How to prevent damage?
The first way to deter a woodpecker from getting at your trees is to protect the trees. You can use a bird netting, which is commonly used to protect fruit trees. You can also get commercial products that can be installed around the tree that is sticky on one side preventing the birds from landing on it. Another solution is to wrap the tree with a mesh or cloth so the woodpecker can’t get to the tree. Something that might be a little unconventional is to hang mirrors, old CDs, or anything else that’s reflective. The woodpecker won’t be able to tell the difference and think it’s another bird who has already taken up residence.
Can I repair the damage the woodpecker did?
It depends on how much damage the woodpecker did. In most cases when the holes are an inch or smaller, the best thing to do is to leave the damage alone and let the tree heal on its own. If you attempt to plug up any of the holes, you might accidentally trap the disease inside the tree. You can treat the tree with some fungicide, as a precaution, but basically the tree will handle the rest.
If the holes are larger than an inch, treat the area with a fungicide and then cover the holes with galvanized mesh, also known as hardware wire. Covering up the area will still allow it to breathe and get rid of any diseases it might have, but no insect will be able to get into the tree while it’s vulnerable.