Laboratoire de Probabilités et Modèles Aléatoires, Université Pierre et Marie Curie, Paris, France.
Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
J R Soc Interface. 2018 Oct 17;15(147):20180444. doi: 10.1098/rsif.2018.0444.
Whether plants can evolve to promote flammability is controversial. Ecologically, fire only spreads in landscapes when many plants are flammable, but collective behaviours among large groups are difficult to evolve at the individual level. Here, we formulate a model that examines how flammability can spread from rarity, combining individual-level costs and payoffs of flammability with landscape-level fire spread, sufficiently generic to analogize flammability among grasses, Mediterranean systems, and others. We found that fire-prone and fire-suppressing landscapes, composed of flammable and non-flammable plants, respectively, were alternatively stable in some environments, and flammability therefore only increased from rarity in environments when fire-proneness was the only stable state. Thus, fire-vegetation feedbacks alone probably did not drive the evolution and spread of flammability. However, evolution of flammability did promote fire-proneness in temporally and spatially heterogeneous environments: when flammable plants already occupied some substantial fraction of a fire-prone landscape, a positive feedback with fire could maintain flammability in a decreasingly favourable environment, and fire feedbacks could expand the distribution of flammability traits from fire-prone into fire-suppressing areas in a heterogeneous landscape. Thus, fire feedbacks could potentially have promoted the widespread invasion and persistence of flammability traits to their current widespread prominence.
植物是否能够进化为促进易燃性一直存在争议。从生态学角度来看，只有当许多植物易燃时，火才会在景观中蔓延，但在个体层面上，群体的集体行为很难进化。在这里，我们制定了一个模型，研究易燃性如何从稀有性中传播，将易燃性的个体成本和收益与景观级别的火灾蔓延结合起来，该模型足够通用，可以类比草类、地中海系统和其他系统中的易燃性。我们发现，由易燃植物和不可燃植物组成的易燃性和抑制性景观在某些环境中分别是稳定的，因此，只有在易燃性是唯一稳定状态的环境中，易燃性才会从稀有性中增加。因此，火-植被反馈本身可能并没有驱动易燃性的进化和传播。然而，易燃性的进化确实促进了在时间和空间上不均匀的环境中火的易燃性：当易燃植物已经占据了易燃性景观的相当大的一部分时，与火的正反馈可以在不利的环境中维持易燃性，并且火反馈可以将易燃性特征的分布从易燃性区域扩展到异质景观中的抑制性区域。因此，火反馈可能潜在地促进了易燃性特征的广泛入侵和持续存在，使其达到目前的广泛突出地位。
