Is climate change increasing the growth of ivy?

Now I know ivy can be a contentious issue and is frequently the subject of heated debates, which historically have been relatively evenly matched, with the outcome really dependant on the location and management context of the tree concerned.

However, in recent years I have been asked to consider the influence of climate change on the growth rate and competitive success of ivy. There are a number of hypotheses that have been raised, which include:

a) Longer growing seasons for ivy allow it to take advantage of trees that have lost their leaves in autumn. This means that the ivy can gain the upper hand and could possible smother the crown of even a healthy tree.

b) The increased CO2 in the atmosphere is beneficial to the ivy and is increasing its growth rate and enabling it to compete successfully with healthy trees that would have historically maintained the upper hand.

c) Trees are suffering increased attacks from introduced pests and diseases, at the same time as being compromised by low water levels and as a result ivy is able to smother more trees.

These are just three possible scenarios that could be happening, but I have had a number of reports of situations where people have observed ivy smothering trees and hedgerows.

Now the issue is that the reports are not necessarily an unusual thing, particularly in the autumn and winter when the presence of ivy becomes more obvious, so what we need is some form of historical evidence to substantiate whether there is an issue here or not.

That is the reason for this thread, because I would like to know your thoughts on the issue, with consideration to the three scenarios described above, and others that you may have.

We also need to start a few trials to observe the growth of ivy and the health of trees it is growing up, and this really means getting out there with the camera and taking pictures of trees with ivy. Then getting the tape measure out and keeping a record of the respective growth rates of tree and ivy The following things need to be considered:

1. tree species

2. length of time it is in leaf, from full canopy in spring to leaf loss in autumn

3. health and growth rate of the tree

4. species of ivy (although best to keep to Hedera helix for the moment)

5. length of growing season for the ivy, from when it first starts growing in the spring, to when the annual extension growth stops at the onset of winter.

6. health and growth rate of the ivy

Again these are just a few key points that we need to consider, and of these I think 5 is one of the most significant, because I would be interested to know how much of our ivy actually continues to grow through out our mild winters and at what rate.

Interesting, but how would you implement a control in order to determine that climate was the causal factor??

Interesting, but how would you implement a control in order to determine that climate was the causal factor??

Very good point, and perhaps impossible to tell definitively without some investment in scientific research on how ivy reacts to different growing conditions and therefore whether it is able to grow proportionally better in the current warmer climate with high levels of C02 .

Any volunteers……?

However, it would be extremely useful to have some observational data from people working out in the field observing trees on a day in day out basis, because there are some very simple questions that we do not know the answers to. Like does ivy grow all year round?

Having done a little digging around the subject there is very little in the way of useful information that is of practical help to the arborists responsible for managing trees. So I think it is time we did something about it.

The sort of information we need can be gathered by anyone with a tape measure and camera, with the common sense to make consistent records.

Saw this ivy covered hedgerow Oak, on the way home from work this evening.

Interesting that the successional growth smothering the canopy has not particularly got hold of the scafold on the northern side of the tree.

Always thought Ivy would grow in partially shaded environment

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Well to stir this thread up a bit I though the following article would provide a little more information.....

Ivy c.pdf

Had to know what was going on underneath so near to target.

It's somehow retrenching down through the ivy canopy.

So stripped completely, guys over dead wooded - 'understatement'

But have left to see what, if any regrowth is facilitated, or whether over exposure to temp change/sunlight will do for the old girl good an propper.

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What a mess mate....better with ivy intact imo...at least some conservation value that way.....sorry, derailing thread!!

edit: Also failed to note concerns re target...I get used to seeing them everywhere in norfolk roadside...like beacons, signposts in the wilderness and natural milestones...no-one gives a care really...we all just passing.

BTW, the more I read about the capabilities of thermal imaging the more impressed I am with the volume of information it yields for interpretation and how easily it gives up the haul.....it remains prohibitively expensive however....

I am by no means an expert but for what it's worth here's my take on it:

a) Longer growing seasons for ivy allow it to take advantage of trees that have lost their leaves in autumn. This means that the ivy can gain the upper hand and could possible smother the crown of even a healthy tree.

A longer growing season for Ivy would surely mean a longer growing season for the host and I would have thought that any advantage Ivy has would be negligible as even on the brightest of days through the winter months there is very little useable light maybe a couple of hours a day?

b) The increased CO2 in the atmosphere is beneficial to the ivy and is increasing its growth rate and enabling it to compete successfully with healthy trees that would have historically maintained the upper hand.

Again I would have thought that any advantage Ivy has due to supposed increased CO2 levels would also give the host the same advantage. This would be quite an easy and interesting experiment to set up. Mmmm now wheres that old glasshouse:idea:

c) Trees are suffering increased attacks from introduced pests and diseases, at the same time as being compromised by low water levels and as a result ivy is able to smother more trees.

Maybe true in some cases but I think too specific in relation to the general explosion of Ivy we have seen in the past decade or so. And again if the trees are suffering low water levels then surely so is everything else although I suspect Ivy is a lot better equipped to deal with lack of water than the majority of our trees.

I believe the real reason Ivy is flourishing is more to do with social and economic change. In the not too distant past Ivy would have been managed by browsing animals such as cattle, deer and horses. Native Deer no longer roam as I suspect they once did, due to habitat loss and busy roads, non native Deer that do freely roam are generally grazers and not browsers. Farmers and cattle men no longer drive their herds (or what's left of them) up and down the highways and byways or indeed cut the Ivy (and trees) as winter fodder for their livestock. Sheep (what's left of them) love Ivy if you cut it and chuck it in a field for them. The majority of Horses would no longer be allowed to eat it as horse owners believe it to be poisoinous and it most probably is a bit too rich for the thoroughbreds that seem to be the most common creature in the countryside these days.

Householders that used to sweep the pavement outside their house and take a pride in the area around their property would have undoubtedly not allowed Ivy to encroach into the crowns of their or adjacent trees.

Throw in as well the fact that diesel power has replaced man power in the seasonal work of hedging and ditching and you have Ivy left almost completley unmanaged and rampant.

Hope this helps.

p.s. As "Arborists" I believe it is our duty, that if the need arises to help out an otherwise healthy tree, it just take 5 or 10 minutes out of our day to stick in a few cuts to sever the vines and give the tree a fighting chance.

Unless global warming is making the days longer the effects are surely minimal

I think Tony's point, above, is fundamental: without a control (ie a population of ivy that is unaffected by the projected effects of global warming) what do you expect to be able to determine?