According to the pilot, he was on a one mile final approach to runway 36 at 800 feet with the glider engine stowed. He noted that the winds were changing and extended the flaps. The airspeed was between 55 and 60 knots when the airbrakes were extended to start a descent. The altitude was high and the glider began to descend at a rapid rate. The pilot closed the airbrakes to arrest the descent rate but realized he was too low and unable to land on the intended runway. The glider collided with a tree, and a post-accident examination revealed that the left wing was substantially damaged. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.