And therein lies the big question, David! I might refer you two threads for extensive discussion on the subject:

Folklore: The Green Man

Any info about the green man?

Basically, over the last forty years The Green Man has become an Icon of Pagan Fakelore to the extent where he has become detached from the theology of Re-Reformation Roman Catholicism which was his original context. A bizarre state of affairs to be sure! Even to the extent where the Anglican custodians of the great Medieval Cathedrals (Durham included) promote their precious Green Men as being pre-Christian / Pagan rather than Catholic.   

Another of Mr Eatough's fine carvings at Whalley: Foliate Head, Whalley Abbey, 1430

And another from Whalley Abbey that presently resides in Blackburn Cathedral: The Fall, Whalley Abbey, 1430