If I want to create a 3D archery course in Germany on public land, which authorities do I have to contact? First of all I need to know which authority administrates the land but also if I have to talk to the ranger, game tenant etc.
Any authority in Germany is required by law to direct you to the correct office to deal with your question (Amtshilfe). A good starting point would be the receptionist at the local council (this could be a Gemeindeverwaltung, Samtgemeindeverwaltung or Kreisverwaltung depending on where you are). Public land may be owned by them, the Country or the Federation. They will help you find the right place. Wikipedia is a great source for information about finding the web page for the local authority.
Another good alternative would be asking at a local restaurant or hotel for advice on whom to approach first, as they have a natural interest in any event that would increase tourism in the area. They may direct you to someone who is especially sympathetic to requests as yours.