The tree people were supposed to be a race that could slightly communicate with trees. But then the fountain of life came along and they became able to communicate with not only trees, but with animals too. After achieving transcendence, they became able to control plants and accelerate their growth.
Their divine ability awakened further at the titan of law stage to make them capable of creating life bonds with any living thing. This binding is pretty similar to the connection of the soul sphere between clones of Legion. But Wood elves can only bind with a single entity.
They can use that binding to assist the entity with energy, vitality, and life force. That means they can heal the entity across large distances and also prevent the entity that they bonded with from dying.
