Density - Snags - 30" - 39.9"

The number of standing dead trees (snags) on the landscape is important to forest managers; high densities of standing dead trees are known to contribute to extreme fire events while snags of certain sizes provide critical habitat to wildlife. For this metric, the snag density for all species and all decay classes with diameters of 20" dbh and greater have been estimated.

Data and Resources

Additional Info

Field Value
Version Version 5.0
Last Updated March 28, 2025, 08:36 (UTC)
Created March 7, 2025, 07:52 (UTC)
category /Forest and Shrubland Resilience/Structure/Density - Snags
collection_name California Landscape Metrics
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 generated several raster surfaces of snags per acre for all species and all decay classes in non-overlapping, predefined size classes. For this metric, the three largest, predefined non-overlapping size categories have been included: 20-29.9", 30-39.9", and >=40". 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. Each of the predefined non-overlapping size category trees per acre rasters (TPA_x) were adjusted following the same procedure. The MMI value for canopy cover loss was used as a direct proxy to estimate TPA loss, using the formula: _2021 TPA_x = 2019 TPA_x '€“ (2019 TPA_x * 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 loss per individual size class, depending on location. This loss of live trees per acre (TPA) between 2019 and 2021 was then added to the 2019 estimate for snag density (of the same size category; SNG_x) from F3. The layers for Snag Density were each derived from F3 layers (2021) using the following formula: _(2019 TPA_x '€“ 2021 TPA_x) + 2019 SNG_x_
data_resolution 30m Raster
data_vintage 2021
date_updated August 2024
element Structure
encoding utf8
file_name SNV_DensitySnags30_202111_202209_T2_v5
format GeoTiff
harvest_object_id 3d706aa3-c91b-4ce5-8d45-92360c69cee4
harvest_source_id a2637971-af12-457f-ae4a-831d2202a539
harvest_source_title WIFIRE Commons
maximum_value 24.3
metric_definition_and_relevance The number of standing dead trees (snags) on the landscape is important to forest managers; high densities of standing dead trees are known to contribute to extreme fire events while snags of certain sizes provide critical habitat to wildlife. For this metric, the snag density for all species and all decay classes with diameters of 20" dbh and greater have been estimated.
minimum_value 0.0
pillar Forest and Shrubland Resilience
spatial {"type": "Polygon", "coordinates": [[[-122.2883616476824, 35.05769372687348], [-117.5563290826801, 35.05769372687348], [-117.5563290826801, 42.00332292672577], [-122.2883616476824, 42.00332292672577], [-122.2883616476824, 35.05769372687348]]]}
sub_element Density - Snags
tier 2