According to the pilot, he performed three off airport, soft field landings, in a field and that he was landing in a southerly direction. He added that after the third landing, he turned the aircraft around and took off to the north, "because of all the tall trees on the south end of the strip". He remarked that the wind was calm on the ground, but during his takeoff climb he encountered "wind shear and my airspeed dropped from 50 kts. to 30 kts.". He recalled that the airplane struck a tree, descended, and impacted terrain. According to the nearest Meteorological Aerodrome Report (METAR) from an aerodrome located about three miles northeast of the accident site, the wind about the time of the accident was 210° at 13kts. The METAR revealed that the prevailing wind throughout the day was a southerly wind. According to the Pilot's Handbook of Aeronautical Knowledge, specifically the section on Takeoff Performance, pg. 10-14, para. 5: The effect of wind on takeoff distance is large, and proper consideration also must be provided when predicting takeoff distance. The effect of a headwind is to allow the aircraft to reach the lift-off speed at a lower groundspeed while the effect of a tailwind is to require the aircraft to achieve a greater groundspeed to attain the lift-off speed. A headwind that is 10 percent of the takeoff airspeed will reduce the takeoff distance approximately 19 percent. However, a tailwind that is 10 percent of the takeoff airspeed will increase the takeoff distance approximately 21 percent. The pilot reported that there were no pre-accident mechanical malfunctions or failures with the airplane that would have precluded normal operation.