Murray Brad R, Hardstaff Lyndle K, Murray Megan L, Xirocostas Zoe A
School of Life Sciences, University of Technology Sydney, 2007, NSW, Australia.
Am J Bot. 2025 Jul 10:e70073. doi: 10.1002/ajb2.70073.
The flammability of live leaves in canopies varies considerably among plant species. Identifying macroevolutionary processes that shape variation in leaf flammability contributes to an understanding of the phylogenetic underpinnings of wildfire dynamics.
We used a phylogenetic comparative approach to examine the macroevolution of live-leaf flammability in 75 plant species of fire-prone dry sclerophyll forests in eastern Australia. We estimated phylogenetic signal in leaf flammability, fitted a series of evolutionary models to test macroevolutionary hypotheses about leaf flammability, and assessed evolutionary correlations between leaf flammability and leaf water content (LWC), leaf mass per area (LMA), leaf area (LA), plant growth form, and fire response strategy.
We detected weak phylogenetic signal, indicating that leaf flammability exhibited greater variation among closely related species than would be expected under phylogenetic conservatism. The evolution of leaf flammability was equally well described by an Ornstein-Uhlenbeck model and a Pagel's δ model, implying weak stabilizing selection and an acceleration in leaf flammability evolution over time. We found significant evolutionary correlations such that high leaf flammability was related to low LWC, low LMA, and large LA.
Our results show that live-leaf flammability is an evolutionarily labile trait in plant species of fire-prone forests. We suggest that the evolution of the three leaf traits in response to prevailing environmental conditions (such as LWC to water availability, LA to light capture, and LMA to herbivore defence) provide antagonistic selective forces that produce a macroevolutionary pattern of weak stabilising selection on leaf flammability.
树冠层中活叶的可燃性在不同植物物种间差异很大。识别塑造叶可燃性变化的宏观进化过程有助于理解野火动态的系统发育基础。
我们采用系统发育比较方法来研究澳大利亚东部易发生火灾的干燥硬叶林的75种植物活叶可燃性的宏观进化。我们估计了叶可燃性的系统发育信号，拟合了一系列进化模型以检验关于叶可燃性的宏观进化假说，并评估了叶可燃性与叶含水量（LWC）、单位面积叶质量（LMA）、叶面积（LA）、植物生长形式和火灾响应策略之间的进化相关性。
我们检测到微弱的系统发育信号，表明叶可燃性在亲缘关系较近的物种间表现出比系统发育保守性预期更大的变异性。叶可燃性的进化同样能被奥恩斯坦-乌伦贝克模型和佩格尔δ模型很好地描述，这意味着稳定选择较弱且叶可燃性进化随时间加速。我们发现了显著的进化相关性，即高叶可燃性与低LWC、低LMA和大叶面积相关。
我们的结果表明，在易发生火灾的森林植物物种中，活叶可燃性是一个进化上不稳定的性状。我们认为，这三种叶性状响应主要环境条件（如LWC响应水分可利用性、LA响应光捕获、LMA响应食草动物防御）的进化提供了拮抗选择力，从而产生了对叶可燃性弱稳定选择的宏观进化模式。
