It's just slow going. Groups get broken up on the stuff rather quickly, but no one is going to be flying by any means. It's just a long slugfest.
For short section with a paved section beforehand, you gotta get a bigger gear up to speed and ram through the stuff. You have to post a bit and allow the bike to dance underneath you, but keep pedaling. Get on the tops, and allow your arms to relax and absorb the front end. Keep your butt of the seat so the rear can dance as well. You might pedal without being in contact with the ground, but eventually you'll touch down again. Be a rock getting skipped across a lake.
A long section is a mental battle. The ground might be flat, but treat it like a long road climb. Keep the pressure on until you reach the end, but don't end your effort there. Once on the pavement, get the bike up to speed and carry some momentum. Ok, now try and recover some.