Background

Forest ecosystems function as the largest terrestrial carbon sink globally. In the Western US, fires play a crucial role in modifying forest carbon storage, sequestration capacity, and the transfer of carbon from live to dead carbon pools. We utilized remeasurements of more than 700,000 trees from 24,000 locations from the US Department of Agriculture Forest Service’s Forest Inventory and Analysis program (FIA) and incorporated supplementary information on wildfires from the Monitoring Trends in Burn Severity dataset. These datasets allowed us to develop models that examined the impact of fires, in conjunction with other abiotic and biotic drivers, on estimates of carbon stocks, stock changes, and sequestration capacity in forested areas in the Western US.

Results

Wildfires were a primary factor contributing to the reduction of aboveground carbon storage in Western U.S. forests. All models indicated that biotic factors (e.g., tree density, canopy coverage, and tree height) played a more significant role than abiotic factors (e.g., elevation, mean annual temperature and drought severity) in determining fire effects on forest carbon storage and sequestration capacity. Due to a lower occurrence of fires and higher precipitation, forests in the Pacific Northwest-West region with lower-elevation exhibited higher productivity compared to other regions.

Conclusions

The findings of this study enhance our understanding of the influence of fires on carbon dynamics in forest ecosystems in the Western US. In particular, the importance of understanding biotic conditions such as forest structure and composition was revealed as a primary determinant of carbon emissions from fire. These insights are valuable for forest carbon estimation beyond FIA sampling plots, extending to inaccessible forest land in future studies. Consequently, they are beneficial for forest managers developing strategies for storing and sequestering carbon in fire-prone forest ecosystems.