The pilot was taking off from a sloping beach in his tailwheel-equipped airplane. The pilot stated that the tide had come in, narrowing his takeoff path. During the takeoff roll, the airplane's right main landing gear tire hit an object on the beach, the airplane pivoted to the left, and the left wing struck a group of alders. The airplane ground looped, sustaining substantial damage to the right wing and horizontal stabilizer. The pilot reported that there were no preaccident mechanical anomalies with the airplane that would have precluded normal operation.