On October 16, 2003, at 1800 central daylight time, an experimental amateur built Croke Zenith CH 701, N701US, collided with trees during a forced landing one-quarter mile from the pilot's private airstrip following a go-around from runway 18 (1,000 feet by 20 feet, grass) in Brussels, Wisconsin. The pilot was not injured. The airplane was substantially damaged. The 14 CFR Part 91 personal flight was being conducted in visual meteorological conditions without a flight plan. The local flight originated from the private airstrip at 1730. The pilot reported that after a local flight he returned to the airstrip to land. He stated he was not happy with the approach so he initiated a go-around from an altitude of about 15 feet above the ground. He reported the engine only produced about 4,000 rpm instead of the normal 5,300 rpm when he applied full power. The pilot reported he was unable to sustain a climb with the reduced power and the airplane settled into trees in a wooded area off the south end of the airstrip. The airplane was powered by a Rotax 912 UL, 80 horsepower engine. The engine had accumulated about 100 hours when the pilot purchased it with an additional 2 hours since it was installed on the accident airplane. On the NTSB Form 6120.1/2, the pilot reported there were no mechanical malfunctions or failures.