I would disagree. I don’t think we should be conflating “weedy” with “invasive”.
I assume you mean sweet potatoes and not true yams (which Polynesians brought from SE Asia but AFAIK did not exchange with South America). That part at least is not really controversial; there was a paper a couple of years ago claiming that sweet potatoes are actually native to the Pacific islands but TBQH it’s kind of nonsensical.
What if there’s no further vegetation dynamics, if the pioneers never recede?
I really don’t like the idea of labeling native plants as invasive. It’ll just further encourage people to go ‘look see that’s invasive!’ and then turn around and pull up all their goldenrod, thistle, milkweed, and fleabane volunteers because they think they look weedy.
Who am I kidding, they’re going to do that anyway - but it still doesn’t mean they aren’t extremely important plants in the ecosystem.
Aggresive native is fine, I guess, but I’d still rather see lots of Virginia Creeper than English Ivy, Kudzu, or non-native bindweeds.
(at least in my area, of course this changes area to area)
Picture an uninhabited oceanic island. A drifting raft of vegetation washes ashore, along with seeds, a few lizards, and maybe some dormant snails sealed by mucus into their shells. If they were able to survive in the new habitat, isn’t it likely that in the absence of predators and competitors, these would go through an “invasive” stage before dverging into island endemics? They also fit the criterion of having come from somewhere else. The difference is, humans were not involved.
Re: Leptospermum laevigatum, I find myself wondering: Would a natural range expansion, facilitated by some natural environmental change or the happenstance of dispersal, look any different?
As far as i can tell, we seem to be defining “invasive” by whether or not human agency was involved.
Jason, this would seem to be a straightforward example of “colonization” (as you say, in a scenario “without competitors”). As others have pointed out, I focus on the aspect that “invasive” species are displacing other plant species and typically altering natural processes and pathways in the local area. That’s why in Texas, some of us consider the (native) Ashe Juniper invasive in certain pasturelands, and (non-native) Chinese Tallow to be invasive in coastal prairie ecosystems. In both cases, human-mediated ecological alterations allowed these species to take hold and spread and their abundance has substantially altered the whole dynamic of the invaded terrain.
I have never studied that in detail.
But for example Tokai was fynbos.
Then pine plantation. Felled.
That fynbos is steadily returning.
A lot from the seedbank, some from surrounding pockets or birds or baboons.
And some deliberately restoration planted.
Blocks deliberately burned to encourage the good stuff.
https://www.inaturalist.org/observations/111452102
https://www.inaturalist.org/observations?place_id=154749
Actually, that’s exactly what these invaders do, they crowd out any pre-existing vegetation that might have survived the avalanche (or other “clearing” event). But I suppose, everything comes down to the connotations we attribute to a word: pioneer = good, invader = bad, but in nature it’s not always, perhaps never, that simple. Maybe these species would be best described as “temporary pioneer invasives” 
.
What I ‘see’ when I read that … is a sea of Australian wattle saplings … once head and shoulder high … nightmare. That feels less pioneer, than bluntly invasive.
See what you mean 
. At the end of the day, it all comes down to language, how we use it and how nature often refuses to remain within the boundaries of our definitions.
IIRC pioneers = early (fast) colonizers, but usually poor competitors (hence species usually relaying/replacing these pioneers, years or decades later).
Invaders OTOH could be pioneers or not (arriving on top of already established communities), and are necessarily good competitors (at least at a local scale to existing species), enough to alter significantly and durably (century- to millennia-scale) the “usual”, expected pathways.
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On the topic of invasive native species, some IUCN booklet for the French Overseas territories (pdf) gives two examples (p.39, “Le cas de la gestion des espèces indigènes envahissantes” = the case of managing invasive native species) in Mayotte and New Caledonia.
Sorry, SQFP. What is “IIRC”?
IIRC If I remember correctly
OTOH On the other hand
sorry for the abbrevs
I think that the underlying problem is that often researchers attribute species to aliens or natives on a regional or country basis. Regions here in Europe are generally smaller than the average American state but, at least here in Italy, there are examples of plants that can have both native and introduced populations in the same region.
Anyway, species that enlarge their distribution where they are native is somehow subtly a different case. This often has to do with natural phenomena or also to habitat homogeneization which is usually caused by human activities. But there are also examples of species that in the same state/region move exploiting the trasportation network (e.g. Crepis bursifolia from southern Italy has spread almost to the whole country in less than one century and now has arrived to Portugal).
I agree, invasiveness is just the ability to spread, and there are species that have invaded extremely vast areas where, at least apparently, they can coexist with natives without exerting any negative impacts. At the same time, there are emerging invasive species that have never been evaluated for their possible impacts because they were never been seen as invasive before. Moreover, there are species that are both invasive and ecologically impacting in well-defined climate but are not able to do the same elasewhere.
The species which is always near the front of my mind is bracken Pteridium aquilinum, because I spend about 25 hours per week cutting and pulling it. It invades long-established stable plant communities by its rhizomes growing below the surface and putting up large robust fronds. It doesn’t require a disturbance event, though it is quite able to take advantage of one, such as fire. It is native here (UK) but there is a slight twist. There are three subspecies. Two occupy small areas of Scotland and it has been suggested that the third one which is invasive is a hybrid between the other two. I don’t know whether there is any suggestion of human involvement in bringing the subspecies together. Nor do I know whether this applies in continental Europe. It would be a coincidence if the same two subspecies occur in Europe and have undergone the same hybridisation.
And no, I don’t have a separate term for it. I call it an invasive.
Interesting, if it is invasive then how has the environment dealt with it before? I’d be more inclined to think it’s just an aggressive species. It acts like an invasive but since it’s native it’s reforming the environment in a more natural way. Invasives are invading and destroying, the Pteridium is just reshaping the environment completely naturally. On a nature reserve for example: removing an invasive would be good, removing the bracken would be bad because it’s fulfilling its natural role of reshaping the environment. Any species that go endangered due to this would not be our responsibility to save because it’s just nature being nature, if we had a part in them becoming endangered however then we would have responsibility
There’s little “natural” (if this kind of vocabulary makes sense; invasions are a fact of life on earth) in native bracken ferns invading varied habitats following loss of grazing-harvesting activities (rural depopulation, disruption of wild and domestic grazers…). That’s some profound change in ecological diversity and function happening in a snap (‘good or bad’, and to whom, is another interesting question).
In this specific case, I’d say the “unnatural” part was the previous man-derived/maintained habitats, while the “invasion” by bracken is a natural phase in the reconstitution of more natural habitats after human activities have ceased. Of course, these new habitats may well be different from the original, given the inevitable differences in the conditions (soil, climate etc.), but in most cases, I’m a great believer in leaving nature to sort these things out by itself, in its own time.
I’m a great believer in having as livable as possible - if regularly human-tended - habitats, rather than “natural” deserts in their stead. Keep those little biogeochemical cycles and evolutionary pathways movin’ :)
And I suppose the “natural” orchids and slugs, threatened by 2 decades of man-made abandonment of land causing man-made ecological upheaval, after 8 millennia of man-made management of land, would share this viewpoint.
That loss of herbivores, due to urbanisation, triggered the Gantouw project.
Using a small herd of eland to open up space for remnants of previous vegetation. Particularly the little ones (annuals, orchids, bulbs), which would emerge after fire - but that isn’t an easy option on the urban edge.
The case you describe is certainly complicated from the standpoint of the sequence of human-induced landscape changes. However, the perspective evinced by the above quote seems to set aside or relinquish what might be considered the ethical/moral obligations our species might bear in undoing ecosystem changes we have wrought. In saying that, I really don’t want to divert the discussion in that direction; I’d like to stay on track with the definitional issue I raised in the OP.