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* Metric Name: Total Dead/Down Fuels  

* Tier: 2  

* Data Vintage: 2021  

* Unit Of Measure: Short tons/acre  

* Metric Definition and Relevance: Stephens et al. (2022) note that total dead/down values over 20 (short) tons/ac (40 Mg/ha) resulted in high severity in 56% of the pixels. Higuera and Abatzoglou (2020) note that fuel and fuel aridity, **where fuel is “non-limiting”** , are a primary control on area burned at interannual to millennial timescales. Thus, it is more important than ever to define fuel limitation and map where it is on the landscape as a fundamental metric for where, even under hotter climates, low to moderate severity fire is still a strong likelihood.  

* Creation Method: This data layer currently exists only for the Sierra Nevada region. Efforts are underway to explore development of F3 data for the rest of California. The [F3 model](https://docs.google.com/document/d/15tXCMkEzUEgQKHoXL74cftwtLuz3z-Rm/edit#heading=h.1t3h5sf) generated several different raster surfaces of fuel loading estimates of the coarse woody debris by non-overlapping predefined size classes; including 1, 10, 100, 1000-hour fuels (FLOAD_1-5). The model also produced estimates for coarse woody debris of heavy fuels by non-overlapping predefined size classes which are greater than the 1000-hour fuel size (>=12”; FLOAD_6-9) and for litter and duff. 

2019 to 2021 Update: No adjustments were made for 2021 due to uncertainties in
conversions based on the limits with which change detection information can
quantify the individual components of this metric. For areas with disturbance
2019-2021 (defined as eDaRT MMI >= 10% canopy cover loss), total dead/down
fuel values are not represented for 2021 (i.e., NULL). For areas undisturbed
2019-2021, it is a reasonable assumption that total dead/down fuels did not
change significantly over the course of two years.

This layer for the Total Dead/Down Fuels metric is derived from F3 layers
(2021) using the following formula:

_sum(FLOAD_1-9, LITTER, DUFF)_

  

* Credits: USDA Forest Service, Region 5, MARS Team