On 05/05/2014 22:49, David Hill wrote:
On 05/05/2014 22:11, Another John wrote:
In article ,
David Hill wrote:

My question: is there any truth in the old saw that ivy, once securely
established on a tree, will become genuinely parasitic, and will draw
sustenance from the tree itself?

None at all. The greatest danger is that the ivy will increase windage
on the tree and may cause its downfall during gales, esp. following wet
weather.

You might find this item of interest
http://www.arborecology.co.uk/article_forf.htm

An interesting article, although it doesn't mention ivy on conifers.

Although I would never expect ivy to act like a strangler fig, I
sometimes wonder if excessive coverage inhibits tree growth. Also, does
it weaken the wood or strengthen it? Old ivy "wood" seems quite tough
to me, requiring several strikes with an axe to sever it. So does it add
support to a tree, and if so does the tree react by not needing to
llignify quite to much to support its own weight? Or is the ivy just
added weight, so the tree then needs additional lignification to support
the weight of the ivy as well as its own weight?

--

Jeff