When a fire in a conifer forest stand crowns, additional fuel is consumed primarily in the form of needle foliage but also in mosses and lichens, bark flakes, and small woody twigs. The additional canopy fuel consumed by a crown fire combined with the increase in rate of fire spread after crowning can easily lead to the quadrupling of fireline intensity and, in turn, a dramatic increase in flame size within a few seconds (for example: from 800 to 3,200 British thermal units/second-foot [Btu/sec-ft]). Spotting activity can also very quickly increase in both density and distance. in such cases, there is little wonder why crown fires just seem to literally 'blow up' (Byram 1959).