Canopy Bulk Density (CBD) is an optional raster theme that is needed to determine the characteristics of crown fires.
Within the United States, pre-made Canopy Bulk Density Themes can be found at www.landfire.gov.
The values in the raster theme can be integers or decimal values in either kg/m3 or lb/ft3. The precision of canopy bulk density values are used to the nearest 100th kg/m3 or 1000 lb/ft3. Thus, if you have integer values in your canopy bulk density theme, you must use the calculator features of your GIS to multiply the original canopy bulk density units by 100 (kg/m3) or 1000 (lb/ft3). This conversion is optional for decimal bulk density values.
Thus, if the actual canopy bulk density were in metric units (say 0.25 Kg/m3), the value in the raster map would be multiplied by 100 to give an index of 25 for those cells. If the actual canopy bulk density were in English units (say .015 lb/ft3), the value in the raster map would be multiplied by 1000 to give an index of 15 for those cells.
A value of zero for CBD is invalid, zero values will be assumed to be 0.1 when encountered in a simulation.
However, if the canopy cover theme has a value of zero for a cell then the data in the canopy bulk density theme (as well as canopy base height and stand height themes) is ignored for that cell in a simulation since FlamMap assumes there is no tree cover for that cell.
IMPORTANT NOTE: When developing the CBD theme for your Landscape (.LCP) File you need to consider the crown fire calculation method. There are two ways of calculating crown fire available in the Input tab of the "Run" dialog box. The Scott and Reinhardt (2001) crown fire calculation assumes using the 15 ft. running mean method of determining canopy bulk density found in FVS-FFE and FMA Plus. The Finney (1998) calculation requires significantly higher canopy bulk densities, a crude approximation is to double the CBD calculated with the 15 ft. running mean method.