Canopy Base Height (CBH) is an optional raster theme that is important for determining transition from surface fire to crown fire. For a single tree it is the height to the bottom of the live crown, it gets tricky when attempting to expand this concept to a stand or area basis. CBH should incorporate the effects of ladder fuels (if present) in increasing vertical continuity and assisting transition to crown fire. Typically a mature, dense, multi-storied Spruce/Subalpine Fir stand would have a CBH of 1 to 3 feet while an open park of old growth Ponderosa Pine would have a CBH of 30 feet or more. Conditions in between these two extremes are more difficult to estimate.
Values can be in meters or feet. The precision of the fire behavior calculations are limited to the nearest 1/10th meter or foot. Thus, if you have integer values and you want greater precision you should use the calculator features of your GIS to multiply the original crown base units by 10 and select meters*10 or feet*10 in the "Generate Landscape (.LCP) File" dialog box. This conversion is optional for decimal crown base height values.
Within the United States, pre-made Canopy Base Height Themes can be found at www.landfire.gov.