The pilot had landed his tailwheel-equipped airplane on a rough and uneven, soft, off-airport landing site in gusty wind conditions. He reported that he had landed at the same spot the previous day, but at a higher gross weight. While back taxiing the airplane became stuck, he applied near full power and the airplane began to roll. In an effort to avoid becoming stuck again, he chose to taxi at a higher than normal speed and power setting. He stated that the airplane began to accelerate and in an effort to slow down, he applied the main wheel brakes while simultaneously hitting a large tussock. The airplane nosed over sustaining substantial damage to the rudder and vertical stabilizer. The pilot stated that there were no preaccident mechanical anomalies that would have precluded normal operation. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot stated that the accident may have been prevented if he had shut down the airplane and walked the landing zone prior to taxi to look for hazards, or if he had a better understanding of how gross weight affects airplane control while on the ground.