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

Abstract

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.

Regional variation in fire weather controls the reported occurrence of Scottish wildfires

“…As with Scottish shrub fuels, summer drought and “curing” of vegetation are not particularly important—rather seasonal patterns of flammability are associated with the autumn-die back of grasses in response to changes in day length (Salim et al, 1988). Notwithstanding this, particularly high values of the DMC and DC may relate to the potential for smouldering of deeper duff and organic soil layers and thus higher severity fires (Davies et al, 2013; Davies et al, 2016b). …”

“…and plant litter. During typical managed burning activities, and many wildfires, these fuels are often too wet to burn (Davies et al, 2016b). Critically therefore, many fires only burn through the heather canopy or the Molinia litter and the high moisture content of the moss and litter actually plays an important role in controlling the efficacy of the traditionally-used “firebeaters” to control and extinguish burns.…”

“…At present The Met Office do not make the underlying codes and indices of the FWI system available, though the full suite of outputs are available from the European Forest Fire Information System which provides up to six-day forecasts on a 10-km grid for the whole of Europe. Previous research in the UK has suggested that the Duff Moisture Code and Drought Code of the FWI system (relating respectively to the moisture content of partially decomposed and deep organic matter) show promise in forecasting fire severity (Davies et al, 2013; Davies et al, 2016b), and that the Fine Fuel Moisture Code (FFMC) may be a tolerable predictor of the wildfire activity (Legg et al, 2007). …”

Development and participatory evaluation of fireline intensity and flame property models for managed burns on Calluna-dominated heathlands

“…Specific details on methods used to assess rate of spread, and the resulting spread patterns observed for these fires, are described in Davies et al (2009). Variation in fuel consumption data are discussed in Davies et al (2016b).…”

“…spp., to fire Taylor et al 2017); and (3) unquantified trade-offs between multiple ecosystem services such as carbon sequestration in organic and peat soils (Ward et al 2007), regulation of catchment hydrology and water quality (Holden et al 2012;Brown et al 2013), agricultural and game production, and the conservation of unique moorland biodiversity (Thompson et al 1995). Attention has also been focused by recent severe wildfires (e.g., Davies et al 2016b), which have the potential to drive long-lasting changes in the ecological function of these peatland systems (Maltby et al 1990).…”