Pyrogenic fuels produced by savanna trees can engineer humid savannas
Pyrogenic fuels produced by savanna trees can engineer humid savannas
复制标题
稀树草原树木产生的热解燃料可以改造潮湿的稀树草原
DOI：
10.1002/ecm.1224
复制
发表时间：
2016
影响因子：
6.1
通讯作者：
B. Beckage
中科院分区：
文献类型：
--
作者：
W. Platt;Darin P. Ellair;J. Huffman;S. E. Potts;B. Beckage
干旱后的雷击引发的自然火灾经常被认为是维持稀树草原中不连续的树木覆盖和以草为主的地层的生态机制。然而，此类火灾可能无法可靠地维持潮湿的稀树草原。我们认为，产生热原脱落叶子的稀树草原树木可能会设计火灾特性，以维持潮湿稀树草原的方式影响地面植物。我们在降雨量大、经常被烧毁的松树稀树草原中探索了我们的假设，其中的主要树木长叶松（Pinus palustris）会产生树脂针，这些针在脱落和干燥后变得高度易燃。我们假设，与其他丰富的精细燃料（脱落的橡树叶和草秆）相比，热解针对地面火灾特征的影响要大得多，因此对主要灌木和草的火灾后反应也有更大的影响。我们进一步推断，这些影响应该随着针头数量的增加而增加。我们管理影响燃料的场地条件（火灾发生后的时间、主要植被），控制地面地块中的针叶数量，规定燃烧地块，并测量地面的火灾特征。我们还测量了火灾发生前、火灾后 2 个月和 8 个月时底层橡树和草的特征。我们测试了关于热解松燃料对火灾特征和植被再生的影响的假设，并使用结构方程模型探索了燃料对火灾特征和植被的直接和间接影响。松针影响火灾特性，提高最高温度升高，加热时间超过 60°C，并且精细燃料消耗大大高于仅使用其他稀树草原植物燃料时的测量值。松针的存在降低了火灾后橡树茎和草秆的数量，特别是在草基因组的内部，以及火灾后草的开花。结构方程模型表明从松针到橡树和草的火灾后反应有很强的直接和间接途径。由结构方程模型支持的假设实验现场测试表明，热解精细燃料改变了地面规定火灾的特征，对主要地面层橡树和草产生负面影响。热解针引发的频繁火灾应该会维持潮湿的稀树草原，并产生影响松树稀树草原地面植被的组成和动态的空间火多样性。
Natural fires ignited by lightning strikes following droughts frequently are posited as the ecological mechanism maintaining discontinuous tree cover and grass‐dominated ground layers in savannas. Such fires, however, may not reliably maintain humid savannas. We propose that savanna trees producing pyrogenic shed leaves might engineer fire characteristics, affecting ground‐layer plants in ways that maintain humid savannas. We explored our hypothesis in a high‐rainfall, frequently burned pine savanna in which the dominant tree, longleaf pine (Pinus palustris), produces resinous needles that become highly flammable when shed and dried. We postulated that pyrogenic needles should have much greater influence on fire characteristics at ground level, and hence post‐fire responses of dominant shrubs and grasses, than other abundant fine fuels (shed oak leaves and grass culms). We further reasoned that these effects should increase with amounts of needles. We managed site conditions that affect fuels (time since fire, dominant vegetation), manipulated amounts of needles in ground‐layer plots, prescribed burned the plots, and measured fire characteristics at ground level. We also measured characteristics of ground‐layer oaks and grasses before, then 2 and 8 months after fires. We tested our hypotheses regarding effects of pyrogenic pine fuels on fire characteristics and vegetation regrowth and explored direct and indirect effects of fuels on fire characteristics and vegetation using a structural equation model. Pine needles influenced fire characteristics, elevating maximum temperature increases, durations of heating above 60°C, and fine fuel consumption considerably above measurements when fuels only included other savanna plants. Presence of pine needles depressed post‐fire numbers of oak stems and grass culms, especially in the interior of grass genets, as well as post‐fire flowering of grasses. The structural equation model indicated strong direct and indirect pathways from pine needles to post‐fire responses of oaks and grasses. The experimental field tests of hypotheses, bolstered by structural equation modeling, indicate pyrogenic fine fuels modify characteristics of prescribed fires at ground level, negatively affecting dominant ground‐layer oaks and grasses. Frequent fires fueled by pyrogenic needles should maintain humid savannas and generate spatial pyrodiversity that affects composition and dynamics of pine savanna ground‐layer vegetation.