Abstract
Wildfires are an important factor in controlling forest ecosystem dynamics across the circumpolar boreal zone. An improved understanding of their direct and indirect, short- to long-term impacts on vegetation cover and permafrost–vegetation coupling is particularly important to predict changes in carbon, nutrient and water cycles under projected climate warming. Here, we apply dendrochronological techniques on a multi-parameter dataset to reconstruct the effect of wildfires on tree growth and seasonal permafrost thaw depth in Central Siberia. Based on annually-resolved and absolutely dated information from 19 Gmelin larch (Larix gmelinii (Rupr.) Rupr.) trees and active soil layer thickness measurements, we find substantial stand-level die-off, as well as the removal of ground vegetation and the organic layer following a major wildfire in 1896. Reduced stem growth coincides with increased δ13C in the cellulose of the surviving trees during the first decade after the wildfire, when stomatal conductance was reduced. The next six to seven decades are characterized by increased permafrost active soil layer thickness. During this period of post-wildfire ecosystem recovery, enhanced tree growth together with positive δ13C and negative δ18O trends are indicative of higher rates of photosynthesis and improved water supply. Afterwards, a thinner active soil layer leads to reduced growth because tree physiological processes become limited by summer temperature and water availability. Revealing long-term effects of forest fires on active soil layer thickness, ground vegetation composition and tree growth, this study demonstrates the importance of complex vegetation–permafrost interactions that modify the trajectory of post-fire forest recovery across much of the circumpolar boreal zone. To further quantify the influence of boreal wildfires on large-scale carbon cycle dynamics, future work should consider a wide range of tree species from different habitats in the high-northern latitudes.
Highlights
Destroying more than 1% of the global boreal forest each year, wildfires have substantial impacts on vegetation structure and composition, the soil organic layer, as well as zoobiota and microbial communities (Viereck and Schandelmeier 1980, Moore 1996, Certini 2005, Waldrop and Harden 2008, Gibson et al 2018)
To understand the effects of wildfires on permafrost, the active soil layer (ASL) thickness was repeatedly measured at many sites in northern North America (MacKay 1995, Brown et al 2000, Viereck et al 2008), and upper permafrost thaw dynamics were estimated from the rate of forest ecosystem recovery after burning (Brown et al 2015)
tree-ring width (TRW) index chronologies are characterized by high synchrony of year-to-year and multidecadal fluctuations, both for prior- and post-wildfire tree generations, with high inter-series correlation (Rbar = 0.504, Expressed Population Signal (EPS) > 0.85 since 1873 and Rbar = 0.460, EPS > 0.85 since 1936) (figures 2(b), S1)
Summary
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Alexander V Kirdyanov1,2,3, Matthias Saurer4, Rolf Siegwolf4, Anastasia A Knorre3,5, Anatoly S Prokushkin2,3, Olga V Churakova (Sidorova)3,4 , Marina V Fonti3,4 and Ulf Büntgen1,4,6,7 Keywords: active soil layer, boreal forest, permafrost, Siberia, stable isotopes, tree rings, wildfire
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