At the completion of a cross-country flight, while on a left downwind for landing on runway 03, the pilot encountered a wind shift and the aircraft started to descend. Despite the application of go-around procedures, the aircraft continued descending. The pilot executed a forced landing in a open area, but the aircraft was damaged. The wind was reported to be from 340 degrees at 8 knots, but the pilot said the wind was gusting from the north to 15 knots.