An 80-foot-square plot in a red pine plantation was burned at extreme fire danger as part of a study of fire behavior and effect. When the wind reversed its direction, the original slow-moving back-fire changed within a few minutes to a fast-spreading crown fire. The transition from surface to crowns is described in terms of rate of spread, fuel weight consumed and energy output. © The Canadian Institute of Forestry/Institut forestier du Canada. Abstract reproduced by permission.