The pilot reported to a state trooper that he was taxiing the light sport airplane on his private property to take off on a local flight. According to the pilot, he added power, and as he taxied the airplane up a hill, it was hit by a gust of wind. The airplane then turned left, traveled down an embankment and struck a tree, resulting in serious injuries to the pilot. The pilot reported no mechanical anomalies that would have precluded normal operations. About the time of the accident, wind velocity was recorded at an airport approximately 10 miles away at 4 knots. A state trooper photograph, taken about ½ hour after the accident, had a large body of water in the background of the crash site with small surface ripples and intermittent calm areas, indicative of winds up to about 6 knots.