Estimates of CO2 from fires in the United States: implications for carbon management

<p>Abstract</p> <p>Background</p> <p>Fires emit significant amounts of CO₂to the atmosphere. These emissions, however, are highly variable in both space and time. Additionally, CO₂emissions estimates from fires are very uncertain. The combination of high spatial and temporal variability and substantial uncertainty associated with fire CO₂emissions can be problematic to efforts to develop remote sensing, monitoring, and inverse modeling techniques to quantify carbon fluxes at the continental scale. Policy and carbon management decisions based on atmospheric sampling/modeling techniques must account for the impact of fire CO₂emissions; a task that may prove very difficult for the foreseeable future. This paper addresses the variability of CO₂emissions from fires across the US, how these emissions compare to anthropogenic emissions of CO₂and Net Primary Productivity, and the potential implications for monitoring programs and policy development.</p> <p>Results</p> <p>Average annual CO₂emissions from fires in the lower 48 (LOWER48) states from 2002–2006 are estimated to be 213 (± 50 std. dev.) Tg CO₂yr^-1and 80 (± 89 std. dev.) Tg CO₂yr^-1in Alaska. These estimates have significant interannual and spatial variability. Needleleaf forests in the Southeastern US and the Western US are the dominant source regions for US fire CO₂emissions. Very high emission years typically coincide with droughts, and climatic variability is a major driver of the high interannual and spatial variation in fire emissions. The amount of CO₂emitted from fires in the US is equivalent to 4–6% of anthropogenic emissions at the continental scale and, at the state-level, fire emissions of CO₂can, in some cases, exceed annual emissions of CO₂from fossil fuel usage.</p> <p>Conclusion</p> <p>The CO₂released from fires, overall, is a small fraction of the estimated average annual Net Primary Productivity and, unlike fossil fuel CO₂emissions, the pulsed emissions of CO₂during fires are partially counterbalanced by uptake of CO₂by regrowing vegetation in the decades following fire. Changes in fire severity and frequency can, however, lead to net changes in atmospheric CO₂and the short-term impacts of fire emissions on monitoring, modeling, and carbon management policy are substantial.</p

Fire decline in dry tropical ecosystems enhances decadal land carbon sink

The terrestrial carbon sink has significantly increased in the past decades, but the underlying mechanisms are still unclear. The current synthesis of process-based estimates of land and ocean sinks requires an additional sink of 0.6 PgC yr⁻¹ in the last decade to explain the observed airborne fraction. A concurrent global fire decline was observed in association with tropical agriculture expansion and landscape fragmentation. Here we show that a decline of 0.2 ± 0.1 PgC yr⁻¹ in fire emissions during 2008–2014 relative to 2001–2007 also induced an additional carbon sink enhancement of 0.4 ± 0.2 PgC yr⁻¹ attributable to carbon cycle feedbacks, amounting to a combined sink increase comparable to the 0.6 PgC yr⁻¹ budget imbalance. Our results suggest that the indirect effects of fire, in addition to the direct emissions, is an overlooked mechanism for explaining decadal-scale changes in the land carbon sink and highlight the importance of fire management in climate mitigation

Effects of Mountain Pine Beetle on Fuels and Expected Fire Behavior in Lodgepole Pine Forests, Colorado, USA

In Colorado and southern Wyoming, mountain pine beetle (MPB) has affected over 1.6 million ha of predominantly lodgepole pine forests, raising concerns about effects of MPB-caused mortality on subsequent wildfire risk and behavior. Using empirical data we modeled potential fire behavior across a gradient of wind speeds and moisture scenarios in Green stands compared three stages since MPB attack (Red [1–3 yrs], Grey [4–10 yrs], and Old-MPB [∼30 yrs]). MPB killed 50% of the trees and 70% of the basal area in Red and Grey stages. Across moisture scenarios, canopy fuel moisture was one-third lower in Red and Grey stages compared to the Green stage, making active crown fire possible at lower wind speeds and less extreme moisture conditions. More-open canopies and high loads of large surface fuels due to treefall in Grey and Old-MPB stages significantly increased surface fireline intensities, facilitating active crown fire at lower wind speeds (>30–55 km/hr) across all moisture scenarios. Not accounting for low foliar moistures in Red and Grey stages, and large surface fuels in Grey and Old-MPB stages, underestimates the occurrence of active crown fire. Under extreme burning conditions, minimum wind speeds for active crown fire were 25–35 km/hr lower for Red, Grey and Old-MPB stands compared to Green. However, if transition to crown fire occurs (outside the stand, or within the stand via ladder fuels or wind gusts >65 km/hr), active crown fire would be sustained at similar wind speeds, suggesting observed fire behavior may not be qualitatively different among MPB stages under extreme burning conditions. Overall, the risk (probability) of active crown fire appears elevated in MPB-affected stands, but the predominant fire hazard (crown fire) is similar across MPB stages and is characteristic of lodgepole pine forests where extremely dry, gusty weather conditions are key factors in determining fire behavior

Legacy of pre-disturbance spatial pattern determines early structural diversity following severe disturbance in mountain spruce forests in Czech Republic

Background Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how predisturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. Methods Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. Results Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, predisturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand’s height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights

Fire Emissions and Carbon Uptake in Severely Burned Lenga Beech (Nothofagus pumilio) Forests of Patagonia, Argentina

Los incendios forestales son reconocidos como fuentes de emisión de CO2 y otros gases de efecto invernadero (GHG) que, alterando la dinámica del intercambio entre el carbono (C) terrestre y el atmosférico, influencian el clima global. En la región central de la Patagonia Andina Argentina, incendios de características severas han afectado los bosques de lenga (Nothofagus pumilio Poepp. & Endl. Krasser), incrementando de esa manera las emisiones de CO2 a la atmósfera y alterando asimismo sus patrones sucesionales. En este estudio, determinamos las emisiones y el secuestro de C en tres rodales, quemados en 1976 (Lago Guacho), 1983 (La Torta), y 2008 (la Colisión). La estructura forestal, y los compartimientos de biomasa aérea y broza fueron cuantificados en cada rodal quemado y en sus adyacentes sin quemar. El stock de C y de otros GHG (CO2 , CO, CH4 , NO2 , NOx y Ce) emitidos por cada incendio, el CO2 capturado y el C anual incorporado a la biomasa fueron determinados en base a las guías propuestas por el Panel Internacional para el Cambio Climático. El carbono total (biomasa aérea más radical) antes de los incendios fue de 301,8 Mg C ha-1 para La Colisión, 258,13 Mg C ha-1 para La Torta, y 270,7 Mg C ha-1 para Lago Guacho, mientras que las pérdidas de C debido a los incendios fueron de 104,6 Mg C ha-1, 90,7 Mg C ha-1, and 94,7 Mg C ha-1 para cada uno de los sitios, respectivamente. Diferencias en la estructura forestal y en la biomasa de cada sitio previo a los incendios explican los valores de emisión de CO2 y otros GHG observados después de éstos. Al presente, el balance de C es negativo en los tres sitios. Sin ninguna acción de restauración activa y usando las tasas actuales de crecimiento para cada sitio, el tiempo estimado de recuperación del C perdido es de 105,5 años para La Colisión, 94,2 años para La Torta, y 150,2 años para Lago Guacho. Mediante el uso de tasas de captura de C variables (que decrecen a medida que la sucesión avanza), el tiempo de recuperación sería de 182 años para La Colisión, 154 años para La Torta, y 162 para Lago Guacho. El ambiente post-incendio y las condiciones de cada sitio parecen tener una mayor influencia en la recuperación de la vegetación que los efectos primarios del fuego. Tareas de restauración activas aparecen como necesarias para incrementar la tasa de recuperación del C post-fuego y ayudar a re-establecer el paisaje original en bosques de lenga.Forest wildfires are recognized as sources of CO2 and other greenhouse gases (GHG) that, altering the dynamics between terrestrial and atmospheric carbon (C) exchange, influence global climate. In central Andean Patagonia, Argentina, severe wildfires affect temperate lenga beech (Nothofagus pumilio Poepp. & Endl. Krasser) forests, thereby increasing atmospheric CO2 emissions and changing natural succession paths. In this study, we determined fire emissions and C uptake in three lenga beech forests stands burned in 1976 (Lago Guacho site), 1983 (La Torta site), and 2008 (La Colisión site). Forest structure and aboveground biomass and litter compartments in burned and adjacent unburned stands were quantified for each fire. Carbon stocks and GHG (CO2 , CO, CH4 , NO2 , NOx and Ce) released by the fires, CO2 removals, and mean annual C uptake were determined by following the International Panel of Climate Change guidelines. Total (aboveground plus root) C stock before fires was 301.8 Mg C ha-1 for La Colisión, 258.13 Mg C ha-1 for La Torta, and 270.7 Mg C ha-1 for Lago Guacho, while C losses due to the fires were 104.6 Mg C ha-1, 90.7 Mg C ha-1, and 94.7 Mg C ha-1 for the three sites, respectively. Differences in pre-fire forest structures and biomass explained the values observed in CO2 and other GHG emissions after the fires. Currently, the C balance is negative for the three sites. Without any active restoration and using actual growth rates for each site, the estimated C recovery time is 105.5 yr for La Colisión, 94.2 yr for La Torta, and 150.2 yr for Lago Guacho. By using variable rates of C uptake (which decrease as early succession proceeds), this recovery time will take 182 yr for La Colisión, 154 for La Torta, and 162 yr for Lago Guacho. Post-fire environmental and site conditions appeared to have a greater influence in forest recovery than primary fire effects. Active restoration activities may be necessary to increase C recovery rates and help to re-establish former lenga beech forest landscapes.Fil: Bertolin, María Lila. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Urretavizcaya, María Florencia. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Defossé, Guillermo Emilio. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin