I think this is a good first guess at the best management practice. But it’s often not the best choice, because we humans have modified environments so that they cannot take their own course. Often, we have to actively manage an ecosystem in order to produce desirable results, like preventing extinction. Too often, “Let nature take its course” or some equivalent is used as an excuse for inaction when we could do, should do, something beneficial.
Basically, I agree with the definitions @leytonjfreid provides.
Goodness, it’s so difficult to resist the temptation to go into this further but…
… you’re quite right, it would be way off theme. Maybe I’ll open a new question . The best of days to you all .
I am conscious of the plea to stay on topic, but I have to reply to a couple of points.
I’m disappointed to hear I am doing a bad thing in removing the bracken. I reckon the centuries-old turf with its four species of orchid and 26 species of waxcap is worth keeping. It is a farmed landscape that has escaped the reseeding, herbicides etc. that have devastated farmland wildlife in UK and the way to keep the biodiversity is to carry on grazing it. There are other places in UK where Nature is being allowed to take its course, but I feel those schemes are most worthwhile where they start from a degraded landscape such as arable so that everything that happens is a plus. Knepp is the most famous example. There is plenty on the web about Knepp. Bracken already covers about 10% of Wales. I don’t feel it needs nature reserves to be deliberately turned over to it.
There was the question why is bracken a problem now and not previously. It has always been a problem but when a there was a farming family living here, there was constant effort against the bracken and it didn’t cover such a large area of the farm. Since they left in 2002 there has been a decade of haphazard grazing at Moelyci which has allowed bracken to expand so it is now a bigger fight to control it. Cattle may also be a factor. When the farmers lived on site, they had a mix of sheep and cattle. Cattle reputedly control bracken by their trampling. But cattle need more attention than sheep and now that there is no one here 24 hours a day, the grazing has become sheep only.
- Transformers - aliens that change the ecosystem dynamics (hydrology, nutrient cycling, fire regime)
- Encroachers (a horrible term, I would prefer Increasers) - indigenous species proliferating in a system, usually as a result of mismanagement (and then blamed as the problem, rather than the symptom).
- Frankenflora/fauna - hybrids (hybrid swarms) resulting from the introduction of an alien that interbreeds with an indigenous species and then spreads (occ. swallowing up the indigenous species).
I think it is essential to keep the alien-indigenous dichotomy separate from the invasive-non-invasive dichotomy. All four combinations are possible.
- Ruderals - invasive species in croplands, rather than ecosystems
- Commensals - species (alien or indigenous) favouring human-modified ecosystems.
- Extralimitals - species expanding their distribution ranges by natural means (in southern Africa, usually because of the increase in watering, gardens, fields, trees and other man-made or altered landscapes (in s Africa there hardly any species that can cross the summer-rainfall/Meditterranean (Cape) climate divide, but summer watering changes all that.)
All your terms must have the “region” specified. A plant species is not indigenous: it is indigenous to a place, and alien everywhere else. The more precise the specification of the area, the more valuable the concept. Scaling up the terms become less useful - all known Life is indigenous to Earth, and no alien life forms to Earth are currently known.
Lower Tokai: https://www.inaturalist.org/projects/tokai-park-restoration-study
Upper Tokai: https://www.inaturalist.org/projects/upper-tokai-park-restoration
staying on topic: lower Tokai has 239 recorded alien species (on 160 ha)
((Note #2 on the list is a Garden Route species - an alien from 400km away - it is #15 in the total species records, and totally dominates large areas! It does not appear to have replaced its sister species but has taken a slightly different niche: cooler fires (or areas with lower fuel loads) - like S. rigidus it is largely disappeared by 5 years and does not seem to affect subsequent community trajectories (it is not a seral succession, as the entire community regenerates after a fire, but there is a rapid turnover of maturation times up to 10-15 years after which the community becomes moribund, and the climax reseeders repress the resprouters). ))
Actually I find all my descriptions work very well as instead of specifying a specific place they specify where you are, which changes. Thank you for those good terms though, mind if I add them to my list up above?
Well, having read further discussion, all I can do is reiterate what I said before:
As far as i can tell, we seem to be defining “invasive” by whether or not human agency was involved.
Yes. Introduced + spreading and causing problems = invasive. Native and causing problems = aggressive if it’s commented on.
This is a really good intro into the technical literature on this topic. I found a downloadable version of the brief article on ResearchGate, if you have access there.
Not a plant but the common house fly (Musca domestica) is listed as a native species in the U.S. despite most likely originating in the old world. There could be a time component there as it has become naturalized in the US, and that may apply to some plants as well?
There are many plants that while they are native to a specific region in the US they are not native to the rest of the US, some aggressive natives have been found to be invasive in parts of the US they aren’t native to. I can think of Black locust which is considered invasive in some parts of the US. I think that is reasonable.
The issue I see is when aggressive natives are described as invasive in the region they are native to.
Whatever the reason for listing house flies as native in North America, it isn’t that they were naturalized a long time ago. Species that arrived in the New World after 1492 are introduced (always will be) though many are now naturalized there (spreading on their own). Species that are native to part of the Americas but have been introduced elsewhere in these continents are native where they were living before 1492 and introduced (perhaps naturalized) where they were introduced after 1492.
Yes, I know there can be practical difficulties with applying these standards, but that’s the idea. And a further complication is that Native Americans moved plants around within the Americas. Sigh. In biology, the phrase “but it’s actually more complicated than that!” is always applicable.
We just had a discussion about this at a Native Plant Society walk this weekend with several people saying natives can be invasive, too. So yes they are a “thing” that people hear and talk about. I like to call them aggressive natives and prefer to leave the term invasive to alien plants but there is no denying that some natives are classified as noxious weeds, for example. Usually this happens in the context of them interfering negatively with agriculture, e.g. parasitic plants attacking crops or poisonous plants in pastures threatening the well-being of livestock grazing there. I find it ironic that often these cases of “invasive natives” involve a native species negatively impacting alien species introduced for human benefits (crops, livestock).
This recent thread is still open and, if a continued discussion of “Native Invasives” is desired, would be a good place for that:
Yes, the terminology is in the end quite arbitrary and subjective. For instance, is an Ashe juniper seedling “invasive” or “aggressive” when it simply germinates and grows because some bird pooped the seed over an over-grazed pasture and no fire came through to knock it out? Could my beloved Ashe juniper be considered “passive-aggressive”? ;-)
A term I’ve seen for native plants in undesirable locations is “off-site”. Mostly referring to successional species growing in fire-suppressed natural communities when the objective is to return the fire regime.
I don’t see it in the full summary either. I wonder if adapting the following definition would suffice for your interests, Chuck:
Moved comments to keep threads organized.
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