When does Ivy become dangerous or harmful up a tree

Question

I am a part of a volunteer group in local ancient woodland and we have very many trees there which I completely covered in Ivy, we can also from time to time expect high winds of up to 40 Mph gusts. This is in England so we have a variety of different kinds of trees and a reasonably diverse natural habitat which is left to mostly grow wild apart from really the work that we do.

I am aware of the fact that other woodland nearby does have any Ivy on its trees because the park keepers are there and paid to remove it since if it grows on the tree too much it becomes quite heavy and if said gusts come the tree can be more likely to be knocked over by it.

Generally I understand that it doesn't damage the tree much more than that though because the branches just push further outwards to get to the sunlight and the Ivy is actually quite good nesting material for the birds. So it certainly does serve its purpose.

But as many of the trees are quite tall there and old, they may have the falling over problem. So I going to write a letter to the management of the group to suggest surveying the woodland and then removing any Ivy which is becoming a danger.

But I wanted to be well informed first about what actually constitutes as actually 'dangerous' before contacting them so we know what to actually survey.

I could find anything on government websites about this or woodland sites. So I was wondering if there are any guidelines and an established definition of how much Ivy is too much? What the specific dangers there are if there is just too much of it covering the entire tree? And judging by the size of the tree and maybe type, how much Ivy is too much?

I searched around a bit but I really couldn't find a comprehensive guide on this.

Answer 1

Well, that's a 64 dollar question, it depends who you ask. It's generally thought that ivy, left to grow unchecked up a tree, will eventually cause its death, either by its weight pulling the tree down during high winds, or because, as it climbs, it roots firmly into the bark and causes some damage to it, though it's fair to say that might be because the ivy's grown up a weak, old, dying tree as a support. Over time then (quite a long time), ivy can conceivably 'kill' a tree, largely because the tree wasn't in great condition originally. It doesn't take sustenance from the tree, merely uses it to cling to; because it adheres to and penetrates a little into whatever it's climbing up, it should not be ripped off a tree, but cut at the base, or you risk ripping off the bark. Once the ivy topgrowth has completely died, it might then be possible to strip most of the growth off the tree without damaging it further, but that will take some time.The only other option is to get up the tree and cut excessive topgrowth back to the trunk/branches of the tree to reduce the risk of toppling in high winds more immediately.

This link explains that https://www.gardeningknowhow.com/ornamental/groundcover/english-ivy/kill-english-ivy.htm and gives a method of killing the ivy, but I'm fairly sure you will not want to do that. Once it's been cut at the base (all stems) the topgrowth will die, but it will reshoot from the base and will need to be kept cut ongoing to prevent it from climbing back up the tree all over again.

Although I can't find an official resource nor clear 'rules' or guidance, this RHS page might be helpful to a degree https://www.rhs.org.uk/advice/profile?PID=192. Note the warning about having any old, tall tree swamped by ivy checked by a professional for safety - propping a ladder against it and going up high could be very dangerous indeed for the person doing it and any people standing in the vicinity. However, I note the Woodland Trust categorically states ivy does not kill trees, nor does it only grow up weak or damaged trees, so there's a conflict of opinion between the RHS and them right there - hardly surprising good guidance is hard to find, sorry I can't be more help. I'm not personally convinced that ivy only grows up weak trees; in my experience, it will grow up anything it can, (though I have observed the ivy seems to get bigger faster on poorly or dead trees) but I don't have extensive experience of woodland, only gardens.

It might be worth your trying the Forestry Commission, see if they have any advice to offer https://www.forestry.gov.uk