9.  Classify the ecological interactions described: Moss lives on the bark of trees.

The ecological interaction described here, where moss lives on the bark of trees, is classified as Commensalism.

Commensalism is a type of ecological relationship where one organism (in this case, the moss) benefits, while the other organism (the tree) is neither helped nor harmed. The moss benefits by living on the tree because it can grow and reproduce in a location that provides access to sunlight and water. The tree, on the other hand, doesn't receive any particular benefit from the moss, but it isn't harmed by its presence either.