• Authors:
    • Keeton, W. S.
    • Mika, A. M.
  • Source: Research Article
  • Volume: 7
  • Issue: 3
  • Year: 2015
  • Summary: The long-term greenhouse gas emissions implications of wood biomass ('bioenergy') harvests are highly uncertain yet of great significance for climate change mitigation and renewable energy policies. Particularly uncertain are the net carbon (C) effects of multiple harvests staggered spatially and temporally across landscapes where bioenergy is only one of many products. We used field data to formulate bioenergy harvest scenarios, applied them to 362 sites from the Forest Inventory and Analysis database, and projected growth and harvests over 160 years using the Forest Vegetation Simulator. We compared the net cumulative C fluxes, relative to a non-bioenergy baseline, between scenarios when various proportions of the landscape are harvested for bioenergy: 0% (non-bioenergy); 25% (BIO25); 50% (BIO50); or 100% (BIO100), with three levels of intensification. We accounted for C stored in aboveground forest pools and wood products, direct and indirect emissions from wood products and bioenergy, and avoided direct and indirect emissions from fossil fuels. At the end of the simulation period, although 82% of stands were projected to maintain net positive C benefit, net flux remained negative (i.e., net emissions) compared to non-bioenergy harvests for the entire 160-year simulation period. BIO25, BIO50, and BIO100 scenarios resulted in average annual emissions of 2.47, 5.02, and 9.83 Mg C ha -1, respectively. Using bioenergy for heating decreased the emissions relative to electricity generation as did removing additional slash from thinnings between regeneration harvests. However, all bioenergy scenarios resulted in increased net emissions compared to the non-bioenergy harvests. Stands with high initial aboveground live biomass may have higher net emissions from bioenergy harvest. Silvicultural practices such as increasing rotation length and structural retention may result in lower C fluxes from bioenergy harvests. Finally, since passive management resulted in the greatest net C storage, we recommend designation of unharvested reserves to offset emissions from harvested stands.
  • Authors:
    • Van Dael, M.
    • Witters, N.
    • Njakou Djomo, S.
    • Gabrielle, B.
    • Ceulemans, R.
  • Source: Article
  • Volume: 154
  • Year: 2015
  • Summary: Bioenergy (i.e., bioheat and bioelectricity) could simultaneously address energy insecurity and climate change. However, bioenergy's impact on climate change remains incomplete when land use changes (LUC), soil organic carbon (SOC) changes, and the auxiliary energy consumption are not accounted for in the life cycle. Using data collected from Belgian farmers, combined heat and power (CHP) operators, and a life cycle approach, we compared 40 bioenergy pathways to a fossil-fuel CHP system. Bioenergy required between 0.024 and 0.204MJ (0.86MJth+0.14 MJel)-1, and the estimated energy ratio (energy output-to-input ratio) ranged from 5 to 42. SOC loss increased the greenhouse gas (GHG) emissions of residue based bioenergy. On average, the iLUC represented ~67% of the total GHG emissions of bioenergy from perennial energy crops. However, the net LUC (i.e., dLUC+iLUC) effects substantially reduced the GHG emissions incurred during all phases of bioenergy production from perennial crops, turning most pathways based on energy crops to GHG sinks. Relative to fossil-fuel based CHP all bioenergy pathways reduced GHG emissions by 8-114%. Fluidized bed technologies maximize the energy and the GHG benefits of all pathways. The size and the power-to-heat ratio for a given CHP influenced the energy and GHG performance of these bioenergy pathways. Even with the inclusion of LUC, perennial crops had better GHG performance than agricultural and forest residues. Perennial crops have a high potential in the multidimensional approach to increase energy security and to mitigate climate change. The full impacts of bioenergy from these perennial energy crops must, however, be assessed before they can be deployed on a large scale. © 2015 The Authors.
  • Authors:
    • Louw,E. L.
    • Hoffman,E. W.
    • Theron,K. I.
    • Midgley,S. J. E.
  • Source: South African Journal of Botany
  • Volume: 99
  • Year: 2015
  • Summary: Rising temperatures associated with global climate change may alter the physiology and phenology of Protea species and cultivars. Protea species are assumed to be well adapted to warm summers characteristic of their natural Mediterranean-type habitat, but their plasticity in responding to higher growth temperatures is not known. Using infrared lamps, a greenhouse-based temperature gradient was constructed, with temperatures ranging from ambient to ambient + 3.1°C. Potted plants of Protea 'Pink Ice' ( P. compacta R. Br * P. susannae Phill.) were grown at five positions along this gradient for 12 months under irrigation. Simultaneously, a field verification experiment in a nearby commercial 'Pink Ice' orchard was conducted under ambient temperature and ambient + 2.9°C. Increased sclerophylly (leaf dry weight per unit area) with increasing temperature indicated leaf structural changes. While leaf area based gas exchange (net CO 2 assimilation rate, stomatal conductance and dark respiration rate) did not differ across the temperature gradient, leaf weight based CO 2 assimilation rate and dark respiration rate decreased significantly towards the upper end of the temperature range. The optimum temperature for net CO 2 assimilation rate (T opt) showed seasonal adjustments, but increased in response to experimental warming only in the field experiment. Significant temperature elevation resulted in an earlier onset of spring bud break, but warming extended inflorescence initiation from the spring flush to the summer flush, leading to delayed flowering. Aboveground biomass allocation shifted from inflorescences to leaves and to a lesser degree to stems, with elevated temperatures, whereas root growth was stimulated in the middle of the warming range. The results of this study suggest that elevated temperature may prolong the vegetative growth period in some Protea cultivars where water is not limiting, at the expense of flower production. This could have significant economic and marketing consequences for commercial cut flower production systems. The findings are also of significance to ecologists studying the responses of Proteaceae to climate change.
  • Authors:
    • Miao ShuJie
    • Qiao YunFa
    • Zhang FuTao
  • Source: Polish Journal of Environmental Studies
  • Volume: 24
  • Issue: 3
  • Year: 2015
  • Summary: In converting cropland to grassland and forest, more carbon is sequestered in grassland soil and forest biomass, but the mitigation of global warming potential (GWP) is not clear. In this study, we use the longterm conversion from cropland to grassland (28 y) and forest (14 y) to comprehensively assess the impact on GWP of soil carbon (C), nitrogen (N), CO 2, and N 2O emissions. The results showed that compared to the original cropland, conversion to grassland increased soil C content by 51.1%, soil N content by 28.4%, soil C stock (SCS) by four times, CO 2 emission by 17%, and N 2O emission by 40%; soil N stock (SNS) decreased by half. The corresponding values after afforestation were 7.2%, 5.2%, three times, 3%, -80%, and half, respectively. Overall GWP in the cropland system was calculated using the fuel used for farming production, the change in soil C, and N 2O emissions. Due to large C sequestration, the GWP of conversion to grassland (-1667 kg CO 2-C equivalent ha -1.y -1) and forest (-324 kg CO 2-C equivalent ha -1.y -1) were significantly lower than the cropland system (755 kg CO 2-C equivalent ha -1.y -1). The relationship between GWP and greenhouse gas, between GWP and the change of total C and N, suggest that in rain-fed agricultural systems in northeast China, the conversion from cropland to grassland and forest can mitigate GWP through changing CO 2 and N 2O emissions.
  • Authors:
    • Monier,Erwan
    • Gao,Xiang
  • Source: Climatic Change
  • Volume: 131
  • Issue: 1
  • Year: 2015
  • Summary: In this study, we analyze changes in extreme temperature and precipitation over the US in a 60-member ensemble simulation of the 21st century with the Massachusetts Institute of Technology (MIT) Integrated Global System Model-Community Atmosphere Model (IGSM-CAM). Four values of climate sensitivity, three emissions scenarios and five initial conditions are considered. The results show a general intensification and an increase in the frequency of extreme hot temperatures and extreme precipitation events over most of the US. Extreme cold temperatures are projected to decrease in intensity and frequency, especially over the northern parts of the US. This study displays a wide range of future changes in extreme events in the US, even simulated by a single climate model. Results clearly show that the choice of policy is the largest source of uncertainty in the magnitude of the changes. The impact of the climate sensitivity is largest for the unconstrained emissions scenario and the implementation of a stabilization scenario drastically reduces the changes in extremes, even for the highest climate sensitivity considered. Finally, simulations with different initial conditions show conspicuously different patterns and magnitudes of changes in extreme events, underlining the role of natural variability in projections of changes in extreme events.
  • Authors:
    • Russell,J. R.
    • Bisinger,J. J.
  • Source: Journal of Animal Science
  • Volume: 93
  • Issue: 6
  • Year: 2015
  • Summary: Beyond grazing, managed grasslands provide ecological services that may offer economic incentives for multifunctional use. Increasing biodiversity of plant communities may maximize net primary production by optimizing utilization of available light, water, and nutrient resources; enhance production stability in response to climatic stress; reduce invasion of exotic species; increase soil OM; reduce nutrient leaching or loading in surface runoff; and provide wildlife habitat. Strategically managed grazing may increase biodiversity of cool-season pastures by creating disturbance in plant communities through herbivory, treading, nutrient cycling, and plant seed dispersal. Soil OM will increase carbon and nutrient sequestration and water-holding capacity of soils and is greater in grazed pastures than nongrazed grasslands or land used for row crop or hay production. However, results of studies evaluating the effects of different grazing management systems on soil OM are limited and inconsistent. Although roots and organic residues of pasture forages create soil macropores that reduce soil compaction, grazing has increased soil bulk density or penetration resistance regardless of stocking rates or systems. But the effects of the duration of grazing and rest periods on soil compaction need further evaluation. Because vegetative cover dissipates the energy of falling raindrops and plant stems and tillers reduce the rate of surface water flow, managing grazing to maintain adequate vegetative cover will minimize the effects of treading on water infiltration in both upland and riparian locations. Through increased diversity of the plant community with alterations of habitat structure, grazing systems can be developed that enhance habitat for wildlife and insect pollinators. Although grazing management may enhance the ecological services provided by grasslands, environmental responses are controlled by variations in climate, soil, landscape position, and plant community resulting in considerable spatial and temporal variation in the responses. Furthermore, a single grazing management system may not maximize livestock productivity and each of the potential ecological services provided by grasslands. Therefore, production and ecological goals must be integrated to identify the optimal grazing management system.
  • Authors:
    • Walter,Katja
    • Don,Axel
    • Flessa,Heinz
  • Source: GCB Bioenergy
  • Volume: 7
  • Issue: 4
  • Year: 2015
  • Summary: Wood from short rotation coppices (SRCs) is discussed as bioenergy feedstock with good climate mitigation potential inter alia because soil organic carbon (SOC) might be sequestered by a land-use change (LUC) from cropland to SRC. To test if SOC is generally enhanced by SRC over the long term, we selected the oldest Central European SRC plantations for this study. Following the paired plot approach soils of the 21 SRCs were sampled to 80cm depth and SOC stocks, C/N ratios, pH and bulk densities were compared to those of adjacent croplands or grasslands. There was no general trend to SOC stock change by SRC establishment on cropland or grassland, but differences were very site specific. The depth distribution of SOC did change. Compared to cropland soils, the SOC density in 0-10cm was significantly higher under SRC (17 +/- 2 in cropland and 21 +/- 2kgCm(-3) in SRC). Under SRC established on grassland SOC density in 0-10cm was significantly lower than under grassland. The change rates of total SOC stocks by LUC from cropland to SRC ranged from -1.3 to 1.4 MgCha(-1)yr(-1) and -0.6MgCha(-1)yr(-1) to +0.1MgCha(-1)yr(-1) for LUC from grassland to SRC, respectively. The accumulation of organic carbon in the litter layer was low (0.14 +/- 0.08 MgCha(-1)yr(-1)). SOC stocks of both cropland and SRC soils were correlated with the clay content. No correlation could be detected between SOC stock change and soil texture or other abiotic factors. In summary, we found no evidence of any general SOC stock change when cropland is converted to SRC and the identification of the factors determining whether carbon may be sequestered under SRC remains a major challenge.
  • Authors:
    • Bagley,Justin E.
    • Miller,Jesse
    • Bernacchi,Carl J.
  • Source: Plant Cell Environment
  • Volume: 38
  • Issue: 9
  • Year: 2015
  • Summary: The potential impacts of climate change in the Midwest United States present unprecedented challenges to regional agriculture. In response to these challenges, a variety of climate-smart agricultural methodologies have been proposed to retain or improve crop yields, reduce agricultural greenhouse gas emissions, retain soil quality and increase climate resilience of agricultural systems. One component that is commonly neglected when assessing the environmental impacts of climate-smart agriculture is the biophysical impacts, where changes in ecosystem fluxes and storage of moisture and energy lead to perturbations in local climate and water availability. Using a combination of observational data and an agroecosystem model, a series of climate-smart agricultural scenarios were assessed to determine the biophysical impacts these techniques have in the Midwest United States. The first scenario extended the growing season for existing crops using future temperature and CO2 concentrations. The second scenario examined the biophysical impacts of no-till agriculture and the impacts of annually retaining crop debris. Finally, the third scenario evaluated the potential impacts that the adoption of perennial cultivars had on biophysical quantities. Each of these scenarios was found to have significant biophysical impacts. However, the timing and magnitude of the biophysical impacts differed between scenarios. This study assessed the biophysical impacts of several climate-smart agricultural practices in the Midwest United States. Specifically we investigated the biophysical impacts of adapting crops to extended growing season length, expanding no-till agriculture, and the adoption of perennial cultivars. We found that each of these practices had significant biophysical impacts, but the seasonality and extent of the impacts differed between scenarios.
  • Authors:
    • Karki,S.
    • Elsgaard,L.
    • Larke,P. E.
  • Source: Biogeosciences
  • Volume: 12
  • Issue: 2
  • Year: 2015
  • Summary: Cultivation of bioenergy crops in rewetted peatland (paludiculture) is considered as a possible land use option to mitigate greenhouse gas (GHG) emissions. However, bioenergy crops like reed canary grass (RCG) can have a complex influence on GHG fluxes. Here we determined the effect of RCG cultivation on GHG emission from peatland rewetted to various extents. Mesocosms were manipulated to three different ground water levels (GWLs), i.e. 0, -10 and -20 cm below the soil surface in a controlled semi-field facility. Emissions of CO 2 (ecosystem respiration, ER), CH 4 and N 2O from mesocosms with RCG and bare soil were measured at weekly to fortnightly intervals with static chamber techniques for a period of 1 year. Cultivation of RCG increased both ER and CH 4 emissions, but decreased the N 2O emissions. The presence of RCG gave rise to 69, 75 and 85% of total ER at -20, -10 and 0 cm GWL, respectively. However, this difference was due to decreased soil respiration at the rising GWL as the plant-derived CO 2 flux was similar at all three GWLs. For methane, 70-95% of the total emission was due to presence of RCG, with the highest contribution at -20 cm GWL. In contrast, cultivation of RCG decreased N2O emission by 33-86% with the major reductions at -10 and -20 cm GWL. In terms of global warming potential, the increase in CH 4 emissions due to RCG cultivation was more than offset by the decrease in N 2O emissions at -10 and -20 cm GWL; at 0 cm GWL the CH 4 emissions was offset only by 23%. CO 2 emissions from ER were obviously the dominant RCG-derived GHG flux, but aboveground biomass yields, and preliminary measurements of gross photosynthetic production, showed that ER could be more than balanced due to the photosynthetic uptake of CO 2 by RCG. Our results support that RCG cultivation could be a good land use option in terms of mitigating GHG emission from rewetted peatlands, potentially turning these ecosystems into a sink of atmospheric CO 2.
  • Authors:
    • Rong,Yuping
    • Ma,Lei
    • Johnson,Douglas A.
  • Source: Atmospheric Environment
  • Volume: 116
  • Year: 2015
  • Summary: Land-use types and management practices of temperate semiarid steppes may affect soil sink activity for atmospheric methane (CH4). Most previous studies related to CH4 have focused primarily on the growing season with only a few studies evaluating CH4 fluxes throughout the entire year. With CH4 exchange largely undocumented during the non-growing season, the annual CH4 uptake in different land-use types under various management practices is uncertain. The aim of this study was to investigate the annual variation of CH4 fluxes from four land-use types (ungrazed grassland, moderately grazed grassland, perennial pasture and cropland), which are the dominant land-use types in the agro-pastoral region of northern China. Fluxes of CH4 were measured throughout the year in four land-use types using a mobile greenhouse gas analyzer. Results showed that soils were a sink for atmospheric CH4 throughout the year for all land-use types. Annual CH4 uptake patterns were similar (but with quite different magnitudes) for all land-use types with low, spiky uptake during the two freeze-thaw periods, low and constant uptake during the frozen period and highly variable uptake with some emission events during the growing season. Seasonality of CH4 uptake was related to monthly mean temperature and precipitation. Monthly mean temperature and precipitation explained 56% (range: 40-83%) of the variability in monthly cumulative soil CH4 uptake. Annual CH4 uptake across all land-use types averaged 3.9 +/- 0.3 kg C ha(-1) yr(-1) (range: 1.0-10.2). CH4 uptake during the non-growing season represented about 50% (range: 41-59%) of annual CH4 uptake for the grassland types and 21% (range: 20-22%) for the cropland and perennial pasture land-use types. Moderate grazing (stocking rate 1.43 sheep ha(-1) yr(-1)) significantly increased annual CH4 uptake by 78% (P < 0.05) compared to ungrazed grassland. The highest annual CH4 uptake was observed for cropland (10.2 +/- 0.2 kg C ha(-1) yr(-1)), followed by 2.7 kg +/- 0.1C ha(-1) yr(-1) for perennial pasture. Our results documented year-long CH4 fluxes in four important land-use types in the expansive agro-pastoral region of northern China and contribute to our understanding of soil uptake levels of atmospheric CH4. (C) 2015 Elsevier Ltd. All rights reserved.