Resilience of peaty systems to low-severity wildfires in the Cairngorms
Wildfires are a major disturbance affecting a variety of Earth’s ecosystems, including ecosystems containing peat. Fires test the resilience of peaty systems through their impacts on interconnected ecosystem components, many of which are understudied. Understanding the role of fire in peaty systems is critical, because peatlands are the most carbon-dense terrestrial environment, they face an increased fire risk due to shifting fire regimes, and there is a need to understand the current resilience of our landscapes to fire. Peaty systems exist in a broad range of environments with diverse ecologies, land-use histories, and climates, all of which are combined with a wide range of associated fire regimes, which we introduce in Chapter 1. Existing research typically examines fire effects on specific peaty environments in isolation and only at one point in time. These as well as other factors result in substantial variability across the literature in how peaty systems respond to fire. This thesis investigates how fire modifies ecosystem functioning (peatland ecology and biogeochemistry) and subsequent ecosystem resilience across different types of peaty systems, and over time. We conducted field studies in the Cairngorms National Park in northern Scotland (undertaken 2022-2023) across three peaty systems affected by wildfire (peatland, forested peatland, and forest), measured one growing season post-fire, plus a Pinus sylvestris forest chronosequence (3 weeks to 22 years post-fire). We used these sites to investigate vegetation community resilience to fire using detailed surveys (Chapter 2) and to investigate post-fire soil organic matter (SOM) persistence using soil sampling and laboratory analyses (Chapter 3). In Chapter 4, we present a global meta-analysis of fire effects on peatland carbon (C) stocks and fluxes, contextualising our primary data analyses. Lastly, in Chapter 5, we synthesise our findings, evaluate ecosystem resilience, assess broader applicability, consider climate change implications, discuss management strategies, and identify future research needs. We find that following low-severity fire, vegetation communities across peaty systems are resilient via fire-adapted traits of dominant species groups in drier habitats and fire-resistant traits of specific species in wetter habitats (Chapter 2). We find that soil organic matter is able to persist following fire across environments: in carbon rich deep peatlands, a reduced SOM decomposition capacity minimises losses, whereas in shallow-peat forests, improved litter quality and microbial transformation within mineral-associated organic matter pools may enhance persistence (Chapter 3). These results align with our global meta-analysis, which shows that despite a high level of heterogeneity between studies, many peatlands exhibit minimal soil carbon losses from fire, especially when they are unmodified (Chapter 4). However, evidence from a higher-severity burn in our study, and results from our meta-analysis, suggest that the mechanisms supporting vegetation recovery, the persistence of SOM and soil C under low-severity fire can be overwhelmed by more severe burns. Overall, our results demonstrate that a range of peaty systems are resilient to low-severity wildfire. However, climate change and land management decisions will interact to determine whether peaty systems maintain their resilience under future fire regimes.
Cairngorms National Park, Carbon, Disturbance regimes, Ecology, Fire, Peaty systems, Resilience, Scotland, Soil organic matter, Vegetation recovery
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