Abstract: Pinus massoniana is a pioneer species in the coniferous forest in southern China, which is one of the flammable forest community types. The knowledge on pyrolysis characteristics of surface fuels in Pinus massoniana forests is of great significance to improve fire behavior model and forest surface fuels management measures. Pyrolysis processes and parameters of both 1 h dead fuel (1 h fuel) and 10 h dead fuel (10 h fuel) for different stand age groups of Pinus massoniana forest in Mount Wuyi were examined by the thermogravimetric analysis. The kinetic analysis of rapid pyrolysis stage was examined using Coats-Redfem integration method. A four-dimensional feature of their combustibility was evaluated based on four pyrolysis parameters (ignition temperature, average weight loss rate of healzocellulose, decomposition time of healzocellulose, and total mass consumed by combustion). The results showed four stages in the pyrolysis process of surface dead fuels in different stand age groups of Pinus massoniana forest. The pyrolysis temperature of holocellulose ranged from 170 ℃ to 371 ℃, and the weight loss was 50%-60%. The pyrolysis temperature of lignin ranged from 358 ℃ to 496 ℃, and the weight loss was 20%-40%. In the pyrolysis stage of dead surface fuels, the activation energy of holocellulose ranged from 50.03 kJ·mol^-1 to 61.83 kJ·mol^-1, and that of lignin ranged from 17.39 kJ·mol^-1 to 64.48 kJ·mol^-1. Across stand age groups, 1 h fuel and 10 h fuel in young Pinus massoniana forest were the most ignitable, with lasting burning duration, high consumption but low intensity. In terms of shady slope and sunny slope, there was relatively consistent ignitability in the 1 h fuel, but quite different for the features of combustibility, sustainability and consumability. There was different for four-dimensional flammability features for 10 h fuel. The results of four-dimensional flammability evaluation showed that the flammability of surface dead fuels in Pinus massoniana forest had distinct heterogeneity among different stand age groups and aspects. Therefore, the effects of heterogeneity characteristics of both aspect and stand age should be fully considered in the construction of fire behavior model for higher simulation accuracy.

Key words: thermogravimetric analysis, Coats-Redfem integration method, combustibility, pyrolysis characteristics, Mount Wuyi National Park.