Is it illegal to dump Christmas (pine) trees in a dumpster at a storage lot?

These girls threw 5 Christmas (pine) trees out in front of my house I have no idea what I am going to do with them I told my dad that I would go take them to my friends storage lot and we will just dump them in the dumpster there but he said that that is illegal and we cant get caught doing that because we will get fined. I live in Michigan and I was just wondering if there is a law prohibiting this or can I get fined for doing it.