This paper offers some suggestions and field guides with respect to the operational application of C.E. Van Wagner's (1997, Can. J. For. Res. 7:23-34) theory to calculate the threshold conditions for the start and spread of crown fires in conifer forests. Three categories of crowning are recognized (passive, active, and independent); they are determined by three crown fuel properties (live crown base height, foliar moisture content, and bulk density) and two characteristics of fire behavior (spread rate and surface intensity).
Alexander, M. E. 1988. Help with making crown fire hazard assessments. In: Fischer, W. C.; Arno, S. F., comps. Protecting people and homes from wildfire in the Interior West, proceedings of the symposium and workshop. Gen. Tech. Rep. GTR-INT-251. Ogden, UT: USDA Forest Service, Intermountain Research Station. p. 147-156.