The glider pilot reported that he was in the traffic pattern adjoining the downwind leg for the runway. He turned onto the base leg at 650 feet above ground level (agl) and then turned onto final approach at 450 feet agl. The glider was high and he could not attain a normal glide slope using the dive brakes. He closed the dive brakes and performed a 360-degree turn in an effort to lose altitude. At mid-field, with the glider about 100 feet agl, he decided to circle right and attempt a landing on a perpendicular runway. The glider was 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.