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Objective: An indicator that identifies where tree density has exceeded the levels presumed to be present in pre-Euro-American settlement non-forest vegetation. By our definition, non-forest areas cannot exceed 25% tree canopy cover. Fire exclusion, climate, and human activities affect the progression of trees into non-forested ecosystems. Encroached areas may require restoration to meet ecological objectives. Restoration practices will be ecosystem specific.

Data: The indicator uses areas identified as grasslands using LANDFIRE’s Biophysical Settings (BpS) raster dataset (US_140BPS_20180618) along with a cross-walk based on Reeves MC, Mitchell JE (2011) (https://research.fs.usda.gov/treesearch/41872) to identify BpS units that were likely to be grasslands during pre-European times. Presence of conifer tree species was developed using USGS National Landcover Database (NLCD) legend class “42 – Evergreen Forest”. The Evergreen Forest class represents “areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover. More than 75% of the tree species maintain their leaves all year. Canopy is never without green foliage.” Grassland conifer encroachment is identified where raster pixels are identified as both “grasslands” and NLCD “Evergreen Forest”. This indicator is only run in years there is an updated NLCD version available. NLCD versions used: NLCD 2011 (TCA Assessment 2020), NLCD 2019 (TCA Assessment 2022), NLCD 2021 (TCA Assessment 2023), NLCD 2024 (TCA Assessment 2025). Encroachment for the 2023 TCA Assessment is 1-bit and therefore only contains values of 1 indicating where encroachment was observed, rather than the binary data from other years.

Format: Raster data are binary: (1) likely encroached or (0) not encroached

Resolution: 30m

Source: Custom grassland-BpS crosswalk, NLCD conifer presence

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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