[Pen N Popper]

A NWN PW I played on long ago had a system they called a "biosphere." It consisted of a triad of resources: plant, animal, and mineral. These had to be kept in balance in the druidy sense. Over harvesting plant material would mean a loss animal, etc. All well-defined in scripting. The druids could detect nature's balance and offer specific suggestions to the hunter/gatherers of the land to restore balance (and CNR material production).

Another side-effect addressing Chongo's request was that the "monsters" also had a balance. Wipe out the deer in an area and the wolves get hungrier (and meaner). Fail to kill off the wandering orcs and they'd expand territories and grow in number.

Basically, a database was kept of everything that was killed or harvested and then spawns would adjust off of that based upon a formula. As long as the players have an IC way to get a sense of where the problem areas are, they can work ICly to maintain (or disrupt) the world's balance.

A further concept was this: Since all the killings were tracked, if one PC was repeatedly "farming" an area of bandits, at some point that PC would get a price put on their head by the intelligent creatures. So as they skipped along some valley road far away, a group of thugs might ambush him. (Since the bandits would have to pay for this, their loot drops might decrease for a time or they might branch out into other areas for a while.) Again, if the paladin goody-goodies have a way to discover the imbalance, they may themselves seek to stamp out the PC problem themselves.