A question about the abandoned cars: are you allowed to let them stand around on public streets?

In Germany it's forbidden to park a car without a valid registration on areas with public access, so on private groud, which is not fenced to the open street, too.
An on private ground, even fenced one, it's forbidden to store non-registrated cars and wrecks on natural ground, only on concrete and plastered surface.
There are punishments for that and abandoned cars on public ground will be towed and brought to a junk-yard. And the owner of the car has to pay for it afterwards.