Fire Behavior, Fuel Consumption, and Forest-floor Changes Following Prescribed Understory Fires in Sierra Nevada Mixed Conifer Forests

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Journal/Book Title/Conference

Canadian Journal of Forest Research

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NRC Research Press

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We quantified fire behavior, fuel consumption, and forest-floor responses to understory fires prescribed to cover a wide range and variable combination of fuel loadings, fuel moisture levels, and weather conditions in Sierra Nevada mixed conifer forests. At each of three locations, five burns were conducted under each of four different prescriptions (n = 60). Fuel loads ranged from 75–102 Mg/ha on an open site of low productivity to 125–177 Mg/ha on more productive sites. Total fuel consumption ranged from 15% in early spring burns to 92% in early fall burns. Organic horizons (litter and duff) composed 62–84% of the total fuel load. Consumption of the organic horizons ranged from 11 to 94%. Lower duff (Oa horizon) moisture content was 135% in the former and 15% in the latter. Consumption of the organic horizon was significantly correlated with lower duff moisture content (r2 = 0.51). More than 72% of all fuel was consumed after the flaming front had passed over an area. Postburn mineral soil exposure was strongly influenced by fuel consumption, season of burn, and characteristics of the site. In the late spring burns at one site, bare ground exposure was 3% before fire, 60% two months after fire, and 8% thirteen months after fire. There were slight to nonexistent increases in bare ground exposure from burns prescribed during early spring or late autumn (i.e., burns of low to moderate consumption).