Traditionally, hardwoods are preferred for firewood (Oak, Charm, and beech for example), especially in central and eastern North America, but softer woods make fine fuel for spring and fall use. More generally, it is the density and moisture content that influences firewood behavior in the fire and its value. Hardwoods like maple and oak have a higher energy content per cord and so release more heat per firebox load. They also produce long-lasting fires and coal beds. Softer woods like birch, pine, spruce, and poplar are less dense, burn faster and do not produce a long-lasting coal bed when burned.