According to the pilot, approximately 30 minutes into the instrument flight after reaching a cruise altitude of 7,000 feet in the clouds the engine surged, and began to lose power. The pilot switched fuel tanks, and turned on the electric fuel pump. No fuel pressure was noted on the fuel gauge, and the engine did not regain full power. The pilot reported that he did not apply carburetor heat during the loss of engine power. The pilot radioed air traffic control, and declared an emergency. During the emergency landing the airplane collided with trees. Post-accident examination of the airplane revealed the fuselage was buckled; both wing assemblies were separated from the fuselage. Post-accident examination of the airplane revealed no mechanical or flight control anomalies. Review of Advisory Circular 20-113 item 7.A-8 states: "If induction system ice is suspected of causing a power loss, apply full heat or alternate air. Do not disturb the throttle until improvement is noted. Expect a further power loss momentarily and then a rise in power as the ice is melted."