The pilot of the glider took off under aerotow for a flight in the local soaring area. During the return trip to the airport, the pilot reported that the “good lift” in the area had weakened. The pilot then reported that while looking for an area of lift, he performed a turn over a ridge, which resulted in a loss of altitude. During one the pilot’s turns to find lift, one of the wingtips impacted a tree, and the glider subsequently impacted the forest canopy. After impacting trees, the glider came to rest about 30 ft above ground level. The pilot was rescued from the tree canopy five hours after the accident and was uninjured. The tree impacts resulted in the glider sustaining substantial damage to both wings. The pilot reported there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.