"Alan Holmes" wrote in message
...

You will have severed the roots so the ivy will die, ivy does not get
sustenance
from aerial roots, thiose roots are there just to help the ivy hold on,
they
have
no other purpose.

But you can *very easily* take cuttings from ivy by cutting off a piece and
weighing it down on the soil. Will it not produce proper roots just as
easily in the tree if there is enough soil and moisture - effectively
air-layering. I'd expect this would happen as soon as the conditions were
right so it may have rooted before you cut it. It's not taking anything from
the tree directly, just using the rotting debris getting trapped up there.

I've never seen ivy do this but when I was younger and regularly up trees I
remember seeing all sorts of plants germinate in the pocket formed where the
main trunk splits and several inches of moist, well rotted leaves
accumulate.

Martin.