Fire ignition patterns affect production of charcoal in southern forests

Abstract

Although charcoal represents a relatively minor portion of available biomass burned in wildfires and prescribed burns, its recalcitrant properties confer residence times ranging from centuries to millennia, with significance for carbon sequestration in frequently burned forests. Here, we determined whether charcoal formation differed between the two most common prescribed fire spread patterns in southern forests: head (with the wind) and backing (against the wind). Pine wood samples were distributed randomly within a mesic flatwoods burn unit in north-central Florida, and subjected either to a head fire (n ¼ 34) or a backing fire (n ¼ 34). Backing fires formed more than twice as much charcoal as head fires (1.53 v. 0.38% of available biomass), presumably because of differences in residence times, oxygen availability and fire intensity between the two fire spread patterns. These results suggest that the contribution of charcoal to ecosystem carbon sequestration is greater when flatwoods forests are burned against the prevailing wind direction, and that further investigation of these trends is warranted.Additional keywords: black carbon, carbon sequestration, prescribed fire, pyrogenic carbon.

Long and Short-Term Effects of Fire on Soil Charcoal of a Conifer Forest in Southwest Oregon

“…A number of laboratory and field studies identify the most important factors in assessing charcoal production rates. Fire intensity, fire return interval, vegetation type, fire behavior, and fuel loading represent common factors identified [5,7,13,16,18,38,40]. The Siskiyou-LTEP results provide a clear relation between fuel consumption and charcoal production under wildfire and prescribed fire conditions.…”

“…Different percentages of charcoal are produced under different fire conditions. In an experimental field study in Florida forest, prescribed fire moving with the wind produced less than half the charcoal percentage as fire moving against the wind [18]. Fire intensity, oxygen availability and fire duration were cited as possible causes of the difference. )…”

“…In a prescribed fire in Florida scrub oak forest, pre and post-fire sampling indicated burned stem and leaf biomass yielded 4-6% charcoal from initial mass [17]. In another prescribed fire in Florida, wood experimentally placed on the forest floor produced 0.4-1.5% charcoal [18]. In a lodgepole pine (Pinus contorta) forest in a Yellowstone National Park wildfire, Wyoming, USA, post-fire analysis indicated 8% of coarse woody debris consumed by the fire was converted into charcoal [19].…”

“…The production of charcoal measured by physical determination and consumption of experimentally placed wood in experimental and prescribed fires ranges from 0.4-8.1% of the fuels consumed [17,18,25,26]. Production of charcoal in a Wyoming wildfire was about 8% of coarse woody debris consumed, as estimated from post-fire observations of volumetric conversion of wood to charcoal or visual determination of charcoal on the forest floor [26].…”

“…Prescribed fire comparisons are limited to fossil or lake sediment charcoal and rarely use pre-fire charcoal samples from forest soils [17][18][19]. One prescribed fire study in Florida analyzed pre-fire and post-fire forest floor samples and found increased charcoal concentrations [17].…”