Not long ago, two young women took shelter from the heavy rain beneath a tree. It was in a park, in the middle of a large city. Lightning struck the tree and killed them both.
Two other young women, hiking in the rain forest in Panama, probably slipped on a mountain slope and fell to their deaths. Only a few of their bones were found.
What if nature is not only dangerous, but actively hostile to you? What if you'd never know if you're alive past the next tree or swamp? What if it could turn you into a part of it, in a more than horrendous way? What if you decided to accept it, because, after all, you were created there? Would you accept the hostility of your birth ground?
Acceptance, the last part of the Southern Reach trilogy Annihilation-Authority-Acceptance, gives some answers about the "what" and "why". For some people it wasn't enough. For me it was more than enough. Area X should remain an absolute riddle with only the faintest hint that it might have been an accident from our perspective, but a logical step from the view of Area X. And in some way, it's also a bit sad what happened to Area X.
Jeff VanderMeer has written a nice mix of science fiction and horror, which leaves you wondering about our own relation to uncivilized nature. The idea of nature being a malevolent force in itself, for those of us who are the uninitiated. Those who have science and measurements, not accepting unwilling anti-technology. Those of us who don't believe that nature can triumph science, getting disoriented about the logic of their lives and ultimately cynical about the meaning of it when nature strikes with precision.
Maybe you should read the trilogy as a story of man coping with an environment he has been estranged from, and the final acceptance by the few who start to understand, because they realize that in the end they're cut from the same cloth. Ashes to ashes, but then, in a different way.