Forest fires in Canadian permafrost region: the combined effects of fire and permafrost dynamics on soil organic matter quality

Abstract

Wildfires burn approximately 1% of boreal forest yearly, being one of the most significant factors affecting soil organic matter (SOM) pools. Boreal forests are largely situated in the permafrost zone, which contains half of global soil carbon (C). Wildfires advance thawing of permafrost by burning the insulating organic layer and decreasing surface albedo, thus increasing soil temperatures. Fires also affect SOM quality through chemical and physical changes, such as the formation of resistant C compounds. The long-term post-fire effects on SOM quality, degradability and isotopic composition are not well known in permafrost forests. We studied the effect of forest fires on the proportional sizes of SOM pools with chemical fractionation (extracting with water, ethanol and acid) of soil samples (5, 30 and 50 cm depths) collected from a fire chronosequence in the upland mineral soils of the Canadian permafrost zone. We also determined the 13 C and 15 N isotopic composition of soil after fire. In the topsoil horizon (5 cm) recent fire areas contained a smaller fraction of labile SOM and were slightly more enriched with 15 N and 13 C than older fire areas. The SOM fraction ratios reverted towards pre-fire status with succession. Changes in SOM were less apparent deeper in the soil. Best predictors for the size of recalcitrant SOM

Determination of Soil Properties and Fungal Interrelations Influenced by Forest Restoration on a Contaminated Zinc Mining Area

“…At high elevations, fast growing trees would have the most detrimental consequences on soil formation [27]; native species are generally preferable for forest restoration. In younger restored forests, the canopy cover provides insufficient protection from rain impacts, resulting in severe soil erosion; the foliage and ground litter is also degraded rapidly in the tropics [2,29]. However, this decomposition was insufficient to help build up sufficient reserves of SOM.…”

“…Additionally, organic matter and total organic carbon content for the 3-year-old restored forest were higher than for older restored forest, due to the impacts of human activities such as wood cutting and wild fires on organic matter and soil nutrients [29], as well as the nutrient cycling when SOM is decomposed by microorganisms to form organic, soluble carbon (dissolved organic carbon). Organic carbon dissolved in water plays an important role in soil processes and contributes to maintaining nutrient balance [31].…”

Decadal‐Scale Recovery of Carbon Stocks After Wildfires Throughout the Boreal Forests

“…Fires reduce forest C stocks in the short term (Kashian et al, 2013;Köster et al, 2016;Seedre et al, 2014;Wang et al, 2003) and increase CO 2 emissions to the atmosphere (Ghimire et al, 2012;van der Werf et al, 2017). Over longer time scales, fires can affect C dynamics by altering forest regrowth (Johnstone et al, 2016;Kashian et al, 2013), succession (Williams et al, 2016), organic matter decomposition (Aaltonen et al, 2019;Dooley & Treseder, 2012;O'Neill et al, 2006), permafrost thawing (Köster et al, 2017), and the fluxes of energy and nutrients Randerson et al, 2006;Wirth et al, 2002).…”

Carbon dynamics in forest fire affected permafrost soils

“…Chemical fractions of SOM from the 5, 30 and 50 sampling depths, presented as percentage of total SOM (Study I). The error bars show standard errors of mean(Aaltonen et al, 2019a).…”

“…Natural δ 13 C-values of bulk soil samples at 5, 30 and 50 cm depths from each fire area (Study I). The letters denote significant differences between age classes and error bars represent standard errors(Aaltonen et al, 2019a).…”