At approximately 0706 mountain time, a Cessna 182L struck trees while trying to land at Donnelly. The pilot was seriously injured and the flight instructor reported minor injuries. The pilot was a customer at a commercial mountain/canyon flying seminar, while the instructor said his role was as an observer on the flight. The instructor pilot said they were making a canyon approach to U84, which involved flying at 50 to 55 mph with full flaps and full nose-up trim. The airplanes operators manual give airplanes power-off stall speed as 55 mph and a short-field approach speed of 69 mph. At approximately 5 feet agl, the instructor told the pilot to add power, but the pilot didnt respond in time and the airplane hit hard and bounced. The instructor told the pilot to push on the yoke, but the pilot added full power. The airplane veered to the left and struck trees. The instructor said all seminar participants must sign a document indicating that they will be pilot-in-command and that the seminar was not instructional in nature.