Climate change and permafrost thaw-induced boreal forest loss in northwestern Canada

Abstract

Permafrost distribution throughout the western Canadian subarctic is not well understood due to the remoteness and size of the region, its spatial and temporal heterogeneity, limited data availability, and sparse monitoring networks. These factors severely challenge investigations of how climate warming might affect the distribution of permafrost and provide strong justification for new methods of evaluating permafrost extent using remote sensing platforms. This study quantifies forest loss at ten subarctic boreal sites in the southern Northwest Territories and northeastern British Columbia between 1970 and 2010. Historical air photos and optical remote sensing images were assessed using a change detection approach over the ten sites, each 10 km 2 spanning a north/south transect of 200 km. This study is the first to apply change detection methods to a large-scale gradient and spans the southern margin of discontinuous permafrost where results demonstrate variable patterns of net forest loss at each site ranged from 6.9% to 11.6% over the 40 year study period. Here we show that these differential rates of landcover change can be explained in part through climatic and environmental factors that vary latitudinally across the selected sites. Change statistics-net change, forest gain and forest loss were significantly correlated with an assortment of factors that varied across the ten-site transect.

Extensive land cover change across Arctic–Boreal Northwestern North America from disturbance and climate forcing

“…While harvest only occurred in 0.57% of the study domain, it was associated with a significant portion (7,117 km 2 , or 14.1%) of Deciduous Forest Gain, suggesting relatively outsize role of harvest in forest type transitions. We attribute the remaining 76,818 km 2 (29.6%) of Evergreen Forest Loss to a combination of insect infestations (Volney & Fleming, ), permafrost thaw‐induced forest mortality (Carpino et al, ; Helbig et al, ), and resource exploration (Williams et al, ). We note that approximately 17% of Evergreen Forest Loss resulted in Fen and Bog expansion (Figure S3), which is observed in the Taiga Plain along the southern extent of permafrost extent and may occur due to permafrost degradation (Carpino et al, ; Helbig et al, ).…”

“…We attribute the remaining 76,818 km 2 (29.6%) of Evergreen Forest Loss to a combination of insect infestations (Volney & Fleming, 2000), permafrost thaw-induced forest mortality (Carpino et al, 2018;Helbig et al, 2016), and resource exploration (Williams et al, 2013). We note that approximately 17% of Evergreen Forest Loss resulted in Fen and Bog expansion ( Figure S3), which is observed in the Taiga Plain along the southern extent of permafrost extent and may occur due to permafrost degradation (Carpino et al, 2018;Helbig et al, 2016). Conversely, we attribute 21,416 km 2 (33.5%) of Evergreen Forest Gain and 25,548 km 2 (50.5%) of Deciduous Forest Gain to tree line expansion and regrowth following unrecorded fires.…”

“…Rapid climate warming is changing the structure and composition of Arctic and Boreal biomes, influencing land cover both directly (e.g., via warming-induced shrub growth) and indirectly (e.g., by altering disturbance regimes; Soja et al, 2007). In the Boreal biome, changes in climate and fire regimes, in addition to resource extraction, infrastructure development activities, and permafrost degradation, are inducing tree mortality and triggering successional processes (Carpino, Berg, Quinton, & Adams, 2018;Helbig, Pappas, & Sonnentag, 2016;Williams, Quinton, & Baltzer, 2013). In the Arctic biome, climate change, including warming and changes in the growing season length, is inducing expansion of woody shrub cover (Elmendorf et al, 2012;Tape, Sturm, & Racine, 2006).…”

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

“…Permafrost peatlands make up >25% of land cover and peat deposits vary in thickness from 2 to 6 m throughout the sporadic-discontinuous permafrost zone of boreal western Canada (Bauer et al, 2003;Beilman et al, 2008;Hugelius et al, 2014;Vitt et al, 2000). Permafrost in this region is warm (near 0°C), fragmented, and susceptible to extensive and rapid permafrost thaw (Carpino et al, 2018;Gibson et al, 2018;Smith et al, 2009).…”

Fluvial CO2 and CH4 patterns across wildfire‐disturbed ecozones of subarctic Canada: Current status and implications for future change

“…Permafrost thaw and increasing wildfire frequency are especially pronounced in the Western Canadian Taiga, which is a subset of the larger boreal biome (Marshall, Schut, & Ballard, 1999). This region has been substantially affected by recent megafires (Walker et al, 2018), while permafrost warming (Biskaborn et al, 2019) has resulted in significant changes in permafrost extent and landscape composition (Carpino, Berg, Quinton, & Adams, 2018;Haynes, Connon, & Quinton, 2018). Compounding these changes, there is evidence that wildfire is accelerating permafrost thaw in this region (Gibson et al, 2018).…”