Where forest may not return in the western United States

Area of Science:

• Forest Ecology
• Disturbance Ecology
• Remote Sensing

Background:

• Increasing frequency and severity of droughts, pest outbreaks, and fires raise concerns about western US forest recovery.
• Existing field studies and meta-analyses offer insights but lack a comprehensive estimate of impaired forest succession extent.
• Variability in study methods hinders a unified assessment of forest resilience.

Purpose of the Study:

• To estimate the area of potentially impaired forest succession in the western United States.
• To identify primary disturbance agents and factors hindering forest regrowth.
• To quantify the spatial extent of forests at risk of not returning to prior composition and structure.

Main Methods:

• Modeling an 18-year time series of land cover and Normalized Difference Vegetation Index (NDVI).
• Utilizing an extensive ancillary dataset to support the modeling.
• Estimating the proportion of impaired areas with limited seed sources within a defined neighborhood.

Main Results:

• An upper bound estimate of approximately 3470 km² of disturbed forest may not recover or reattain its prior state.
• Wildfire is identified as the principal disturbance agent, though climatic factors are also significant.
• Approximately 20% of the estimated impaired area lacks forest cover within a 4.4-ha neighborhood, indicating seed source limitations.

Conclusions:

• The study provides a quantitative estimate of potentially impaired forest succession in the western US.
• Fire is a major contributor to impaired forest recovery, alongside climate change impacts.
• Limited seed availability exacerbates the challenge of forest regeneration in affected areas.