Differences in soil chemistry remain following wildfires on temperate heath and blanket bog sites of conservation concern

Wildfires have the potential to change the physico-chemical characteristics of soils, and further research is required to establish the nature, extent and duration of these impacts. The extent to which the impacts of wildfires differ from the more frequently studied prescribed burns is an active area of investigation with serious implications for landscape managers and conservation biologists. Here, we take advantage of multiple large wildfires which occurred in vulnerable upland habitats of conservation importance, to measure in-situ differences in soil conditions between burnt and unburnt areas ca. 1.5 years and 3.5 years after fires. There were no detectable differences in pH, total nitrogen, total carbon, potassium or magnesium concentrations between burnt and unburnt locations 15-18 months after wildfires, suggesting that these were either unaffected by the fires, or more likely, as suggested by previous research, had exhibited transient differences immediately after the wildfires which had returned to baseline conditions within 1.5 years. By contrast, burnt and unburnt locations differed with respect to phosphorus and calcium concentrations which remained elevated up to 3.5 years post-fire. Calcium concentrations remained greater in burnt plots across all three habitat types, whilst available phosphorus concentrations remained elevated in blanket bog but returned to the same level as unburnt control plots in wet and dry heath. Taken together, our findings suggest that there is the potential for wildfires to have longer-lasting effects on phosphorus and calcium concentrations in some temperate European Annex I habitats of conservation concern, particularly blanket bog, than previously expected based on results of studies of experimental burning or wildfires in other habitat types. The magnitude and duration of fire impacts on soils depends largely on the environmental and meteorological characteristics of the region. Hence, this study highlights the need for more research across a broader range of sites taking advantage of unexpected wildfires, to assess the extent to which their impacts may differ between habitat types and from those of experimental or controlled burning.