Empirical modelling of surface fire behaviour in maritime pine stands

An experimental burning program took place in maritime pine (Pinus pinaster Ait.) stands in Portugal to increase the understanding of surface fire behaviour under mild weather. The spread rate and flame geometry of the forward and backward sections of a line-ignited fire front were measured in 94 plots 10-15m wide. Measured head fire rate of spread, flame length and Byram's fire intensity varied respectively in the intervals of 0.3-13.9 m min(-1), 0.1-4.2 m and 30-3527 kW m(-1). Fire behaviour was modelled through an empirical approach. Rate of forward fire spread was described as a function of surface wind speed, terrain slope, moisture content of fine dead surface fuel, and fuel height, while back fire spread rate was correlated with fuel moisture content and cover of understorey vegetation. Flame dimensions were related to Byram's fire intensity but relationships with rate of spread and fine dead surface fuel load and moisture are preferred, particularly for the head fire. The equations are expected to be more reliable when wind speed and slope are less than 8 km h(-1) and 15 degrees, and when fuel moisture content is higher than 12%. The results offer a quantitative basis for prescribed fire management.