Additional Funding Sources
This research is supported by the Adele Berklund Undergraduate Research Award.
Abstract
Wildfires throughout the western United States are expected to increase in frequency and severity in the coming years due to climate change and the disruption of natural fire regimes over the past century. As the belowground microbial community plays a critical role in the storage and transfer of carbon in terrestrial ecosystems, understanding how wildfire impacts belowground functioning will be key in our ability to respond to future disturbances. While past studies have focused on the belowground responses to prescribed burns or to wildfires at the stand level, we are the first to couple tree-level belowground measurements with visible aboveground damage at variable levels of fire damage. We measured soil moisture, root density, and microbial biomass underneath individual trees in a mature ponderosa pine stand, one and two years after a mixed-severity wildfire. In 2021, (one-year post-fire), overall root density declined as the severity of tree damage increased (p < 0.01, R2 = 0.11). In 2022, we separated the roots by size class and found that specifically fine (< 0.2mm) root density decreased with tree damage (p = 0.01, R2 = 0.2). In addition, we found that soil moisture significantly increased with tree damage (p = 0.02, R2 = 0.29). The lower fine root density coupled with higher soil moisture under the most severely burned trees suggests changes in belowground functioning. Supporting this notion, preliminary microbial biomass measurements indicate a possible decrease in microbial carbon associated with increasing severity of aboveground damage. Quantifying belowground thresholds (e.g., degree of loss of roots and microbial biomass) beyond which whole-tree recovery is improbable is paramount for predicting ecosystem carbon trajectories and informing post-fire management practices.
How Does Belowground Functioning Vary Among Trees with Different Levels of Fire Damage?
Wildfires throughout the western United States are expected to increase in frequency and severity in the coming years due to climate change and the disruption of natural fire regimes over the past century. As the belowground microbial community plays a critical role in the storage and transfer of carbon in terrestrial ecosystems, understanding how wildfire impacts belowground functioning will be key in our ability to respond to future disturbances. While past studies have focused on the belowground responses to prescribed burns or to wildfires at the stand level, we are the first to couple tree-level belowground measurements with visible aboveground damage at variable levels of fire damage. We measured soil moisture, root density, and microbial biomass underneath individual trees in a mature ponderosa pine stand, one and two years after a mixed-severity wildfire. In 2021, (one-year post-fire), overall root density declined as the severity of tree damage increased (p < 0.01, R2 = 0.11). In 2022, we separated the roots by size class and found that specifically fine (< 0.2mm) root density decreased with tree damage (p = 0.01, R2 = 0.2). In addition, we found that soil moisture significantly increased with tree damage (p = 0.02, R2 = 0.29). The lower fine root density coupled with higher soil moisture under the most severely burned trees suggests changes in belowground functioning. Supporting this notion, preliminary microbial biomass measurements indicate a possible decrease in microbial carbon associated with increasing severity of aboveground damage. Quantifying belowground thresholds (e.g., degree of loss of roots and microbial biomass) beyond which whole-tree recovery is improbable is paramount for predicting ecosystem carbon trajectories and informing post-fire management practices.