title: Effects of experimental fuel additions on fire intensity and severity: unexpected carbon resilience of a neotropical forest.
abstract: Global changes and associated droughts, heat waves, logging activities, and forest fragmentation may intensify fires in Amazonia by altering forest microclimate and fuel dynamics. To isolate the effects of fuel loads on fire behavior and fire-induced changes in forest carbon cycling, we manipulated fine fuel loads in a fire experiment located in southeast Amazonia. We predicted that a 50% increase in fine fuel loads would disproportionally increase fire intensity and severity (i.e., tree mortality and losses in carbon stocks) due to multiplicative effects of fine fuel loads on the rate of fire spread, fuel consumption, and burned area. The experiment followed a fully replicated randomized block design (N = 6) comprised of unburned control plots and burned plots that were treated with and without fine fuel additions. The fuel addition treatment significantly increased burned area (+22%) and consequently canopy openness (+10%), fine fuel combustion (+5%), and mortality of individuals ≥5 cm in diameter at breast height (dbh; +37%). Surprisingly, we observed nonsignificant effects of the fuel addition treatment on fireline intensity, and no significant differences among the three treatments for (i) mortality of large trees (≥30 cm dbh), (ii) aboveground forest carbon stocks, and (iii) soil respiration. It was also surprising that postfire tree growth and wood increment were higher in the burned plots treated with fuels than in the unburned control. These results suggest that (i) fine fuel load accumulation increases the likelihood of larger understory fires and (ii) single, low-intensity fires weakly influence carbon cycling of this primary neotropical forest, although delayed postfire mortality of large trees may lower carbon stocks over the long term. Overall, our findings indicate that increased fine fuel loads alone are unlikely to create threshold conditions for high-intensity, catastrophic fires during nondrought years.
authors.affiliation: Instituto de Pesquisa Ambiental da Amazônia, SHIN CA 5, Bloco J2, Sala 309, Bairro, Lago Norte, Brasília-DF, 71503-505, Brazil.|Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA, 02450, USA.|Carnegie Institution for Science, 260 Panama Street, Stanford, CA, 94305, USA.
authors.forename: Paulo M
authors.initials: PM
authors.lastname: Brando
authors.affiliation: Instituto de Pesquisa Ambiental da Amazônia, SHIN CA 5, Bloco J2, Sala 309, Bairro, Lago Norte, Brasília-DF, 71503-505, Brazil.
authors.forename: Claudinei
authors.initials: C
authors.lastname: Oliveria-Santos
authors.affiliation: Instituto de Pesquisa Ambiental da Amazônia, SHIN CA 5, Bloco J2, Sala 309, Bairro, Lago Norte, Brasília-DF, 71503-505, Brazil.
authors.forename: Wanderley
authors.initials: W
authors.lastname: Rocha
authors.affiliation: Instituto de Pesquisa Ambiental da Amazônia, SHIN CA 5, Bloco J2, Sala 309, Bairro, Lago Norte, Brasília-DF, 71503-505, Brazil.|Programa de Pós-Graduação em Ciências Biológicas, Universidade Estadual de Londrina, Londrina-PR, 86051-990, Brazil.
authors.forename: Roberta
authors.initials: R
authors.lastname: Cury
authors.affiliation: Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA, 02450, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Coe
mesh_terms: D002244:Carbon / Q000032:analysis; D057486:Carbon Cycle; D005390:Fires; D065928:Forests; D012987:Soil / Q000737:chemistry; D013020:South America; D014197:Trees / Q000254:growth & development; D014329:Tropical Climate
chemical_list: D012987:Soil; D002244:Carbon
keywords: Amazon; Brazil; carbon emissions; forest degradation; tree mortality