Far from Enough

After all, there were no zombies in this world in the beginning. It was only because of the environment that zombies slowly appeared. 

"In other words, we must plant large patches of green plants in places where zombies can't see while the people in the base are still safe underground. We can let someone keep an eye on them and throw some seeds that can grow here.

"Once the zombies think of a way, they will attack the underground base. In case something happens to the people in the base, the person keeping an eye on them will have to water the seeds of these trees in the space. It would grow into a towering tree in a short while. Once the zombies see it, they will have to do something. They will have no choice but to come over to destroy it.