29 May 2024

Soil, wildfires and recovery: how much do we know?

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A U.S. study reviews current knowledge about wildfires and the resilience of ecosystems. Some factors can promote regeneration. Others end up impeding it

by Matteo Cavallito

 

The most severe wildfires can alter soil chemistry with obvious consequences for ecosystem recovery and human health. These mechanisms, however, are still poorly understood, suggesting the need for more intensive monitoring and subsequent theoretical modeling. This is supported by a study by a group of scientists from Stanford University and Colorado State University.

A better understanding of the mechanisms at work would help make more informed decisions on some key issues, a statement from the authors points out. Such as “how to treat drinking water sourced from burned areas, support reforestation, and protect workers against toxins during cleanup, rebuilding, or revegetation.”

Wildfires can lay the groundwork for regeneration

The investigation falls into the category of so-called review studies, or those researches that, by reviewing the major works already carried out, draw a picture of the overall knowledge about the phenomenon at the global level. “In this Review,” the study says, “we outline the molecular-scale transformations and biogeochemical interactions of soil organic matter (SOM) and metals induced by wildfires and explore their impacts on post-fire human health and ecosystem recovery.”

Wildfires, in particular, “enhance organic matter solubility and increase the number of nitrogen-containing SOM molecules by up to 32%.” These effects, the researchers note, set the stage for regrowth.

…or hinder it

Regeneration, however, also depends on the presence of other chemicals, the authors note. These include certain types of organic molecules called karrikin that are formed in the soil during fires and are necessary for the germination of many seeds. If local soil chemistry and fire conditions do not produce enough of these, the note points out, regeneration can be hindered.

In addition, flames can significantly increase the concentration of toxic hydrocarbons in the soil that inhibit ecosystem recovery. These molecular-scale effects, the researchers point out, could explain the still-mysterious phenomenon observed in large areas of the Rocky Mountains in the western United States, where trees have struggled to regrow after wildfires.

The impact on climate

Among the issues to be clarified, the study notes, is also the impact of wildfires on climate. For a long time it was thought that the remains of burned material could act as reservoirs by trapping carbon and thus preventing its release into the atmosphere as CO2. This hypothesis, however, is now questioned. Although, on balance, the understanding and ability to quantify the phenomenon still appear limited today.

Over the past 50 years, the study further points out, “the frequency of high-severity fires and the extent of total burn area have increased, transforming both the organic and inorganic composition of soil.” This phenomenon, which generates increasing costs, obviously imposes the need to better understand all the mechamisms involved. “ to better understand and mitigate the negative effects of wildfires,” the authors conclude.