Department of Plant Pathology, University of California, Davis, California, 95616, USA.
Department of Biology, Lewis & Clark College, Portland, Oregon, 97219, USA.
Ecology. 2018 Oct;99(10):2217-2229. doi: 10.1002/ecy.2493. Epub 2018 Sep 10.
Human-altered ecological disturbances may challenge system resilience and disrupt biological legacies maintaining ecosystem recovery. Yet, the extent to which novel regimes challenge these legacies varies. This may be partially explained by differences in the vulnerability of life history strategies to disturbance characteristics. In the fire-prone, resprouter-dominated coast redwood forests of California, the introduced disease sudden oak death (SOD) alters fuel profiles, fire behavior, and aboveground tree mortality; however, this system is dominated by resprouting trees that are well-adapted to aboveground damage, and belowground survival of individuals may represent the principal biological legacy connecting pre- and post-fire communities. Much of the research exploring altered disturbances and forest recovery has focused on legacies determined by seed dispersal and aboveground survival of adults. In this work, we use pre- and post-fire data from a long-term monitoring network to assess the impacts of novel disturbance interactions between wildfire and SOD on the belowground survival and vegetative reproduction of resprouters. We found that increasing accumulation of coarse woody surface fuels from SOD-killed hosts decreased the likelihood of belowground survival for resprouting tanoak trees, but not for redwoods. Tanoaks' belowground survival was negatively related to substrate burn severity, which increased with the volume of surface fuels from hosts, suggesting heat damage as a possible mechanism influencing altered patterns of resprouter mortality. These impacts increased with decreasing tree size. By contrast, redwood and tanoak trees that survived both disturbances resprouted more vigorously, regardless of post-fire infection by P. ramorum, and generated similar recruitment at the stand level. Our results demonstrate that disease-fire interactions can narrow recruitment filters for resprouters, which could impact long-term population and demographic structure; yet, compounded disturbance may also reduce stand density and disease pressure, allowing competitive release of survivors. Resprouters displayed vulnerabilities to altered disturbance, but our research suggests that legacies maintained by resprouting may be more resilient to certain compounded disturbances, compared to seed-obligate species, because of high rates of individual survival under increasingly severe events. These trends have important implications for conservation of declining tree species in SOD-impacted forests, as well as predictions of human impacts in other disturbance-prone systems where resprouters are present.
人为干扰的生态破坏可能挑战系统的弹性，破坏维持生态系统恢复的生物遗产。然而，新的生态系统对这些遗产的挑战程度有所不同。这可能部分解释为生活史策略对干扰特征的脆弱性差异。在加利福尼亚州火灾多发、以更新芽为主的海岸红杉林中，引入的疾病突然橡树死亡（SOD）改变了燃料分布、火灾行为和地上树木死亡率；然而，该系统以更新芽为主，这些树木适应了地上的破坏，个体的地下生存可能是连接火灾前后群落的主要生物遗产。探索改变的干扰和森林恢复的大部分研究都集中在由种子传播和成年地上生存决定的遗产上。在这项工作中，我们使用长期监测网络的火灾前后数据来评估野火和 SOD 之间新型干扰相互作用对更新芽的地下生存和营养繁殖的影响。我们发现，来自 SOD 杀死宿主的粗木质表面燃料的积累增加，降低了更新芽的糖槭树的地下生存可能性，但对红杉没有影响。糖槭树的地下生存与基质燃烧严重程度呈负相关，而基质燃烧严重程度随宿主表面燃料体积的增加而增加，这表明热损伤可能是影响更新芽死亡率变化模式的一个可能机制。这些影响随着树木尺寸的减小而增加。相比之下，无论是在火灾后感染 P. ramorum 与否，能够同时存活两种干扰的红杉和糖槭树都能更有力地更新芽，并且在林分水平上产生类似的繁殖。我们的结果表明，疾病-火灾相互作用可以缩小更新芽的繁殖过滤，这可能会对长期种群和种群结构产生影响；然而，复合干扰也可能降低林分密度和疾病压力，从而使幸存者的竞争力得到释放。更新芽对改变的干扰表现出脆弱性，但我们的研究表明，与种子依赖性物种相比，更新芽维持的遗产可能对某些复合干扰更具弹性，因为在越来越严重的事件下，个体的存活率很高。这些趋势对受 SOD 影响的森林中衰退树种的保护以及其他易受干扰系统中人类影响的预测具有重要意义，这些系统中存在更新芽。
