Understanding factors driving fire activity helps reveal the degree and geographical variability in the resilience of boreal vegetation to large scale climate forces. We studied the association between sea ice cover in the Baffin Bay and the Labrador Sea and observational records of forest fires in two Nordic countries (Norway and Sweden) over 1913–2017. We found a positive correlation between ice proxies and regional fire activity records suggesting that the Arctic climate and the associated changes in North Atlantic circulation exercise an important control on the levels of fire activity in Scandinavia. Changes in the sea cover are likely correlated with the dynamic of the North Atlantic Current. These dynamics may favor the development of the drought conditions in Scandinavia through promoting persistent high-pressure systems over the Scandinavian boreal zone during the spring and summer. These periods are, in turn, associated with an increased water deficit in forest fuels, leading to a regionally increased fire hazard. The Arctic climate will likely be an important future control of the boreal fire activity in the Nordic region.

Understanding long-term forest fire histories of boreal landscapes is instrumental for parameterizing climate–fire interactions and the role of humans affecting natural fire regimes. The eastern sections of the European boreal zone currently lack a network of annually resolved and centuries-long forest fire histories. To fill in this knowledge gap, we dendrochronologically reconstructed the 600-year fire history of a middle boreal pine-dominated landscape of the southern part of the Republic of Komi, Russia. We combined the reconstruction of fire cycle (FC) and fire occurrence with the data on the village establishment and climate proxies and discussed the relative contribution of climate versus human land use in shaping historic fire regimes. Over the 1340–1610 ce period, the territory had a FC of 66 years (with the 90% confidence envelope of 56.8 and 78.6 years). Fire activity increased during the 1620–1730 ce period, with the FC reaching 32 years (31.0–34.7 years). Between 1740–1950, the FC increased to 47 years (41.9–52.0). The most recent period, 1960–2010, marks FC's historic maximum, with the mean of 153 years (102.5–270.3). Establishment of the villages, often as small harbors on the Pechora River, was associated with a non-significant increase in fire occurrence in the sites nearest the villages (p = 0.07–0.20). We, however, observed a temporal association between village establishment and fire occurrence at the scale of the whole studied landscape. There was no positive association between the former and the FC. In fact, we documented a decline in the area burned, following the wave of village establishment during the second half of the 1600s and the first half of the 1700s. The lack of association between the dynamics of FC and the dates of village establishments, and the significant association between large fire years and the early and latewood pine chronologies, used as historic drought proxy, indirectly suggests that the climate was the primary control of the landscape-level FCs in the studied forests. Pine-dominated forests of the Komi Republic may hold a unique position as the ecosystem with the shortest history of human-related shifts in fire cycles across the European boreal region.

Dendrochronological reconstructions inform us about historical climate-fire-human interactions, providing a means to calibrate projections of future fire hazard. Most of these reconstructions, however, have been developed in landscapes with a considerable proportion of xeric sites that could potentially inflate our estimates of the historic levels of fire activity. We provide a 420-year long reconstruction of fires in a mire-dominated landscape of the Veps Nature Park, North-West Russia. The area has mostly escaped large-scale forestry operations in the past and is an example of pristine mid-boreal vegetation with a high (approximately 30% for the area studied) proportion of waterlogged areas with ombrotropic mires. The historical fire cycle was 91.4 years (90% confidence intervals, CI 66.2–137.6 years) over the 1580–1720 period, decreasing to 35.9 (CI 28.1–47.6 years) between 1730 and 1770, and then increasing again to 122.7 years (CI 91.0–178.0 years) over the 1780–2000 period. Early season fires dominated over late season fires during the reconstruction period. We documented a higher fire activity period between 1730 and 1780, resulting from the increase in early season fires. This period coincided with one of the largest multi-decadal declines in the reconstructed spring precipitation since 1600 CE, although we found no significant relationship between fire and precipitation over the whole reconstructed period. The nine largest fire years were associated with negative summer precipitation and positive summer temperature anomalies over the study region. Land-use history of the area did not appear to have an effect on historical fire dynamics. Modern (1996–2016) fire records indicate a regional fire cycle of ∼ 1300 years, featuring a pronounced pattern with early (April–May) and late (July–September) season fires. The uniform fire cycle in the area since 1780, occurrence of nine largest fire years during years with spring-summer droughts, and low ignition frequencies over the last 420 years (0.005 to 0.037 ignitions per year and km2) suggest that the fire regime of the Veps Highland remained largely natural until the onset of the 20th century.

Understanding factors driving fire activity helps reveal the degree and geographical variability in the resilience of boreal vegetation to large scale climate forces. We studied the association between sea ice cover in the Baffin Bay and the Labrador Sea and observational records of forest fires in two Nordic countries (Norway and Sweden) over 1913–2017. We found a positive correlation between ice proxies and regional fire activity records suggesting that the Arctic climate and the associated changes in North Atlantic circulation exercise an important control on the levels of fire activity in Scandinavia. Changes in the sea cover are likely correlated with the dynamic of the North Atlantic Current. These dynamics may favor the development of the drought conditions in Scandinavia through promoting persistent high-pressure systems over the Scandinavian boreal zone during the spring and summer. These periods are, in turn, associated with an increased water deficit in forest fuels, leading to a regionally increased fire hazard. The Arctic climate will likely be an important future control of the boreal fire activity in the Nordic region.

Fire is a major disturbance agent in the boreal forest, affecting the structure, dynamics and biogeochemical cycles in this biome. In the Asian section of boreal forest, the records of long-term fire history are few that limits our understanding of factors forcing regional fire dynamics. We presented an annually-resolved 352-year (1666–2017) fire chronology based on fire scars of Scots pine (Pinus sylvestris L.) and Siberian larch (Larix sibirica Ledeb) from the Transbaikal area in the southeastern Siberia. Fire activity showed an increasing trend from 1720 to 1929 (R2 = 0.80, P < 0.0001), and a significant decreasing trend from 1920 to 2010 (R2 = 0.62, P < 0.001). We assessed the potential relationships between drought (as represented by the Palmer Drought Severity Index, PDSI, and the Monthly Drought Code, MDC), ocean-atmosphere circulation and forest fire by Superposed epoch analyses, cross-wavelet analysis and Granger causality analysis. Increased fire activity was associated with stronger drought from previous winter to current summer of fire event years and positive Arctic Oscillation (AO) before and during major fire season (February and April to May), as revealed by superposed epoch analysis. Granger causality pointed to the significant role of drought in driving forest fires. Our findings provide insights into the climate drivers of forest fire activity and its prediction in the Transbaikal region.

Fire remains one of the main natural disturbance factors in the European boreal zone and understanding climatic forcing on fire activity is important for projecting effects of climate change on ecosystem services in this region. We analyzed records of annually burned areas in 16 administrative regions of the European boreal zone (countries or administrative units within countries) and fire weather variability to test for their spatio-temporal patterns over the 1901-2017 period.

Over the 1992-2017 period, the region exhibited large variability in forest fire activity with the fire cycles varying from ~1600 (St. Petersburg region) to ~37000 years (Finland). The clustering of administrative units in respect to their burned area, suggested the presence of sub-regions with synchronous annual variability in burned areas. Large fire years (LFYs) in each of the clusters were associated with the development of the high pressure cell over or in immediate proximity of the regions in question in July, indicating climatic forcing of LFYs. Contingency analysis indicated that there was no long-term trend in the synchrony of LFYs observed simultaneously in several administrative units. We documented a trend towards higher values of Monthly Drought Code (MDC) for the months of April and May in the western (April) and northern (April and May) sections. The significant positive correlation between biome-wide fire activity index and June SNAO (Summer North Atlantic Oscillation) (r = 0.53) pointed to the importance of large-scale atmospheric circulation, in particular the summer European blocking pattern, in controlling forest fires across EBZ. The forest fire activity of the European boreal zone remains strongly connected to the annual climate variability. Higher frequency of strongly positive SNAO states in the future will likely synchronize years with a large area burned across the European boreal zone.

The Sala fire in the Västmanland County of central Sweden that burned about 14,000 ha in 2014 has been the largest fire recorded in the modern history of Sweden. To understand the long-term fire history of this area, we dendrochronologically dated fire scars on Scots pine (Pinus sylvestris L.) trees (live and deadwood) to reconstruct the fire cycle and fire occurrence in the area affected by the 2014 fire. We identified 64 fire years, using a total of 378 pine samples. The earliest reconstructed fire dated back to 1113 AD. The spatial reconstruction extended over the period of 1480–2018 AD. Lower levels of fire activity (fire cycle, FC = 43 years, with the central 90% of the distribution limited by 35 to 57 years) dominated in the earlier period (1480–1690 AD) that was followed by a strong decrease in fire activity since 1700 (FC = 403 years, with 90% of the distribution being within 149 to 7308 years), with a fire-free period between 1756 and 2014. Sala area, therefore, features the earliest known onset of fire suppression in Scandinavia. The high demand for timber during the peak in mining activities in the study area around the 1700–1800s, accompanied by passive fire suppression policies, were possibly the main drivers of the decline in fire activity. Superposed epoch analysis (SEA) did not show significant departures in the drought proxy during the ten years with the largest area burned between 1480 and1690. It is unclear whether the result is due to the relatively small area sampled or an indication that human controls of fires dominated during that period. However, significant departures during the following period with low fire activity (1700–1756), which just preceded the last fire-free period, suggested that the climate became an increasingly important driver of fire during the onset of the suppression period. We speculate that the lack of major firebreaks, the homogenization of forests, and the lack of burned areas with low fuel loads might contribute to the occurrence of the exceptionally large 2014 fire in Sala.

Spatially explicit reconstructions of fire activity in European boreal forest are rare, which limits our understanding of factors driving vegetation dynamics in this part of the boreal domain. We have developed a spatially explicit dendrochronological reconstruction of a fire regime in a 25 × 50 km2 area within boreal biome located within the Kalevalsky National Park (Kalevalsky NP), over the 1400–2010 CE period. We dated 184 fire years using 212 fire-scarred living and dead Scots pine (Pinus sylvestris L.) trees collected on 38 sites.

The studied period revealed a pronounced century-long variability in forest fire cycles (FC). The early period (1400–1620 CE) had low fire activity (FC = 178 years), which increased during the 1630–1920 period (FC = 46 years) and then decreased over the 1930–2000 period (FC = 283 years). Dendrochronological results did not provide a conclusive answer on the origins of FC dynamics, although several lines of evidence suggest that climate drove the increase in fire activity in the early 1600s, while human-related factors were largely responsible for its decline in the early 1900s. The current FC in the Kalevalsky NP is close to the estimates reported for the pre-industrial colonisation period in Scandinavia, which suggests that the forests of the area currently maintain their close-to-natural fire regime. Fire has been the pivotal factor of forest dynamics in this biome and forest management should acknowledge that fact in developing conservation strategies in Karelia and other areas of European boreal forest. Introduction of prescribed burns of varying severity could be an important element of such strategies.