Ivy IS a real problem

[Dan Maynard]

2 hours ago, sime42 said:

I think I read about it in this book;-
 

The Walker's Guide to Outdoor Clues and Signs : Tristan Gooley (author), : 9781444780109 : Blackwell's

BLACKWELLS.CO.UK

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Readers may be familiar with such things as natural weather forecasting, basic tracking and natural navigation, but this...

 

That's it, my Mrs got it for Christmas. I didn't find myself absolutely agreeing with everything he says about trees so not sure it's a completely reliable source but it is an interesting read.

Edited April 26, 2022 by Dan Maynard

[sime42]

That's it, my Mrs got it for Christmas. I didn't find myself absolutely agreeing with everything he says about trees so not sure it's a completely reliable source but it is an interesting read.

I've only dipped into it a few times really; I don't have a copy but my mum does so I've thumbed through when visiting her. The thing about ivy stuck in my mind for some reason. I noticed that it had somewhat mixed reviews online.

[sime42]

I wonder if it "knows" when a tree is dead. It would be to the plant's advantage to single out a dead host tree if it can, so it isn't wasting energy climbing something it will have to compete with for light. Which goes back to my earlier mention of elder. You rarely see a living elder that's been colonised by ivy, but equally you rarely see a dead one that isn't engulfed. 

Is it just pot luck that the ivy picks a dead one and then capitalises? Or is it in some way attracted to dead ones? If it were just pot luck, you'd expect to see more partially colonised elders. 

It's known that most climbing plants are stimulated by a chemical trigger to climb when they contact a likely host. Could that chemical trigger also identify whether the host is alive or dead?

 

Interesting trees Elder. They're almost unique in being by far the most common host, of a very small group of trees to do so, Jelly Ear, (or less PC; Jew's Ear!) Fungus. Good to eat if you're feeling adventurous, a nice crunchy texture.

 

 

[Guest Gimlet]

Massive amount of folklore around elder as well. It is an oddity and a fascinating tree. A bloody nuisance in a hedge, but a fascinating nuisance. 

[Guest Gimlet]

16 hours ago, Dan Maynard said:

Plants are sensitive to chemical triggers, I guess alive or dead should be really easy to tell from water content or how much water vapour is around the plant so yes absolutely plausible it responds to the host being dead.

Makes sense. It which case, if ivy can detect a dead tree from chemical signals (or lack of them), maybe it can detect a dying one as well. If transpiration water vapour levels and oxygen emissions drop below a certain point, can ivy detect irreversible demise? It would be greatly in its favour if it can. After all a tree that is alive when the ivy commences its climb but is likely to be dead by the time it reaches the crown is the perfect host, better than a tree that's already dead and starting to decay as it offers an extended window of opportunity in which the ivy can reach the light, photosynthesise, set seed and reproduce (the whole object of the exercise) before the host collapses and the process has to begin again.

 

It would explain why people deduce mistakenly that ivy kills trees. We see a veteran tree that is alive and in leaf. Ivy finds the tree and begins to climb. By the time it has reached the crown and engulfed the tree, the tree dies. The human observer assumes not unreasonably that the ivy has killed the tree, when it may be that the tree was doomed already and the ivy has detected that imminent mortality and specifically selected it as a host for that very reason. 

In which case, ivy is a benefit to the forest, not a threat since it extends the life-supporting span of a tree rather than reducing it. 

Edited April 27, 2022 by Gimlet

[Dan Maynard]

1 hour ago, Gimlet said:

Makes sense. It which case, if ivy can detect a dead tree from chemical signals (or lack of them), maybe it can detect a dying one as well. If transpiration water vapour levels and oxygen emissions drop below a certain point, can ivy detect irreversible demise? It would be greatly in its favour if it can. After all a tree that is alive when the ivy commences its climb but is likely to be dead by the time it reaches the crown is the perfect host, better than a tree that's already dead and starting to decay as it offers an extended window of opportunity in which the ivy can reach the light, photosynthesise, set seed and reproduce (the whole object of the exercise) before the host collapses and the process has to begin again.

 

It would explain why people deduce mistakenly that ivy kills trees. We see a veteran tree that is alive and in leaf. Ivy finds the tree and begins to climb. By the time it has reached the crown and engulfed the tree, the tree dies. The human observer assumes not unreasonably that the ivy has killed the tree, when it may be that the tree was doomed already and the ivy has detected that imminent mortality and specifically selected it as a host for that very reason. 

In which case, ivy is a benefit to the forest, not a threat since it extends the life-supporting span of a tree rather than reducing it. 

Elder is quite a good one to pick as well, as it has a naturally short lifespan - be a rubbish strategy if you always picked oaks and then waited for them to die.

[Doug Tait]

This topic has become a lot more thought provoking recently, interesting opinions.

[Old Mill Tree Care]

Anyway...
For those genuinely interested:
https://www.trees.org.uk/Trees.org.uk/files/f0/f0e3a76b-926f-4cde-b703-417563ae93df.pdf
 
In summary, the greatest threat Ivy poses to mature trees is from windbreak to weakened veterans that are already in decline. It poses little threat to younger, healthy trees. It isn't parasitic (ie. it takes nothing directly from the tree itself) and it doesn't out-compete with large trees for nutrients since those trees will have a more extensive root network than the Ivy. But it can rob hedgerows of nutrients and cause them to become impoverished because their root systems will not be as large as those of similar trees which have not had their growth suppressed by clipping. In my view, it will out compete hedgerows for light as well, if their owners are in the habit of clipping/flailing new growth into neat shapes all the time. The Ivy will fill out the gaps and the tree's leaves barely get to see the sun and the tree will age and sicken.  

Ivy quite simply covers trees and hedges then the tree or hedge dies inside a shroud of Ivy.

[Mick Dempsey]

53 minutes ago, Old Mill Tree Care said:

Ivy quite simply covers trees and hedges then the tree or hedge dies inside a shroud of Ivy.

Simply not true.

[Old Mill Tree Care]

Simply not true.

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