This is really a request about game progression, and that's really difficult to do in any "sandbox" game.
Players must start in a relatively easy state (zone, game stage, whatever). If they don't they'll just get killed all the time and leave the game. But there has to be some kind of progression so that players still feel challenged as they gain more power.
If the game difficulty depends upon biome, this is difficult to do. Players start in an easy biome so they don't quit, but once they master that biome they need a reason to go to the next one.
What you're asking for is essentially to do away with the forest biome being the easy biome, and making it more difficult. But that's what the other biomes are for.
The mere fact that you are asking it should be a message to the devs that they are not doing biome progression properly. If they were, then it wouldn't matter that the forest biome is easy, because players wouldn't even be in it by the time they are powerful enough to not be killed in it.
So the real question to the devs is this: Why aren't you giving us good reasons to abandon the pine forest when we're powerful enough to go into different biomes?
It's not an easy question to answer. If anyone has ideas I'm all for it, even if the devs don't like it then maybe a modder will.
EDIT: And the answer probably can't be "because you'll get better weapons" because the only reason they would need better weapons is if they leave the easy biome. No leaving the easy biome, no need for better weapons.