The vegetation and fire history at the Coastal Douglas-fir (CDF) and Coastal Western Hemlock (CWH) boundary on east-central Vancouver Island was reconstructed. A basal non-arboreal assemblage at the most inland site likely represents an open parkland community during the cold early late-glacial interval. Widespread Pinus woodland followed under cold, dry climate, yielding to closed-canopy mixed conifer forest as climate moistened. While fire disturbance was initially rare, it increased in the late-glacial mixed conifer forest. In the early-Holocene, dry coastal temperate forest replaced the mixed-conifer assemblage. Fire disturbance was widespread, characterized by frequent, possibly lower severity burns. These CDF-like forests expanded northward and westward under warm, dry conditions, attaining maximum extent 9500 – 10 500 calendar years before present, retreating thereafter towards the modern CDF–CWH boundary, which established ∼6000 years ago as climate moistened. Quercus garryana communities were scattered along the coast at this time, maintained by surface fire. Throughout the remainder of the record, the forest canopy closed as modern forests developed and a mixed-severity fire regime developed. The extended early-Holocene range of CDF-like forest suggests that the existing CWHxm biogeoclimatic subzone may be replaced by CDF stands with climate change.

Wildfire is a dominant disturbance process across Canada’s forested landscapes. It consumes organic material, releases stored carbon, and alters vegetation structure, composition, and function. Within this context, fire severity emerges as an important metric that not only reflects the extent of fuel consumption, but also serves as a key proxy for assessing overall ecosystem impacts. As fire regimes change in response to anthropogenic climate forcing, the post-fire environment is also likely to change. In consequence, this review focuses on the post-fire environment in Canada and synthesizes various post-fire effects, including the fate of residual fuels and fire impacts on carbon cycling, soil, microclimate, and plant communities. Following a fire, the residual fuel complex evolves rapidly in response to changing biotic and abiotic conditions, often defying simple prediction schemes. While photosynthesis and net primary production initially decline due to the loss of vegetation, heterotrophic respiration may increase because of the greater availability of dead organic matter. At surface level, wildfires alter soils in different ways, including modifying structure, chemical composition, biological activity, moisture retention, and erosion risk, with consequences for nutrient cycling and ecological recovery. Following the loss of canopy, burned forests also experience altered microclimates that are often characterized by higher near-surface temperatures and wind speeds. These changes alter both radiation balance and hydrological regime, impacting stream temperature, snowpack, and seedling survival, thereby affecting site regeneration. At higher latitudes, changing microclimates can also enhance permafrost thaw. As sites recover from disturbance, regeneration and successional pathways are influenced by interactions amongst fire severity, species traits, and site conditions. Notably, future ecological trajectories may potentially become more variable in response to changing climate and fire regime, with regeneration failures potentially leading to the development of altered ecosystems (i.e. non-arboreal or deciduous). As wildfire activity intensifies across Canada, there is a need to address outstanding knowledge gaps, including cumulative effects and feedbacks, and to evaluate when post-fire restoration interventions may be required. Meeting these challenges is critical for forecasting ecosystem change and supporting adaptive forest management.

Sediment cores were collected from Wrong (WL) and Lenore (LL) lakes in boreal central Yukon Territory, Canada, spanning circa 6000 years. Analyses of pollen, charcoal, magnetic susceptibility, levoglucosan, and down-scaled paleoclimatic data reveal the vegetation history and character/drivers of Holocene fire disturbance. Boreal forest has persisted in the region for millennia, with a regional mid-Holocene expansion of Picea mariana (Mill.) Britton, Sterns & Poggenb. followed by expansion of Pinus contorta var. latifolia Douglas ex Loudon Engelm. ex S. Watson in the latest Holocene. The shortest reconstructed fire return intervals (FRIs; ca. 110–125 years) occurred in the mid-Holocene, coincident with the development of highly flammable Picea-dominated forest and warm, dry summers that were characterized by elevated June-August 500 hPa geopotential height anomalies (JJA Z500) and associated with an eastward/intense Aleutian Low. In the late-Holocene, FRI increased to ca. 240 years at WL and 280 years LL. Drivers of this change include regional cooling and increased precipitation, with a westward/weaker Aleutian Low position delivering more moisture to interior Yukon. Longer FRIs allowed for greater fuel accumulation between fires, enhancing fire size/severity. While higher fire frequency is noted in the mid-Holocene and increased fire size/severity in the late-Holocene, recent changes in Yukon fire disturbance suggest that the fire regime may soon lie outside the natural range of mid- and late-Holocene variability.

Boreal forests store a large proportion of the world’s carbon (C) stocks in forest floor and mineral soils. Fire produces charcoal and other pyrogenic carbon (PyC) compounds that accumulate in soil, representing a poorly understood component of C stocks in boreal regions. Understanding the amount and decay rate of PyC is important for improving the accuracy of C budget models for boreal forests. In this study, charcoal, the predominant component of PyC was extracted and quantified using soil samples collected in the Northwest Territories (NWTs), Canada. The concentration of soil and charcoal C was determined using elemental analysis, while the age of charcoal was ascertained by radiocarbon dating. The proportion of charcoal C relative to total soil organic C was similar in forest floor and <2 mm mineral fractions, averaging 2.2% ± 0.5% and 2.0% ± 0.4%, respectively. Estimates of charcoal C quantities and proportion of the soil organic matter were comparable to other boreal and temperate forests but differed from grasslands. Charcoal ages were on centennial to multi-centennial scales, with charcoal C concentrations negatively correlated with age. Overall, charcoal represents a small but important component of organic C in NWT boreal forest soils and persists for centuries.

Multi-centennial C budgets in forested watersheds require information on forest growth, detritus turnover, and disturbances, as well as the transfer to and fate of terrestrial C in aquatics systems. Here, a sediment gravity core was collected from a drinking water reservoir in Canada, and analyzed for temporal changes in charcoal, magnetic susceptibility, carbon, and nitrogen. These indicators were used to assess disturbance history and terrestrial C sequestration in sediments. During the reservoir development period from 1910 to 2012, charcoal flux and magnetic susceptibility increased ca. 10 years after nearby fire and forest-clearing events associated with reservoir expansion. Total C and δ¹³C gradually declined during the development period, likely due to increased inputs of mineral soil from human activity. Concurrently, total terrestrial C sequestered in sediments, estimated using three or eight marker compounds, ranged between 3557 and 5145 Mg C/100 yrs, accounting for 11%–17% of DOC exports to the reservoir (30,640 Mg C/100 yrs), as estimated from a previously developed terrestrial carbon budget model. In comparison, mixed-severity fires burned around the reservoir during the pre-development period (pre-1910), as evidenced by stand ages and/or increases in charcoal flux. In general, decreased terrestrial C flux was associated with higher-severity fires that burned between 1870 and 1890 and perhaps around 1790. Further, comparisons show that soil erosion was up to 3× greater in the development versus the pre-development period. Overall, this investigation revealed the impact of land use change and fire on watershed carbon budgets and advanced a previously developed pyGC-MS methodology that demonstrated the amount of terrestrial and aquatic C being buried in sediment. It also identified the fraction of terrestrial C that was exported from the forest to the reservoir and sequestered in the sediment, uncommon data that could inform current and future landscape C budget modelling studies in this region.