Description: - Metric Name: Density – Trees Per Acre
- Tier: 2
- Data Vintage: 2022
- Unit Of Measure: Live trees/acre
Trees per acre (TPA) is a common forest structure measurement that provides a useful index of forest and habitat condition. Many other metrics can be derived from having accurate estimates of trees per acre.
- Creation Method: The F3 model generated several raster surfaces of trees per acre as estimates of tree density on the landscape. This raster surface represents all live trees greater than 1” dbh (TPA). Reference conditions can be generated from contemporary reference sites for mature forest conditions outside of the WUI.
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 TPA loss, using the formula:
2021 TPA = 2019 TPA – (2019 TPA * MMI/100)
Although the assumption of direct correlation between canopy cover and TPA 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).
Service Item Id: 4b948257d9be47ffb335528ab78ae5fd
Copyright Text: F3 data outputs, Region 5, MARS Team
USDA Forest Service - Region 5 - Pacific Southwest Region
Description: - Metric Name: Basal Area
- Tier: 2
- Data Vintage: 2021
- Unit Of Measure: Sq ft/acre
Basal area (BA) is a common forest structure measurement that provides a useful index of forest and habitat condition. Basal area is the cross-sectional area of the bole of a tree at diameter breast height (dbh). It is measured at the stand level as the cumulative sum of basal area of all trees and expressed as square feet per acre.
- Creation Method: The F3 model generated several raster surfaces as estimates of basal area. This raster surface represents all live trees greater than 1” dbh (BASATOT).
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 basal area loss, using the formula:
2021 Basal Area = 2019 Basal Area – (2019 Basal Area * MMI/100)
Although the assumption of direct correlation between canopy cover and basal area 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).
Service Item Id: 4b948257d9be47ffb335528ab78ae5fd
Copyright Text: F3 data outputs, Region 5, MARS Team
USDA Forest Service - Region 5 - Pacific Southwest Region
Description: - Metric Name: Stand Density Index
- Tier: 2
- Data Vintage: 2021
- Unit Of Measure: Number of trees per acre expressed as an equivalent density in a stand with a quadratic mean diameter of 10 inches
Stand density index (SDI) helps vegetation managers to identify levels of site utilization and competition to determine management scenarios to meet objectives and is often used for forest health-oriented treatments. SDI was also proposed by North et al., (2022) as an operational resilience metric for western fire adapted forests. This metric is a quantitative measure that relates the current stand density to the size class distribution of the stand. Reineke uses quadratic mean diameter, a weighted mean, to estimate the stand size class, whereas the Zeide method (also known as the summation method) uses Dr (Reineke’s diameter). For additional details on both calculations, see the Essential FVS Guide.
- Creation Method: FVS generated estimates of the stand density index metric using either the Reineke 1933 or the Zeide 1983 index calculations for all trees greater than or equal to 1.0” dbh based on max SDI derived from FIA plot data. Then the F3 model imputed the SDI calculations to the landscape.
2019 to 2021 Update: SDI values were adjusted for 2021 following the same procedure as outlined for density – trees per acre (described below).
Tree density values for 2021 were adjusted independently for each predefined non-overlapping diameter size class (10-inch bins) 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 TPA loss, using the formula:
2021 TPA = 2019 TPA – (2019 TPA * MMI/100)
Although the assumption of direct correlation between canopy cover and TPA 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 the predefined size classes may result in over- or under-estimates of actual tree density per individual size class, depending on location.
QMD was then recalculated for 2021 using adjusted tree densities and by assigning trees in each size class to the respective mid-point diameter of that class.
Service Item Id: 4b948257d9be47ffb335528ab78ae5fd
Copyright Text: F3 data outputs, Region 5, MARS Team
USDA Forest Service - Region 5 - Pacific Southwest Region
Description: - Metric Name: Shrub Cover
- Tier: 1
- Data Vintage: 12/2021
- Unit Of Measure: Fractional non-overlapping absolute cover; continuous variable from 0 to 1.
- Metric Definition and Relevance: Total shrub cover as measured by the fractional non-overlapping absolute shrub cover, viewed vertically. Provides a first order measure of vegetation type when combined with parallel observations of tree and herbaceous cover. Data from the National Land Cover Database (NLCD) are used for training, and NLCD definitions for cover (for example, the distinction between tree vs shrub) are expected to be similar in the CECS data sets.
- Creation Method: Machine learning (Random Forest) using the National Land Cover Database for training and Landsat observations as predictors. See, a, for further information.
Description: - Metric Name: Seral Stage
- Tier: 2
- Data Vintage: 04/2023
- Unit Of Measure: Categorical 1 - 3 (seral stage), continuous variable 0-1 representing percentage of a HUC (early and late seral stage)
- Metric Definition and Relevance: The seral stages are categories that represent the developmental progression of forest ecosystems from initial establishment or following a stand replacing event (e.g., high severity fire) to a forest dominated by trees in the upper age classes for a given forest type. Late seral forests are also often characterized by multiple ages of forest trees and dead and dying trees in some form of equilibrium. Seral conditions across landscapes were highly variable prior to major European settlement in the western US. These patterns were highly attuned to dominant disturbance regimes and the multi-scaled variability in environmental conditions across topographic and climatic gradients. These patterns helped to reinforce fire regimes dominated by low- to moderate-severity fire across much of the region and provided for multiple habitat requirements for a wide variety of species., p, - Creation Method: The FVEG data, used in characterizing vegetation and habitat conditions for a number of metrics in this kit, contain data on tree size (, a, ). Seral stages for forested lands are binned into one of three categories of tree size (Early, Mid, Late) and those are defined by tree diameter, per the CWHR system., p, p, p
Service Item Id: 4b948257d9be47ffb335528ab78ae5fd
Copyright Text: FVEG 2023
--CALFIRE, CDFW, LANDFIRE, California Forest Observatory (SALO), USDA Forest Service