Surely there is an ordinance, and they would get a ticket if they are caught. Phone the sheriff's non-emergency number and report it as soon as you see a decorated tree. Most states have a $500 fine for littering the highways. Check with your county. How many trees are we talking about here?
To stop the practice and prevent future mess like that, you gotta educate the dummies doing it.
Maybe alert the local TV station to do a short piece on it, including the potential dangers of the stuff to wildlife.
I'm not unsympathetic, but I feel the same about roadside memorials. Their loved ones should be remembered at home, not on the spot where they died.
Next year, put up signs near the trees that have been decorated - you may need to get a permit. Maybe:
"Decorations are a threat to wildlife and become an eyesore very quickly".
"Would you decorate a tree in your neighbor's yard?"
"Please do not decorate the beautiful trees on public lands."
If you clean it up and don't take steps to prevent it, it's going to keep happening.
