Articles | Volume 13, issue 2
Research article
21 Jan 2016
Research article |  | 21 Jan 2016

Vegetation structure and fire weather influence variation in burn severity and fuel consumption during peatland wildfires

G. M. Davies, R. Domènech, A. Gray, and P. C. D. Johnson

Abstract. Temperate peatland wildfires are of significant environmental concern but information on their environmental effects is lacking. We assessed variation in burn severity and fuel consumption within and between wildfires that burnt British moorlands in 2011 and 2012. We adapted the composite burn index (pCBI) to provide semi-quantitative estimates of burn severity. Pre- and post-fire surface (shrubs and graminoids) and ground (litter, moss, duff) fuel loads associated with large wildfires were assessed using destructive sampling and analysed using a generalised linear mixed model (GLMM). Consumption during wildfires was compared with published estimates of consumption during prescribed burns. Burn severity and fuel consumption were related to fire weather, assessed using the Canadian Fire Weather Index System (FWI System), and pre-fire vegetation type. pCBI varied 1.6 fold between, and up to 1.7 fold within, wildfires. pCBI was higher where moisture codes of the FWI System indicated drier fuels. Spatial variation in pre- and post-fire fuel load accounted for a substantial proportion of the variance in fuel loads. Average surface fuel consumption was a linear function of pre-fire fuel load. Average ground fuel combustion completeness could be predicted by the Buildup Index. Carbon release ranged between 0.36 and 1.00 kg C m−2. The flammability of ground fuel layers may explain the higher C release-rates seen for wildfires in comparison to prescribed burns. Drier moorland community types appear to be at greater risk of severe burns than blanket-bog communities.

Short summary
We examined the variables controlling fire severity and the amount of vegetation burnt during wildfires and prescribed burns. Fire severity varied strongly within and between wildfires in relation to fire-weather conditions and vegetation type. The amount of surface vegetation burnt was a function of the amount present pre-fire, whilst moss layer consumption related to prolonged dry periods. Moss flammability may explain the higher carbon-release during wildfires compared to prescribed burns.
Final-revised paper