Temporal evolution of the European forest sector carbon sink from 1950 to 1999

Estimates of the role of the European terrestrial biosphere in the global carbon cycle still vary by a factor 10. This is due to differences in methods and assumptions employed, but also due to difference in reference periods of the studies. The magnitude of the sink varies between years because of inter‐annual variation of short‐term climate, but also due to long‐term trends in development of the vegetation and its management. For this purpose, we present the results of an application of a carbon bookkeeping model to the forest sector of the European forests from 1950 to 1999. The analysis includes the compartments trees, soils, and wood products. The model uses statistics on European (30 countries excl. CIS) stemwood volume increment, forest area change, fellings, wood products and their international trade, and natural disturbances, supplemented with conversion coefficients, soil parameters and information on management. An (almost uninterrupted) increasing sink (Net Biome Production) in the European forest sector was found, increasing from 0.03 Pg C year ^?1 in the 1950s to 0.14 Pg C year ^?1 in the 1990s (for resp. 132 million hectares and 140 million hectares of forest). The sink in the tree and the soil compartment were approximately of the same size until 1970. After the 1970s the size of the sink in the tree biomass increases quickly, causing the tree biomass to account for some two thirds of the total sink in the 1990s. The results as presented here have to be regarded with caution especially with regard to the early decades of the analysis and with regard to the soil compartment.     

CO2 stabilization,climate change and the terrestrial carbon sink

A nonequilibrium, dynamic, global vegetation model, Hybrid v4.1, with a subdaily timestep, was driven by increasing CO₂ and transient climate output from the UK Hadley Centre GCM (HadCM2) with simulated daily and interannual variability. Three IPCC emission scenarios were used: (i) IS92a, giving 790 ppm CO₂ by 2100, (ii) CO₂ stabilization at 750 ppm by 2225, and (iii) CO₂ stabilization at 550 ppm by 2150. Land use and future N deposition were not included. In the IS92a scenario, boreal and tropical lands warmed 4.5 °C by 2100 with rainfall decreased in parts of the tropics, where temperatures increased over 6 °C in some years and vapour pressure deficits (VPD) doubled. Stabilization at 750 ppm CO₂ delayed these changes by about 100 years while stabilization at 550 ppm limited the rise in global land surface temperature to 2.5 °C and lessened the appearance of relatively hot, dry areas in the tropics. Present‐day global predictions were 645 PgC in vegetation, 1190 PgC in soils, a mean carbon residence time of 40 years, NPP 47 PgC y^?1 and NEP (the terrestrial sink) about 1 PgC y^?1, distributed at both high and tropical latitudes. With IS92a emissions, the high latitude sink increased to the year 2100, as forest NPP accelerated and forest vegetation carbon stocks increased. The tropics became a source of CO₂ as forest dieback occurred in relatively hot, dry areas in 2060–2080. High VPDs and temperatures reduced NPP in tropical forests, primarily by reducing stomatal conductance and increasing maintenance respiration. Global NEP peaked at 3–4 PgC y^?1 in 2020–2050 and then decreased abruptly to near zero by 2100 as the tropical source offset the high‐latitude sink. The pattern of change in NEP was similar with CO₂ stabilization at 750 ppm, but was delayed by about 100 years and with a less abrupt collapse in global NEP. CO₂ stabilization at 550 ppm prevented sustained tropical forest dieback and enabled recovery to occur in favourable years, while maintaining a similar time course of global NEP as occurred with 750 ppm stabilization. By lessening dieback, stabilization increased the fraction of carbon emissions taken up by the land. Comparable studies and other evidence are discussed: climate‐induced tropical forest dieback is considered a plausible risk of following an unmitigated emissions scenario.     

江西省森林碳蓄积过程及碳源/汇的时空格局

森林碳蓄积是研究森林与大气碳交换以及估算森林吸收或排放含碳气体的关键参数,不同年龄森林的碳源/汇功能差异则体现出森林生态系统碳蓄积过程的时间特征。以森林资源清查的样方数据作为数据源,通过刻画主要树种的林分蓄积生长曲线、林龄与净初级生产力(NPP)之间的关系,驱动区域碳收支模型(InTEC)模拟江西省1950—2008年的森林碳蓄积过程,了解山江湖工程实施以来的森林碳源/汇状况。结果表明,20世纪80年代以前,江西省森林年平均NPP波动于450—813 gCm-2a-1之间,年净增生物量碳26.55—36.23 TgC/a,年净增木质林产品碳0.01—0.3 TgC/a;80年代初,NPP和年净增生物量碳分别降至307.39 gC m-2a-1和17.31 TgC/a,而年净增木质林产品碳却高达0.6 TgC/a,说明森林被大量砍伐进入林产品碳库;1985年山江湖工程实施后,大面积造林使得年净增碳蓄积呈现急剧上升趋势,生物量和木质林产品碳蓄积分别上升至目前的42.37 TgC/a和0.79 TgC/a,而平均NPP值增加缓慢、碳汇功能降低,说明林分质量有待提高;90年代后碳汇功能开始稳步增强,说明造林面积的迅速增加是引起江西省森林碳增汇的主要驱动因素,但未来森林增汇潜力应源于森林生长和有效的经营管理。     

The high-latitude terrestrial carbon sink: a model analysis

A dynamic, global vegetation model, hybrid v4.1 ( Friend et al. 1997 ), was driven by transient climate output from the UK Hadley Centre GCM (HadCM2) with the IS92a scenario of increasing atmospheric CO₂ equivalent, sulphate aerosols and predicted patterns of atmospheric N deposition. Changes in areas of vegetation types and carbon storage in biomass and soils were predicted for areas north of 50°N from 1860 to 2100. Hybrid is a combined biogeochemical, biophysical and biogeographical model of natural, potential ecosystems. The effect of periodic boreal forest fires was assessed by adding a simple stochastic fire model. Hybrid represents plant physiological and soil processes regulating the carbon, water and N cycles and competition between individuals of parameterized generalized plant types. The latter were combined to represent tundra, temperate grassland, temperate/mixed forest and coniferous forest. The model simulated the current areas and estimated carbon stocks in the four vegetation types. It was predicted that land areas above 50°N (about 23% of the vegetated global land area) are currently accumulating about 0.4 PgC y^?1 (about 30% of the estimated global terrestrial sink) and that this sink could grow to 0.8–1.0 PgC y^?1 by the second half of the next century and persist undiminished until 2100. This sink was due mainly to an increase in forest productivity and biomass in response to increasing atmospheric CO₂, temperature and N deposition, and includes an estimate of the effect of boreal forest fire, which was estimated to diminish the sink approximately by the amount of carbon emitted to the atmosphere during fires. Averaged over the region, N deposition contributed about 18% to the sink by the 2080 s. As expected, climate change (temperature, precipitation, solar radiation and saturation pressure deficit) and N deposition without increasing atmospheric CO₂ produced a carbon source. Forest areas expanded both south and north, halving the current tundra area by 2100. This expansion contributed about 30% to the sink by the 2090 s. Tundra areas which were not invaded by forest fluctuated from sink to source. It was concluded that a high latitude carbon sink exists at present and, even assuming little effect of N deposition, no forest expansion and continued boreal forest fires, the sink is likely to persist at its current level for a century.     

红树林湿地碳储量及碳汇研究进展

红树林是生长在热带和亚热带地区潮间带的特殊的湿地森林,在防风固田、促进淤泥沉积、抵御海啸和台风等自然灾害和保护海岸线方面起着重要的作用.全球约有红树林152000 km²,占陆地森林面积的0.4%,我国约有230 km².热带红树林湿地的碳储量平均高达1023 Mg C·hm^-2,全球红树林湿地的碳汇能力在0.18～0.228 Pg C·a^-1.影响红树林碳储量和碳汇能力的主要因子除了植物种类组成以外,气温、海水温度、海水盐度、土壤理化性质、大气CO₂浓度及人类干扰等均有着重要作用.红树林湿地碳储量、碳汇能力的研究方法以实测法为基础,包括异速方程、遥感反演和模型模拟等.研究红树林湿地碳储量及碳汇能力,有利于深入认识红树林湿地碳循环过程及其调控机制,对红树林湿地的保护和合理利用具有重要意义.     

Impact of changing wood demand,climate and land use on European forest resources and carbon stocks during the 21st century

We used the European Forest Information Scenario Model (EFISCEN) to project the development of forest resources for 15 European countries from 2000 to 2100 under a broad range of climate scenarios, which were based on the a1fi, a2, b1 and b2 storylines of the Special Report on Emissions Scenarios of the Intergovernmental Panel on Climate Change. Each climate scenario was associated with consistent land-use change and wood demand assumptions. Climate change-induced growth changes were incorporated into the calculations by scaling inventory-based stem growth in EFISCEN by net primary productivity estimated from the Lund–Potsdam–Jena dynamic global vegetation model. The impact of changes in wood demand, climate and forest area were studied separately, and in combination, in order to assess their respective effects. For all climate scenarios under consideration, climate change resulted in increased forest growth, especially in Northern Europe. In Southern Europe, higher precipitation in spring and the projected increased water-use efficiency in response to rising atmospheric CO₂ concentrations mitigated the effects of increasing summer drought. Climate change enhanced carbon sequestration in tree biomass. The climate change-induced increase in tree growth led to a faster increase in growing stocks compared with the simulation using current climate. As productivity decreased in higher stocked forests, the positive impact of climate change began to level off during the second half of the 21st century in the scenarios where wood demand was low. Afforestation measures had the potential to increase growing stock and annual increment; however, large areas were needed to obtain notable effects. Despite noticeable differences in the growth response between the climate scenarios, changes in wood demand proved to be the crucial driving force in forest resource development. Tree carbon stocks increased by 33–114% between 2000 and 2100 when only changes in wood demand were regarded. Climate change added another 23–31% increase, while changes in forest area accounted for an additional increase of 2–40%. Our results highlight potential future pathways of forest resource development resulting from different scenarios of wood demand, land use and climate changes, and stress the importance of resource utilization in the European forest carbon balance.     

增汇型气候保护的经济影响模拟分析

目前,将增汇作为气候保护的手段已在世界上引起了广泛重视。那么,增汇的经济可行性如何呢?我们认为,在经济发展的前提下,这个问题需要在宏观经济一般均衡的框架内进行讨论。针对这个问题,本文提出了对增汇型气候保护的经济影响进行评估的技术路线,建立了动态宏观经济分析模型进行模拟分析,得到了一些有意义的结论。     

Effects of forest management on the carbon dioxide emissions of wood energy in integrated production of timber and energy biomass

The aim of this work was to study the sensitivity of carbon dioxide (CO₂) emissions from wood energy to different forest management regimes when aiming at an integrated production of timber and energy biomass. For this purpose, the production of timber and energy biomass in Norway spruce [Picea abies (L.) Karst] and Scots pine (Pinus sylvestris L.) stands was simulated using an ecosystem model (SIMA) on sites of varying fertility under different management regimes, including various thinning and fertilization treatments over a fixed simulation period of 80 years. The simulations included timber (sawlogs, pulp), energy biomass (small‐sized stem wood) and/or logging residues (top part of stem, branches and needles) from first thinning, and logging residues and stumps from final felling for energy production. In this context, a life cycle analysis/emission calculation tool was used to assess the CO₂ emissions per unit of energy (kg CO₂ MWh^?1) which was produced based on the use of wood energy. The energy balance (GJ ha^?1) of the supply chain was also calculated. The evaluation of CO₂ emissions and energy balance of the supply chain considered the whole forest bioenergy production chain, representing all operations needed to grow and harvest biomass and transport it to a power plant for energy production. Fertilization and high precommercial stand density clearly increased stem wood production (i.e. sawlogs, pulp and small‐sized stem wood), but also the amount of logging residues, stump wood and roots for energy use. Similarly, the lowest CO₂ emissions per unit of energy were obtained, regardless of tree species and site fertility, when applying extremely or very dense precommercial stand density, as well as fertilization three times during the rotation. For Norway spruce such management also provided a high energy balance (GJ ha^?1). On the other hand, the highest energy balance for Scots pine was obtained concurrently with extremely dense precommercial stands without fertilization on the medium‐fertility site, while on the low‐fertility site fertilization three times during the rotation was needed to attain this balance. Thus, clear differences existed between species and sites. In general, the forest bioenergy supply chain seemed to be effective; i.e. the fossil fuel energy consumption varied between 2.2% and 2.8% of the energy produced based on the forest biomass. To conclude, the primary energy use and CO₂ emissions related to the forest operations, including the production and application of fertilizer, were small in relation to the increased potential of energy biomass.     

城市森林碳汇及其抵消能源碳排放效果——以广州为例

城市森林及其管理相关政策作为减少CO₂排放的有效策略得到了较为广泛的关注。采用材积源生物量方程与净初级生产力方法来定量分析了广州市城市森林碳储量和碳固定量,根据化石能源使用量及其碳排放因子核算了广州城市能源碳排放,最后评估了城市森林碳抵消效果。结果显示广州市城市森林碳储量为654.42×10⁴t,平均碳密度为28.81 t/hm²,而森林碳固定量为658732 t/a,平均固碳率为2.90 t·hm^-2·a^-1。2005-2010年广州市年均能源碳排放则达到2907.41×10⁴t。广州城市森林碳储量约为城市年均能源碳排放的22.51%,其通过碳固定年均能够抵消年均碳排放的2.27%,不过从城市森林综合效益来看其仍是城市低碳发展重要举措之一。分析了林型组成和林龄结构对于广州森林碳储量和碳固定量的影响,并从森林管理角度为城市森林碳汇提升提出建议。这些结果和讨论有助于评估城市森林碳汇在抵消碳排放中所起的效果。     

The contributions of land-use change, CO2 fertilization, and climate variability to the Eastern US carbon sink

Atmospheric measurements and land‐based inventories imply that terrestrial ecosystems in the northern hemisphere are taking up significant amounts of anthropogenic cabon dioxide (CO₂) emissions; however, there is considerable disagreement about the causes of this uptake, and its expected future trajectory. In this paper, we use the ecosystem demography (ED) model to quantify the contributions of disturbance history, CO₂ fertilization and climate variability to the past, current, and future terrestrial carbon fluxes in the Eastern United States. The simulations indicate that forest regrowth following agricultural abandonment accounts for uptake of 0.11 Pg C yr^?1 in the 1980s and 0.15 Pg C yr^?1 in the 1990s, and regrowth following forest harvesting accounts for an additional 0.1 Pg C yr^?1 of uptake during both these decades. The addition of CO₂ fertilization into the model simulations increases carbon uptake rates to 0.38 Pg C yr^?1 in the 1980s and 0.47 Pg C yr^?1 in the 1990s. Comparisons of predicted aboveground carbon uptake to regional‐scale forest inventory measurements indicate that the model's predictions in the absence of CO₂ fertilization are 14% lower than observed, while in the presence of CO₂ fertilization, predicted uptake rates are 28% larger than observed. Comparable results are obtained from comparisons of predicted total Net Ecosystem Productivity to the carbon fluxes observed at the Harvard Forest flux tower site and in model simulations free‐air CO₂ enrichment (FACE) experiments. These results imply that disturbance history is the principal mechanism responsible for current carbon uptake in the Eastern United States, and that conventional biogeochemical formulations of plant growth overestimate the response of plants to rising CO₂ levels. Model projections out to 2100 imply that the carbon uptake arising from forest regrowth will increasingly be dominated by forest regrowth following harvesting. Consequently, actual carbon storage declines to near zero by the end of the 21st century as the forest regrowth that has occurred since agricultural abandonment comes into equilibrium with the landscape's new disturbance regime. Incorporating interannual climate variability into the model simulations gives rise to large interannual variation in regional carbon fluxes, indicating that long‐term measurements are necessary to detect the signature of processes that give rise to long‐term uptake and storage.     

近20年我国森林碳汇政策演变和评价

巩固提升生态系统碳汇能力是碳达峰十大行动计划之一,是助力碳中和目标实现、应对气候变化的重要举措。森林作为陆地生态系统中最大的碳库,是我国当前碳汇政策的主体。研究梳理了2000年以来我国森林碳汇有关政策的发展演变历程,并从生态政策、经济政策和保障体系建设三个维度分析和评价了政策成效与存在问题,以期为构建适应“双碳”目标的碳汇政策体系提供决策依据。研究结果表明：(1)从生态政策看：天然林保护、退耕还林还草和“三北”防护林三大林业工程增加了我国森林面积和蓄积量,显著提升了森林碳汇增量,但森林可持续经营管理体系尚未健全,需进一步精准提升森林质量,健全成果长效巩固机制,增强森林固碳能力;(2)就经济政策而言：我国已形成多层级林业碳汇交易市场,有效推动林业碳汇项目建设,同时各类金融产品的开发和补贴政策的实施为碳汇项目提供了多元化资金支持体系,但整体融资规模和补贴范围有限,需拓宽融资渠道,强化资金支持;(3)在保障体系建设方面：我国森林碳汇保障体系处于重点建设阶段,需完善森林碳汇有关法律法规、加快各类森林技术研发与标准制定,保障我国森林碳汇政策平稳运行。     

森林生态效益补偿优先级机制研究及应用——基于碳汇总量与变化量视角

森林生态效益补偿制度对于提高森林建设者积极性、促进森林生态效益提升具有重要意义。然而,我国森林生态效益补偿实践中依然存在仅以森林面积为补偿依据导致激励错位的问题。基于此,结合国家"双碳"目标,提出一种基于碳汇总量与变化量双向视角的综合森林生态效益补偿优先级机制,选取我国重要生态功能区秦巴山区为案例,分别从森林碳汇总量与变化量视角量化各区县生态补偿优先级,并构建二者结合的综合优先级模型,以促进在生态补偿实践中的资金分配公平性与激励性。研究发现,(1)在研究期内大多区县森林碳汇总量增长,但存在个别区县森林碳汇功能降低的现象,具体原因存在差异;(2)碳汇总量优先级与碳汇变化量优先级清单存在差异。总量优先级高的区县,变化量优先级较低,因此,生态补偿应综合考虑各区县森林碳汇在两个维度的表现;(3)综合优先级排名结果呈现"高值-中值-低值"的不同区间特征,该补偿机制在综合优先级高值区激励区县扩建森林、新增森林碳汇,在中值区激励区县保育森林,在低值区鼓励区县结合森林现状从扩建与保育两个方向提升森林碳汇功能。以森林碳汇保育与增汇成果为导向,有效探索碳汇功能在生态补偿中的实践价值,为我国区域森林生态效益补偿实践的公平性与科学性提供研究基础。     

天然林保护工程区近20年森林植被碳储量动态及碳汇(源)特征

分析近20年来天保工程区森林植被碳储量的动态变化及碳汇（源）特征,以期为我国天然林保护的政策制订和措施实施提供数据支撑。利用天然林资源保护工程区6-9次森林资源连续清查数据,把森林植被划分乔木林、灌木林、竹林、疏林地、散生木、四旁树,基于行业标准的生物量模型和碳计量参数、采用生物量加权平均法等方法,估算整个工程区和各省的森林植被总碳储量;对乔木林分起源、龄组、优势树种（组）估算碳储量和碳密度;量化森林植被总碳储量和乔木林碳储量随时间变化的消长,明确其碳汇/源特征。研究结果表明：6-9次清查,天保工程区森林植被总碳储量分别为2999 TgC、3254 TgC、3585 TgC和4097 TgC,年均增长率为1.65%、1.96%和2.70%;碳储量集中分布于我国东北和西南区域,其中四川碳储量最高,4期碳储量均占天保工程区总量20%以上;乔木林碳储量是森林植被碳储量的主体,每期占比均稳定在80%以上,其中天然林比例由94.67%下降至90.28%,人工林比例稳步上升,但到9次清查时其碳密度仍低于天然林50%;不同龄组间,中龄林碳储量最高,近熟林碳储量增长最快,碳密度从幼龄林到过熟林逐渐上升,4期趋势一致;乔木林中纯林碳储量占60%以上,大部分树种（组）碳储量和碳密度随时间推移而增加。7-9次清查,天保工程区森林植被总固碳量（当期相对于前期）分别为255.33 TgC、331.46 TgC和511.53 TgC,对全国森林植被总碳汇量的贡献由8次连清的53.78%上升到9次的67.46%,其中,乔木林对全国乔木林碳汇的贡献为68.71%;天保工程区内天然林对乔木林碳汇的贡献为75.90%;不同清查期,乔木林各龄组的碳汇变化较大,幼龄林和中龄林碳汇占比明显上升,近熟林和过熟林下降,9次清查时各龄组碳汇量大小顺序为：中龄林 > 近熟林 > 幼龄林 > 成熟林 > 过熟林;不同清查期,各个优势树种的碳汇/源表现不一,总体上,混交林的碳汇比例最大,到9次清查时,阔叶混交林和针阔混交林对乔木林碳汇的贡献分别为62.59%和17.23%,纯林中柏木碳汇贡献最大,为5.43%。天保工程区森林植被总碳储量随时间稳步增长,乔木林是总碳储量的主体,天然林是碳汇的主要来源,天然林保护增强了我国天然林碳汇的碳汇功能,促进了人工林碳汇作用提升,未来天保工程区碳汇潜力很大。     

Simulation of soil carbon cycling and carbon balance following clear-cutting in a mid-temperate forest and contribution to the sink of atmospheric CO2

A simulation model of soil carbon cycling was developed based on the data observed in a mid-temperate forest in Yoshiwa, Hiroshima Prefecture, Japan, and soil carbon cycling and carbon budget in a mature forest stand and following clear-cutting were calculated on a daily basis using daily air temperature and precipitation data. The seasonal change in the amount of the A₀ layer was characterized by a decrease from spring to autumn due to rapid decomposition of litter, and recovery in late autumn due to a large litterfall input. There was little change in the amount of humus in mineral soil. These estimates coincides closely with those observed in the field. Most flow rates and the accumulation of soil carbon decreased very markedly just after clear-cutting. The A₀ layer reached its minimum in 10 years, and recovered its loss within 50–60 years after cutting. A large loss of carbon was observed just after cutting, but the balance changed from negative to positive in 15 years after cutting. The total loss of soil carbon following cutting recovered within 30 years, and nearly the same amount of carbon as that stocked in the timber before harvesting accumulated 70–80 years after cutting. The calculation by the simulation model was made using the assumption that the increase in atmospheric CO₂ promoted the primary production rate by 10% over the last three decades. The result suggests that about 8 t C ha^-1 was sunk into soils of the mid-temperate forest over the same period. It indicates that forest soils may be one of the main sinks for atmospheric CO₂.     

省域视角下中国森林碳汇空间外溢效应与影响因素

森林碳汇空间相关性与溢出效应对林业产业的区域统筹发展具有重要作用,科学核算各地区的森林碳汇量并分析其空间关联特征是制定差异化碳汇发展政策的重要基础。以森林蓄积量扩展法核算我国31个省(市、自治区)1993—2018年6次森林资源清查期间的森林碳汇量,探究省域间森林碳汇量的相关性特征,并利用空间计量模型分析森林碳汇的外溢效应和影响因素。结果表明：(1)我国整体森林碳汇量不断增加,不同地区的森林碳汇量差别较大。西南省份和东北林区森林碳汇量处于第一梯队,上海和北京碳汇增速较快。(2)研究期间内的Moran′s I指数先呈现倒“V”形的变化特征,之后又以较为稳定的趋势上升,我国各地区的森林碳汇分布存在显著的空间关联性。(3)森林碳汇的空间外溢效应显著,根据空间杜宾模型将外溢效应分解为直接效应、间接效应和总效应。林业管理水平和森林蓄积水平对本地和相邻地区森林碳汇量有正向影响,林业产业发展水平对本地区的森林碳汇量有负向影响。综上,我国各地方政府对差异化林业碳汇政策的制定和执行应兼顾区域因素,以我国林业政策的总体空间规划来综合统筹各区域森林政策,在“山水林田湖草沙”的命运共同体理念引领下,实现林业的...     

Terrestrial fluxes of carbon in GCP carbon budgets

The Global Carbon Project (GCP) has published global carbon budgets annually since 2007 (Canadell et al. [2007], Proc Natl Acad Sci USA, 104, 18866–18870; Raupach et al. [2007], Proc Natl Acad Sci USA, 104, 10288–10293). There are many scientists involved, but the terrestrial fluxes that appear in the budgets are not well understood by ecologists and biogeochemists outside of that community. The purpose of this paper is to make the terrestrial fluxes of carbon in those budgets more accessible to a broader community. The GCP budget is composed of annual perturbations from pre‐industrial conditions, driven by addition of carbon to the system from combustion of fossil fuels and by transfers of carbon from land to the atmosphere as a result of land use. The budget includes a term for each of the major fluxes of carbon (fossil fuels, oceans, land) as well as the rate of carbon accumulation in the atmosphere. Land is represented by two terms: one resulting from direct anthropogenic effects (Land Use, Land‐Use Change, and Forestry or land management) and one resulting from indirect anthropogenic (e.g., CO₂, climate change) and natural effects. Each of these two net terrestrial fluxes of carbon, in turn, is composed of opposing gross emissions and removals (e.g., deforestation and forest regrowth). Although the GCP budgets have focused on the two net terrestrial fluxes, they have paid little attention to the gross components, which are important for a number of reasons, including understanding the potential for land management to remove CO₂ from the atmosphere and understanding the processes responsible for the sink for carbon on land. In contrast to the net fluxes of carbon, which are constrained by the global carbon budget, the gross fluxes are largely unconstrained, suggesting that there is more uncertainty than commonly believed about how terrestrial carbon emissions will respond to future fossil fuel emissions and a changing climate.     

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.     

The impact of nitrogen deposition on carbon sequestration in European forests and forest soils

An estimate of net carbon (C) pool changes and long‐term C sequestration in trees and soils was made at more than 100 intensively monitored forest plots (level II plots) and scaled up to Europe based on data for more than 6000 forested plots in a systematic 16 km × 16 km grid (level I plots). C pool changes in trees at the level II plots were based on repeated forest growth surveys At the level I plots, an estimate of the mean annual C pool changes was derived from stand age and available site quality characteristics. C sequestration, being equal to the long‐term C pool changes accounting for CO₂ emissions because of harvest and forest fires, was assumed 33% of the overall C pool changes by growth. C sequestration in the soil were based on calculated nitrogen (N) retention (N deposition minus net N uptake minus N leaching) rates in soils, multiplied by the C/N ratio of the forest soils, using measured data only (level II plots) or a combination of measurements and model calculations (level I plots). Net C sequestration by forests in Europe (both trees and soil) was estimated at 0.117 Gton yr^?1, with the C sequestration in stem wood being approximately four times as high (0.094 Gton yr^?1) as the C sequestration in the soil (0.023 Gton yr^?1). The European average impact of an additional N input on the net C sequestration was estimated at approximately 25 kg C kg^?1 N for both tree wood and soil. The contribution of an average additional N deposition on European forests of 2.8 kg ha^?1 yr^?1 in the period 1960–2000 was estimated at 0.0118 Gton yr^?1, being equal to 10% of the net C sequestration in both trees and soil in that period (0.117 Gton yr^?1). The C sequestration in trees increased from Northern to Central Europe, whereas the C sequestration in soil was high in Central Europe and low in Northern and Southern Europe. The result of this study implies that the impact of forest management on tree growth is most important in explaining the C pool changes in European forests.