- Metric Name:  Biomass

- Data Vintage:  2021

- Unit Of Measure: Dry weight tons/acre

This metric expresses the total amount of existing biomass volume (measured in dry weight tons per acre) from all live tree crowns (branchwood and foliage) and the tree stems less than 10” dbh. This metric can be used to assess the volume of biomass present at the 30m cell level. It is recognized in some forest types, shrub biomass can be a significant contributor to the total biomass, however due to the aforementioned limitations of the F3 model, the shrub component has not been included.- Creation Method:  The F3 model generated several raster surfaces to provide an estimate of the total aboveground live tree crown (including foliage) biomass for all trees (ABGDLVBR) and estimates of the tree stem biomass of live small trees (BMSTM; less than 10” dbh). Since the F3 model data is driven by FIA plot data (which is an incomplete source for shrub metrics), the shrub biomass cannot currently be generated.

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. Values for each non-overlapping predefined small tree size class for stemwood biomass (BMSTM_x) raster and for the total aboveground live tree crown biomass for all trees (ABGDLVBR) raster were adjusted for 2021 following the same procedure using eDaRT MMI. The MMI value for canopy cover loss was used as a direct proxy to estimate biomass loss using the MMI percent adjustments, e.g.:

2021 BMSTM_x  = 2019 BMSTM_x  – (2019 BMSTM_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 tree stem biomass, depending on location.

This layer for the available Biomass metric is derived from F3 layers (2021) using the following formula:  

sum(ABGDLVBR, BMSTM_0, BMSTM_2, BMSTM_7)

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