The pilot reported that prior to departure he checked the weather and performed a preflight inspection. He observed the direction of the windsock, and stated that it favored a takeoff from runway 23. He completed an uneventful run-up, and began the takeoff roll. Halfway down the turf runway he observed the airplane's airspeed to be indicating 60 knots. He stated that at this point on the takeoff roll he expected the airspeed to have reached 70 knots. The airplane continued to accelerate to 65 knots, and with the end of the runway approaching, the pilot 'forced' the airplane airborne and retracted the landing gear. The airplane settled to the ground and then collided with trees at the end of the runway. The pilot observed the wind direction after the accident, and noted that it was out of the northeast. He opined that the airplane had encountered a sudden wind shift or downdraft during the takeoff roll.