Fire severity is more sensitive to low fuel moisture content on Calluna heathlands than on peat bogs

摘要

AbstractMoorland habitats dominated by the dwarf shrubCalluna vulgarisprovide important ecosystem services. Drought is projected to intensify throughout their range, potentially leading to increased fire severity as moisture is a key control on severity. We studied the effect of low fuel moisture content (FMC) on fire severity by using 2 ×2m rain-out shelters prior to completing 19 experimental fires in two sites in Scotland (UK): a dry heath with thin organic soils and a raised bog with deep, saturated peat, both dominated byCalluna vulgaris. Reduced FMC of the moss and litter (M/L) layer at both sites, and the soil moisture of the dry heath, increased fire-induced consumption of the M/L layer and soil heating at both sites. Increase in fire severity was greater at the dry heath than at the raised bog, e.g. average maximum temperatures at the soil surface increased from 31°C to 189°C at the dry heath, but only from 10°C to 15°C at the raised bog. Substantial M/L layer consumption was observed when its FMC was below 150%. This led to larger seasonal and daily soil temperature fluctuation, particularly at the dry heath during warm months. The results suggest that low FMC following predicted changes in climate are likely to increase wildfire severity and that the impact on vegetation composition and carbon stores may be greater at heathlands than at peatlands. Managed burning aiming to minimise fire severity (e.g. ignition of the M/L layer and exposure to lethal temperatures of ericoid seeds) should be carried out when the FMC of the M/L layer is above 150% and the FMC of the soil is above 200–300%.Graphical abstractDisplay OmittedHighlights•Altered fire regimes due to drought may impact onCallunaecosystem services.•Low fuel moisture content before managed burning increased fire severity.•Increase was stronger at the dry heath than at the raised bog.•Moss layer and soil moisture contents were key controls on fire severity.•Heathlands may be more susceptible to burning under drought than peatlands.