The short answer is, in small chunks – no. But a good amount can be extremely dangerous. Ivy – in almost every case – should be removed. It likes to grow in nooks and crannies and as a result – can find its way into the cavities and defects in your tree’s trunk.
Additionally, both trees and ivy depend on the same natural resource to sustain themselves – water. Ivy is a far more aggressive plant than trees tend to be and as a result tend to skim more of those much-needed nutrients off the top than other invasive species.
Another threat that Ivy poses is in the canopy of the tree itself. Not only can it weight tree branches down and block light, they can also make branches more susceptible to breaking in storms. Over time, they can weaken trees and even cause inopportune breaks that can leave a tree exposed to pests, diseases and plenty of other baddies.
So how do I get rid of it?
The trick to killing ivy is to get to it as close to its root system as possible. Like any kind of weeding, it’s always a good idea to wait for a little rain before you try to pull it up from the ground by hand. That way, the ground is a little softer and it makes it easy to get the entire plant. If you wish to try to cut it, make sure you almost cut into the ground and clear as much of it out from around the tree’s trunk as possible. You can also save yourself a little time by not removing the ivy from further up the tree. With the root system destroyed, it’ll eventually die and fall off.
The other remedy you can use is vinegar. One cool trick you can use is to buy and/or use a garden sprayer and fill it up with white vinegar. Long story, short – you can absolutely soak the ivy with it and kill it within a week. Just be careful to not get it on the grass and other, leafy parts of the tree as vinegar can have the same exact effect on those parts of the tree that it does on the ivy itself, so be careful! Once the ivy is brown and looking awfully dead – you can remove it from the tree – but just like the ‘by hand’ approach – start by trying to pull up the root system, first.