Invasive versus Native Question

Discussions and news related to invasive and exotic species affecting our trees and forests.

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eliahd24
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Invasive versus Native Question

Post by eliahd24 » Fri May 13, 2011 8:03 pm

It's curious to me that the English Ivy on the Lombardy Poplar is confined to the base. Is this common of ivy infestation in Europe? I have read that it can be invasive in it's native range as well. It's probably the worst invasive plant in the temperate deciduous forests around Atlanta, and I've always wondered how it behaved in it's home land.

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KoutaR
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Re: Invasive versus Native Question

Post by KoutaR » Sat May 14, 2011 5:10 am

Ivy often grows up to high branches, too. I cannot say, why ivy on the poplar is confined to its base. One guess: because this is an open-grown tree. An analogue: the forest-grown trees become tall, the open-grown trees remain relatively low because they have no need to become tall. It may be that ivy in (open) forest in particular reaches high branches. The latter is more a mental image than any series of observations.

Kouta

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eliahd24
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Re: Invasive versus Native Question

Post by eliahd24 » Sat May 14, 2011 7:43 am

Kouta- do you have any knowledge of ivy being invasive and harmful in Europe?

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KoutaR
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Re: Invasive versus Native Question

Post by KoutaR » Sat May 14, 2011 2:55 pm

Ivy can surely be harmful to trees. If ivy is very dense and reaches high branches it can "suffocate" the supporting tree. I do not have any photos of such trees, but they can be found from the Internet. E.g.:

http://www.flickr.com/photos/werner_sch ... /lightbox/

The caption says it is a Prunus avium tree overgrown by ivy.

I have never considered ivy being invasive as it is native. In quite open forest densely overgrown trees can be sometimes seen, but I do not remember such trees in old-growth or otherwise dense forests. Perhaps there is not enough light for ivy becoming very dense (although it is shade-tolerant).

I must say I do not know enough about the ecology of ivy - it is not a tree ;) . - I am sure Jeroen knows more. I think he is in France now (and hopefully finds many record trees), but perhaps he comments this topic when he is at home again.

Kouta

Jeroen Philippona
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Re: Invasive versus Native Question

Post by Jeroen Philippona » Mon May 23, 2011 5:27 pm

About Ivy: while it is native in Europe here it cannot be considered as an invasive species. Indeed it can overgrow and suffocate the supporting trees, but this is often the case with older and week specimen of the smaller tree-species like the Prunus avium tree. Also it can make trees more vulnerable for windfall. Because of this it is often cut from the trees in urban as well as rural areas. Its optimal wild habitat is in riverine forests.
In an old, natural forest in SW Germany along the river Rhine research has been done in 1999 if the ivy is harmfull to the supporting trees. Here grow very large ivy plants, especially on old oaks (Quercus robur) as well as black poplar (Populus nigra) and ash (Fraxinus excelsior). The ivy is in medium about 18 m (60 ft) tall and has trunks up to 30 cm (1 ft) diameter and often over 50 years old. It was seen that very few healthy trees were completely overgrown by ivy, most trees had over 4 m (13 feet) free branches out of reach of the ivy, except for hawthorn (Crataegus monogyna and C. laevigata), wich were quite often overgrown. The largest and oldest ivy grew in old oaks (dbh up to 1,8 m - 6ft) wich were mostly very vital. The ivy is very important for breeding, feeding and shelter for many birdspecies as well as insects.

Jeroen

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James Parton
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Re: Invasive versus Native Question

Post by James Parton » Mon Jun 06, 2011 11:08 am

I have never considered ivy being invasive as it is native.
_Kouta
About Ivy: while it is native in Europe here it cannot be considered as an invasive species.
_Jeroen

Technically, they are right. In Europe the Ivy is native. It's habit reminds me of Poison Ivy here. It often has a very invasive habit of climbing and taking over trees, often en masse. Especially in human disturbed areas. It would be easy to think of Poison Ivy as an invasive but like the Ivy in Europe it technically is not. It is native here.

I think plants like English Ivy ( Europe ) and Poison Ivy ( US ) can exhibit invasive behavior. Even if they are native to an area. Here in the US it seems that human disturbance of natural forests gives the Poison Ivy a competitive edge. It often overgrows forests near populated areas and old homesteads, often mixed in with true invasives like Oriental Bittersweet and Multiflora Rose. I usually don't see this deep in say, the Great Smokies. Maybe Ivy in Europe is the same way. Does human activity give it an edge?
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Rand
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Re: Invasive versus Native Question

Post by Rand » Mon Jun 06, 2011 12:06 pm

James Parton wrote:
I have never considered ivy being invasive as it is native.
_Kouta

I think plants like English Ivy ( Europe ) and Poison Ivy ( US ) can exhibit invasive behavior. Even if they are native to an area. Here in the US it seems that human disturbance of natural forests gives the Poison Ivy a competitive edge. It often overgrows forests near populated areas and old homesteads, often mixed in with true invasives like Oriental Bittersweet and Multiflora Rose. I usually don't see this deep in say, the Great Smokies. Maybe Ivy in Europe is the same way. Does human activity give it an edge?
Interesting. In Ohio I see plenty of poison ivy, but have never seen it overgrow any trees it is climbing on (Native grapevines do it a lot though). I've seen a few vines ~ 2" diameter, but it usually doesn't get that big. It may because large vines are habitually cut because the plant is such a nuisance.

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eliahd24
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Re: Invasive versus Native Question

Post by eliahd24 » Mon Jun 06, 2011 5:41 pm

Natives can certainly be invasive in my opinion. Though ivy is native to Europe, I wonder if it can dominate forests, outcompete species, degrade biodiversity and cause trees to prematurely fall/die like it does here. I can't imagine it being "tame" for lack of a better word. Even in it's home. I have to second the notion that though PI can grow aggressively, I've never seen it take over an entire tree to the point of (possibly) killing the tree due to light exclusion or acting as a sail in the wind... again this is all personal observations and anecdotal at best. :)

~Eli

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edfrank
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Re: Invasive versus Native Question

Post by edfrank » Mon Jun 06, 2011 6:14 pm

ENTS

Whether a native species can be "invasive" or not depends on your definition of invasive. In a typical forest situation certain species are present in certain proportions. In some situations those population frequencies become dramatically altered. If a formerly minor species in a forest suddenly increases its population dramatically to the point that it "can dominate forests, out-compete species, degrade biodiversity and cause trees to prematurely fall/die" then this in my opinion should be considered to be a "native invasive species." Forest change over time through succession from one dominant tree species to another. The difference is the rate of change. Slow progressive change over decades and centuries is succession. Rapid change in dominant species in a year, or a few years to a couple of decades is an invasion. Change from a typical succession sequence to an entirely different sequence with different atypical dominant species is an invasion. The new dominant species driving or defining the change should be considered an invasive species.

Ed Frank
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KoutaR
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Re: Invasive versus Native Question

Post by KoutaR » Wed Jun 08, 2011 6:10 am

Ok, I now understand better the word "invasion". So, a native species may also be invasive if it, for example, with the help of man invades a habitat where it would not naturally occur. Maybe I should not meddle with definitions of English words, as I am not a native English speaker, but I am still not fully convinced of defining invasiveness by the rate of change. During initial succession cummunities change rapidly. For example, after fire or clearcutting intitial grass/herb dominated communities may change well within "a couple of decades" to tree/shrub dominated communitites. On the another hand, an invasion by an alien late successional tree species may take very long time. I do not know what would be a better definition. Maybe something like: a species which does not "belong to" the place by nature, althoug invasions can also happen from natural causes.

About the English ivy: "if human activity gives it an edge" I would say yes, in some habitats where it would not naturally occur. "if it can dominate forests" I would say not. "outcompete species" I would say not. "degrade biodiversity" I would say not. "cause trees to prematurely fall/die". I some cases yes. But as I wrote, I don't know enough about ivy to be sure.

Kouta

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