Pioneering environmental activist David Brower resigned from the board of the Sierra Club yesterday, complaining that the group has become too bureaucratic and its leadership has lost its sense of urgency. He accused the club’s board of inadequate action on such issues as wilderness protection and mass transit, and criticized it for refusing to take a stand on U.S. immigration issues. “Overpopulation is perhaps the biggest problem facing us, and immigration is part of that problem,” he said. Brower has had a long, rocky relationship with the Sierra Club: He served as its first executive director from 1952 to 1969, until he was ousted by the board. He was later elected to the board in 1983, 1986, 1995, and 1998.