LANDFIRE Remap Forest Canopy Base Height (CBH) HI

LANDFIRE’s (LF) Remap Canopy Base Height (CBH) supplies information used in fire behavior models to determine the critical point at which a surface fire will transition to a crown fire. CBH data are continuous from 0 to 9.9 meters (to the nearest 0.1 meter) and describe the lowest point in a stand where there is enough available fuel (0.25 in dia.) to propagate fire vertically through the canopy. Critical CBH is defined as the lowest point at which the canopy bulk density is .012 kg m-3. The CBH mapping process starts by deriving field referenced estimates of canopy characteristics through LF Reference Database (LFRDB) plot analysis. Utilizing LFRDB plots, a training data set to model CBH was created. Field referenced CBH values are calculated for each plot using the canopy fuel estimation software in Forest Vegetation Simulator (FVS). Statistical analysis of plot variables indicates that LF Remap Existing Vegetation Type (EVT) and Existing Vegetation Height (EVH) demonstrate some influence on CBH, with Existing Vegetation Cover (EVC) affecting CBH values within certain EVTs. To model this relationship LF Remap Canopy Cover (CC) and Canopy Height (CH) are used as predictors of CBH; developing a linear regression equation per EVT and disturbance type/severity. These CBH regression models account for roughly two-thirds of EVT assignments. To account for missing EVTs, regression equations from similar EVTs are utilized as surrogates ensuring consistent values throughout. In some, instances LF Remap assumes the potential burnable biomass in the tree canopy has been accounted for in the surface fuel model. For example, young or short conifer stands where the trees are represented by a shrub type fuel model will not have canopy characteristics. For tree stands dominated by broadleaf species that are fire resistant (e.g. Populus spp.) are coded with a CBH of 10 meters. This artificial increase in CBH is done to prevent false simulation of crown fires that rarely occur in these areas. All non-forest values, including herbaceous/shrub systems and non-burnable types (urban, barren, snow and ice, and agriculture) are coded as 0. However, certain types of agriculture and urban vegetation that are burnable are assigned a constant value by LF Remap Total Fuel Change Toolbar (LFTFC) rulesets based on region and vegetation type. LF Remap Annual Disturbance products are incorporated into CBH to provide informed changes by disturbance type, severity, and time since disturbance (TSD). Annual Disturbance products provide a pre-disturbance scenario represented by LF Remap existing vegetation products. The combination of pre-disturbance and non-disturbance vegetation are used to calculate CBH by vegetation type, cover, and height acted on by a disturbance event. Vegetation adjustments are modeled in disturbed areas based on disturbance type and severity using FVS derived linear equations. With the use of Annual Disturbance products, CBH also has capable fuels functionality. Capable fuels calculate TSD assignments for disturbed areas using an “effective year." For example, year 2020 fuels may be calculated for the year 2020. This new process considers all the existing disturbances included in LF Remap and adjusts the TSD for these to the effective year (2020 in this example), making the products "2020 capable fuels." More information about capable fuels can be found at https://www.landfire.gov/lf_remap.php.