The pilot stated that after takeoff he began a southbound climb until he felt that sufficient altitude had been gained to maintain terrain clearance followed by a turn to the north-northeast. He continued to climb as he followed a canyon reporting that he experienced light turbulence throughout the flight. As the pilot flew up the valley he elected to follow the northwestern side expecting to gain extra lift from the wind. The pilot reported that the airplane was climbing but as the valley narrowed, the airplane’s climb rate decreased and then the airplane began to descend. The pilot began to shift to the other side of the valley, which only increased the rate of descent. As the pilot attempted to maintain altitude, the airspeed began to decrease. As the airspeed continued to decrease the pilot verified that full power was still being applied. The stall warning horn periodically activated as the pilot attempted to avoid trees. The airplane collided with a tree and nosed over as the airplane impacted terrain resulting in substantial damage.