The glider pilot reported that he was in the traffic pattern, setting up for a left downwind for runway 18. He turned base at 650 feet agl and then turned onto final at 450 feet agl. He found himself high on final and could not attain a normal glide slope using the dive brakes. He closed the dive brakes and performed a 360-degree turn to lose altitude. At mid-field and 100 feet agl, he decided to circle right and attempt a landing on runway 36. He “got too low” and impacted a tree short of the runway. A witness reported that the dive brakes remained full open during the accident sequence. The Federal Aviation Administration inspector who examined the wreckage reported that the dive brakes were in the deployed, or up position, when he arrived at the accident site.