An interloper is an intruder. In the story it is Ulrich, Georg, and their families who are the intruders. Both men feel that the forest belongs to them. They look upon the land as a piece of property, something that can be bought and sold. But their unfortunate experience with the falling tree reminds them that this is not the case. Irrespective of Georg and Ulrich's legal claims, nature has a life of its own; ultimately it belongs to no one. The forest has been around since time immemorial; it was there long before either of these men and their families even existed, and it will still be there long after they've died. The Von Gladwitzes and the Znaeymses are interlopers, trespassers on a piece of land which in actual fact doesn't really belong to either family.