Spot fire increase the difficulty of fire-fighting and threaten public safety, and therefore it is important to study ignition probabilities of fuel bed by different firebrands, in order to understand ignition mechanisms and analyze the formation of spot fires. This will provide an important basis for further study to improve the fire-fighting efficiency and reduce casualties. In this study, the ignition probabilities of larch (Larix gmelinii) fuel beds with different moisture levels and packing ratios by diffreent firebrands, including cones and twigs of different sizes, was investigated. Ignition experiments were conducted at different wind speeds generated by fans. The results show that, regardless of moisture content and packing ratio, ignition probability is zero when there is no wind. Both moisture content and wind speed significantly influence ignition probability, while packing ratio has almost no effect. The maximum moisture content at which firebrand ignition occurred was 50%, and ignition probability increased with wind speed and decreased with moisture content. Cones have the highest ignition probability, followed by large twigs and by small twigs. Ignition probability is also affected by firebrand shapes and sizes that determine their potential heat and contact area to the fuel bed. Two empirical models were established to link ignition probability with fuel properties and wind speed. This study will help clarify the mechanism of spot ignition and reduce corresponding losses.

To evaluate the applicability of the hourly Fine Fuel Moisture Code (FFMC) to the south-eastern Great Xing’an Mountains, dead fine fuel moisture (Mf) was observed under less-sheltered and sheltered conditions in Scots pine (Pinus sylvestris var. mongolica), larch (Larix gmelinii) and oak (Quercus mongolicus) stands during the summer and autumn of 2014. Standard FFMC and locally calibrated FFMC values calculated hourly were tested using Mf observations and weather data, and the results showed that the Mf loss rate in the less-sheltered forest floor was markedly higher than that in the sheltered forest floor (P < 0.05). The standard hourly FFMC underestimated Mf, especially in stands of larch, the dominant species in the Great Xing’an Mountains, and Mf for rainy days in Scots pine and oak stands. However, the calibrated hourly FFMC predicted Mf in all three forest stands very well (R2 ranged from 0.920 to 0.969; mean absolute errorfrom 2.93 to 6.93, and root-mean-squared errorfrom 4.09 to 7.87), which suggested that it was sufficiently robust for those stands around the observation period. This study will improve the accuracy of Mf predictions to aid fire control efforts in the Great Xing’an Mountains and provide a basis for hourly FFMC model calibration.