In this case it would be better to see the tree as pulling the nutrients it needs from wherever they happen to be available. The fungus network it's connected to is simply trying to balance nutrient availability across it's subunits, and is also pulling nutrients from wherever they are available, even if that is other trees in the network. Those other trees end up suffering (or at best grow more slowly) but it's not like they can complain. That this adds up to improved odds of survival for the forest as a whole is merely good robust system design. One day we'll take as much care in our own work. The internet is certainly not so robust.