Each of those situations offers a different habitat for forest regeneration, encouraging different kinds of seeds to germinate and grow in the burn, Beaver explains. For example, the blackened ground in the middle of a large burn is likely to be repopulated first by plants like fireweed and poplar, whose seeds are carried long distances by the wind. Spruce and pine seeds are not carried as far, so they are more likely to take root around the edges of the burnt area. New growth can also come from seeds held in the duff layer and exposed to heat and sunlight by the fire. Rhizomes, or underground stems, often survive the fire and throw up new plants.
Plants can also grow as suckers from the roots of trees damaged by the fire.
How quickly regeneration starts depends on a range of variables, says Beaver. With an early spring fire, seeds have all summer to germinate and grow. But if the fire is in late fall, they might germinate and then freeze. Topography has an effect as well, Beaver adds. A warm southerly slope offers a very different habitat from a cool north-facing slope.