They call it "perpetual motion" ( don´t know if its the guy or the girl who is talking )
But really, he is just useing the new arrivals for fuel.
So that is nice and all mr uber depression, great system you got here even if the means might be fairly iffy.
But that does not explain why its nessesary to frame people and then kill them to turn thier corpses into monsters.
He is just delaying the inevititable becouse eventually people are going to catch on that the total population never increases.
And if the total population does increase, even if very slowly its eventually is not going to be enouth to just "skim off the top"
The energy to sustain a constantly growing population is likelly also going to surpass the trees ability to produce aswell.
Also If he truelly wanted to be efficent about all of this
He should just hunt down the survivors themselves and feem them to the tree instead of leting the monsters waste resorces.