"Birnam Wood is on the move . . . A landslide has closed the Korowai Pass on New Zealand’s South Island, cutting off the town of Thorndike and leaving a sizable farm abandoned. The disaster presents an opportunity for Birnam Wood, an undeclared, unregulated, sometimes-criminal, sometimes-philanthropic guerrilla gardening collective that plants crops wherever no one will notice. For years, the group has struggled to break even. To occupy the farm...