How did drought affect soil moisture in burned Amazonian forest?

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Soil moisture mediates water exchange among soil, vegetation and the atmosphere. As climate and land use change, more frequent and intense extreme weather and disturbances will likely alter feedbacks between ecosystem functions and soil moisture.

In a field experiment in a transitional forest in southeastern Amazonia, researchers evaluated how extreme drought in 2015/2016 and postfire vegetation regrowth affected seasonal soil water content at depths of 0–8 m. The experiment had three treatment plots: an unburned Control, a plot burned every three years (B3yr), and a plot burned annually (B1yr) between 2004 and 2010.

The researchers hypothesized that B1yr and B3yr would initially have more soil moisture than the Control because of lower transpiration, but that differences between the burned plots would decrease as vegetation regrew. They also expected dry-season soil water deficits to be significantly greater in all plots during drought years as plants responded to greater evaporative demand. Finally, they expected postfire recovery to increase evapotranspiration over time, especially in the topsoil.

Contrary to the first expectation, the burned plots had lower volumetric water content than the Control. Drought significantly reduced soil moisture in all plots compared with non-drought years (15.6%), and the effect was amplified in the burned plots (19%). The results indicate that, although compounding disturbances such as wildfires and extreme droughts alter forest dynamics, deep soil moisture is an essential water source for vegetation recovery.