火烧强度对山西太岳山油松林地表可燃物的影响

Effects of fire intensity on surface fuel of Pinus tabuliformis in Taiyue Mountain,Shanxi Province

【目的】分析不同火烧强度下油松林地表可燃物负荷量特征及其与火后环境因子间的关系,并研究林下草本和灌木层的物种多样性特征,为有效管理油松林地表可燃物及探索火烧迹地林下植被早期更新提供依据。【方法】以山西太岳山天然油松林火烧迹地为研究对象,根据不同火烧强度(轻度火烧、中度火烧和重度火烧)分别设置3块20 m×20 m的样地,以未过火样地为对照,统计各样地中未烧死木株数百分比、树木平均熏黑高度、平均胸径、林分密度等林分因子及坡向、坡度、海拔等地形因子;每块样地中再设置2 m×2 m和1 m×1 m的样方各5个,调查样方内未分解落叶、半分解枯叶、1 h时滞枯枝、10 h时滞枯枝等死可燃物负荷量和灌木、草本等活可燃物负荷量,并测量灌木和草本层的物种数、株数、盖度、密度和频度,计算物种多样性指数。利用多重比较(LSD)法分析不同强度火烧迹地地表可燃物负荷量和林下草本与灌木层的物种多样性,通过冗余分析(redundancy analysis,RDA)探讨各林分因子和地形因子对地表可燃物负荷量的影响。【结果】①不同火烧强度对油松林地表可燃物总负荷量影响显著(P<0.05),未分解落叶(P<0.05)、半分解落叶(P<0.05)、1 h时滞枯枝(P<0.05)、10 h时滞枯枝(P>0.05)等死可燃物负荷量随着火烧强度的增加呈下降趋势,草本(P<0.05)、灌木(P<0.05)等活可燃物负荷量则呈先下降后上升趋势。②RDA分析表明,半分解落叶可燃物负荷量与未烧死木株数百分比呈正相关,与平均熏黑高度呈负相关;1 h时滞枯枝、草本可燃物负荷量与平均胸径呈显著负相关;未分解落叶可燃物负荷量与坡度呈正相关,灌木可燃物负荷量与海拔呈正相关。③不同火烧强度对油松林草本层Shannon-Wiener指数、Pielou均匀度指数均有显著影响(P<0.05),但对丰富度指数影响不显著(P>0.05),上述指数均以轻度火烧迹地最高;不同火烧强度对灌木层Shannon-Wiener指数、Pielou均匀度指数、丰富度指数均有显著影响(P<0.05),且均以中度火烧迹地最高。【结论】中、重度火烧可以有效降低油松林地表可燃物负荷量;不同火烧强度干扰下,林分、地形因子共同对地表可燃物负荷量产生影响;轻度火烧可以促进草本层的物种多样性,中度火烧可以促进灌木层的物种多样性。因此,对地表可燃物进行合理管理,可以降低森林火灾风险,并可促进火烧迹地林下植被的初期恢复。

【Objective】The characteristics of surface fuel load and its relationship with post-fire environmental factors in Pinus tabuliformis under different fire intensities were analyzed and the species diversity characteristics of understory herb and shrub layers were studied to provide basis for effective management of surface fuel in P.tabuliformis and early regeneration of understory vegetation in burned areas.【Method】Three plots of 20 m×20 m were set up according to different fire intensities(light fire,moderate fire and severe fire)in the burned area of natural P.tabuliformis in Taiyue Mountain,Shanxi using unburned area as control.Stand factors including percentage of unburned trees,average blackened height,average breast diameter and stand density and topographic factors including slope aspect,slope and altitude were determined.Five subplots of 2 m×2 m and 1 m×1 m were set up in each plot.Dead combustible load indexes of undecomposed fallen leaves,semi-decomposed fallen leaves,1 h lag dead branch and 10 h lag dead branch and living combustible load indexes of shrubs and herbs were investigated.Species number,plant number,coverage,density and frequency of shrub and herb layers were measured,and the species diversity index was calculated.Multiple comparison(LSD)method was used to analyze the surface fuel load and species diversity of understory herb and shrub layers in sites with different intensities.The redundancy analysis(RDA)was used to explore the effects of stand factors and topographic factors on the loading of surface fuel.【Result】①Different fire intensities had significant effects on the total surface fuel load of P.tabuliformis(P<0.05).The combustible material loads of undecomposed fallen leaves(P<0.05),semi-decomposed fallen leaves(P<0.05),1 h lag dead branch(P<0.05)and 10 h lag dead branch(P>0.05)showed a downward trend with the increase of fire intensity,while the combustible material load of herbs(P<0.05)and bushes(P<0.05)showed a trend of decreasing first and then increasing.②Redundancy analysis(RDA)showed that the combustible material load of semi-decomposed fallen leaves was positively correlated with the percentage of unburned trees,and negatively correlated with the average blackened height.The 1 h lag dead branch load and herbal fuel load of P.tabuliformis were negatively correlated with the average breast diameter.The combustible material load of undecomposed fallen leaves was positively correlated with slope and that of bushes was positively correlated with altitude.③The influence of different fire intensities on Shannon-Wiener index and Pielou evenness index of herb layer of P.tabuliformis was significant(P<0.05),while there was no significant difference on Richness index(P>0.05),with the highest indexes in light fire sites.The influence of different fire intensities on Shannon-Wiener index,Pielou evenness index and Richness index of shrub layer of P.tabuliformis was all significant(P<0.05),with the highest values in moderate fire sites.【Conclusion】Moderate and severe fire effectively reduced the surface fuel load of P.tabuliformis.Forest stand and topographic factors had effects on the loading of surface fuel under different fire intensities.Light fire promoted species diversity in herb layer and moderate fire promoted species diversity in shrub layer.Therefore,reasonable management of surface fuel under different fire intensities can reduce the risk of forest fire and promote the initial recovery of understory vegetation in burned areas.