I haven't spent nearly as much time in the WOC relevant forests, but I will say that visibility was really high, and that the footing was pretty soft, so that you sink in with every step, sapping your energy. It will pay to have the raw power to be explosive especially in the long distance after the first hour.
I never thought about the ground being so soft it saps your energy, but I guess that's like running on the soft sand of the beach. Gets tiring quickly. Tough to train for, just do a lot of running on soft ground I guess.
Interesting analogy! Sand running requiring greater strength, shorter stride and higher cadence. Ankle strength work and plyos to supplement terrain work would be my prescription :-)