Influence of fuel moisture content on the burning of cistus shrubs exposed to a low-intensity fire

The aim of this study was to investigate experimentally the influence of fuel moisture content on the fire behaviour of Cistus monspeliensis, when exposed to a fire front spreading across a fuel bed. Shrubs of Cistus monspeliensis with leaf moisture contents ranging between 10 and 100 % were placed under a Large Scale Heat Release Calorimeter and a bed of wood wool was used before and under the branches to mimic an ignition from an underneath burning herbaceous layer. Mass loss, heat release rate (HRR) and total heat release (THR) were measured. The peak of HRR, the THR and the effective heat of combustion decreased linearly with the leaf moisture content. Two thresholds, characteristics of the fire behaviour of Cistus monspeliensis, were obtained. The ignition threshold, equals to 85%, is the maximum leaf moisture content at which the cistus will ignite. The spreading threshold, equals to 55%, is the maximum leaf moisture content at which the flame front will spread through the branches.