In a post on the Titanfall website, level designer Chris Dionne said Swampland was first prototyped in 2011 as a completely flat map punctuated by redwoods and swathed with yellow fog.
Later iterations included IMC buldings, temples and "massive Infrastructure", but Dionne found this robbed the map of its personality. During playtesting, the huge trees were found to be a lot of fun, so Dionne brought them into the centre of the map, and pushed the buildings to the outside.
"With Swampland I tried to add a unique experience to Titanfall while staying true to the original themes of the level, like overwhelming nature and its intersection with technology. This was a level born of heavy experimentation and iteration," Dionne said.
You can take a look at the evolution of the level design in the video below. Expedition is coming this month and will be $10 standalone, but is available in the $25 season pass.