Have Altered Fire Regimes Reduced Forest Resilience to Climate Change?

野火是森林动态的关键驱动因素。气候和土地利用的细微变化引发的火情变化对森林有潜在的重大影响。当前气候变化的速度和幅度有可能超过历史和进化的极限，危及生态恢复能力，使生态系统无法从干扰中恢复。因此，了解火情驱动因素对于预测气候变化的潜在后果和制定有效的适应和缓解战略以增强森林复原力至关重要。我的研究表明，历史上，在不列颠哥伦比亚省（BC）和阿尔伯塔省山麓的许多山地科迪勒森林中，混合严重程度的火灾制度占主导地位。在这些森林中，区域气候与地形和人类土地利用的当地控制相互作用，导致难以量化的复杂火灾制度。由于气候变化和火灾排除的综合影响，这些生态系统似乎特别容易受到快速变化的影响。迫切需要更好地了解混合严重火灾制度的动态和驱动因素，以确保这些森林的复原力。我的长期研究计划解决了这一知识缺口。在接下来的5年里，我和我的研究生将完成一系列相互关联的研究项目，旨在实现3个短期目标：1。比较山地科迪勒拉生态区各地区的火灾历史，并确定20世纪火灾制度的变化是否普遍存在。量化驱动火灾状态及其相互作用的机制的相对重要性。启动新的研究，研究改变火种对燃料危害和森林对树冠火的抵抗力的影响——混合严重程度火种中恢复力的两个指标。本研究的第一阶段是对加拿大西部山地科迪勒森林中四个不同气候区域的火灾历史进行比较分析：落基山脉、库特奈斯、奥卡那根和卡里布。我们将使用多种证据来比较这些研究区域的火灾历史。这种方法将使我们能够确定历史火灾制度的变化是否在气候区域和海拔梯度中普遍存在。第二个研究阶段调查气候作为火灾制度的驱动因素。我们将汇编1991-2010年的现代火灾和天气记录，以解释与不列颠哥伦比亚省干燥山地森林中闪电引起的点火有关的火灾天气条件的范围。从更长远的角度来看，我们将使用我们的多世纪火疤记录来测试区域内和区域间广泛的火年。我们将把我们的火灾记录与代理气候数据进行比较，以检验气候变化和历史火灾发生的影响。最后，我们将量化20世纪防火对不列颠哥伦比亚省干燥山地森林的影响。实地调查将量化在没有地面火灾的情况下森林组成、结构和燃料的变化程度。火灾行为模型将用于模拟燃料负荷、气候及其相互作用的变化，最终测试它们对森林抵抗树冠火灾的影响。4名博士，3名硕士和至少10名本科生将全面参与本研究。我们对火灾制度驱动因素的研究将有助于(1)预测气候变化影响下的未来火灾制度，(2)确定因火灾排除而降低恢复力的景观部分，以及(3)确定优先事项和目标，以指导BC省生态恢复计划，加拿大公园和加拿大野生动物管理局实施的生态恢复和燃料缓解。

Wildfire is a key driver of forest dynamics. Changes to fire regimes triggered by subtle changes in climate and land use have potential major impacts on forests. The current rate and magnitude of climate change have the potential to exceed historical and evolutionary limits, jeopardizing ecological resilience so that ecosystems are unable to recover from disturbance. Thus, understanding fire regimes drivers is essential to anticipate potential consequences of climate change and develop effective adaptation and mitigation strategies to enhance forest resilience. My research has shown that mixed-severity fire regimes historically dominated in many montane cordilleran forests in British Columbia (BC) and the foothills of Alberta. In these forests, regional climate interacts with local controls by topography and human land use, resulting in complex fire regimes that can be difficult to quantify. These ecosystems appear particularly susceptible to rapid change due to the combined effects of climate change and fire exclusion. Improved understanding of the dynamics and drivers of mixed-severity fire regimes is urgently needed to assure the resilience of these forests. My long-term research program addresses this knowledge gap. Over the next 5 years my graduate students and I will complete a series of inter-related research projects designed to meet 3 short-term objectives: 1. To compare fire histories among regions in the montane cordilleran ecozone and determine if changes to fire regimes in the 20th century are pervasive 2. To quantify the relative importance of the mechanisms driving fire-regimes and their interactions3. To initiate new research on the consequences of altered fire regimes on fuel hazards and forest resistance to crown fire – two indicators of resilience in mixed-severity fire regimes.The first phase of this research is a comparative analysis of fire histories in four distinct climatic regions in the montane cordilleran forests of western Canada: Rocky Mountains, Kootenays, Okanagan and Cariboo. We will use multiple lines of evidence to compare fire history among these study areas. This approach will enable us to determine if changes to historic fire regimes are pervasive among climatic regions and along elevation gradients.The second research phase investigates climate as a driver of fire regimes. We will compile modern fire and weather records for 1991-2010 to interpret the range of fire weather conditions associated with lightning-caused ignitions in the dry montane forests in BC. For a longer-term perspective, we will use our multi-century fire-scar records to test for widespread fire years within and among regions. We will compare our fire records with proxy-climate data to test for the influence of climatic variation and historic fire occurrence.Finally, we will quantify the consequences of 20th century fire exclusion on dry montane forests in BC. Fieldwork will quantify the degree to which forest composition, structure and fuels have changed in absence of surface fires. Fire behavior models will be used to simulate changes to fuel loads, climate and their interaction, ultimately testing their effects on forest resistance to crown fires. Four PhD, 3 MSc and at least 10 undergraduate students will be integrally involved with this research. Our research on fire regime drivers will help to (1) anticipate future fire regimes under the influence of climate change, (2) identify segments of the landscape where resilience has been reduced by fire exclusion, and (3) establish priorities and targets to guide ecological restoration and fuels mitigation implemented by the BC Ecological Restoration Program, Parks Canada and the Canadian Wildlife Service.