On June 23, 2001, at 1803 eastern daylight time, a Kaines Kitfox 2, N789MK, operated by a private pilot, sustained substantial damage when it struck a tree and terrain after taking off from runway 32 (900 feet by 45 feet, grass/turf) at a privately-owned airstrip near Mt. Morris, Michigan. During the takeoff and initial climb, the pilot reported a partial loss of engine power. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of 14 CFR Part 91 without a flight plan. The pilot reported no injuries. The local flight was originating at the time of the accident. The pilot said that during the takeoff roll, everything seemed to be all right. He said he began to notice that the power was diminishing as he got further down the runway. He said that he was beyond the point where he could safely abort. He got about 30 feet into the air and realized the airplane was not going to sustain flight. The pilot said he decided to put the airplane down in a nearby pasture. During the landing attempt, the airplane's wing struck a tree and then the ground. The pilot said that both of the airplane's wings were bent aft, the main landing gear were broken aft, and one propeller blade was broken off. Flight control continuity was confirmed. An examination of the engine, engine controls and other airplane systems revealed no anomalies.