@CivilSky
It's actually a real sustainability problem. The problem is, Matthias killed every single thing in the forest, he didn't choose which ones were on the board. Everything, even the ones not on the board were equally masaccred. Because of Matthias, all the monsters are dead. You may think this is a good thing, but it is not. It is very bad. What Matthias did has essentially crippled the economy of the town.
1) You now have a lot of adventurers without jobs.
2) You also no longer have continuous access to the materials provided by these monsters.
3) Now if the town wants more materials after the ones Matthias brought in has run out, they have to import it from somewhere else at a higher price.
4) Since the adventurers no longer have a job, the adventurers guild no longer have a purpose.
5) Since materials are now extremely finite, the crafters will leave the town as soon as they realize there will be no more monster materials.
6) With the crafters leaving, the merchants will also leave, unless this town can survive as trading post alone.
7) With no merchants, no crafters and no jobs, the locals will also leave.
8) With everyone leaving, the lord will not have enough money to sustain the town and it will become a ghost town very quickly.
If the author realize this, he would've realized that this is an act of war on another country.