Multiscale variation in drought controlled historical forest fire activity in the boreal forests of eastern Fennoscandia

Abstract

Abstract. Forest fires are a key disturbance in boreal forests, and characteristics of fire regimes are among the most important factors explaining the variation in forest structure and species composition. The occurrence of fire is connected with climate, but earlier, mostly local-scale studies in the northern European boreal forests have provided little insight into fire-climate relationship before the modern fire suppression period. Here, we compiled annually resolved fire history, temperature, and precipitation reconstructions from eastern Fennoscandia from the mid-16th century to the end of the 19th century, a period of strong human influence on fires. We used synchrony of fires over the network of 25 fire history reconstructions as a measure of climatic forcing on fires. We examined the relationship between fire occurrence and climate (summer temperature, precipitation, and a drought index summarizing the influence of variability in temperature and precipitation) across temporal scales, using a scale space multiresolution correlation approach and Bayesian inference that accounts for the annually varying uncertainties in climate reconstructions. At the annual scale, fires were synchronized during summers with low precipitation, and most clearly during drought summers. A scale-derivative analysis revealed that fire synchrony and climate varied at similar, roughly decadal scales. Climatic variables and fire synchrony showed varying correlation strength and credibility, depending on the climate variable and the time period. In particular, precipitation emerged as a credible determinant of fire synchrony also at these time scales, despite the large uncertainties in precipitation reconstruction. The findings explain why fire occurrence can be high during cold periods (such as from the mid-17th to early-18th century), and stresses the notion that future fire frequency will likely depend to a greater extent on changes in precipitation than temperature alone. We showed, for the first time, the importance of climate as a decadal-scale driver of forest fires in the European boreal forests, discernible even during a period of strong human influence on fire occurrence. The fire regime responded both to anomalously dry summers, but also to decadal-scale climate changes, demonstrating how climatic variability has shaped the disturbance regimes in the northern European boreal forests over various time scales.

The climate, the fuel and the land use: Long‐term regional variability of biomass burning in boreal forests

“…In accordance with other studies (Blarquez et al, ; Carcaillet, Bergman, Delorme, Hornberg, & Zackrisson, ; Marlon et al, ), our statistical analyses did not highlight a significant relationship between land use and BB in any of the northern boreal forests clusters. However, we did not rule out the potential influence of first American nations on local fire activity in North America before the European colonization and the impact of the first settlements since the 19th century (Blarquez et al, ; Fastie, Lloyd, & Doak, ; Natcher et al, ; Weir, Johnson, & Miyanishi, ), as well as the anthropogenic use of fire between the 18th and the 20th centuries in northern Fennoscandia (Aakala et al, ; Granström & Niklasson, ; Segertröm, Bradshaw, Hörnberg, & Bohlin, ; Zackrisson, ).…”

Post-Fire Vegetation Succession and Surface Energy Fluxes Derived from Remote Sensing

“…For example, extended periods of snow cover heavily influences both vegetation activity and recovery time; ultimately, such changes modify the energy fluxes. Therefore, a detailed record of post-fire boreal forest recovery and hydrothermal environments is crucial to understanding the disturbances in ecosystem services and succession processes.Although post-fire forest recovery has been demonstrated through field surveys in ecological studies [11][12][13], the time and space limitations of field-investigation methods have limited their extent, especially under the context of climate change. Remote sensing offers considerable potential for the inversion of the regeneration trajectory of post-fire forests via time-series data or remote sensing indices, such as the normalized difference vegetation index (NDVI) [14,15], the enhanced vegetation index (EVI) [16], and the normalized difference shortwave infrared index (NDSWIR) [17], alongside the albedo [9], land-surface temperature (LST) [18], net primary productivity (NPP) [19], fractional vegetation coverage (FVC) [20] and fraction of absorbed photosynthetically active radiation (FAPAR) [21].…”

Human responses to early Holocene climate variability in eastern Fennoscandia

“…During the increasing human influence over the last two millennia, the fire frequency has undoubtedly risen because of humaninduced fires. However, even during the last few centuries the climatic conditions have remained the most important driver of fire frequency in the boreal forest of Fennoscandia (Aakala et al 2017) The accuracy and reliability of chronologies used in the palaeoclimate records used in our study vary substantially. Most of the sediment cores have been dated with AMS radiocarbon dating.…”