ObjectiveStand structure is closely related to the fire behavior. Adjusting the stand structure can effectively lower the fire behavior. Analysis of the relationship between the structure of Pinus tabuliformis forest and the potential fire behavior on the surface of Miaofeng Mountain in Beijing provides scientific basis for the development of Miaofeng Mountain combustibles management measures.

MethodIn this paper, the Pinus tabuliformis forest with similar topography and large structural difference was taken as the research object, and the data on trees, shrubs, herbs and fuel in the plot were investigated and measured. The fire behavior index was calculated by Rothermel model. The Pearson correlation analysis method was used to study the potential fire behavior of Pinus tabuliformis forests and its relationship with stand structure.

Result(1) The potential fire spread rate (R), fire intensity (I) and unit area combustible heat (HPA) of Pinus tabuliformis were 2-6m/min, 300-1400kW/m and 4000-5500kJ/m², respectively. There were also several larger values with fire behavior. (2) For the correlation between surface fire behavior and stand structure, in the arbor layer, R, I and average tree height (H) showed significantly positive correlations, and had little correlations with height of the lowest branches(H_t), cverage crown (C_t), the rate of crown length (TCR_t) and diameter at breast height (D_g). In the shrub layer, R, I had a significantly negative correlation with shrub density (BD_s) and N, but less correlated with shrub number (H_s). There was a significantly positive correlation between HPA and H_s. And BD_s, N too large or too small were conducive to enhance the surface fire behavior, but when the shrub was moderate, the surface fire behavior was the lowest. In the layer of herb and fuel, bed height (h), herb coverage (C_h) and I showed a significantly positive correlation. The significant correlation between tightness (β) and logI was significantly correlated with HPA.(3)Interpretation of potential fire behavior on the surface, herbaceous fuel layer structure index>shrub layer structure index>arbor layer structure index. The interaction of herbaceous fuel layer and shrub layer structure index contributed the most.

ConclusionThe potential fire behavior of Pinus tabuliformis forest is generally in low-intensity surface fire, which can cause medium-intensity surface fire and has the possibility of causing high-intensity surface fire. The potential fire behavior on the surface is positively correlated with the structure of the tree layer and the herb fuel layer, but negatively correlated with the shrub layer structure. Among them, the H_t of the arbor layer, the BD_s, N and shrub coverage (C_s) of the shrub layer, and the C_h, h and β of the herb and fuel layer have significant effects on the surface potential fire behavior, and the effects of each level are herbaceous fuel litter layer>shrub layer>arbor layer. On the whole, the potential fire behavior of the surface is mainly affected by the above-ground combustibles, especially the herbaceous fuel layer, while the influence of the arbor layer is relatively small.