Bio-engineering mostly. Artificial plant growth designed to stimulate a functional air processing system. I suppose calling it artificial would be a misnomer. The trees and such are real, just not produced in any naturally occurring way.
With all that Red, White, and Blue, I'd imagine they always saw him coming first anyway? From the stories I know, Captain America doesn't really do subtle. He's right up there with a Special Forces Jellyfish -- and I know one of those.