油松和侧柏林地表可燃物负荷量及影响因素

  目的  研究北京地区典型针叶林地表可燃物负荷量及其影响因素，构建可燃物负荷量模型，为可燃物的科学管理提供依据。  方法  结合林分因子（胸径、树高、郁闭度、冠幅、第1活枝高）和地形因子（海拔、坡度），在北京市7个区选择具有代表性的油松林和侧柏林，每种林型各设置42块样地，调查和测定了2种针叶林的可燃物负荷量（上层枯叶、下层枯叶、灌木、草本、1 h 时滞枯枝、10 h 时滞枯枝），采用冗余分析（RDA）研究地表可燃物负荷量与林分因子和地形因子的关系，利用多元线性回归建立总可燃物负荷量模型。  结果  （1）油松林总可燃物平均负荷量为14.31 t/hm2，侧柏林总可燃物平均负荷量为9.78 t/hm2，下层枯叶负荷量占2种针叶林地表总可燃物负荷量的比重最大。（2）RDA分析表明，油松林上层枯叶、灌木可燃物负荷量与胸径呈正相关，下层枯叶负荷量与郁闭度、坡度呈正相关。侧柏林上层枯叶、下层枯叶负荷量与树高、冠幅呈正相关，与海拔呈负相关。灌木可燃物负荷量与树高、郁闭度呈正相关，与海拔呈负相关。2种针叶林总可燃物、1 h 时滞枯枝、10 h 时滞枯枝负荷量均与胸径呈正相关，草本可燃物负荷量与海拔呈正相关。（3）模型表明，胸径、树高、冠幅能较好推算出油松林总可燃物负荷量，第1活枝高、冠幅、坡度能较好的推算出侧柏林总可燃物负荷量。  结论  油松林有发展成较大森林火灾的可能性，根据地表可燃物负荷量，应当着重对林下枯落物可燃物进行管理，及时清理林下可燃物，降低潜在森林火灾风险。不同林型可燃物负荷量与林分因子以及地形因子之间的关系不同，在进行可燃物管理时，应因地制宜，选择合理适宜的措施。 

Land surface fuel load and influencing factors of Pinus tabuliformis and Platycladus orientalis plantations

  Objective  This paper aims to study the land surface fuel load and influencing factors of typical coniferous forests in Beijing, and to establish a fuel load model, so as to provide research basis for the scientific management of fuel.   Method  Based on stand factors (DBH, tree height, canopy density, crown width, height of the first living branch) and terrain factors (altitude and slope degree), representative Pinus tabuliformis and Platycladus orientalis forests were selected in 7 districts and counties of Beijing. 42 sample plots were set for each forest type to investigate and measure the fuel load of two coniferous forests (upper dead leaves, lower dead leaves, shrubs, herbs, 1 h time-lag dead branches,10 h time-lag dead branches), redundancy analysis (RDA) was used to study the relationship between land surface fuel load and stand factors and terrain factors, and the total fuel load model was established by multiple linear regression.   Result  (1) The average total fuel load of Pinus tabuliformis forest and Platycladus orientalis forest were 14.31 and 9.78 t/ha, respectively. The lower dead leaf load accounted for the largest proportion of total fuel load of the two coniferous forests. (2) Redundancy analysis (RDA) showed that the fuel load of upper dead leaves and shrubs was positively correlated with DBH, and that of lower dead leaves was positively correlated with canopy density and slope degree. The dead leaf load of upper and lower layers of Platycladus orientalis was positively correlated with tree height and crown width, and negatively correlated with altitude. The fuel load of shrub was positively correlated with tree height and canopy density, and negatively correlated with altitude. The total fuel load, 1 h time-lag, 10 h time-lag dead branch load of the two coniferous forests were positively correlated with DBH, and the herbage fuel load was positively correlated with altitude. (3) The model showed that DBH, tree height and crown width can calculate the total fuel load of Pinus tabuliformis forest, and the first living branch height, crown width and slope degree can calculate the total fuel load of Platycladus orientalis forest.  Conclusion  Pinus tabuliformis forest has the possibility of developing into a larger forest fire. According to the land surface fuel load, we should focus on the management of forest litter and fuel, timely clean up the fuel under the forest, and reduce the potential forest fire risk. The relationship between fuel load of different forest types, stand factors and terrain factors is different. In fuel management, we should choose reasonable and appropriate measures according to local conditions.