It is a good area to deal with conservation activities. For your specific question, invasive is not only belongs to alien, but rather both endemic and exotic species can be invasive,  whenever influences the survival of  the other species and during this case can be considered as invasive. 

Regarding your question... Getachew Bantihun is correct.  Invasive is only applied to non-native plant species in which the introduced species significantly changes the composition an ecosystem's flora due to the introduction of the non-native plant.

Hi Nelson,

"Invasive" only refers to natural or human introduced non-native plants exhibiting wild growing and dominating tendencies. 

In east, south and west Africa, Digitaria abyssinica is not an invasive species. A wild growing native plant species despite exhibiting invasive tendencies,can't be termed "invasive".

An invasive species is a plant or animal that is not native to a specific location (an introduced species); and has a tendency to spread, which is believed to cause damage to the environment, human economy and/or human health.

One study pointed out widely divergent perceptions of the criteria for invasive species among researchers and concerns with the subjectivity of the term "invasive"

http://www.esf.edu/efb/parry/502_reading/colautti2004.pdf

Some of the alternate usages of the term are below:

The term as most often used applies to introduced species (also called "non-indigenous" or "non-native") that adversely affect thehabitats and bioregions they invade economically, environmentally, and/or ecologically. Such invasive species may be either plants or animals and may disrupt by dominating a region, wilderness areas, particular habitats, or wildland-urban interface land from loss of natural controls (such as predators or herbivores). This includes non-native invasive plant species labeled as exotic pest plants andinvasive exotics growing in native plant communities.

http://www.cal-ipc.org/ip/inventory/pdf/Inventory1999.pdf

It has been used in this sense by government organizations

(September 21, 2006). National Invasive Species Information Center - What is an Invasive Species?. United States Department of Agriculture: National Agriculture Library. Retrieved on September 1, 2007.

USA (1999). "Executive Order 13112 of February 3, 1999: Invasive Species". Federal Register 64 (25): 6183–6186.

as well as conservation groups such as the International Union for Conservation of Nature (IUCN) and the California Native Plant Society.

The European Union defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution area, and secondly, threaten biological diversity.

Communication From The Commission To The Council, The European Parliament, The European Economic And Social Committee And The Committee Of The Regions Towards An EU Strategy On InvasFpollive Species" (PDF). Retrieved 2011-05-17.

It is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds.

Exotic Pest Plant Council. p. 1. accessed 4/10/2010.

The kudzu vine (Pueraria lobata), Andean Pampas grass (Cortaderia jubata), and yellow starthistle(Centaurea solstitialis) are examples.

An alternate usage broadens the term to include indigenous or "native" species along with non-native species, that have colonized natural areas.

http://www.esf.edu/efb/parry/502_reading/colautti2004.pdf

Deer are an example, considered to be overpopulating their native zones and adjacent suburban gardens, by some in the Northeastern and Pacific Coast regions of the United States.[citation needed].

Sometimes the term is used to describe a non-native or introduced species that has become widespread.

http://www.esf.edu/efb/parry/502_reading/colautti2004.pdf

However, not every introduced species has adverse effects on the environment. A nonadverse example is the common goldfish (Carassius auratus), which is found throughout the United States, but rarely achieves high densities.

http://www.esf.edu/efb/parry/502_reading/colautti2004.pdf

Thanks alot every one for your answers. 

The terms are now clear thanks to your contribution.I think the papers mentioned by Julio Pavel especially "Pyšek P. et al. 2004" and "Prach & Wade, 1992" make the concepts really clear.

However, i feel as we focus more on alien invasive species we are forgetting about these really problematic expansive ( i am already using the term :)) species that can also be a threat in those native habitats. The expansion in range of such species is also significantly aided by human activities; a phenomenon similar to alien invasive species. In light of this, maybe focus should also be placed on large scale assessments of natives with invasive tendencies.

Nelson - problematic expansive are common to many countries and some are already reasonable well known. Climbers are an example from Sabah, Malaysia which become issue after logging  e.g. https://www.researchgate.net/profile/FE_Putz/publication/237510667_VINE_INFESTATION_OF_LARGE_REMNANT_TREES_IN_LOGGED_FOREST_IN_SABAH_MALAYSIA_BIOMECHANICAL_FACILITATION_IN_VINE_SUCCESSION/links/00463528966562f748000000.pdf

Article Vine infestation of large remnant trees in logged forest in ...

Previous answers provided clarity.

In addition: weeds in crop fields may, or may not, be aliens. However, the classification of a species as alien versus indigenous/native may depend on your historical time scale. Weeds do migrate with crops beyond the origin of both. A Germanic tribesman invading the Roman empire in western Europe may have seen Legousia in a cereal field as a native plant. Similarly, the current generation botanist may see tropical grass weeds in maize fields as indigenous, al least as indigenous as the maize at the same sites. For the previous generation, both maize and grass were aliens.

In southern Africa, we have these problematic native/indigenous "bush encroachers", that are as invasive, expansive and transforming as some alien bushes in the same environment. In other words, the new environment invites the invasion/expansion.To me the emphasis should be at the environments that lead to invasion/expansion of weeds, invasive or alien. Please see my earlier Q&A answer.

In the UK  Pearman (2004) has discussed "native thugs" whose impacts are possibly worse than alien invasives. For example, one such "thug" is bracken (Pteridium aquilinum), originally unshackled from its position in the habitat mosaic by deforestation. By origin it is component of open woodland habitats, but its range has broadened, and on open ground it displays competitive and invasive characteristics. Bracken is thus regarded as a pest and in the UK it encroaches into habitats of greater conservation and economic value, notably in the uplands where control is difficult.

Hi Nelson,

According to the standard definition, an invasive species is a plant/animal which is not native to that specific location. Invasive species are mostly alien species and have been introduced into that eco-region from other places and have a very high growth and reproductive ability. Thereby, such species have a high tendency to spread, often at the expense of native species; and may cause multi-fold damage to the environmental and socio-ecological system.

Often, even native species exhibit many 'characteristics' of invasive species, such as rapid growth and reproduction; and may often out-compete other native species, stunting their growth. In such a scenario, such native species are generally regarded as pest or weed species.

Best,

Anindita.

I think that native species can not be considered invasive.

The concept of invasive species implies that it is a non-native species. We need to separate between the aspects related to changes in the reproductive strategies in response to disruptions of ecosystems and invasion by alien species. These are completely different things.

I agree with Julian about bracken, and would add that 'invasive' species would include any which spread onto, or within, habitats where they are not wanted.  In the UK this term is commonly used for various native species including Molinia caerulea and Ulex europaea as well as bracken, and even scrub (often including Betula, Salix, Quercus spp) invading open grassland and heathland can be considered invasive.

To some extent, our concern about these species derives from the semi-natural nature of much of our vegetation.  We value open habitats, like lowland heathland or grassland, but these can only be maintained by management - otherwise they will be 'invaded' by scrub. In the uplands, grazing pressure has led to loss of woodland (and other palatable plants) over large areas - as a result, unpalatable species, which are not used by grazing animals, come to predominate.  These particularly include bracken (as Julian says above), as well as Molinia and gorse.

A note on the terminology - it's quite usual for words to be used differently in different circumstances/ cultures, and in Britain 'invasive' is commonly used for native as well as non-native species.  I have never heard the term 'expansive' used here and, whilst 'weedy' might be used, this is usually for ruderal species (e.g. Epilobium or Digitalis) rather than the invasive ones referred to above.  Non-native problems are distinguished as INNS (Invasive Non-Native Species), although this term has only been in common use for a few years - before that it was 'aliens'.  I'm not sure how much the term matters though - we seem to be agreed that native species can be problematic.

Strictly going by convention, it may not be possible to report a native species as an 'invasive'. Primarily because 'invasive species' is a bio-geographical idea, and there must be an indication that the species has indeed spread to newer areas (bio-geographically). Whether local increase in abundance can be considered an invasion? Or is it simply a case of population fluctuation in response to nutrients or such? Particularly in an agricultural landscape, you could refer to this species as a 'weed'.

There certainly are native plants (and animals) that are over-abundant in the sense that they have unwanted consequences: they reduce native biodiversity and/or reduce the economic value of the site and/or create a nuisance.  In general, they are over-abundant for some reason related to human management, such as over-grazing; fire suppression; predator extirpation; or simply (as Jeanette Hall pointed out above in the context of woody plant invasion of temperate humid grasslands and heaths) they interfere with our land management goals. 

I prefer not to call over-abundant natives 'invasive,' because the situations are so different.  Over-abundant natives are usually a symptom of bad land management, and the solution is to adjust land management.  For example, in central Texas, stop overgrazing and re-introduce fire to control over-abundant juniper; the cause of the problem is overgrazing and fire suppression, not juniper per se.  Better land management is often not a sufficient solution for non-native invasives and targeted removal, bio-control, etc are necessary. 

In my opinion, the distinction matters because (a) confusing the two leads to ignoring the underlying land management issues and (b) sometimes suggestions are made to introduce non-native biocontrol species to control over-abundant native species.  That's how Cactoblastis got to North America, where as it spreads it may become a real disaster.

There are two statutory definitions of “invasive species” that have been in place for some time (see following). That there is some confusion with the term is due to popular media, particularly arising from (a) false balance, (b) conflict-driven reporting, and (c) a pervasive ignorance/avoidance of science. A native species may exhibit “weedy” characteristics, but as noted in previous comments, this is a result of 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 IAS will be dominant 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.

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/

"Invasive" is a loaded term, and I agree with Suresh and Norma that it isn't appropriate when considering natives. Range extensions & contractions occur all of the time in natural, (relatively) undisturbed areas. That does not mean that native species can't become a problem in managed landscapes, and "weedy" seems to be a good term as Ruark suggests. Over-grazed or deforested areas provide many examples

As anthroprogenic climate change progresses, we certainly should expect major changes in species assemblages. Species responses will be highly idiosyncratic, and those best adapted to climate variability will likely spread most quickly.

Dear All

I think we have weedy example which have been invasive/ dominant in their native habitats e.g. Bromus spp.because of some driving forces like climate changes etc. Regarding to weeds we have both native weeds and invasive one. We just use terms to make life easy.

It seems the USA Presidency and logic are at loggerheads here. From a logic perspective, "alien invasive plants" would seem to imply its antonym native/indigenous invasive plants. Anyhow, never fight about words, but define unambiguously.

Now to the issue beyond definition. Pinus mugo is invasive within (Alps/Apennines) and outside its native territory (e.g. dunes in Germany; mountains Czech Republic). Similarly, Pteridium aquilinum (as above) plus Netherlands, Belgium,,Germany is invasive as an alien in Sri Lanka and other places.  Chromolaena odorata is also invasive in its native and alien territory. Mesquite is another case in point. 

In other words, evasiveness depends on land management history, as earlier answers indicate. Fighting the alien is taken the the symptom for the disease.  

Article Efficacy of Chromolaena odorata control in a South African c...

Article Invasion of an alien shrub across four land management regim...

Before reading this insightful discourse, I thought that there can be native plants that can manifest into being invasive, even in their native habitats. But now, I am impressed by the concept of 'expansive' native species. I think that the concept of 'expansive' species is less popular here in Nepal and I remember reading an IUCN Nepal report that mentioned that Rubus ellipticus (Golden Himalayan Raspberry) and Persicaria perfoliata (Polygonum perfoliatum) are some native species showing invasive character in Nepal.

Thank you all for the interestingly insightful opinions.

There are invasive alien species (IAS) and non-invasive alien species. Many cultivated crops are found in the latter category. 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 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.

Yes, indigenous plants can become invasive if they enter unfamiliar ecosystems both within their native country or in another country. This is particularly disastrous for island ecosystems :-)

I think that land use is what determine the usefulness of the term invader and it does not matter what is the origin of the plant, it could be a native plant that bother us and we are going to think how to get rid of it.

@ Nelson Mujuni

Please have a look at this useful RG link.

Article Invasive species can also be native

Yes, some of the the native plants may developed aggressive characters of an invasive species due to change in environmental factors and other controlling factors for the population of the species. However, Wijesundara (2017) suggested the use of term expansive (Pyšek and Richardson, 2008) or super-dominant species for such species instead of using the term invasive plants.

I agree with the points highlighted by Sandhyarani Khomdram.

Yes.

Of course yes, it can!

Take into account that "we" usually draw the alien species list on a national or regional base thus working with artificial boundaries set by humans. Anyway, the distribution of wild organisms has nothing to do with those artificial boundaries such as state or region limits. In this light, even in a region, if a native species broadens its distribution exploiting human means (roads, transportations, plantations, etc.) towards areas where it had never been reported before, it cannot be considered a native species in the area where it is a newcomer. It has been used the term "alien in" to pinpoint these species which is somehow different from the term "expanding species".

The paper of Alpert et al (2010) has clear point of the native invasion plant.

Alpert, P., Bone, E., Holzapfel, C. 2010. Invasiveness, invasibility and the role of environmental stress in the spread of non-native plants. Perspectives in Plant Ecology, Evolution and Systematics. 3/1:52-66.

Invasiveness is often associated with exotic species. This is a misconception; invasiveness is an expression of nuisance experienced by people. In these forests in the state of Illinois, all tree species that people think are a nuisance, native or non-native, are controlled. Species to be controlled include black cherry and sugar maple, which are among the most common tree species in Illinois. This is the honest way to look at invasive species.

https://www.lcfpd.org/conservation/woody-invasive-species-clearing-project/

I think so. For some of us who study macroalgal proliferations/blooms, we often describe the opportunistic habits of certain native seaweeds as "invasive behavior", rather than emphasizing ostensible origins that we often don't have sufficient information about. In the marine environment, it is a lot more difficult to determine what is native and what is introduced, as species sometimes migrate from or to deeper areas without human intervention, patch dynamics are (perhaps obviously) far more fluid than in terrestrial systems, and we have only recently developed technologies to spend any length of time below a few feet of water.

It might make sense to some for us to develop new phrasing for native species that display invasive behavior, but from a policy standpoint, I think it better that we reconsider what it is to be invasive. Existing government policy and management strategies about nuisance species are often limited due to the prevailing conception of invader-as-alien: when they are presented with a native species that suddenly proliferates to nuisance levels, bureaucratic paralysis can ensue as many mitigation measures apply only to alien species.

To my mind, it would be more useful to extend the concept of invasiveness to native species so managers can act when needed, rather than develop new terminology that may takes years (at best) to get the attention of people who write policy.

It is obvious that one of the main conditions for a species to be listed as an invasive species is to leave the original habitat or the primary natural habitat. Of course, if it shows aggressive and threatening behavior in the new and introduced habitat.

But it should be noted that if a native species spreads threateningly and aggressively in its own habitat and distribution area, in my opinion, it cannot be listed in the list of invasive species. And such a phenomenon should only be called aggressive prosperity caused by population explosion. For such cases, many examples can be cited that have also been experienced in Iran. including the invasion of locusts and other insects, plankton bloom in the coastal-marine areas, excessive density of weedy plants in agricultural fields, etc. . . .

In conclusion, it should be mentioned that in the critical conditions of climate change and its consequences, the change in behavior in plants and especially in invertebrates will be more severe and it is predictable.