At this link, the Aeon website has an article by Richard Smith titled "Folk music was never green". The article confirms the general impression in this thread, that there is not much traditional music about protecting the environment.

However, the article does reference one song from the early 17th century, "The Powte's Complaint", which laments the draining of the fens -- but not for ecological reasons. (A powte is a kind of fish, though it's not clear exactly what kind.)