Objective This paper explored the characteristics of dead fuel in main forest types in Longnan City, Gansu Province of northwestern China, and assessed the risk of forest fires, to provid theoretical support for regional forest fire prevention.

Method Taking four main forest types in Longnan City as the research objects, the paper analyzed the difference of dead fuel load, dry to fresh ratio, equilibrium moisture content, ignition point and calorific value, and evaluated the fire risk of different forest types by membership function fuzzy evaluation method.

Result The total dead fuel load of different forest types was Pinus tabuliformis > Larix gmelinii > Quercus > Pinus armandii. The total dead fuel load of Pinus tabuliformis (16.02 t/ha) was significantly higher than others (P < 0.05), and the dead fuel load of humus layer and litter layer 1 was significantly higher than that of litter layer 2 and 3 (P < 0.05). The dry to fresh ratio of dead fuel in Pinus tabuliformis litter layer 1 was significantly higher than that of Larix gmelinii (P < 0.05). The dry to fresh ratio of dead fuel in litter layer 2 was the highest (58.21%−66.47%) and that in humus layer was the lowest (51.29%−55.56%). The equilibrium moisture content of dead fuel in oak was the largest, while that in larch was the smallest. The equilibrium moisture content of dead fuel in litter layer 3 was the highest (16.78%−20.38%), and that in humus layer was the lowest (12.22%−13.86%). The equilibrium moisture content of dead fuel was directly proportional to the diameter of fuel. The ignition point of humus layer was significantly higher than that of litter layer, while the calorific value was opposite (P < 0.05). The fuzzy evaluation results of membership function showed that the fire risk of Pinus tabuliformis stands was the largest, followed by Quercus sp. and Larix gmelinii, and that of Pinus armandii stands was the lowest.

Conclusion There are differences in dead fuel load, dry to fresh ratiod, equilibrium moisture content, ignition point and calorific value among different forest types and components. Pinus tabuliformis forest has the highest load, the lowest ignition point and equilibrium moisture content, which leads to the highest fire risk. Therefore, in the forest management and forest fire prevention in Longnan City, the management of Pinus tabuliformis forest fuel should be strengthened.