Answer #1 · John Heider's Answer · Melissa-Ivy is not parasitic and does not kill trees. The main problem associated with ivy is that it can significantly increase the ‘sail effect’ and weight of deciduous trees in winter making them more prone to storm damage. Another problem is that ivy can hide defects in the trunk and main branches of a tree. It can hasten the demise of trees that are already dying. The additional weight of ice in winter can cause weakened or smaller trees to collapse. If not the whole tree, limbs can be easily broken with the additional weight. Many times ivy can become so thick in the crown of trees that light needed for healthy tree growth is blocked.

Ivy climbs, not by twining, but by modified stem roots that form a suction-cup structure known as a "hold fast." The older the ivy or length of time these suction cups are attached may determine how well they adhere to the tree bark and remain in place or damage the bark when the ivy is ripped down.

In most cases I believe Ivy has its place on the ground or on structures build for it to climb. It has been proven that ivy out of control in many forested areas has hurt the ecosystem within that area for many other reasons not mentioned here. Ivy should be controlled by cutting and removing sections of the ivy stems at the base of the tree. When removing the ivy be careful not to damage (rip or tear) the trees bark.

Hope this helps.
John)