woodpeckers do not damage healthy trees, they make a hole in a tree infected with parasitic insects to eat the problem bug, a small hole in a healthy tree will heal, but if they are able to make a bigger hole it is because that wood was already dead.
Every movement you make requires friction. When you walk, it requires friction. When a woodpecker is pecking a hole in a tree, it requires friction for him to keep his toes in the tree- static friction, to be specific. Hope that helped!
it doesnt the relation between both the organisims is parasitism which means one organism benifites off of the other and the other one gets harmed in some type of way. in this case the woodpecker gets food and shelter from the tree while the tree gets harmed by having a hole on it.