Hostility

Hostility is a points counter. Cutting trees, opening glades, growing your population and surviving years all add points, and so do some effects. Each source has its own weight, and each biome weighs them differently.

Difficulty scales positive Hostility contributions. Flat Hostility reductions from effects are not multiplied; changes to a source’s points apply before its remaining positive contribution is scaled. Woodcutter Hostility follows the number of assigned woodcutters, rather than the number of camps.

Levels

Points accumulate towards a threshold. Crossing it raises the hostility level and carries the surplus into the next band, so a burst of clearing can push you through a level with momentum to spare. Removing the source drops points back, and falling below zero takes a level back off.

Every level up stacks one more resolve penalty on each species that carries one. That is the direct line from cutting trees to villagers walking out, described in The resolve engine.

Forest mysteries

Seasonal effects, the ones the game calls forest mysteries, each sit behind a hostility level. The active set is recalculated whenever the level changes, so climbing a level can switch several on at once. Some carry an extra condition on top of the level and only fire when the settlement is in a particular state.

Each biome also runs its own season table, which is why the same hostility level feels different in the Coral Forest than in the Marshlands.