【Objective】This study aims to reveal the influencing factors, inter-layer relationship and change trend of the flammability of surface litter, in order to provide data support for the assessment of the flammability of the northern forest burned area and its ecological restoration. 【Method】In this paper, the burned slash of natural Larix gmelinii forest in Tahe forestry bureau of Daxing’an Mountains was targeted. The physical and chemical properties (ash content, fat content and calorific value) and enzyme content (cellulase, hemicellulase and ligninase) of the aboveground litter were investigated. One way ANOVA was used to compare the significant differences in litter flammability and enzyme activities in each recovery period since fire. Pearson correlation and redundancy analysis were used to explore the correlation of each factor. Paired sample t-test was used to compare the temporal change trend of flammability and enzyme activity in litter and fermentative layer. Linear regression equation was used to fit the coupling model of crude fat, ash content and calorific value, and the linear slope significance test was used to verify the consistency of inter-layer slope. 【 Result】 1) The flammability of litter layer increased with the recovery time, and the crude fat content and high calorific value were significantly higher than those of the control group in the late recovery period, while the ash content was significantly lower than that of the control group. The indexes of semi-decomposition layer changed obviously. In addition, the content of enzymes in the litter ranged as cellulase > hemicellulase > ligninase, and all the three enzymes showed a decreasing trend in the recovery period after fire. 2)The aspect and position of slope were important factors affecting the burning property of litter layer. The crude fat content and high calorific value of litter layer were higher in shady slope and bottom of slope, while ash content was opposite. 3)The crude fat content and higher heating value in litter were significantly higher than that in fermentative layer, and there was not significant correlation between them. The ash content in litter was significantly lower than that in fermentative layer, and there was significant positive correlation between them. The ash free calorific value, hemi cellulase, ligninase and cellulase content in litter were higher than those in fermentative layer, and there was no significant correlation between layers. There was a significant positive correlation between the content of cellulase in litter and fermentative layer. 4) There was a very significant linear relationship between crude fat content, ash content and higher heating value in litter. The slope of the model of crude fat content and higher heating value in fermentative layer was significantly higher than that in Litter, and the slope of the model of ash content and higher heating value was the same in two layers. 【Conclusion】The flammability of aboveground litter in burned area have recovered and exceeded the original habitat 16-27 years after the fire. The combustibility in litter is stronger than that in fermentative layer, and the difference between layers decreases as the recovery time increases. Terrain factors have a significant impact on the flammability of aboveground litter, thus it is necessary to make a comprehensive assessment of forest combustibility by multi factors in accordance with local conditions. Cellulase content can affect the ash content, crude fat and higher heating value of aboveground litter. The linear model of ash content and high calorific value of aboveground litter is y = 21. 225 - 0. 207 x (y is high calorific value, x is ash content, P < 0. 001, R2 = 0. 908), which has a good goodness of fit. After further verification, it can be used as a reference to add a new way to rapidly estimate calorific value and combustibility of surface fuel and predict forest fire occurrence. © 2022 Chinese Society of Forestry. All rights reserved.
