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My Own Observations
In seven years the ivy has grown 7 m+ The ivy in B has 7-8 vines of 15-17mm thickness and many smaller ones of 5mm. I sent the bigger vines to a dendrologist who confirmed the 7 years. From A Forester A third generation forester told me that as soon as the Ivy started to enter the crown of the tree the Ivy vine was cut at its roots. Until this height the Ivy did not seem to damage large trees. Age of Vine You can more or less tell the age of a vine from the thickness. 3yrs……….….5mm It does vary from plant to plant - but it is possible to count the rings on the cross-section of a vine and get within 2 or 3 years its age. Three to six year old vine rings are very difficult to decipher. I believe many of the oaks I have looked at are probably between 150-200 years old with ivy vines of 40-60 years growing up them. The ivy being well into the crown. .Can the trees live for another 200 years with ivy growing on it? Is there anywhere records of ivy living to 260 years being supported by an oak? Oaks can live up to 400-500 years or more. From my observation, once the ivy is a certain age, depending of course on the tree size, the foliage of the ivy crowds out that of the tree, stopping photosynthesis and hence the death of the tree. (Apparently a sugerbeet only needs 20% of its foliage to produce the same size beet with all its foliage!!!) I was told this by someone who has spent his life doing research. If this is true, do trees have the same capabilities? And does this explain why the ivy does not kill the tree quicker? I have read somewhere that pollarded trees live for ever. Even if a tree is hollow, it is known that oaks can go on living for many hundreds of years. However, with the continuing growth of ivy the tree stands no chance.
At what stage does ivy finally kill the tree? I suggest when there are not enough of the trees leaves left to photosynthesise:--such as B+C.
How does ivy spread? (1) By seed dispersal carried by birds. Particularly wood-pigeons. From the scientific journal “Birds” are the following figures :- 1990 in Britain 2.1-2.6 million breeding pairs
wood pigeons. (2) By creeping along the ground. In Carlisle I saw a perfect example of seed dispersal. On a piece of “no-mans land” between odd buildings and the edge of a golf course.
Another good example of this is a row of poplar trees which has ivy growing like this. The ivy which is the tallest is where the seed happened to be dropped near that tree and then fanned out along the ground climbing each poplar in its path.
My father bought a wood in Norfolk in 1952. It has never had any ivy cut in it except 38 years ago, when an uncle cut ivy vines that were about 30 years old, on 4 oaks. Some of the vines are still just clinging on and
are totally wood wormed. No ivy has grown up the trees again except
one, where there is now a 6 yr vine. Why in those 38 years has no
ivy grown up those four trees again, yet the other trees around
are now smothered? Pumping Water. A recent study of increment cores taken from trees and ivy show growth reductions due to periodic droughts. However ivy showed a more rapid recovery in growth than several tree species. Oak showed depression on ivy covered trees compared to trees with no ivy. If we are going into dryer hotter summers and you have both the ivy and its host tree pumping out water, surely that leaves the tree with less available water. Also when it rains the mesh-like growth of the ivy with its aerial roots acts like a sponge collecting water which would otherwise run down the trunk of the tree into the ground. One oak I investigated had matted ivy a foot thick from the bottom of the tree upwards. When cutting into it I discovered it was full of rat runs and droppings. I doubt if any birds would be roosting or nesting in that tree. Hedgerows Before the 2nd W.W. hedgerows were cut by hand and ivy was automatically pulled out and off the hedgerow tress. Since that war mechanical trimmers have done the job, with the result that ivy was no longer pulled. So gradually over time the ivy has spread. Once ivy has set mature foliage it is only a matter of time (I would like to know?) before the hedge will be smothered and dies, leaving it to the whim of gales or just collapsing. Or will the hedges simply become ivy hedges strong enough to stand up on their own?
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