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Objective: Identify ecosystems that have a significant proportion of their area burning less frequently than what occurred under historic fire regimes. Often, missed fire cycles were due to human factors, principally fire suppression since early in the 20th Century.

Data: The area of a landscape with a deficient fire frequency was estimated by comparing observed fire frequencies to historical mean fire return intervals. Observed fire frequencies were calculated by determining the frequency of fire for each pixel based on raster data of observed fires from the Monitoring Trends in Burn Severity (MTBS) project. Areas in the unburned to low severity class were removed from this analysis. The ratio of observed to historical fire frequencies (as determined by Landfire MFRI) was used to determine pixels that are burning less frequently than expected. These pixels were then used to determine the percent area of the landscape deficient in fire. For areas with fire return intervals longer than the remote sensing record, the history of effective fire suppression was used to assume not enough fire occurred back to the implementation of widespread suppression starting in the 1920s through 1930s with policies such as the 10 AM rule. Prior to the 1920s, it is assumed fire return intervals were closer to the historic range of variation, although likely reduced due to the constrained role of Indigenous stewardship. Beginning with the 2022 TCA Assessment, areas highly modified by anthropogenic activities (i.e., those with developed landcovers or agricultural landcovers of pasture and crop cultivation) and areas with a landcover that does not typically burn (i.e., barren or ice) were not included in the calculation. There is a 2 year lag between the most recent MTBS data and the TCA Assessment year (i.e. in the 2024 TCA Assessment, available MTBS data were from 1984-2022). To reduce this lag to 1 year, we compute the Composite Burn Index (CBI) for the year prior to the current assessment year using fire perimeters from National Interagency Fire Center (NIFC) with methods adapted from Parks et al. 2019. The CBI methods were added for the 2021 assessment. Landfire versions used for MFRI and the associated Alaska TCA Assessment are: Landfire 2010 (TCA Assessment 2020-2022) and Landfire 2014 (TCA Assessments 2023 and 2024).

Format: Raster data are ordinal: (1) Deficient (2) Sufficient (3) Excessive.

Resolution: 90m (2023 and 2024 assessments), 30m (2020-2022 assessments).

Source: MTBS fire perimeters, expected fire return interval , CBI methods, National Interagency Fire Center Perimeters (for CBI)

Additional Resources:

Details on Method Changes and Source Data Versions

Overview of the Terrestrial Condition Assessment: TCA Hubsite or Landfire Office Hour Presentation

Explore the results of the most recent assessment: TCA Interactive Data Viewer

Learn more about the TCA KPI: TCA Dashboard

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