The Terrestrial Condition Assessment (TCA) is a model created and used by the USDA Forest Service to determine the ecological condition of National Forest System (NFS) lands and identify potential opportunities for restoration and maintenance work. In 2019, the interdisciplinary TCA team updated the model to version 2 (TCA v2). Four major changes were made based on feedback from field-going experts and Forest Service scientists: 1) new indicators added, 2) new metrics added, 3) underlying datasets updated, and 4) model structure improved. New indicators of grassland productivity and grassland encroachment expand TCA’s ability to assess non-forested ecosystems. New metrics better account for ecosystems with moderate fire regimes impacted by fire suppression and management activities; these metrics were added to the Uncharacteristic Disturbance Indicator and Wildfire Hazard Potential Indicator. Additional metrics incorporate ozone impacts into the Air Quality Indicator and better capture the scope of tree mortality impacts. The dataset underlying the Roads Indicator has been updated to a standard agency dataset. Finally, the process by which fire frequencies are compared to historical conditions was improved in the Ecological Process Indicator to better account for heterogeneity within analysis units. Finally, the model structure incorporated physiognomic types to better assess non-forested ecosystems.
Results/Conclusions
The TCA v2 uses 12 indicators composed of 31 metrics to assess ecological integrity at the landscape scale. Mapped ecological units range from 2,000 to 35,000 acres in size. The TCA utilizes the power of the Ecosystem Management Decision Support (EMDS) system to synthesize these metrics and indicators into an overall rating of ecosystem condition. Condition values range between -1 (Very Poor) and +1 (Very Good). The TCA v2 found that 35.2% of NFS lands (approximately 73.2 million acres) are in Poor or Very Poor condition (score between -1 and -0.2) with most of these areas occurring in the western United States. The TCA v2 also found that 44.4% of NFS lands (approximately 86.3 million acres) are in Good or Very Good Condition (score between +0.2 and +1.0) and 23.4% or approximately 48.8 million acres are in Moderate condition (score between -0.2 and +0.2). The improved TCA v2 is now being applied to track the outcomes of management activities carried out by the USDA Forest Service. It also provides ecological context for determining restoration priorities and for land management and project planning.