云南现代山火炭屑形态分析及其环境意义

作为地表生态系统的重要影响因子, 火在全球植被环境变迁、气候变化、以及人类演化方面发挥着重要作用。在当今全球极端火灾不断加剧的背景下, 基于炭屑指标重建火的演化历史及其驱动机制, 是各国政府以及科学界重点关注的科学问题。文章基于对云南现代自然山火炭屑进行形态测量分析, 揭示了不同植物燃料来源的炭屑粒径差异, 避免了室内模拟实验的不确定性。研究选取了云南松林与细叶芒草丛进行对比分析, 结果表明两种植被类型燃烧产生的炭屑形态差异较为明显。以云南松木本植物为燃料来源的炭屑形态多为方形、近圆形等, 边缘较平整, 而细叶芒草本植物炭屑形态多为细长形、长条形, 边缘不规则。此外, 云南松林炭屑的平均长度、宽度分别是25 μm和17 μm, 面积为326 μm², 而细叶芒草丛炭屑的平均长度、宽度分别为11 μm和8 μm, 面积为74 μm²。值得注意的是, 二者长宽比分布范围接近, 均集中在1.0~2.5之间, 表明炭屑长宽比并不是区分燃料类型的有效指标。经过后期埋藏作用以后, 炭屑粒径明显缩小, 其长度、宽度以及面积均发生降低, 而长宽比则相对保持稳定。综合自然野火背景下不同植物炭屑现代过程研究, 在未来基于炭屑指标判断燃料来源时, 应当全面考虑不同参数的指示意义, 从而系统揭示自然野火与植被环境之间的相互关系。

Morphological analysis and environmental significance of charcoal in modern mountain fire in Yunnan Province

As one of the most important agents in shaping earth landscape, the fire regime plays a significant role in the evolution of terrestrial ecosystems and human societies. With the continuous increasing of extreme fires all over the world, the reconstruction of fire history and its driving mechanism based on charcoal is of great significance to governments and scientists. In this paper, we chose 4 sample sites to collect charcoal samples from modern mountain wildfires that occurred in Yuxi, Yunnan Province. The site A(24°20'39″N, 102°40'37″E) and site B(24°20'49″N, 102°40'47″E) are located in Pinus yunnanensis forest, and the site C(24°20'48″N, 102°40'45″E) is in Miscanthus sinensis grassland. The site D(24°19'52″N, 102°40'59″E) is located in an unburnt area. By obtaining charcoal fragments through pollen extraction method, and measuring them with ImageJ software, we analyzed the difference in charcoal morphology and size between different vegetations. Our result shows that the morphology of charcoal from Pinus yunnanensis forest is predominately square and round, with flat edges, and the average length and width are 25 μm and 17 μm respectively. The mean acreage is about 326 μm2. For the charcoal from the Miscanthus sinensis grassland, its morphology is much different to that of Pinus yunnanensis forest and the size is relatively smaller. The morphological types are mostly elongated, with irregular edges and the average length and width are 11 μm and 8 μm respectively, with the mean acreage at about 74 μm2. It is worth noting that the length-width ratio of charcoal fragments from two vegetation types is close, mostly between 1.0~2.5, indicating that the length-width ratio is not an effective index to distinguish charcoal from woods or herbs. Meanwhile, the later taphonomic processes exerted an evident impact on charcoal size, as the mean length, width and acreage all decreased, while the length-width ratio remained stable. Based on the analysis of charcoal from different plants under wildfire, this study highlights the importance of both charcoal morphology and size in differentiating fuel sources, and provides important clues to the complex relationship between the fire regimes and vegetation.