The commercial certificated pilot was landing in an open area of tundra next to a creek. As the airplane touched down, the pilot said he realized that the tundra surface was soft and wet. During the landing roll, the main landing gear tires dug into the soft terrain, and the airplane nosed over. The pilot, who is a certificated aviation mechanic, reported that the airplane received damage to the left wing lift strut, the rudder, and the vertical stabilizer.