What counts as a Forest?

I'm trying to make homes for my NPCs to make them happy, but my merchant and Zoologist both keep saying they want to be in a forest

Bellow is their current houses

I'm quite sure i'm in a forest Biome and there's trees outside of their places and bellow them.

So what do i need to do to make this into a forest to make them happy?

1 Answer

NPCs don't say what biome or neighbours they like, they say what they think of their current biome and neighbours. Your Merchant and Zoologist are mentioning liking the forest because they're living in the forest.