Fire Increases Ecosystem Vulnerability to Future Disturbance Events

The Science

Multiple disturbances to an ecosystem that follow in close succession have the potential to compound their independent effects and strongly alter ecosystem structure and function. In this work, a team of scientists examined how back-to-back extreme events in the form of a burned landscape followed by extreme precipitation could affect a forest landscape. They found that a forest fire leaves marks far deeper than the destruction visible on the surface, making the soil more vulnerable to damage from subsequent flooding.

The Impact

This study is among the very few that have been able to examine the ecosystem effects of multiple disturbances in natural settings. It bridges scientific disciplines by linking changes in soil chemistry, microbiome structure, and biogeochemical function using methods from ecological theory.

Summary

Extreme natural events are often thought to be in isolation from each other—a big wildfire in one season, heavy rains in another. But as climate change makes such disturbances more frequent and intense, ecosystems are likely to face chains of disturbance events in relatively quick succession, with one instance affecting the ability to recover from the next. The compounding effects of multiple disturbances on ecosystem health remain poorly understood, since the unpredictability of natural events makes them challenging to study.

To better understand the issue, a team of researchers repeatedly collected soil samples in Boulder, Colorado’s Four Mile Canyon for over three years after a major wildfire. At the 37-month mark, an extreme precipitation event dropped more than 400 millimeters of rain within a week. Samples were collected from an undisturbed forest landscape and an adjacent fire-disturbed landscape, allowing the researchers to investigate the combined effects of multiple disturbances in comparison to a landscape experiencing only flooding. Researchers assessed the samples’ soil edaphic properties (moisture, pH, percent nitrogen, and percent carbon); bacterial community composition and assembly; and soil enzyme activities. They found that previous fire exposure caused forests to be more strongly affected by a subsequent flooding event than unburned forests. This was driven by increases in pH, shifts in microbiome structure, and increased microbial investment in nitrogen versus carbon cycling.

Principal Investigator

Emily B. Graham
Pacific Northwest National Laboratory
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the U.S. Department of Energy’s Office of Biological and Environmental Research, as part of the Environmental System Science program’s Scientific Focus Area at Pacific Northwest National Laboratory.

References