I have just returned from England where I was surprised to notice how many large trees are being felled by strangulation by ivy.  Whole forests were full of dead trees leaning precipitously but held in place by thick ivy.  Some ivies develop trunks up to 6" in diameter and as the vines twist and grow around the trunk of the host tree they slowly stop that tree's ability to thrive.  Occasionally I saw that ivy had been cut from large ancient oak trees, but that varied depending on the landowner.   Ivy has had a long time to grow in England, but it has not been in California for very long, and see how prevalent it has already become.