Watching it Burn: Soil Microbes vs. Wildfires



Los Angeles County "Station Fire" view from LAX

Wildfires can devastate ecosystems across the world. In 2012, over 67,000 wildfires raced across more than 9 million acres of land in the US alone. Fuelled by wind and parched vegetation, wildfires burn through everything in their path: plants don’t stand a chance, and even mobile animals struggle to outpace the flames.
But what impact do wildfires have on the beasties that live deep down in the soil? For example, soil-dwelling microbes, like bacteria? These incredibly important organisms help ecosystems to flourish, but their ability to recover after a forest fire – and to help other parts of the ecosystem recover, too – has been largely uncharacterised. Until now.
A team of scientists in China recently calculated that 70-80% of soil microbial biomass (the organic material made up of bacteria and fungi) was lost after wildfires swept through forests in the Greater Khingan mountains. But the flames didn’t fry the bacteria directly. Rather, the fire dramatically altered the soil biochemistry, most importantly changing its pH but also impacting moisture content, carbon/nitrogen ratio’s and ammonium levels.
This meant that the classes of bacteria that were more flexible at growing at an increased pH – like Bacteriodetes and Betaproteobacteria – were able to persist in the soil after the wildfire had swept through. The populations of other bacteria, like Acidobacteria, plummeted, since they were less equipped to grow in their newly scorched and acidified home.
It took 11 years for the original community of bacterial species to re-establish themselves. While this seems staggering, it’s actually a lot quicker than the above ground vegetation, which typically takes 20-100 years to reappear. Intriguingly, the bounce back of soil bacteria and the gradual re-emergence of a happy soil environment probably plays a huge role in the re-establishment of plants, and the animals that eat them.
This research may help to guide environmental efforts by aiming to adjust soil environments to help ecosystems make a speedy recovery after a wildfire.

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