According to the pilot, prior to a cross-country glider flight, his preflight weather assessment led him to believe that he would find thermal lift near the ridge enabling him to climb. He reported that when he arrived at the ridge he did not find any thermal lift activity and his circumstance seemed "urgent and imperative" to find an off airport landing area. He recalled that very high trees outlined the 300 meter field where he elected to land. He reported that he made two descending, spiraling patterns over his selected landing site. He recalled that he made a final turn into the field, however the glider's outboard left wing struck several trees and spun the glider counter-clockwise and it impacted the ground. The glider sustained substantial damage to the empennage and the left wing and canopy. The pilot reported that there were no mechanical failures or anomalies with any portion of the glider during the flight that would have prevented normal flight operations.