Interactive effects of vegetation, soil moisture and bulk density on depth of burning of thick organic soils

Abstract

The boreal biome is characterised by extensive wildfires that frequently burn into the thick organic soils found in many forests and wetlands. Previous studies investigating surface fuel consumption generally have not accounted for variation in the properties of organic soils or how this affects the severity of fuel consumption. We experimentally altered soil moisture profiles of peat monoliths collected from several vegetation types common in boreal bogs and used laboratory burn tests to examine the effects of depth-dependent variation in bulk density and moisture on depth of fuel consumption. Depth of burning ranged from 1 to 17 cm, comparable with observations following natural wildfires. Individually, fuel bulk density and moisture were unreliable predictors of depth of burning. However, they demonstrated a cumulative influence on the thermodynamics of downward combustion propagation. By modifying Van Wagner's surface fuel consumption model to account for stratigraphic changes in fuel conditions, we were able to accurately predict the maximum depth of fuel consumption for most of the laboratory burn tests. This modified model for predicting the depth of surface fuel consumption in boreal ecosystems may provide a useful framework for informing wildland fire management activities and guiding future development of operational fire behaviour and carbon emission models.

Experimental drying intensifies burning and carbon losses in a northern peatland

“…Yet, only a few studies have quantified combustion losses in pristine northern peatlands [30][31][32] . Previous studies have shown that depth of burn is primarily controlled by fire weather, soil moisture and seasonal ice conditions, as well as fuel bulk density 30,31,33 . In general, the combustion values measured in our pristine plots (2.0 ± 0.5 kg C m − 2 ) were consistent with these previous studies, in which combustion rates averaged 2.4 kg C m − 2 .…”

Interactions of Earth's atmospheric oxygen and fuel moisture in smouldering wildfires

“…For wildfires, similar critical values have been found associated to fuel moisture (Frandsen, 1997;Rein et al, 2008;Benscoter et al, 2011;Watson and Lovelock, 2013;Watts, 2013). Atmospheric oxygen and fuel moisture are two of the most crucial factors governing the ignition and spread of wildfires throughout Earth's history, more important than other properties like mineral content, chemical composition, and bulk density.…”

“…Atmospheric oxygen and fuel moisture are two of the most crucial factors governing the ignition and spread of wildfires throughout Earth's history, more important than other properties like mineral content, chemical composition, and bulk density. Organic soils like peat are porous and are able to hold a wider range of moisture contents 1 (MC), ranging from about 10% under drought conditions to well in excess of 300% under flooded conditions (Benscoter et al, 2011;. Similar to flaming fires, the fuel moisture represents a significant energy sink to prevent smouldering fires.…”

“…Several studies have investigated the critical MC under the current atmosphere (X O 2 ∼ 21%) for smouldering peat fires through both experimental (Frandsen, 1997;Rein et al, 2008;Benscoter et al, 2011) and computational approaches. Their results confirmed for a given X O 2 , MC dominates smouldering, and different critical values exist for ignition (MC * ig ) and extinction (MC * ex ).…”

Influence of Fuel Load Dynamics on Carbon Emission by Wildfires in the Clay Belt Boreal Landscape

“…resulted in lower depth of burn, and, consequently, in lower forest floor fuel consumption (FFFC) in comparison with other boreal forest types [36]. In the CanFIRE model, FFFC is a function of duff load and climate conditions [37], and does not consider the lower depth of burn for calculations. Therefore, FFFC equations had to be modified to reflect specific carbon emission in BS forests dominated by Sphagnum spp.…”