Biomass and litter accumulation patterns in species-rich shrublands for fire hazard assessment

Abstract

Fuel age is an imprecise surrogate for fire hazard in species-rich Mediterranean-type shrublands. We present an efficient method for aerial biomass and litter estimation of shrublands on sandy and calcareous substrates in south-western Australia that enables fuel accumulation patterns to be compared independently of vegetation age. For sites ranging 3–16 years since last fire, total available fuel loads were 2.7–7.6 t ha–1 for the sandplain and 2.6–8.14 t ha–1 for the calcareous shrublands. Despite calcareous shrublands having higher soil nutrient concentrations and winter rainfall, total available fuel loads were similar between community types over the range of fuel ages examined. Sandplain biomass was dominated by resprouters and calcareous sites, by non-sprouters. Topographic variation in fuel loads was observed among sandplain sites, with greater available biomass and litter on the deeper sands of dunes compared to swales. More rapid fuel accumulation at the youngest sites and more uniform canopy structure in the calcareous shrublands indicate that they have the potential to support fire at shorter intervals than the sandplain. For each community type, an allometric equation based on the relationship between average maximum plant height and total available fuel was derived that enables rapid estimation of fuel loads that is more accurate than using fuel age.