Computer simulations of fire behaviour in garrigue in southern France

Garrigue is a low shrubland covering extensive areas in southern Europe, in which recurrent fire is both a natural ecological process and hazard. To analyse some aspects of this dualism, detailed descriptions of fuel types were entered into a computer simulation of fire behaviour. Samples of fuel types were collected for stands of 3, 9, and 33 years since last fire in garrigue of dense Quercus coccifera in southern France. To represent spring and autumn conditions, respectively, two models were used: one with herbaceous biomass evenly divided between living and dead categories, and a second with all herbaceous biomass counted as dead. The moisture contents for these models were estimated from prior observations and for relatively dry conditions. To incorporate the impact of a common fire-fighting tactic, a third fuel model was created by calculating the moisture that would be added to the surface areas of standing fuel by an aircraft water drop of 0.5 kg m −2 on the second, autumn, fuel type. These three fuel models for each of the three stand ages were entered in a computer simulation that calculated several measures of fire intensity, including fire power, rate of spread, and the temporal pattern of heat release following the passage of the flaming front. The simulations show that the added water extinguishes fire. Without the added water the fire burns relatively slowly, especially if compared to fires observed and simulated in southern California, where water drops are often ineffective. The simulations indicate that prescribed burns could be conducted with low risk at an interval of 10–15 years.