Disentangling Modern Fire-Climate-Vegetation Relationships across the Boreal Forest Biome

Abstract:

Fire regimes differ between Eurasian and North American boreal forests, due in part to differences in climate and the dominant forest types. While North American boreal forests are dominated by stand-replacing fires, much of the Eurasian boreal forest is characterized by lower intensity surface fires. These different fire regimes have important consequences for continental-scale biogeochemical cycling and surface-energy fluxes¹. Here, we use generalized linear models (GLM) and boosted regression trees (BRT) to explore the relative importance of vegetation, annual climatic factors, and their interactions in determining annual fire occurrence across Eurasian and North American boreal forests. We use remotely sensed burned area (MCD64A1), land cover (MCD12Q1), and observed climate data (CRU) from 2002-2012 at 0.25° spatial resolution to quantify these relationships at annual temporal scales and continental spatial scales.

The spatial distribution of boreal fire occurrence was well explained with climate and vegetation variables, with similarities and differences in fire-climate-vegetation relationships between Eurasia and North America. For example, while GLMs indicate vegetation is a significant factor determining fire occurrence in both continents, the effect of climate differed. Spring temperature and precipitation are significant factors explaining fire occurrence in Eurasia, but no climate variables were significant for explaining fire occurrence in North America. BRTs complement this analysis, highlighting climatic thresholds to fire occurrence in both continents. The nature of these thresholds can vary among vegetation types, even within each continent, further implying regional sensitivity to climate-induced shifts in wildfire activity. To build on these results and better understand regional sensitivity of northern-high latitude fire regimes, future work will explore these relationships in forest-tundra and arctic tundra ecosystems, and apply historical relationships to 21^st-century climate scenarios.

¹B. M. Rogers et al., Nat Geosci 8, 228 (Mar, 2015)