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Carbon debt and carbon sequestration parity in forest bioenergy production
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The capacity for forests to aid in climate change mitigation efforts is substantial but will ultimately depend on their management. If forests remain unharvested, they can further mitigate the increases in atmospheric CO2 that result from fossil fuel combustion and deforestation. Alternatively, they can be harvested for bioenergy production and serve as a substitute for fossil fuels, though such a practice could reduce terrestrial C storage and thereby increase atmospheric CO2 concentrations in the near-term. Here, we used an ecosystem simulation model to ascertain the effectiveness of using forest bioenergy as a substitute for fossil fuels, drawing from a broad range of land-use histories, harvesting regimes, ecosystem characteristics, and bioenergy conversion effi- ciencies. Results demonstrate that the times required for bioenergy substitutions to repay the C Debt incurred from biomass harvest are usually much shorter (< 100 years) than the time required for bioenergy production to substitute the amount of C that would be stored if the forest were left unharvested entirely, a point we refer to as C Sequestration Parity. The effectiveness of substituting woody bioenergy for fossil fuels is highly dependent on the factors that determine bioenergy conversion efficiency, such as the C emissions released during the har- vest, transport, and firing of woody biomass. Consideration of the frequency and intensity of biomass harvests should also be given; performing total harvests (clear-cutting) at high-frequency may produce more bioenergy than less intensive harvesting regimes but may decrease C storage and thereby prolong the time required to achieve C Sequestration Parity.
Keywords: bioenergy, biofuel, C cycle, C sequestration, forest management
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Changes in climate and land use have a larger direct impact than rising CO2 on global river runoff trends
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The significant worldwide increase in observed river runoff has been tentatively attributed to the stomatal ‘‘antitranspirant’’ response of plants to rising atmospheric CO2 [Gedney N, Cox PM, Betts RA, Boucher O, Huntingford C, Stott PA (2006) Nature 439: 835– 838]. However, CO2 also is a plant fertilizer. When allowing for the increase in foliage area that results from increasing atmospheric CO2 levels in a global vegetation model, we find a decrease in global runoff from 1901 to 1999. This finding highlights the importance of vegetation structure feedback on the water balance of the land surface. Therefore, the elevated atmospheric CO2 concentration does not explain the estimated increase in global runoff over the last century. In contrast, we find that changes in mean climate, as well as its variability, do contribute to the global runoff increase. Using historic land-use data, we show that land-use change plays an additional important role in controlling regional runoff values, particularly in the tropics. Land-use change has been strongest in tropical regions, and its contribution is substantially larger than that of climate change. On average, land-use change has increased global runoff by 0.08 mm/year2 and accounts for 50% of the reconstructed global runoff trend over the last century. Therefore, we emphasize the importance of land-cover change in forecasting future freshwater availability and climate.
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Invited Review: Quantifying surface albedo and other direct biogeophysical climate forcings of forestry activities
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By altering fluxes of heat, momentum, and moisture exchanges between the land surface and atmosphere, forestry and other land-use activities affect climate. Although long recognized scientifically as being important, these so-called biogeophysical forcings are rarely included in climate policies for forestry and other land management projects due to the many challenges associated with their quantification. Here, we review the scientific literature in the fields of atmospheric science and terrestrial ecology in light of three main objectives: (i) to elucidate the challenges associated with quantifying biogeophysical climate forcings connected to land use and land management, with a focus on the forestry sector; (ii) to identify and describe scientific approaches and/or metrics facilitating the quantification and interpretation of direct biogeophysical climate forcings; and (iii) to identify and recommend research priorities that can help overcome the challenges of their attribution to specific land-use activities, bridging the knowledge gap between the climate modeling, forest ecology, and resource management communities. We find that ignoring surface
biogeophysics may mislead climate mitigation policies, yet existing metrics are unlikely to be sufficient. Successful metrics ought to (i) include both radiative and nonradiative climate forcings; (ii) reconcile disparities between biogeophysical and biogeochemical forcings, and (iii) acknowledge trade-offs between global and local climate benefits. We call for more coordinated research among terrestrial ecologists, resource managers, and coupled climate modelers to harmonize datasets, refine analytical techniques, and corroborate and validate metrics that are more amenable to analyses at the scale of an individual site or region.
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Forecasting the response of Earth’s surface to future climatic and land use changes: A review of methods and research needs
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In the future, Earth will be warmer, precipitation events will be more extreme, global mean
sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes
will also occur at an accelerated rate as developed areas increase in size and population density. We now
have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC)
that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do
not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we
have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models
and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system
modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to
forecast changes in the state of Earth’s surface as a result of likely future C&LUC. We also propose strategies
for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration
across disciplines are necessary. The main body of the paper addresses cross-cutting issues, including the
importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment
transport, as well as the importance of alternate stable states and extreme, rare events for understanding
and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process
zones (global-scale assessments and fluvial, aeolian, glacial/periglacial, and coastal process zones) in
detail.
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Introduction to LANDFIRE video series
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Through a short series of videos, learn about LANDFIRE: a shared program between federal wildland fire management programs that provides landscape scale geospatial products to support cross-boundary planning, management, and operations. Use LF data for landscape assessment, modeling, analysis, and more.
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