Process and patterns of duff consumption in the mixedwood boreal forest

Abstract

Postfire tree recruitment in the boreal forest is restricted to patches from which the duff (organic layer) has been removed by fire. Duff consumption occurs by smoldering combustion, propagation of which is determined by bulk density, moisture content, and depth. This study investigated interactions among these factors, their spatial distribution, and spatial patterns of duff consumption in two wildfires. A hypothesized positive relationship between moisture content and depth was supported by a laboratory study. Duff characteristic data were collected from two burns and comparable unburned areas of mixedwood forest in western Canada to describe and explain patterns of duff consumption within and between top-slope Pinus banksiana Lamb. -Picea mariana (Mill.) BSP stands and lower slope pure stands of Picea mariana on glaciofluvial hillslopes. In unburned stands, bulk density did not differ significantly between stands, while depths were significantly greater in Picea stands. With moist duff, consumption was significantly greater in Picea than in Pinus-Picea stands as depth limited smoldering in the thin duff of Pinus-Picea stands. With dry duff, smoldering was propagated regardless of depth resulting in no differences between stand types. The spatial correlation between burned patches and fire-killed trees was explained by within-stand spatial variation in duff moisture due to precipitation interception by tree crowns.Résumé : La régénération après feu en forêt boréale est limitée aux parcelles où l'humus (horizon organique) a été dé-truit par le feu. L'humus est consumé par la combustion lente dont la propagation est déterminée par la densité apparente, la teneur en humidité et la profondeur. Cette étude a examiné les interactions entre ces facteurs, leur distribution spatiale et les patrons spatiaux de destruction de l'humus pour deux feux de forêt. L'hypothèse d'une relation positive entre la teneur en humidité et la profondeur a été confirmée par une étude en laboratoire. Les données caractéristiques de l'humus ont été récoltées dans deux brûlis et des superficies non brûlées et comparables de forêt mélangée de l'ouest du Canada pour décrire et expliquer les patrons de destruction de l'humus à l'intérieur et entre des peuplements de Pinus banksiana Lamb. -Picea mariana (Mill.) BSP de haut de pente et des peuplements purs de Picea mariana de bas de pente sur des versants fluvio-glaciaires. Dans les peuplements non brûlés, la densité apparente ne varie pas significativement entre les peuplements alors que la profondeur est significativement plus importante dans les peuplements de Picea. Dans le cas d'un humus humide, la destruction est significativement plus prononcée dans les peuplements de Picea que dans ceux de Pinus-Picea car la profondeur limite la combustion lente dans l'humus mince des peuplements de Pinus-Picea. Avec un humus sec, la combustion lente se propage quelle que soit la profondeur, n'entraînant pas de différence entre les types de peuplement. La corrélation spatiale entre les parcelles brûlées ...

Hydrological properties of duff

“…Measured porosity values range from 0.81 cm 3 cm À3 to 0.92 cm 3 cm À3 and are similar to values found in previous studies on duff [Fosberg, 1977;Ferguson et al, 2002;Miyanishi and Johnson, 2002;Redding et al, 2005] and peat [Heiskanen, 1999;Weiss et al, 1998;Naasz et al, 2005;Wotton et al, 2005;Schwärzel et al, 2002Schwärzel et al, , 2006. The differences within each category exhibit a pattern similar to that seen with conductivity.…”

Propagation probability and spread rates of self-sustained smouldering fires under controlled moisture content and bulk density conditions

“…A smouldering front can then propagate into the peat both vertically and horizontally. However, it is the front propagating horizontally that is primarily responsible for the large areas of peat consumed, as vertical propagation is generally extinguished by deeper layers of wet peat (Wein 1983;Miyanishi and Johnson 2002;Usup et al 2004). The propagation mechanisms of smouldering fires in peats are complex and further research is needed to understand how peat conditions affect the dynamics of self-sustained fire propagation.…”

“…roots, stones) may also play a role in creating variability in peat conditions that could affect the propagation of smouldering fires. Twigs and roots, for example, have been reported to promote the propagation of smouldering fires (Miyanishi and Johnson 2002;Davies et al 2013); this is likely a result of local changes to MC around the root.…”

“…These gases contribute significantly to global emissions of greenhouse gases . Smouldering peat fires also affect the roots of vegetation close to the surface, often causing lethal plant damage and habitat losses (Miyanishi and Johnson 2002;Page et al 2002;Davies et al 2013). The landscape after a peat fire is often heterogeneous, as peat is consumed in irregular patches (Shetler et al 2008).…”

Mitigating old tree mortality in long-unburned, fire-dependent forests: a synthesis

“…Duff is generally drier under tree crowns than between them due to crown interception of precipitation and radiation (Hille and den Ouden 2005;Miyanishi and Johnson 2002). Tree crowns intercept precipitation, reducing moisture input directly beneath the crowns.…”