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Positive feedbacks between wildfire emissions and climate are expected to increase in strength in the future; however, fires not only release carbon (C) from terrestrial to atmospheric pools, they also produce pyrogenic C (PyC) which contributes to longer-term C stability. Our objective was to quantify wildfire impacts on total C and PyC stocks in California mixed-conifer forest, and to investigate patterns in C and PyC stocks and changes across gradients of fire severity, using metrics derived from remote sensing and field observations. Our unique study accessed active wildfires to establish and measure plots within days before and after fire, prior to substantial erosion. We measured pre-and post-fire aboveground forest structure and woody fuels to calculate aboveground biomass, C and PyC, and collected forest floor and 0-5 cm mineral soil samples. Immediate tree mortality increased with severity, but overstory C loss was minimal and limited primarily to foliage. Fire released 85% of understory and herbaceous C (comprising <1.0% of total ecosystem C). The greatest C losses occurred from downed wood and forest floor pools (19.3 ± 5.1 Mg ha −1 and 25.9 ± 3.2 Mg ha −1 , respectively). Tree bark and downed wood contributed the greatest PyC gains (1.5 ± 0.3 Mg ha −1 and 1.9 ± 0.8 Mg ha −1 , respectively), and PyC in tree bark showed non-significant positive trends with increasing severity. Overall PyC losses of 1.9 ± 0.3 Mg ha −1 and 0.5 ± 0

Increases in pinyon and juniper woodland cover associated with land-use history are suggested to provide offsets for carbon emissions in arid regions. However, the largest pools of carbon in arid landscapes are typically found in soils, and aboveground biomass cannot be considered long-term storage in fire-prone ecosystems. Also, the objectives of carbon storage may conflict with management for other ecosystem services and fuels reduction. Before appropriate decisions can be made it is necessary to understand the interactions between woodland expansion, management treatments, and carbon retention. We quantified effects of prescribed fire as a fuels reduction and ecosystem maintenance treatment on fuel loads, ecosystem carbon, and nitrogen in a pinyon-juniper woodland in the central Great Basin. We found that plots containing 30% tree cover averaged nearly 40 000 kg ? ha 21 in total aboveground biomass, 80 000 kg ? ha 21 in ecosystem carbon (C), and 5 000 kg ? ha 21 in ecosystem nitrogen (N). Only 25% of ecosystem C and 5% of ecosystem N resided in aboveground biomass pools. Prescribed burning resulted in a 65% reduction in aboveground biomass, a 68% reduction in aboveground C, and a 78% reduction in aboveground N. No statistically significant change in soil or total ecosystem C or N occurred. Prescribed fire was effective at reducing fuels on the landscape and resulted in losses of C and N from aboveground biomass. However, the immediate and long-term effects of burning on soil and total ecosystem C and N is still unclear. Resumen Incrementos de los bosques de piñ ón y enebro relacionados con el historial del uso de la tierra se han sugerido como una forma de proveer desvíos de las emisiones de carbón en zonas áridas. Sin embargo, los más grandes reservorios de carbono en zonas áridas se encuentran originalmente en el suelo, y la biomasa aérea no puede considerarse almacenamiento a largo plazo en los ecosistemas que están propensos al fuego. También, los objetivos de almacenamiento del carbono pueden entrar en conflicto con el manejo de los servicios de los ecosistemas y la reducción de combustibles. Antes de que se tomen las decisiones adecuadas es necesario el entender las interacciones entre la expansión del bosque y los tratamientos de manejo, así como la retención de carbón. Cuantificamos los efectos de las quemas prescritas como un tratamiento en la reducción del combustible y el mantenimiento del ecosistema en cargas de combustible, carbono del ecosistema, y nitrógeno en el bosque de piñ ón-enebro en la gran cuenca central. Encontramos que parcelas que tenían una cubierta arbórea del 30% promediaron casi 40 000 kg ha 21 en total de la biomasa aérea, 80 000 kg ha en C del ecosistema, y 5 000 kg ha de N del ecosistema. Solamente el 25% del C y el 5% el N del ecosistema existe en la biomasa aérea. Las quemas prescritas reducen la biomasa aérea en un 65%, así como el C aéreo en un 68%, y 78% del N de la superficie. No se encontraron cambios estadísticamente significativos en el C o N del suelo o del ecosistema...

a b s t r a c tSagebrush-steppe ecosystems are one of the most threatened ecosystems in North America due to woodland expansion, wildfire, and exotic annual grass invasion. Some scientists and policy makers have suggested that woodland expansion will lead to increased carbon (C) storage on the landscape. To assess this potential we used data collected from a Joint Fire Sciences Program demonstration area to develop a Microsoft ExcelÔ based biomass, carbon, and nitrogen (N) spreadsheet model. The model uses input for tree cover, soil chemistry, soil physical properties, and vegetation chemistry to estimate biomass, carbon, and nitrogen accumulation on the landscape with woodland expansion. The model also estimates C and N losses associated with prescribed burning. On our study plots we estimate in treeless sagebrush-steppe ecosystems, biomass accounts for 4.5 Mg ha À1 C and 0.3 Mg ha À1 N this is <10% of total estimated ecosystem C and N to a soil depth of 53 cm, but as tree cover increases to near closed canopy conditions aboveground biomass may account for 62 Mg ha À1 C and 0.6 Mg ha À1 N which is nearly 53% of total estimated ecosystem C and 13% of total estimated ecosystem N to a soil depth of 53 cm. Prescribed burning removes aboveground biomass, C and N, but may increase soil C at areal tree cover below 26%. The model serves as a tool by which we are able to assess our understanding of the system and identify knowledge gaps which exist for this ecosystem. We believe that further work is necessary to quantify herbaceous biomass, root biomass, woody debris decomposition, and soil C and N with woodland expansion and prescribed fire. It will also be necessary to appropriately scale these estimates from the plot to the landscape.Published by Elsevier Ltd.