Bandit Spawn(Forest)

No, they spawn only on unmodified chunks. Unmodified chunk is a chunk where you don't do anything (except killing animals/npcs). If cut a tree, pick a rock, destroy terrain, etc the chunk is modified, stored in db and here no longer spawn npc, including bandits! A chunk have size of 32x32 with 64 height. You can use a console command to show chunk borders.

So, if you chop entire forest, no longer bandits spawn here.

But we have hope next update will contain new console command resetchunk to aid to reclaim modified chunk as unmodified one and npc start spawning again ...

Anytime you modify a chunk (32x32 blocks) NPCs won’t spawn in that chunk. Modifying means raking ground, cutting tree down, digging or placing blocks.

They won't spawn in that chunk but may wander there from other, unmodified, chunks