Spatial continuity of fuels in major coniferous forests in Beijing mountainous area: fuel horizontal continuity and crown fire spread

To study the effects of fuel loads and its horizontal distribution on potential fire behavior characteristics, fuel horizontal continuity index (D) and ratings were founded through analyses of crown fuel loads, composition, and physicochemical properties of the crown layers in major coniferous forests (Platycladus orientalis , Pinus tabuliformis) in the mountainous area of Beijing. Based on D and ratings, the hazard of crown fire spread was evaluated and analyzed for the two coniferous forests. The results showed that fuel loads had significant effects on the rate of fire spread; the rate of spread increased with the increase of fuel loads, and the amplitude of increase had much relationship with fuel compactness; the influence of wind speed on rate of spread was very significant, which had a greater effect than slope on fuel horizontal continuity; in the same wind conditions, crown fire spread in P. tabuliformis forest (PTF) was faster than P. orientalis forest (POF); an average of D was 1.470 (highly continuous) in POF, while it was 0.933(moderately continuous) in PTF. Therefore, spread of crown fire in POF is more dangerous than PTF，indicating that POF can more easily cause the high strength crown fire in large area than PTF when forest fire occurs; D is mainly affected by coniferous crown fuel loads and its spatial distribution, wind speed and slope and their synergistic action.