that the concept may have very different connotations depending on the situation.
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I would call those plants pioneers, not invaders. Invaders crowd out existing plants.
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While they do cause damage, it is natural. However if they are causing damage due to human or invasive interactions I would use a separate term. If you could point out an example and give me an example term I would be glad to add it to my list :)
Edit: I read more comments and settled on the term “Aggressive Native”
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