Hi Michael,

This is an age old question and one that fosters considerable debate! There are some people who think that after a certain amount of time, naturalised species should be considered native, but obviously not everyone holds this viewpoint to be correct. Some papers that might help you with the terminology and reasoning are:

http://npj.uwpress.org/content/2/1/5.refs?related-urls=yes&legid=wpnpj;2/1/5

And...

And...

and lastly....

I hope these are of help!

Let me contribute a story about two conifers: Douglas fir from California and Larch from the Alps. Both were imported into the Netherlands a century or so ago. Today, both trees are reproducing profusely by seed and transform poor scots pine forests into a much appreciated timber provider. Without these transformers the sites would arguably develop into broad-leaved deciduous forests (beech or oak). Fir and larch are introductions, aliens, invasives and transformers. A weed for some, a commercial blessing for others. Established, no doubt. Naturalized, you tell me.

I believe if we can historically document when a species was introduced, then it will never be "native" even though it may have become intricitally naturalized. It's all a question of definition, whateveer one you chose will dictate the answer.

Yes, this is a difficult question to answer. The problem is to identify a cut-off point (date) when we can define that an established species has been continuously present to warrant classification as 'native'. Indeed, the term 'native' itself is misleading in many cases, as species complements continuously evolve over time - the term 'native' suggests a stable system, which we know is almost never the case in ecology.

In reference to Australia, it is quite likely that the first human colonisers (the Aborigines) also introduced flora to the landscape - these species are now probably considered 'native', but their appearance was human-mediated (though I am not aware of any studies that examine this).

In Ireland, for animals, officially we use the year 1500 as a cut-off point (with fauna appearing after this date being considered non-native), although there is absolutely no scientific justification for this.

Ultimately, the criteria for defining native and non-native species are region- and taxon-specific and somewhat arbitrary.

Never. An exotic species always will be, no matter if it was introduced or translocated, or is already naturalized. We can observe Mediterranean landscapes, full of introduced plants. But these introductions take centuries, suppose a millennium, however the plant evolutionary process takes millions of years.

The introduction time is still nothing compared to the process of natural selection of the OTU. Possibly humanity not remember when was introduced a specific species, but that does not make it native, in the context of ecology and evolution.

There is a lesson we must learn nature. Occurred in Mexico (Cancun) a major hurricane in 1985. Devastated all ... STOP. Not everything. Remained native mangroves. Then what was it that was destroyed? only what man introduced as palm trees, ornamental plants or plants to produce coconut, banana, etc.. Never mind that these plants were introduced in Cancun for centuries, were not from the area and the hurricane uprooted as if it were nothing. And just what remained native ones. Vegetation that evolved there and therefore had millions of years supporting those catastrophic hurricanes.

This is a very interesting question! My gut reaction is to agree with Pedro, that any species introduced will never be native to the area.

But there are many ways to look at this question. The first thing is that we have the terminology, so we should use it. Endemic. Indigenous. Exotic. Introduced. Naturalized. Invasive. Native. Etc. There are many ways to describe a plants status in a place, so if we are a little more precise with our terms there is no need for confusion about how a plant got there, what it is doing there, and how accepted it is there.

Now I can think of one example that throws a wrench in my agreement with Pedro. And that is the very rare case where a species is introduced to an area, and goes extinct in its homeland. Now that plant can said to be endemic to its introduced home. And endemic to me is the highest "status" a plant can have. Although I would still greatly hesitate to call the plant native to its introduced home, it clearly would have to have some special status.

I also think it is important to remember just how altered humanity has made this world. It is not the world it was 10,000 years ago biologically. We have altered virtually every ecosystem on the planet to the point where I would highly doubt that there is a corner of the earth left where humans have not introduced plants, animals, or at the very least non-native species of bacteria. So if the ecosystems themselves are no longer the "native" ecosystems, perhaps introduced plants do have a place in these new novel systems and can become native, against my own interpretation and value system regarding them.

Noa, you're right, there is no part of the planet without introduced species. And so now than before, talking about studies of landscape ecology, with an ecosystem approach and a holistic approach. But the landscapes are managed, not ecosystems.

The comment you make about what happens when a species disappears from its natural habitat but survives in the place where it has been introduced, it has been debated for at least 50 years that I can remember. And there are two important things to consider: 1) if the introduced species becomes a pest, deteriorates the natural ecological functioning and disturbs the whole balance of the ecosystem, so it must be necessarily controlled. the question is, how far should you monitor? to eradicate it altogether? or to levels as low as a species that persist are minimal environmental impact? this has happened to a species of duck that was introduced in the River Thames in London and became a pest, but in its natural habitat is endangered in many places and has totally disappeared.

2) develop a breeding program then repopulate the wild. This case also raises the question of when and to want to replant still in its habitat, the conditions were similar to those which had already changed or evolved when, if they have changed, a new ecological balance in which the plant has no place. and then becomes an introduced species. That happened with the beavers in Spain, a few centuries were reintroduced after extinct and are now worse than a plague in their natural habitat was 300 years!!

Here is a very clear example of how we have altered the ecological balance too of an ecosystemby configuring landscapes to be useful both to humanity and to the most biological species with which we share the planet. We are a highly destructive and self-destructive species.

Amen Pedro. I completely agree that we are a detriment to the natural world and to ourselves. Although the world will be fine without us. And I really do agree with you on the definitions of native and exotic, but just to play devils advocate and push on your (or anyoneʻs) thoughts a little...

I agree and see the login in your earlier point that plant evolution takes millions of years, and so even an introduction of up to possibly 40,000 years ago in the case of the Americas in insignificant in evolutionary terms. But by that same logic a plant in its own habitat evolves not only to the habitat, but to the composition of species that makes up its habitat. If through human altercations say some of those species go extinct, is that plant now no longer native it its natural range because the habitat with which it evolved is changed? I assume that we will still consider this plant a native, and so why can it never be native to another place, even if that place does have similar biogeochemistry, habitat structure, etc.

There is also the concept of gene expression altering based on environment. I have seen short lived species of introduced plants that express themselves completely differently than they do in their native range after only a few dozen decades. To the point where if we did not know that they were introduced and have genetics to prove it, any botanists 200 years ago would have assumed that they were different species. leaf form, flower form, growth pattern all remarkably different.

Then we have the case of closely related species that can interbreed, so that now there is no native and no introduced species anymore, but only a hybrid species. Is that native or introduced?

Finally, and to me the ultimate irony, is when we have an invasive culture come into an area, and define the "native" biota as a biota that was really introduced by the people before them. I agree that native is the most ambiguous of all the terminologies, because it can become confused with native peoples and the plants that they brought. So when we talk about endemic, indigenous, exotic, I donʻt think there is any room for social interpretation. But can a plant become native is a different question all together (although this is just semantics now).

Very insightful discussion. I have struggled with the numerous terminologies used for describing plant species in the field, Biological invasion. There has been attempt to harmonize these definitions including in the book -Fifty Years of Invasion Ecology: The Legacy of Charles Elton- edited by Richardson but I will say more is still needed. Using subjective terms such as ‘weed’ to define plants we may not have use for at this time, may not in my view help the protection of certain species. Other terminologies like “sleeper weed” for example is also used, eg in Australia, to refer to plants that become established in a region but have not spread widely. We need well defined and consolidated terminologies

Since you mention highly transformed landscapes for human usage, one should consider the example of the development of heathlands in Scotland for peat production. Conservation groups want to bring back the trees that once grew there. But heathlands have become an integral part of the Scottish culture.

I really enjoyed Noa's comments about what humans have done to the land surface of this planet and how murky the term "native species" has become. Originally from Europe, I understand how inappropriate the term "potential vegetation" sounds to European ears interested in vegetation dynamics. In the US where I live, people still think potential vegetation exists and that some ecosystems need to be "restored" to their pre-European settlement state, ignoring the fact that native Americans had already transformed much the landcover to optimize their hunting.

Changes in climate have always forced plants to migrate. At what point do climate refugees become species to conserve rather than eradicate as invasives? Much money is spent to fight invasives but I have heard several colleagues saying you may win a battle but the war has been lost long ago. "Resistance is futile, you have been assimilated". But what manager has the guts to imagine and manage for a future where the land is dominated by new combinations of invasives, those we know or expect and those we do not yet know.

Enjoying the discussion.

Just to toss another term out there to consider - archeonative. My understanding of the term is an introduced species that has been naturalized for so long that it is more or less could be considered a native. In our discussions there were no exacting limits, but "well over 1000 years" was tossed around. I feel like no plant community can ever truly be stable forever. Whether it be humans or animals that move plants around, plants will be moved around.

I also think we need to be aware about tightly we define any category. An interesting example would be worms in the Midwestern United States. So no worms survived the Wisconsin Glaciation, but after it retreated worms started to move back into the area. Would they be non-natives? To me, no. We also had a healthy population of big juicy European night crawlers (great for fishing), which are clearly non-natives. A vermologist (really, that is how he at least defined himself, but he was more into leaches if I recall) told me some people didn't considered any worms native to the area despite their being there due to natural migration. Just a random example of what is too tight a definition of native in my opinion.

that sounds good!

indeed, no climax in an ecosystem that will last forever. When we have a stable community is when we say that there is a climate climax but that does not mean it keep changing the ecosystem. Only that the change in energy balance is slower and we do not perceive it shortly. But mankind has interfered so much in nature that we could well do what Jessica says, speaking of archeonativas for species that originated in an environment that naturally have scattered and distributed across the planet. And we can named like Neonatives those species that humanity has deliberately introduced, that were accidentally introduced or those species that by natural dispersal they can colonize new environments degraded by human activities but in recent times, for example, 100,000 years from the date .....

Oh, how I wish were were all in one room for this!! Dominique, I like your Borg reference.

We had this discussion at work quite a few times. Working in degraded wetlands in urban areas while trying to determine their quality will do that. Perhaps my opinion is a bit jaded but I think to some extent we need to accept the new normal for some areas. Not to say we should not protect the vestiges of 'presettlement' communities, but we need to find a happy medium otherwise you are trying to achieve the impossible.

Change is what evolution is all about, isn't it? Except that in this case humans moving around plants as much as we do hastens the evolution of community.

And now we are moving slightly off topic....sorry!

Exotic plant species unlike human immigrants cannot be considered as native or indigenous plants. They can however, be naturalized.

in reference to the Scottish peat bogs. if we left the peaty areas to recolonise from what is now and historicaly managed heathland. What would we see appear as pioneer plants? would it be aspens, birches as would be expected or would it be sycamore and as it is a colonising and pioneer plant in its own right, but is it a native species? Scotland has already experienced the effects of climate change with many invertebrate species being found on a regular basis in what was once a cooler climate and with this the elms in Perthshire finally succumbing to Dutch elm disease. So surely many plants that were once considered invasive such as sycamore will fill a niche and be considered naturalised.

And oops aswell moved slightly off topic

is true that if ecosystems altered their free ecological conditions are left, would be formed, perhaps, different community associations formerly occurred at first a different successional stages, but the community, once mature, reach resemblance to the prior to our destruction, or something similar climatically, as they say, would lead to a climatic climax of the time as he lives.

But on the other hand, we must remember that by definition no empty niche, so that no species can fill any niche. When a species naturalized form their own niche and realized niche of other species with which it competes changes.

We cannot go for a referendum or for nationalizing a plant that is native to another place.There is no declaration of "plant rights" as there is for humans. Therefore, as long as it is recognized by scientific documents that a plant species/taxon has been introduced from another place by human or natural processes, it shall remain non-indigenous. Why do we want to call it native when we know for sure that it was not there before, anyway?

Good question indeed. The Botanical Society of the British Isles (and other botanical societies in Europe) distinguishes between 'archaeophytes' and 'neophytes', the former comprising alien species that arrived after the start of the Neolithic period but before 1500 AD and the latter comprising species arriving after 1500 AD. However, it is not always easy to classify a species. 

http://www.archive.bsbi.org.uk/Wats26p271.pdf

http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8339.2004.00284.x/abstract

The following paragraph from the paper in Watsonia made me smile :

"We are pleased that the conservation agencies

have decided (Cheffings & Farrell 2005) that

all the archaeophytes and all the species that

we categorised as 'native or alien' are to be

treated as “honorary” natives for conservation

purposes."

(see for extensive discussion paragraph 2.1 here:

http://jncc.defra.gov.uk/pdf/pub05_speciesstatusvpredlist3_web.pdf)

I doubt any botanist is quite 'brave' enough to suggest that in 50 years time, a particular species that can be traced back to have arrived in 1550 should be classified as an archaeophyte: once a neophyte, always a neophyte!

Native is a relative term and the term is referred to the availability of data. In my opinion if a plant naturalizes itself to the alien ecological condition and thrives well for generations together then it should not be treated as a foreign species. There is no harm in including them in native flora. 

Indigenous is not a relative term. A non-indigenous plant may become established after its introduction and may persist for decades to centuries without evidence of harm. Then there is a change in environmental factors that favor the species and its invasive nature becomes apparent. This is often a surprise to people who thought the plant was "native." The longest such "lag time" that I am aware of was 400 years.

Neither is "invasive" a relative term. There are two statutory definitions of “invasive species” that have been in place for some time (see following). While a native species may exhibit “weedy” characteristics, this is most often a result of direct or indirect human land management activities. Climate change will exacerbate the problems of both invasive alien species and native weedy species in the short term; however, research indicates that invasive species will dominate in the long term.

Invasive species are plants, animals, or pathogens that are non-native (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause harm. [emphasis added]

As per [USA] Presidential Executive Order 13112 an “invasive species” is defined as a species that is: 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions. https://www.invasivespeciesinfo.gov/whatis.shtml

An invasive alien species (IAS) is a species that is established outside of its natural past or present distribution, whose introduction and/or spread threaten biological diversity.

An alien species is a species introduced by humans – either intentionally or accidentally – outside of its natural past or present distribution; however, not all alien species have negative impacts, and it is estimated that between 5% and 20% of all alien species become problematic. It is these species that are termed ‘invasive alien species’ (IAS). Convention on Biological Diversity https://www.iucn.org/theme/species/our-work/invasive-species

Invasive alien species are plants, animals, pathogens and other organisms that are non-native to an ecosystem, and which may cause economic or environmental harm or adversely affect human health. In particular, they impact adversely upon biodiversity, including decline or elimination of native species – through competition, predation, or transmission of pathogens – and the disruption of local ecosystems and ecosystem functions. https://www.cbd.int/idb/2009/about/what/

There are invasive alien species and non-invasive alien species. Many cultivated crops are found in the latter category; plants that are unlikely to survive 'in the wild'. Other "non-invasive" alien species could better be termed "not-yet-invasive" due to unknown factors such as propagule pressure, lag time, climate change, etc. Precise terminology matters beyond just science. The ISSG (IUCN) blog [www.issg.org/about_is.htm] has some good articles about how muddled language can distract people from the fact that IAS are a serious threat to biodiversity.

From an ecosystems perspective, introduced species can be integrated into their new environments over evolutionary time scales, usually measured in many generations. This is the time it takes for both the invasive species and the host community to coevolve in in response to one another to generate a new equilibrium. For many macroscopic plant and animal species that time frame can be hundreds to thousands of years or more, varying widely depending on variables like generation times, population sizes, climate, and species richness of host assemblages.