北京山区3种暖温带森林生态系统未来碳平衡的模拟与分析

使用LPJ-GUESS植被动态模型, 在北京山区研究了未来100a以辽东栎 (Quercus liaotungensis) 为优势种的落叶阔叶林、以白桦 (Betula platyphylla) 为主的阔叶林和油松 (Pinus tabulaeformis) 为优势种的针阔混交林的碳变化, 定量分析了生态系统净初级生产力 (NPP) 、土壤异养呼吸 (Rh) 、净生态系统碳交换 (NEE) 和碳生物量 (Carbon bio-mass) 对两种未来气候情景 (SRES A2和B2) 以及相应大气CO2浓度变化情景的响应特征。结果表明:1) 未来100a两种气候情景下3种森林生态系统的NPP和Rh均增加, 并且A2情景下增加的程度更大;2) 由于3种生态系统树种组成的不同, 未来气候情景下各自NPP和Rh增加的比例不同, 导致三者NEE的变化也相异:100a后辽东栎林由碳汇转变为弱碳源, 白桦林仍保持为碳汇但功能减弱, 油松林成为一个更大的碳汇;3) 3种森林生态系统的碳生物量在未来气候情景下均增大, 21世纪末与20世纪末相比:辽东栎林在A2情景下碳生物量增加的比例为27.6%, 大于B2情景下的19.3%;白桦林和油松林在B2情景下碳生物量增加的比例分别为34.2%和52.2%, 大于A2情景下的30.8%和28.4%。     

气候变化对藏北地区草地生产力的影响模拟

利用政府间气候变化委员会(IPCC)排放情景特别报告(SRES)的A2和B2方案,通过区域气候模式系统PRECIS与草地生态模型SPUR相联接,模拟评估未来2071—2100年藏北地区草地生产力的变化。结果表明:2种温室气体排放情景下,温度升高、太阳总辐射降低和降水量增加的区域,各类型草地地上生物量基本呈增加的趋势;降水量减少的区域,高嵩草型草地地上生物量呈减少的趋势;藏北地区的草地生产力不大可能从CO2富集上得到多大好处。     

陆生植物自身能否排放甲烷?

一般认为自然来源的甲烷是在厌氧环境下形成的,而最近研究却发现在有氧环境下植物自身也能释放甲烷,这将对全球甲烷收支产生重大影响。但这一发现目前还存在很大争议,一些研究证实植物在有氧环境下能排放甲烷,果胶、聚半乳糖醛酸等含甲氧基官能团的组分是植物产生甲烷的主要来源物质,甚至纤维素、木质素等植物结构组分也能排放甲烷;而另一些研究却发现植物并不能排放甲烷或者排放速率极小,而观测到的植物甲烷排放可能来自于土壤中,即溶解有甲烷的土壤水分被被植物吸收并通过蒸腾或蒸发作用而排放到大气中。有氧环境下植物排放甲烷的机制仍不清楚,光照、温度、紫外辐射、机械损伤等环境胁迫可能是导致植物排放甲烷的重要原因,但这些因素的影响作用仍存在很大的不确定性。即使如此,一些研究仍对全球或区域植物甲烷排放的通量进行了估算,估计全球植物甲烷排放通量为10-236Tg.a-1。未来研究应在更多地区针对不同生境的各种植物是否排放甲烷进行独立检验,并在此基础上探讨植物排放甲烷的机制。     

基于GEE平台的黄河流域森林植被净初级生产力时空变化特征

黄河流域是我国重要的生态屏障,研究黄河流域森林植被净初级生产力(Net Primary Productivity,NPP)的时空变化特征及驱动机制,对解释黄河流域森林碳汇/源变化具有重要意义。基于Google Earth Engine (GEE)云平台,利用MOD17A3H V6 NPP数据、MCD12Q1 V6土地覆盖类型数据、ECMWF/ERA5气象数据和USGS/SRTMGL1_003高程数据,采用岭回归分析、Hurst指数和冗余分析(Redundancy Analysis,RDA)对黄河流域2001-2019年森林NPP的时空变化特征及影响因子进行分析。结果表明:(1)2001-2019年,黄河流域森林平均总面积为3.66万km²,其中阔叶林、针叶林、混交林平均面积分别为:2.64万km²、0.01万km²和1.01万km²,森林NPP年总量呈线性增加趋势,其均值为8.99Tg C,年均增速为0.36Tg C/a,19a增长率为173.60%;不同森林类型的NPP年总量均值分别为:4.79Tg C (阔叶林)、6.04×10^-5Tg C (针叶林)和0.64Tg C (混交林),年均增速为:阔叶林(0.16Tg C/a)>混交林(0.04Tg C/a)>针叶林(6.98×10^-6Tg C/a)。(2)2001-2019年,黄河流域森林年均NPP呈线性增加趋势,其均值为241.58g C m^-2 a^-1,年均增速为7.18g C m^-2 a^-1,19a增长率为108.63%;不同森林类型的年均NPP均值分别为:178.48g C m^-2 a^-1(阔叶林)、0.60g C m^-2 a^-1(针叶林)和62.49g C m^-2 a^-1(混交林),年均增速为:阔叶林(4.75g C m^-2 a^-1)>混交林(2.39g C m^-2 a^-1)>针叶林(0.04g C m^-2 a^-1)。(3)黄河流域森林NPP呈增加趋势的面积占94.50%,其中显著增加的面积占73.29%;呈减少趋势的面积占5.50%,其中显著减少的面积占1.57%。阔叶林NPP显著增加的面积最高(76.78%),其次为混交林(60.84%),针叶林最少(56.76%)。(4)黄河流域森林NPP的Hurst指数(H)介于0.38-1.00之间,平均值为0.87,其中H≥0.5的像元数约占99.34%,黄河流域森林NPP在未来一段时间内仍保持持续增加趋势。(5)归因分析表明环境因子对黄河流域森林NPP时空变化的总解释率为55.80%,显著影响的环境因子为经度(35.50%)、降水(8.00%)、气温(6.50%)和纬度(5.40%)。2001-2019年黄河流域森林NPP呈增加趋势,且呈现较强的可持续性;GEE云平台结合冗余分析可及时、高效获取黄河流域森林NPP的时空变化并对其进行归因分析。     

基于LEAP的厦门市节能与温室气体减排潜力情景分析

城市是人类社会经济活动的中心,聚集了世界一半以上的人口。在城市发生的温室气体排放量占全球排放总量的75%左右,因此在城市这个尺度上研究温室气体减排意义重大。从城市这个尺度出发,以厦门市为实际研究案例,应用LEAP模型进行节能减排政策情景分析,定量分析评价城市节能减排潜力,并详细分析各种控制情景和各部门的节能减排贡献率。研究结果显示:在综合控制情景下,厦门能源消费总量年均增长率、万元地区生产总值能耗和温室气体排放总量年均增长率都有所下降;清洁燃料替代措施节能减排效果最好,工业部门节能减排潜力最大;优化能源使用结构蕴藏巨大减排潜力。     

东北黑土地区稻田甲烷排放时空演变及排放潜力分析

稻田甲烷排放是农业源甲烷排放的主要来源。东北黑土地区是我国最大的粮食生产基地,农业温室气体减排是实现黑土地永续利用的关键议题之一。运用稻田甲烷排放模型(CH4MOD)核算并分析了2009-2018年东北黑土地区稻田甲烷排放的时空演变特征,结合GOSAT卫星遥感数据探究了水稻生产与区域甲烷排放的时空动态联系,进一步量化了稻田甲烷对区域甲烷排放的贡献程度及不同情景下的排放潜力。结果表明,受水稻生产面积扩张和排放强度提高的影响,东北黑土地区稻田甲烷排放总量从2009年的39.05万t增加到2018年的79.53万t。东北黑土地区区域甲烷排放在季节变化和栅格单元上表现出与稻田甲烷排放较为一致的时空动态,大规模的稻田耕作可能会增加水稻生产与区域甲烷排放直接相关的可能性。随着水稻持续扩种稳产,2018年东北黑土地区水稻生产贡献了区域甲烷排放总量的15.04%,其中黑龙江省的贡献率高达31.06%。在基准发展情景下,预计2035年东北黑土地区稻田CH₄排放量较2018年增加19.5%;在粮食供给保障情景下,维持当前稻田耕作面积,水稻生产集约化程度提高,预计其稻田CH₄排放量较2018年减少0.88%;在此基础上,采取促进秸秆还田、增施有机肥、实施节水间歇灌溉等稻田管理措施将使稻田CH₄排放量增加17.8%-63.6%。以满足膳食需求和供给保障为导向,优化水稻种植结构、控制稻田耕作面积,推动技术进步、品种改良以提升单产水平,采取化肥和有机肥搭配施用、节水间歇灌溉等途径能够缓解稻田甲烷排放。研究综合运用自上而下的遥感数据和自下而上的模型运算,刻画了水稻生产与区域甲烷排放的时空联系,进一步评估了稻田甲烷的排放潜力及减排措施的减排效果,为促进东北黑土地区农业甲烷减排和生产布局优化提供了理论依据和决策参考。     

21世纪上半叶内蒙古草地植被净初级生产力变化趋势

基于中国气象局国家气候中心新发布的中短期适应气候变化的新情景(RCP4.5)和极端情景(RCP8.5)下的气候预估数据,采用空间化后的CENTURY模型模拟探讨2011－2050年内蒙古草地植被净初级生产力(NPP)的时空变化特征.结果表明: 区域尺度上,未来气候变化情景下内蒙古草地NPP年下降速率分别为0.57 g C·m^-2·a^-1(RCP4.5)、0.89 g C·m^-2·a^-1(RCP8.5);相对于基准时段,RCP4.5情景下内蒙古草地NPP在2020s、2030s、2040s分别下降11.6%、12.0%、18.0%,而RCP8.5情景下降幅分别为23.8%、21.2%、30.1%.不同气候情景下内蒙古草地NPP时空变化特征差异较大,但即使在RCP4.5下未来40年绝大部分草地NPP也将呈现下降趋势,15.6%的草地减产超过20%.这表明未来气候变化情景下内蒙古草地降水略增的态势不足以补偿因温度升高对草地植被初级生产力所产生的负面作用,草地资源的可持续发展将面临更大挑战.     

基于模型和GIS技术的中国稻田甲烷排放估计

将一个比较成熟的稻田甲烷排放模型CH4MOD和GIS空间化数据库结合,模拟估计了中国大陆2000年水稻生长季稻田甲烷的排放。模型的空间输入参数包括:逐日气温、耕层土壤砂粒含量、外源有机质施用量、稻田水分管理模式、水稻移栽期与收获期、水稻种植面积与单产,空间分辨率为10km×10km。模拟结果表明:2000年稻田甲烷排放量为6.02Tg,其中:早稻生长季排放1.63Tg、晚稻1.46Tg、单季稻2.93Tg。提高区域稻田甲烷排放估计精度的进一步目标应放在减小输入参数误差和提高空间数据精度上,在现有数据库基础和模型———GIS技术下探讨我国稻田甲烷排放估计的不确定性范围是必要的。     

土地利用变化对三峡库区重庆段植被净初级生产力的影响

研究土地利用变化对区域植被净初级生产力(Net Primary Productivity,NPP)的影响对于明确区域植被固碳能力与土地利用变化的关系,以及维持生态系统结构稳定具有重要意义。以三峡库区重庆段为例,基于2000—2015年MOD17A3数据和土地利用数据,分析研究区NPP时空分布特征并从景观生态学的角度探讨土地利用变化对区域植被NPP的影响。研究表明:(1)NPP年均值16年间波动不大,空间分布上从东到西逐渐减少;(2)研究期内林地面积增加,耕地和草地面积减小,而NPP总量从25.6 TgC增加到了28.5 TgC,其中耕地NPP约占总量的44%,林地次之(40%),草地最少(14%),2000—2005年、2005—2010年、2010—2015年土地利用变化对NPP变化的贡献率分别为26.49%、59.76%、17.27%;(3)区域生态景观指数中的香农多样性指数SHDI、斑块密度PD与NPP呈正相关,而聚合度AI与NPP呈负相关,景观格局类型和景观格局变化均影响区域植被NPP的增长。要提高区域植被NPP,需优化土地利用格局,增加景观异质性和斑块密度,重视培育幼龄林,并控制成熟林的数量。     

若尔盖高原湿地甲烷排放的时空异质性

集中于北美落基山高山湿地甲烷排放的零星报道远不能解析全球高山湿地甲烷源强. 因此,世界范围内其他区域高山湿地甲烷排放的研究对于合理估计全球高山湿地甲烷源强,意义重大.采用静态箱-气相色谱法,基于3种典型湿地类型的甲烷排放数据,认为若尔盖高原湿地生长季甲烷的平均排放量为4.69 mg CH4 m-2 h-1.同时根据2a数据,初步分析了甲烷通量及其对环境因素和生物因素的响应特征,结果表明:(1)甲烷排放昼夜变化具有双峰模式 (主峰出现在15:00,次峰出现在06:00),可由土壤温度以及植物气孔开启来解释.(2)若尔盖湿地甲烷排放季节动态较为典型,即在7月份或8月份出现排放高峰,冬季甲烷排放较少.生长季,对3类群落类型,表面温度与甲烷排放显著相关 (r2=0.55,P<0.05,n=30),地表水位和植物群落高度与甲烷排放相关性更为显著 (r2=0.32,0.61,P<0.01,n=30).分析认为该季节节律是由温度以及植物生长状况直接影响的,而水位则是使该节律发生波动的原因(高原气候).(3)群落尺度下,物候学上相当重要的两个时期,甲烷排放通量均有较高的空间变异 (植物生长高峰变异系数为38%,积雪融化高峰为61%).通过逐步回归线性分析,发现植物生长高峰期,地表水位和群落高度是影响甲烷排放空间差异的主要因素 (r2= 0.43,0.59,P<0.01,n=30).(4)景观尺度下,生长季,景观尺度下甲烷排放有较大的空间变异,湖滨湿地甲烷平排放量最高为11.95 mg CH4 m-2h-1,其次为宽谷湿地,其排放量为2 12 mg CH4 m-2h-1,河岸湿地表现为甲烷吸收,其吸收量为0.007 mg CH4 m-2h-1.地表水位、植物地上生物量以及植物高度能够很好地解释甲烷排放的景观差异.     

The role of vegetation in methane flux to the atmosphere: should vegetation be included as a distinct category in the global methane budget?

Currently, the global annual flux of methane (CH₄) to the atmosphere is fairly well constrained at ca. 645 Tg CH₄ year^?1. However, the relative magnitudes of the fluxes generated from different natural (e.g. wetlands, deep seepage, hydrates, ocean sediments) and anthropogenic sources remain poorly resolved. Of the identified natural sources, the contribution of vegetation to the global methane budget is arguably the least well understood. Historically, reviews of the contribution of vegetation to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands, or the aerobic production of methane within plant tissues. Many recent global budgets only include the latter pathway (aerobic methane production) in estimating the importance of terrestrial vegetation to atmospheric CH₄ flux. However, recent experimental evidence suggests several novel pathways through which vegetation can contribute to the flux of this globally important, trace greenhouse gas (GHG), such as plant cisterns that act as cryptic wetlands, heartwood rot in trees, the degradation of coarse woody debris and litter, or methane transport through herbaceous and woody plants. Herein, we synthesize the existing literature to provide a comprehensive estimate of the role of modern vegetation in the global methane budget. This first, albeit uncertain, estimate indicates that vegetation may represent up to 22 % of the annual flux of methane to the atmosphere, contributing ca. 32–143 Tg CH₄ year^?1 to the global flux of this important trace GHG. Overall, our findings emphasize the need to better resolve the role of vegetation in the biogeochemical cycling of methane as an important component of closing the gap in the global methane budget.     

No evidence for substantial aerobic methane emission by terrestrial plants: a 13C-labelling approach

* The results of a single publication stating that terrestrial plants emit methane has sparked a discussion in several scientific journals, but an independent test has not yet been performed. * Here it is shown, with the use of the stable isotope (13)C and a laser-based measuring technique, that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% (0.4 ng g(-1) h(-1)) of the previously published values. * Data presented here indicate that the contribution of terrestrial plants to global methane emission is very small at best. * Therefore, a revision of carbon sequestration accounting practices based on the earlier reported contribution of methane from terrestrial vegetation is redundant.     

Carbon balance indicator for forest bioenergy scenarios

A carbon (C) balance indicator is presented for the evaluation of forest bioenergy scenarios as a means to reduce greenhouse gas (GHG) emissions. A bioenergy‐intensive scenario with a greater harvest is compared to a baseline scenario. The relative carbon indicator (RC) is defined as the ratio between the difference in terrestrial C stocks – that is the C debt – and the difference in cumulative bioenergy harvest between the scenarios, over a selected time frame T. A value of zero indicates no C debt from additional biomass harvests, while a value of one indicates a C debt equal to the amount of additionally harvested biomass C. Multiplying the RC indicator by the smokestack emission factor of biomass (approximately 110 t CO₂/TJ) provides the net cumulative CO₂ emission factor of the biomass combustion as a function of T, allowing a direct comparison with the emission factors of comparable fossil fuels. The indicator is applied to bioenergy cases in Finland, where typically the rotation length of managed forests is long and the decay rate of harvest residues is slow. The country‐level examples illustrate that although Finnish forests remain as a C sink in each of the considered scenarios, the efforts of increasing forest bioenergy may still increase the atmospheric CO₂ concentrations in comparison with the baseline scenario and use of fossil fuels. The results also show that the net emission factor depends – besides on forest‐growth or residue‐decay dynamics – on the timing and evolution of harvests as well. Unlike for the constant fossil C emission factor, the temporal profile of bioenergy use is of great importance for the net emission factor of biomass.     

Terrestrial plant methane production and emission

In this minireview, we evaluate all experimental work published on the phenomenon of aerobic methane (CH(4) ) generation in terrestrial plants and plant. Clearly, despite much uncertainty and skepticism, we conclude that the phenomenon is true. Four stimulating factors have been observed to induce aerobic plant CH(4) production, i.e. cutting injuries, increasing temperature, ultraviolet radiation and reactive oxygen species. Further, we analyze rates of measured emission of aerobically produced CH(4) in pectin and in plant tissues from different studies and argue that pectin is very far from the sole contributing precursor. In consequence, scaling up of aerobic CH(4) emission needs to take into consideration other potential sources than pectin. Due to the large uncertainties related to effects of stimulating factors, genotypic responses and type of precursors, we conclude that current attempts for upscaling aerobic CH(4) into a global budget is inadequate. Thus it is too early to draw the line under the aerobic methane emission in plants. Future work is needed for establishing the relative contribution of several proven potential CH(4) precursors in plant material.     

Changes in annual CO2 fluxes estimated from inventory data in South Korea

Using a slightly modified IPCC method, we examined changes in annual fluxes of CO2 and contributions of energy consumption, limestone use, waste combustion, land-use change, and forest growth to the fluxes in South Korea from 1990to 1997. Our method required less data and resulted in a larger estimate of CO2released by industrial processes, comparing with the original IPCC guideline. However, net CO2 emission is not substantially different from the estimates of IPCC and modified methods. Net CO2 emission is intimately related to GDP as Koreaneconomy has heavily relied on energy consumption and industrial activities, which are major sources of CO2. Total efflux of CO2 was estimated to be 63.6 Tg C/ain 1990 and amounted to 112.9 Tg C/a in 1997. Land-use change contributed to annual budget of CO2 in a relatively small portion. Carbon dioxide was sequesteredby forest biomass at the rate of 6.5 Tg C/a in 1990 and 8.5 Tg C/a in 1997. Although CO2 storage in the forests increased, the sink effect was overwhelmed by extensive energy consumption, suggesting that energy-saving strategies will be more effective in reducing CO2 emission in Korea than any other practices. It is presumed that plant uptake of CO2 is underestimated as carbon contained in plant detritus and belowground living biomass were not fully considered. Furthermore, the soil organic carbon stored in forest decomposes in various ways in rugged mountains depending on their conditions, such as slope, aspect and elevation, which could have an effect on decomposition rate and carbon stores in soils. Thus, carbon sequestration of forests deserves further attention.     

Seasonal variation in methane emission from a temperate Phragmites-dominated marsh: effect of growth stage and plant-mediated transport

The eddy covariance technique was employed with a tunable diode laser spectrometer to quantify methane flux from a prairie marsh dominated by Phragmites australis in north-central Nebraska, USA. The observations spanned the entire growing season (April to October) and a wide range of weather conditions, allowing a quantitative assessment of the physical and biological controls of methane emission in this ecosystem. Diel patterns in methane emission varied markedly depending on plant growth stage. Prior to plant emergence above water, the rate of methane emission from the marsh was fairly constant throughout the day. After emergence above water, there was a gradual increase in methane emission after sunrise with a peak in late afternoon. Significant changes in diel patterns were observed after tillering. Then, the diel pattern was characterized by a mid- to late-morning peak and a 2-to 4-fold increase in methane emissions from night to daytime. In early stages of plant growth, molecular diffusion through dead/live plants and the standing water column seemed to be the primary transport mechanism. After tillering, a transition occurred in the transport mechanism from a molecular diffusion to a convective throughflow, which is a rapid and active gas transport driven by pressure differences. The role of convective throughflow became less important as the plants senesced. Integrated methane emission over the six-month measurement period (April–October) was about 64 g CH₄ m^–2. On an annual basis, we estimate the annual methane emission from this ecosystem to be ≈ 80 g CH₄ m^–2 and that about 80% of the total methane emission occurred between late April and late October.     

Role of rice in mediating methane emission

Methane emitted at different plant conditions through the different organs of rice plants was studied using a closed chamber technique under the laboratory, phytotron, and greenhouse conditions in order to clarify and quantify the role of different organs of rice plant as methane emission sites. Rice plants grown in flooded soils emit methane to the atmosphere via the aerenchyma of leaves, nodes and panicles. Emission through the rice plants is controlled by diffusion. No methane is emitted via the transpiration stream. Leaves are the major release sites at the early growth stage while nodes become more important later. Cracks and porous structure were found in the nodes. Panicles generally contribute little to methane emission. Increasing water depth temporarily reduces methane emission while concentration gradients in rice plants readjust to unsubmerged emission sites. Methane emissions in rice plants cease only when the plants become totally submerged.     

黄河流域国土空间碳中和度研究——以内蒙古段为例

基于全球气候治理背景以及黄河流域在我国生态文明建设中的重要地位,以黄河流域内蒙古段为例,通过情景分析法,建立改进的IPAT模型和集成生态圈模拟器IBIS,预测不同情景下2018-2060年研究区碳排放变化趋势和达峰情况,并结合对碳汇水平的模拟分析2060年碳中和实现进程。结果显示①在基准情景、节能情景、低碳情景和粗放情景下,黄河流域内蒙古段将分别于2040年、2035年、2030年和2050年实现碳达峰,峰值碳排放量分别为12209万t、11213万t、9784万t和17635万t;②在IPCC RCP2.6和RCP6.0气候变化情景下,黄河流域内蒙古段的陆地生态系统整体分别呈现出碳汇和碳源的不同效应,净初级生产力分别为1533万t和-506万t;③综合能源消费碳排放和碳汇水平,在RCP2.6气候情景下,若碳排放选取基准、节能、低碳和粗放情景,则2060年黄河流域内蒙古段分别可实现碳中和进程的18.42%、22.37%、34.46%和9.90%;在RCP6.0气候情景下,由于研究区陆地生态系统呈现出碳源效应,因此难以对碳中和进程的推进做出贡献。可见,对于黄河流域内蒙古段而言,需要科学制订碳达峰、碳中和目标实现时间,未来要更进一步保护重要碳汇生态系统,提升固碳增汇能力;调整能源消费结构,增加可再生能源发展规划指标;构建碳排放权交易市场,促进碳指标流动;制定土地利用碳排放标准,优化国土空间格局。     

Spatio-temporal changes in biomass carbon sinks in China’s forests from 1977 to 2008

Forests play a leading role in regional and global carbon (C) cycles. Detailed assessment of the temporal and spatial changes in C sinks/sources of China’s forests is critical to the estimation of the national C budget and can help to constitute sustainable forest management policies for climate change. In this study, we explored the spatio-temporal changes in forest biomass C stocks in China between 1977 and 2008, using six periods of the national forest inventory data. According to the definition of the forest inventory, China’s forest was categorized into three groups: forest stand, economic forest, and bamboo forest. We estimated forest biomass C stocks for each inventory period by using continuous biomass expansion factor (BEF) method for forest stands, and the mean biomass density method for economic and bamboo forests. As a result, China’s forests have accumulated biomass C (i.e., biomass C sink) of 1896 Tg (1 Tg=10¹² g) during the study period, with 1710, 108 and 78 Tg C in forest stands, and economic and bamboo forests, respectively. Annual forest biomass C sink was 70.2 Tg C a^?1, offsetting 7.8% of the contemporary fossil CO₂ emissions in the country. The results also showed that planted forests have functioned as a persistent C sink, sequestrating 818 Tg C and accounting for 47.8% of total C sink in forest stands, and that the old-, mid- and young-aged forests have sequestrated 930, 391 and 388 Tg C from 1977 to 2008. Our results suggest that China’s forests have a big potential as biomass C sink in the future because of its large area of planted forests with young-aged growth and low C density.