Have Altered Fire Regimes Reduced Forest Resilience to Climate Change?

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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.