Contrasting litter-layer biomass and thickness following wildfire in a southwestern Amazon forest

Wildfires are becoming frequent in the Amazon rainforest, yet little is known about how litter-layer thickness and biomass following fire disturbance. Using a case study in Humaitá Forest Reserve, southwestern Amazon, Brazil, we investigated how litter-layer thickness and biomass differed among three stands across seasons. We compared a control stand with no recorded fire during the 1985–2026 MapBiomas Fire time series, a single-fire stand with one fire in 2005, and a two-fire stand with fires in 2005 and 2022. Monthly sampling was conducted from December 2024 to November 2025 using a Marimon-Hay litter collector-measurer, a device to collect and quantify litter material accumulating on the forest floor. The two-fire stand had lower litter-layer thickness and biomass than the control, whereas the single-fire stand had lower litter-layer thickness but similar biomass to the control. Litter-layer thickness showed seasonality, with higher values during the dry season and lower values during the rainy season. Litter biomass varied among months and was positively associated with precipitation, whereas litter-layer thickness was not. After nearly two decades without a new fire event, litter biomass in the single-fire stand was comparable to that in the control stand, whereas litter-layer thickness remained lower. The two-fire stand, sampled three years after the last fire, showed lower values for both variables. These contrasting patterns indicate different responses of litter-layer thickness and biomass following fire disturbance. Because fire frequency and time since the most recent fire are confounded, differences among stands cannot be attributed to the number of fire events.