The biogeochemical response of chaparral and oak woodland ecosystems to prescribed fires

Alandra Lopez, Claudia Avila, Katie Huy, Scott Fendorf (Stanford and University of San Diego)

Claudia Christine Avila, Alandra Marie Lopez, Katie Huy, and Samuel Pierce complete a successful day of soil sampling before the prescribed fires occur.

Summary

This project investigates how biogeochemical changes in soils (organic matter, nutrient availability, and soil-borne metals). are influenced by fire conditions, ecosystem type, and geologic parent material.

The chemical composition of soils can be altered depending on burn severity. Previous research (Lopez, Pacheco, Fendorf, 2023, Nature Communications) showed that severe wildfires can generate hazardous forms of soil-borne metals that pose a concern to air quality. This project investigates the immediate effects of pile burning conducted March 2024, as well as the extended biogeochemical impacts of pile burn scars as follows:

What is the extent of fuel and soil heating during pile burns? Researchers will capture soil temperature profiles and soil cores following pile burning to understand the coupling of temperature conditions with soil biogeochemical changes across depth.
What is the quantity and composition of smoke emissions produced from pile burning? What is the inorganic chemical composition of prescribed fire smoke? Filter-based air samplers collected particulate matter during pile burning to analyze the chemical composition and examine particle size, morphology, and characteristics using microscopy and synchrotron methods. This project aim is in collaboration with Jessica Yu.
How do pile burns alter soil biogeochemistry near surface soils, and do these changes depend on ecosystem type and parent geology? By sampling periodically after the burns, researchers will explore how ash and thermally-altered soil minerals are incorporated into the underlying soil profile over time. Changes in soil mineralogy, organic matter content, pH, chemical composition, and the bioavailability of soil-derived metals and nutrients will be measured in both chaparral and oak woodland habitats.
Does geology and associated soil mineralogy control pyrogenic organic matter decomposition in burned soils? By sampling periodically following the pile burns and sequencing microbes, they will assess how post-fire microbial processing changes over time. This project aim is in collaboration with Katie Huy's project.