It's about the lives of wild Empoleons, and their unevolved forms, down in their natural habitat in the southern part of the world. It was written by a Professor Algae, who apparently spent a few years with a group of "Pokemon Rangers" discovering the information written in it.

[One day, the Professors here are going to run out of plant-related names, and then where will they be?]

The "March" describes their long trek from their summer home to their winter one.