- Metric Name:  Standing Dead and Ladder Fuels

- Data Vintage:  2021

- Unit Of Measure: Short tons/acre

This is the material that may burn at the extreme end of the spectrum and contribute to mass fire behavior (Stephens et al., 2022), especially during crown spread type events. Live “ladder” fuels for trees less than 10” in diameter are also included in this calculation.- Creation Method:  The F3 model generated raster surfaces to estimate the small size live trees (those less than 10” DBH) branchwood and foliage plus unmerchantable portions of stemwood above 4-inch diameter (BMCWN_x) as ladder fuels. The model also generated the standing dead estimates for all size classes (including stems, branches, and foliage still present) from the FVS Fire and Fuels extension carbon report (Standing_D).

2019 to 2021 Update:  Values for 2021 were adjusted using the Ecosystem Disturbance and Recovery Tracker (eDaRT), described in the Introduction. All eDaRT events beginning August 1, 2019 through November 30, 2021 were identified, and the corresponding Mortality Magnitude Index (MMI) values for these events was summed, giving the estimated fractional canopy cover loss per 30m pixel over that time period. The MMI value for canopy cover loss was used as a direct proxy to estimate biomass loss, following the formula:

2021 BMCWN_x  = 2019 BMCWN_x  – (2019 BMCWN_x * MMI/100)

Although the assumption of direct correlation between canopy cover and biomass should be viewed with caution, it serves as a reasonable approximation for representative mixed conifer forests in the Sierra Nevada affected by the recent drought (Slaton et al. 2022). The assumption that canopy cover loss, as estimated using eDaRT MMI, was equitably distributed among predefined size classes may result in over- or under-estimates of actual small size trees, depending on location.

Adjustments for the standing dead trees raster (Standing_D) took the difference between 2019 and 2021 live volume (as estimated using eDaRT MMI) converted to short tons/acre using a conversion factor of 32.1 cubic feet/ton and the result was summed with 2019 standing dead. This adjusted value was then added to the non-overlapping, predefined size classes for the small size live trees (less than 10” DBH) branchwood and foliage plus unmerchantable portions of stemwood above 4-inch diameter (BMCWN_x), which had been adjusted for 2021 using MMI percent adjustments.

This layer for the Standing Dead and Ladder Fuels metric is derived from F3 layers (2021) using the following formula:

sum(Standing_D, BMCWN_0, BMCWN_2, BMCWN_7)

- Credits:  F3 data outputs, Region 5, MARS Team
USDA Forest Service - Region 5 - Pacific Southwest Region