No Wildfire Legacy Effect on Peat Carbon Stability Under Severe Drought in a Lowland Peat Mosaic

Abstract

Ongoing climate change, particularly warmer and drier conditions, disrupts hydrological stability in peatland ecosystems and elevates wildfire risk. Higher burn severity and frequency are expected to accelerate carbon (C) losses and amplify climate-carbon feedback. In this study, we used an accidental and short-lived wildfire that occurred in 2020 at Landschap De Liereman (Belgium), a mosaic landscape ranging from poor-fen to bog-like peatlands, to investigate how belowground C dynamics respond to peatland fire in the subsequent four consecutive years under ongoing climatic pressures. A paired plot design was established, consisting of burnt and nearby intact plots, based on field measurements in combination with remote sensing data. Burnt peatland patches with no smoldering fire were significantly altered during the first 2 years after the fire, evidenced by a lower topsoil C:N ratios, reduced C and N isotopic values (Ps < 0.05), and shifts in soil organic matter (SOM) composition. Especially, carbohydrates declined whereas benzenes and N compounds increased (p < 0.05), indicating depletion of labile C and accumulation of recalcitrant aromatic C leading to lower soil organic carbon (SOC) decomposability (i.e., basal respiration per unit peat C, p < 0.05). These differences diminished within 3 years, with very little changes in bulk soil C and N contents between intact and burnt plots, suggesting a relatively high resilience to a low-severity fire. However, in 2022, abrupt changes in soil C and N concentrations, SOM composition, and SOC decomposability were observed in all paired plots, regardless of whether they were affected by the fire, and that were likely related to drought stress, as 2022 was an exceptionally dry year. The damage of this drought was substantial, but not different between intact and burnt plots, indicating that there was no fire legacy effect on soil components and C stability in surface peat.