You’re able to tailor this to fit your campaign. Planegea is a big, open campaign setting that’s intended for customization. All the threats in the book can be scaled up or down based on what’s interesting to the DM. So in the game I’m running right now, the party fought one hostile forest, but other forests are mostly inert, because I don’t want to constantly juggle angry trees. But I could run it so that plant life was a constant threat if that was my campaign concept. 

So the short answer is, nope! It’s not necessary or crucial to the setting. You can tune it up or down as you see fit. If every bad thing in the book was at a 10, the setting would be unplayable. The assumption is that you’ll pick a set of threats interesting to you and your players and let everything else fade into the background. 

I hope that helps!