why is the land owned by the Ulrich family "the most jealously guarded"?

The land had a lot of game and was a mark of territory that people sought after:

The forest lands of Gradwitz were of wide extent and well stocked with game; the narrow strip of precipitous woodland that lay on its outskirt was not remarkable for the game it harboured or the shooting it afforded, but it was the most jealously guarded of all its owner's territorial possessions.