Wood pellets,what else? Greenhouse gas parity times of European electricity from wood pellets produced in the south‐eastern United States using different softwood feedstocks

Several EU countries import wood pellets from the south‐eastern United States. The imported wood pellets are (co‐)fired in power plants with the aim of reducing overall greenhouse gas (GHG) emissions from electricity and meeting EU renewable energy targets. To assess whether GHG emissions are reduced and on what timescale, we construct the GHG balance of wood‐pellet electricity. This GHG balance consists of supply chain and combustion GHG emissions, carbon sequestration during biomass growth and avoided GHG emissions through replacing fossil electricity. We investigate wood pellets from four softwood feedstock types: small roundwood, commercial thinnings, harvest residues and mill residues. Per feedstock, the GHG balance of wood‐pellet electricity is compared against those of alternative scenarios. Alternative scenarios are combinations of alternative fates of the feedstock materials, such as in‐forest decomposition, or the production of paper or wood panels like oriented strand board (OSB). Alternative scenario composition depends on feedstock type and local demand for this feedstock. Results indicate that the GHG balance of wood‐pellet electricity equals that of alternative scenarios within 0–21 years (the GHG parity time), after which wood‐pellet electricity has sustained climate benefits. Parity times increase by a maximum of 12 years when varying key variables (emissions associated with paper and panels, soil carbon increase via feedstock decomposition, wood‐pellet electricity supply chain emissions) within maximum plausible ranges. Using commercial thinnings, harvest residues or mill residues as feedstock leads to the shortest GHG parity times (0–6 years) and fastest GHG benefits from wood‐pellet electricity. We find shorter GHG parity times than previous studies, for we use a novel approach that differentiates feedstocks and considers alternative scenarios based on (combinations of) alternative feedstock fates, rather than on alternative land uses. This novel approach is relevant for bioenergy derived from low‐value feedstocks.     

Damaged forests provide an opportunity to mitigate climate change

British Columbia (BC) forests are estimated to have become a net carbon source in recent years due to tree death and decay caused primarily by mountain pine beetle (MPB) and related post‐harvest slash burning practices. BC forest biomass has also become a major source of wood pellets, exported primarily for bioenergy to Europe, although the sustainability and net carbon emissions of forest bioenergy in general are the subject of current debate. We simulated the temporal carbon balance of BC wood pellets against different reference scenarios for forests affected by MPB in the interior BC timber harvesting area using the Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3). We evaluated the carbon dynamics for different insect‐mortality levels, at the stand‐ and landscape level, taking into account carbon storage in the ecosystem, wood products and fossil fuel displacement. Our results indicate that current harvesting practices, in which slash is burnt and only sawdust used for pellet production, require between 20–25 years for beetle‐impacted pine and 37–39 years for spruce‐dominated systems to reach pre‐harvest carbon levels (i.e. break‐even) at the stand‐level. Using pellets made from logging slash to replace coal creates immediate net carbon benefits to the atmosphere of 17–21 tonnes C ha^?1, shortening these break‐even times by 9–20 years and resulting in an instant carbon break‐even level on stands most severely impacted by the beetle. Harvesting pine dominated sites for timber while using slash for bioenergy was also found to be more carbon beneficial than a protection reference scenario on both stand‐ and landscape level. However, harvesting stands exclusively for bioenergy resulted in a net carbon source unless the system contained a high proportion of dead trees (>85%). Systems with higher proportions of living trees provide a greater climate change mitigation if used for long lived wood products.     

Extent of industrial plantations on Southeast Asian peatlands in 2010 with analysis of historical expansion and future projections

Tropical peatlands cover over 25 Mha in Southeast Asia and are estimated to contain around 70 Gt of carbon. Peat swamp forest ecosystems are an important part of the region's natural resources supporting unique flora and fauna endemic to Southeast Asia. Over recent years, industrial plantation development on peatland, especially for oil palm cultivation, has created intense debate due to its potentially adverse social and environmental effects. The lack of objective up‐to‐date information on the extent of industrial plantations has complicated quantification of their regional and global environmental consequences, both in terms of loss of forest and biodiversity as well as increases in carbon emissions. Based on visual interpretation of high‐resolution (30 m) satellite images, we find that industrial plantations covered over 3.1 Mha (20%) of the peatlands of Peninsular Malaysia, Sumatra and Borneo in 2010, surpassing the area of Belgium and causing an annual carbon emission from peat decomposition of 230–310 Mt CO_2e. The majority (62%) of the plantations were located on the island of Sumatra, and over two‐thirds (69%) of all industrial plantations were developed for oil palm cultivation, with the remainder mostly being Acacia plantations for paper pulp production. Historical analysis shows strong acceleration of plantation development in recent years: 70% of all industrial plantations have been established since 2000 and only 4% of the current plantation area existed in 1990. ‘Business‐as‐usual’ projections of future conversion rates, based on historical rates over the past two decades, indicate that 6–9 Mha of peatland in insular Southeast Asia may be converted to plantations by the year 2020, unless land use planning policies or markets for products change. This would increase the annual carbon emission to somewhere between 380 and 920 Mt CO_2e by 2020 depending on water management practices and the extent of plantations.     

Importance of mangrove plantations for climate change mitigation in Bangladesh

Mangroves have been identified as blue carbon ecosystems that are natural carbon sinks. In Bangladesh, the establishment of mangrove plantations for coastal protection has occurred since the 1960s, but the plantations may also be a sustainable pathway to enhance carbon sequestration, which can help Bangladesh meet its greenhouse gas (GHG) emission reduction targets, contributing to climate change mitigation. As a part of its Nationally Determined Contribution (NDC) under the Paris Agreement 2016, Bangladesh is committed to limiting the GHG emissions through the expansion of mangrove plantations, but the level of carbon removal that could be achieved through the establishment of plantations has not yet been estimated. The mean ecosystem carbon stock of 5–42 years aged (average age: 25.5 years) mangrove plantations was 190.1 (±30.3) Mg C ha⁻¹, with ecosystem carbon stocks varying regionally. The biomass carbon stock was 60.3 (±5.6) Mg C ha⁻¹ and the soil carbon stock was 129.8 (±24.8) Mg C ha⁻¹ in the top 1 m of which 43.9 Mg C ha⁻¹ was added to the soil after plantation establishment. Plantations at age 5 to 42 years achieved 52% of the mean ecosystem carbon stock calculated for the reference site (Sundarbans natural mangroves). Since 1966, the 28,000 ha of established plantations to the east of the Sundarbans have accumulated approximately 76,607 Mg C year⁻¹ sequestration in biomass and 37,542 Mg C year⁻¹ sequestration in soils, totaling 114,149 Mg C year⁻¹. Continuation of the current plantation success rate would sequester an additional 664,850 Mg C by 2030, which is 4.4% of Bangladesh's 2030 GHG reduction target from all sectors described in its NDC, however, plantations for climate change mitigation would be most effective 20 years after establishment. Higher levels of investment in mangrove plantations and higher plantation establishment success could contribute up to 2,098,093 Mg C to blue carbon sequestration and climate change mitigation in Bangladesh by 2030.     

基于CO2FIX模型的长白落叶松人工林碳汇和木材生产模拟

本研究以帽儿山地区长白落叶松人工林为对象,基于样地调查和文献数据,利用CO₂FIX模型定量模拟轮伐期(30、40、50、60年)、立地指数(12、16、20 m)和初植密度(2500、3333、4444 株·hm^-2)对长白落叶松人工林碳平衡过程的影响,并构建林分尺度下生物量碳库、土壤碳库和林产品碳库之间的碳流通过程。结果表明: CO₂FIX模型对帽儿山地区长白落叶松人工林生物量和蓄积量的生长过程模拟结果具有较高的可靠性,模拟值和实测值平均相对误差分别为6.4%和3.7%。在初植密度3333 株·hm^-2、立地指数16 m、轮伐期40年的基准条件下,长白落叶松人工林总碳储量及各碳库碳储量均随轮伐期呈周期性变化。林分总碳储量和蓄积量均随轮伐期的延长、立地指数的提升和初植密度的增加而增加。当轮伐期分别延长10年和20年时,林分碳储量分别增加12.2%和31.2%,林分蓄积增加36.7%和67.8%;而当轮伐期缩短10年时,林分碳储量和蓄积量则分别降低20.9%和40.4%。与初植密度2500 株·hm^-2相比,初植密度为3333和4444 株·hm^-2时,林分碳储量增长率分别为27.8%和50.9%,蓄积量增长率分别为27.4%和49.1%。当立地指数在12～20 m范围时,每提高4 m,林分碳储量增长36.0%、40.3%,蓄积量增长39.3%、44.2%。在一个轮伐期内,每公顷长白落叶松人工林可固定约271.57 t C;当轮伐期结束时,约有27.47和56.75 t C流转到土壤和木材产品碳库中。因此,当立地条件较好时,采用较高初植密度(4444 株·hm^-2)和较长轮伐期(60年)的管理模式更有利于长白落叶松人工林碳汇和木材效益的最大化。     

A meta‐analysis of bird and mammal response to short‐rotation woody crops

Short‐rotation woody cropping (SRWC) refers to silvicultural systems designed to produce woody biomass using short harvest cycles (1–15 years), intensive silvicultural techniques, high‐yielding varieties, and often coppice regeneration. Recent emphasis on alternatives to fossil fuels has spurred interest in producing SRWC on privately owned and intensively managed forests of North America. We examined potential bird and small mammal response at the stand level to conversion of existing, intensively managed forests to SRWCs using meta‐analysis of existing studies. We found 257 effect sizes for birds (243 effect sizes) and mammals (14 effect sizes) from 8 studies involving Populus spp. plantations. Diversity and abundance of bird guilds were lower on short‐rotation plantations compared with reference woodlands, while abundance of individual bird species was more variable and not consistently higher or lower on SRWC plantations. Shrub‐associated birds were more abundant on SRWC plantations, but forest‐associated and cavity‐nesting birds were less abundant. Effects on birds appeared to decrease with age of the SRWC plantation, but plantation age was also confounded with variation in the type of reference forest used for comparison. Both guilds and species of mammals were less abundant on SRWC plantations. These conclusions are tentative because none of these studies directly compared SRWC plantations to intensively managed forests. Plantations of SRWCs could contribute to overall landscape diversity in forest‐dominated landscapes by providing shrubby habitat structure for nonforest species. However, extensive conversion of mature or intensively managed forests to SRWC would likely decrease overall diversity, especially if they replace habitat types of high conservation value.     

Effects of harvesting on spatial and temporal diversity of carbon stocks in a boreal forest landscape

Carbon stocks in managed forests of Ontario, Canada, and in harvested wood products originated from these forests were estimated for 2010–2100. Simulations included four future forest harvesting scenarios based on historical harvesting levels (low, average, high, and maximum available) and a no‐harvest scenario. In four harvesting scenarios, forest carbon stocks in Ontario's managed forest were estimated to range from 6202 to 6227 Mt C (millions of tons of carbon) in 2010, and from 6121 to 6428 Mt C by 2100. Inclusion of carbon stored in harvested wood products in use and in landfills changed the projected range in 2100 to 6710–6742 Mt C. For the no‐harvest scenario, forest carbon stocks were projected to change from 6246 Mt C in 2010 to 6680 Mt C in 2100. Spatial variation in projected forest carbon stocks was strongly related to changes in forest age (r = 0.603), but had weak correlation with harvesting rates. For all managed forests in Ontario combined, projected carbon stocks in combined forest and harvested wood products converged to within 2% difference by 2100. The results suggest that harvesting in the boreal forest, if applied within limits of sustainable forest management, will eventually have a relatively small effect on long‐term combined forest and wood products carbon stocks. However, there was a large time lag to approach carbon equality, with more than 90 years with a net reduction in stored carbon in harvested forests plus wood products compared to nonharvested boreal forest which also has low rates of natural disturbance. The eventual near equivalency of carbon stocks in nonharvested forest and forest that is harvested and protected from natural disturbance reflects both the accumulation of carbon in harvested wood products and the relatively young age at which boreal forest stands undergo natural succession in the absence of disturbance.     

Biomass production in plantations: Land constraints increase dependency on irrigation water

Integrated assessment model scenarios project rising deployment of biomass‐using energy systems in climate change mitigation scenarios. But there is concern that bioenergy deployment will increase competition for land and water resources and obstruct objectives such as nature protection, the preservation of carbon‐rich ecosystems, and food security. To study the relative importance of water and land availability as biophysical constraints to bioenergy deployment at a global scale, we use a process‐detailed, spatially explicit biosphere model to simulate rain‐fed and irrigated biomass plantation supply along with the corresponding water consumption for different scenarios concerning availability of land and water resources. We find that global plantation supplies are mainly limited by land availability and only secondarily by freshwater availability. As a theoretical upper limit, if all suitable lands on Earth, besides land currently used in agriculture, were available for bioenergy plantations (“Food first” scenario), total plantation supply would be in the range 2,010–2,300 EJ/year depending on water availability and use. Excluding all currently protected areas reduces the supply by 60%. Excluding also areas where conversion to biomass plantations causes carbon emissions that might be considered unacceptably high will reduce the total plantation supply further. For example, excluding all areas where soil and vegetation carbon stocks exceed 150 tC/ha (“Carbon threshold savanna” scenario) reduces the supply to 170–290 EJ/year. With decreasing land availability, the amount of water available for irrigation becomes vitally important. In the least restrictive land availability scenario (“Food first”), up to 77% of global plantation biomass supply is obtained without additional irrigation. This share is reduced to 31% for the most restrictive “Carbon threshold savanna” scenario. The results highlight the critical—and geographically varying—importance of co‐managing land and water resources if substantial contributions of bioenergy are to be reached in mitigation portfolios.     

林龄对红松和落叶松人工林土壤温室气体通量的影响

探讨人工林发育过程中土壤温室气体排放及其机制,可为森林温室气体通量估算提供理论依据.采用室内培养方法研究了黑龙江省帽儿山地区不同林龄(15、30和50年生)红松(Pinus koraiensis)和落叶松(Larix gmelinii)人工林土壤温室气体排放/吸收速率及其调控因素.结果 表明:30年生红松和落叶松人工林...     

Carbon dynamics and environmental controls of a hilly tea plantation in Southeast China

Tea plantations are widely distributed and continuously expanding across subtropical China in recent years. However, carbon flux exchanges from tea plantation ecosystems are poorly understood at the ecosystem level. In this study, we use the eddy covariance technique to quantify the magnitude and temporal variations of the net ecosystem exchange (NEE) in tea plantation in Southeast China over four years (2014–2017). The result showed that the tea plantation was a net carbon sink, with an annual NEE that ranged from ?182.40 to ?301.51 g C/m², which was a much lower carbon sequestration potential than other ecosystems in subtropical China. Photosynthetic photon flux density (PPFD) explained the highest proportion of the variation in NEE and gross primary productivity (GPP) (for NEE: F = 389.89, p < .01; for GPP: F = 1,018.04, p < .01), and air temperature (T_a) explained the highest proportion of the variation in ecosystem respiration (RE) (F = 13,141.81, p < .01). The strong pruning activity in April not only reduced the carbon absorption capacity but also provided many plant residues for respiration, which switched the tea plantation to a carbon source from April to June. Suppression of NEE at higher air temperatures was due to the decrease in GPP more than the decrease in RE, which indicated that future global warming may transform this subtropical tea plantation from a carbon sink to carbon source.     

太行山东坡不同林龄杏树林碳储量及其分配特征

在生物量调查的基础上,对太行山东坡4、8、12年生和16年生杏树林生态系统碳储量及其分配特征进行了研究。结果表明:杏树各器官碳含量在447.3—488.1 g/kg;树干碳含量随林龄的增长而显著降低(P0.05),不同林龄间树根、树枝和树叶碳含量无显著差异;土壤层(0—100 cm)碳含量随林龄的增长而增大;随土层深度的增加而降低。林龄对杏树林乔木层、土壤层和生态系统碳储量均有显著影响。4、8、12年生和16年生杏树林生态系统碳储量分别为27.810、72.647、82.450 Mg/hm2和102.336Mg/hm2;土壤层碳储量占总碳储量的90.1%—99.6%,且主要集中于0—40 cm。乔木层碳储量分配随着林龄的增长而增加,土壤碳储量分配则减小。结果揭示了土壤层是杏树林生态系统的主要碳库;杏树人工林生态系统在生长过程中能显著地积累有机碳。研究结果可为经济林经营管理及碳汇功能评价提供参考。     

Litterfall and nutrient dynamics shift in tropical forest restoration sites after a decade of recovery

Multi‐year studies comparing changes in litterfall biomass and nutrient inputs in sites under different restoration practices are lacking. We evaluated litterfall dynamics and nutrient inputs at 5 yr and after a decade of recovery in four treatments (natural regeneration—no planting, plantation—entire area planted, tree islands—planting in patches, and reference forest) at multiple sites in an agricultural landscape in southern Costa Rica. We inter‐planted two native species (Terminalia amazonia and Vochysia guatemalensis) and two naturalized N‐fixing species (Inga edulis and Erythrina poeppigiana) in plantation and island treatments. Although litterfall N was higher in plantations in the first sampling period, litter production and overall inputs of C, N, Ca, Mg, P, Cu, Mn, and Fe did not differ between island, plantation, or reference forest after a decade; however, all were greater than in natural regeneration. Potassium inputs were lower in the natural regeneration, intermediate in island and plantation, and greater in reference forest. The percentage of litterfall comprised by the N‐fixing planted species declined by nearly two‐thirds in both plantations and islands between sampling periods, while the percentage of V. guatemalensis more than doubled, and the percentage from naturally regenerated species increased from 27 to 47 percent in islands. Island and plantation treatments were equally effective at restoring litterfall and nutrient inputs to levels similar to the reference system. The nutrient input changed substantially over the 7‐yr interval between measurements, reflecting shifts in vegetation composition and demonstrating how rapidly nutrient cycling dynamics can change in recovering forests.     

Model simulation of soil carbon dynamics with stand development in Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) plantations

Soil carbon cycling in Japanese cedar plantations after clear-cutting over time was calculated with and without consideration of plantation management (pruning and thinning) using a mathematical model. The model employed a daily time step and used daily air temperature and observed precipitation near the plantations. The results of these calculations of above-ground biomass, carbon flow and accumulation were compared with the field observations reported by Shutou and Nakane (Ecol Res 19:233–244, 2004) observed in the Hiroshima prefecture. For example, the carbon accumulation and total soil respiration rate calculated with the inclusion of plantation management for a 60-year-old stand were 104 and 4.8 t C ha⁻¹year⁻¹, compared with a field observation of 110 and 4.5 t C ha⁻¹year⁻¹, respectively. The results calculated for carbon flow and accumulation were not significantly different from the field observations, assessed using one-way analysis of variance (P > 0.05), and the mean relative errors were very small (e.g., the maximum was 0.05). Consequently, it is suggested that the dynamics of carbon cycling following clear-cutting of a Japanese cedar plantation can be simulated realistically using these calculations with and without consideration of plantation management. Moreover, it is possible that the calculation without consideration of plantation management can yield the change of carbon cycling over time, even if the history of forest management in the plantations is unknown. It is expected that this study will contribute to the development of a more versatile model.     

Carbon stocks in above‐ground biomass of monoculture plantations,mixed species plantations and environmental restoration plantings in north‐east Australia

Summary The emergence of carbon markets has provided a potential source of funding for reforestation projects. However, there is concern amongst ecologists that these markets will promote the establishment of monoculture plantations rather than more diverse restoration plantings, on the assumption that fast‐growing monocultures are likely to store more carbon than restoration plantings. We examined the validity of this assumption for three predominantly rainforest plantation types established in the moist tropical uplands of north‐east Australia: monoculture plantations of native rainforest conifers (n = 5, mean age 13 years); mixed species plantations of rainforest cabinet timber species, rainforest conifers and eucalypts (n = 5, mean age 13 years); and, environmental restoration plantings comprised mostly of a diverse range of rainforest trees (n = 10, mean age 14 years). We found that restoration plantings stored significantly more carbon in above‐ground biomass than monoculture plantations of native conifers (on average, 106 t vs 62 t carbon per ha); and tended to store more carbon than mixed species timber plantations which were intermediate in value (86 t carbon per ha). Carbon stocks were higher in restoration plantings than in monoculture and mixed species plantations for three reasons. First, and most importantly, restoration plantings were more densely stocked than monoculture and mixed species plantations. Second, there were more large diameter trees in restoration plantings than monoculture plantations. Third, the trees used in restoration plantings had a higher average wood density than the conifers used in monoculture plantations. While, on average, wood density was higher in mixed species plantations than restoration plantings, the much higher stocking rate of restoration plantings meant they stored more carbon than mixed species plantations. We conclude that restoration plantings in the moist tropics of north‐east Australia can accumulate relatively high amounts of carbon within two decades of establishment. Comparison with reference rainforest sites suggests that restoration plantings could maintain their high stocking rates (and therefore high biomass) as they develop in future decades. However, because restoration plantings are currently much more expensive to establish than monoculture plantations, restoration plantings are unlikely to be favoured by carbon markets. Novel reforestation techniques and designs are required if restoration plantings are to both provide habitat for rainforest biota and store carbon in biomass at a cost comparable to monoculture plantations.     

Global warming potentials of stemwood used for energy and materials in Southern Finland: differentiation of impacts based on type of harvest and product lifetime

Wood harvesting in boreal forests typically consists of sequential harvesting operations within a rotation: a few thinnings and a final felling. The aim of this paper is to model differentiated relative global warming potential (GWP) coefficients for stemwood use from different thinnings and final fellings, and correction factors for long‐lived wood products, potentially applicable in life cycle assessment studies. All thinnings and final fellings influence the development of forest carbon stocks. The climate impact of a single harvesting operation is generated in comparison with no harvesting, thus encountering a methodological problem on how to handle the subsequent operations. The dynamic forest stand simulator MOTTI was applied in the modelling of evolution of forest carbon stocks at landscape level in Southern Finland. The landscape‐level approach for climate impact assessment gave results similar to some stand‐level approaches presented in previous literature that included the same forest C pools and also studied the impacts relative to the no‐harvest situation. The climate impacts of stemwood use decreased over time. For energy use, the impacts were higher or similar in the short term and 0–50% lower in the midterm in comparison with an identical amount of fossil CO₂. The impacts were to some extent (approximately 20–40%) lower for wood from intermediate thinnings than for wood from final fellings or first thinnings. However, the study reveals that product lifetime has higher relative influence on the climate impacts of wood‐based value chains than whether the stemwood originates from thinnings or final fellings. Although the evolution of future C stocks in unmanaged boreal forests is uncertain, a sensitivity analysis suggests that landscape‐level model results for climate impacts would not be sensitive to the assumptions made on the future evolution of C stocks in unmanaged forest. Energy use of boreal stemwood seems to be far from climate neutral.     

黄土高原不同林龄刺槐林碳、氮、磷化学计量特征

以黄土高原幼龄林、中龄林、成熟林(分别为5～10、11～15、21～30年生)刺槐人工林为对象,研究刺槐根、茎、叶、枯落物的碳、氮、磷化学计量学特征及其相互关系.结果表明: 不同林龄刺槐林各组分的碳、氮、磷含量分别为376.74～486.67、8.66～29.70和0.79～1.95g·kg^-1,刺槐各组分碳含量变异较小,磷含量变异较大.中龄林碳含量较高,成熟林氮、磷含量较高.不同组分间叶碳、氮、磷含量较高,茎的氮含量较低.不同林龄刺槐林各组分的C/N、C/P和N/P分别为15.74～53.40、242.47～606.39和8.10～20.57;中龄林和幼龄林中茎C/N、C/P和N/P显著高于成熟林,不同组分间茎C/N、C/P较高,叶C/N、C/P较低.刺槐叶片和根的碳氮磷含量间不存在相关关系,枯落物与茎的氮含量和磷含量间存在显著相关关系,反映出枯落物和茎的建成过程中对氮磷按比例投入的依赖.与全球尺度相比,黄土高原人工刺槐林具有较高的储碳能力,氮含量丰富,而磷相对缺乏,成为刺槐人工林生长的主要限制因子.     

Thermodynamics of Energy Production from Biomass

With high quality petroleum running out in the next 50 years, the world governments and petrochemical industry alike are looking at biomass as a substitute refinery feedstock for liquid fuels and other bulk chemicals. New large plantations are being established in many countries, mostly in the tropics, but also in China, North America, Northern Europe, and in Russia. These industrial plantations will impact the global carbon, nitrogen, phosphorus, and water cycles in complex ways. The purpose of this paper is to use thermodynamics to quantify a few of the many global problems created by industrial forestry and agriculture. It is assumed that a typical tree biomass-for-energy plantation is combined with an efficient local pelleting facility to produce wood pellets for overseas export. The highest biomass-to-energy conversion efficiency is afforded by an efficient electrical power plant, followed by a combination of the FISCHER-TROPSCH diesel fuel burned in a 35%-efficient car, plus electricity. Wood pellet conversion to ethanol fuel is always the worst option. It is then shown that neither a prolific acacia stand in Indonesia nor an adjacent eucalypt stand is “sustainable.” The acacia stand can be made “sustainable” in a limited sense if the cumulative free energy consumption in wood drying and chipping is cut by a factor of two by increased reliance on sun-drying of raw wood. The average industrial sugarcane-for-ethanol plantation in Brazil could be “sustainable” if the cane ethanol powered a 60%-efficient fuel cell that, we show, does not exist. With some differences (ethanol distillation vs. pellet production), this sugarcane plantation performs very similarly to the acacia plantation, and is unsustainable in conjunction with efficient internal combustion engines.     

Carbon debt repayment or carbon sequestration parity? Lessons from a forest bioenergy case study in Ontario,Canada

Forest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions associated with energy production. We assessed changes in GHG emissions resulting from displacement of coal with wood pellets for the Atikokan Generating Station located in Northwestern Ontario, Canada. Two contrasting biomass sources were considered for continuous wood pellet production: harvest residue from current harvest operations (residue scenario) and fibre from expanded harvest of standing live trees (stemwood scenario). For the stemwood scenario, two metrics were used to assess the effects of displacing coal with forest biomass on GHG emissions: (i) time to carbon sequestration parity, defined as the time from the beginning of harvest to when the combined GHG benefit of displacing coal with biomass and the amount of carbon in regenerating forest equalled the amount of forest carbon without harvest for energy production; and (ii) time to carbon debt repayment, defined as the time from the beginning of harvest to when the combined GHG benefit of displacing coal with biomass and the amount of carbon in the regenerating forest equalled forest carbon at the time of harvest. Only time to carbon sequestration parity was used for the residue scenario. In the residue scenario, carbon sequestration parity was achieved within 1 year. In the stemwood scenario, times to carbon sequestration parity and carbon debt repayment were 91 and 112 years, respectively. Sensitivity analysis showed that estimates were robust when parameter values were varied. Modelling experiments showed that increasing growth rates for regenerating stands in the stemwood scenario could substantially reduce time to carbon sequestration parity. We discuss the use of the two metrics (time to carbon sequestration parity and time to carbon debt repayment) for assessing the effects of forest bioenergy projects on GHG emissions and make recommendations on terminology and methodologies for forest bioenergy studies.     

Carbon cycle of larch plantation based on CO2FIX model

Aims
Plantations play important roles in modifying regional carbon budget and maintaining regional carbon balance. In this study, we assessed larch plantation (Larix gmelinii var. principis-rupprechtii) carbon dynamics in Weichang County from a perspective of the forest biomass-soil-wood-products chain. Our objectives were to elucidate the carbon sink capacity of larch plantation and the influences of biomass, soil and wood product pools on carbon balance.
Methods
CO2FIX model was used to evaluate the carbon storage and flow of larch plantation over a time span of 120 years. Input data for model were derived from practical investigations and published papers. We validated the simulated results and found that this model was suitable in the region and the simulated results were reliable.
Important findings
(1) Soil was the largest carbon pool for larch plantation and the wood product pool had the smallest carbon storage. Meanwhile, carbon storage in wood products gradually increased with time. (2) In a rotation of 50 years from secondary poplar-birch forest to larch plantation, 250 t C·hm^-2 was sequestrated by the larch plantation. 70% of the carbon was transferred into soil in the form of litter and logging slash and the other 30% was transferred into wood products. (3) Larch plantation was a carbon sink during most of its growing period and turned to temporary carbon source when it was harvested. Larch plantation could sequestrate about 0.3 t C·hm^-2·a^-1 in the long term. Our results indicated the importance of wood product carbon pool in carbon dynamics of plantation, which facilitated our understanding in the carbon dynamics and capacity of plantation.     

基于CO2FIX模型的华北落叶松人工林碳循环过程

为了探明华北落叶松(Larix gmelinii var. principis-rupprechtii)人工林的碳循环过程, 该研究以河北围场地区的华北落叶松人工林为例, 基于CO2FIX模型, 以在当地的实际调查数据、文献数据作为输入数据, 从生物量、土壤和木质林产品碳库3个方面探讨了华北落叶松人工林的碳循环过程和碳汇能力。结果表明: 华北落叶松人工林土壤碳库最大, 生物量碳库次之, 林产品碳库最小, 但是林产品碳库随时间呈逐渐增加的趋势; 在一个轮伐期内(50年), 每公顷华北落叶松人工林约固定了250 t碳, 其中约70%通过凋落物和采伐剩余物的方式进入土壤碳库, 约30%进入木质林产品碳库; 华北落叶松人工林在生长的大部分时间是一个碳的吸收汇, 而在森林采伐时成为暂时的排放源, 从长时间尺度上看, 每公顷华北落叶松人工林每年大约固定0.3 t左右的碳。该研究结果表明了木质林产品碳库在人工林碳循环中的重要作用, 这将有助于更加全面地认识人工林的碳循环过程和碳汇能力。