The pilot was departing on a personal local flight from a narrow, tree-lined, private airstrip, located on a small island, in a single-engine, amphibious float-equipped airplane. After lifting off, as he approached the departure end of the runway, the airplane suddenly rolled left into the trees. The airplane came to rest at the base of the trees, standing on its nose and float tips. The pilot said there were no known preaccident mechanical anomalies with the airplane, and that he thought either the flap system or aileron system had malfunctioned causing the abrupt left roll. The airplane sustained substantial damage to both wings and the fuselage. The pilot reported that when he took off the wind was calm. A resident of the island, who was working outside, heard and responded to the accident. He said the wind at his residence was gusty and varying in direction. The departure end of the runway is over a bay, and he said there were whitecaps on the bay when he arrived at the accident site. Two islands, one to the north and one to the west of the accident island, have automated weather reporting stations. The island to the north was reporting wind at 12 knots gusting to 20 knots. The island to the west was reporting calm wind. On site documentation revealed there was a break in the tree-line along the right side of the runway, about the same area where the loss of control occurred. A commercial airplane operator reported that he suspended flight operations to neighboring islands the afternoon of the accident, due to wind/wind shear. A postaccident examination of the airframe did not reveal any mechanical malfunctions or failures that would have precluded normal operation.