Biogenic vs. geologic carbon emissions and forest biomass energy production

In the current debate over the CO₂ emissions implications of switching from fossil fuel energy sources to include a substantial amount of woody biomass energy, many scientists and policy makers hold the view that emissions from the two sources should not be equated. Their rationale is that the combustion or decay of woody biomass is simply part of the global cycle of biogenic carbon and does not increase the amount of carbon in circulation. This view is frequently presented as justification to implement policies that encourage the substitution of fossil fuel energy sources with biomass. We present the opinion that this is an inappropriate conceptual basis to assess the atmospheric greenhouse gas (GHG) accounting of woody biomass energy generation. While there are many other environmental, social, and economic reasons to move to woody biomass energy, we argue that the inferred benefits of biogenic emissions over fossil fuel emissions should be reconsidered.     

The timber and energy biomass potential of intensively managed cloned Norway spruce stands

We used ecosystem model simulations to study the timber and energy biomass potential offered by intensively managed cloned Norway spruce stands. More specifically, we analysed how the use of cloned trees compared with non‐cloned trees, together with thinning, nitrogen (N) fertilisation and rotation length (from 60 to 100 years), affects the annual mean production of timber (i.e., saw logs, pulpwood) and energy biomass (i.e., stumps and harvesting residuals in the final felling) and its economic profitability [annual mean of net present value (NPV) with a 2% interest rate]. Furthermore, we employed a life cycle analysis/emission calculation tool to assess the total net CO₂ emissions per unit of energy (kg CO₂ MW h^?1) produced based on energy biomass. We found that both the annual mean production of timber and the NPV increased substantially, regardless of the management regime, if cloned trees with an annual growth increase of up to 30% compared with non‐cloned trees were used in regeneration. In general, the use of a short rotation with N fertilisation clearly increased the annual mean of the NPV. Consequently, the use of cloned trees also clearly increased the annual mean production of energy biomass and decreased the total net CO₂ emissions per unit of energy produced based on energy biomass. However, the total annual net CO₂ emissions were the lowest if a long rotation was used with N fertilisation. To conclude, the use of cloned trees together with intensive management could potentially be highly beneficial for the cost‐efficient and sustainable production of timber and energy biomass in an integrated way.     

排放与森林碳汇作用下云南省碳净排放量估计

以云南省为例,用马尔科夫链计算能源结构,在经济增长模型基础上基于动态最优化理论估计能源消费碳排放,并基于CO₂FIX模型计算云南省森林碳汇,预测在能源消费碳排放和森林碳汇共同作用下的从2008到2050年碳净排放量。研究发现云南省能源消费碳排放量和碳净排放量曲线都呈"倒U"型,在2035年达到高峰,高峰值分别为和129.71 MtC和118.89 MtC;在森林碳汇中,原有森林的碳汇作用在现在和未来一段时间内处于主导地位,但新造林有着巨大的碳汇潜力,所以在保护原有森林的同时要植树造林,从生态学角度抵消碳排放;森林碳汇只能减少小部分碳排放,更主要的是改善云南省的能源结构,加快技术进步速度,开发水电等新能源,从根本上减少温室气体的排放。     

Life cycle assessment of forest biomass energy feedstock in the Northeast United States

Life cycle assessment (LCA) was combined with primary data from nine forest harvesting operations in New York, Maine, Massachusetts, and Vermont, from 2013 to 2019 where forest biomass (FB) for bioenergy was one of several products. The objective was to conduct a data‐driven study of greenhouse gas emissions associated with FB feedstock harvesting operations in the Northeast United States. Deterministic and stochastic LCA models were built to simulate the current FB bioenergy feedstock supply chain in the Northeast US with a cradle‐to‐gate scope (forest harvest through roadside loading) and a functional unit of 1.0 Mg of green FB feedstock at a 50% moisture content. Baseline LCA, sensitivity analysis, and uncertainty analyses were conducted for three different FB feedstock types—dirty chips, clean chips, and grindings—enabling an empirically driven investigation of differences between feedstock types, individual harvesting process contributions, and literature comparisons. The baseline LCA average impacts were lower for grindings (4.57 kg CO_2eq/Mg) and dirty chips (7.16 kg CO_2eq/Mg) than for clean chips (23.99 kg CO_2eq/Mg) under economic allocation, but impacts were of similar magnitude under mass allocation, ranging from 24.42 to 27.89 kg CO_2eq/Mg. Uncertainty analysis showed a wider range of probable results under mass allocation compared to economic allocation. Sensitivity analysis revealed the impact of variations in the production masses and total economic values of primary products of forest harvests on the LCA results due to allocation of supply chain emissions. The high variability in fuel use between logging contractors also had a distinct influence on LCA results. The results of this study can aid decision‐makers in energy policy and guide emissions reductions efforts while informing future LCAs that expand the system boundary to regional FB energy pathways, including electricity generation, transportation fuels, pellets for heat, and combined heat and power.     

森林管理在全球CO2减排中的作用

综述了各种森林管理措施在全球CO₂减排中的作用.这些管理措施主要包括减少森林砍伐速度,增加森林覆盖面积,加强对现存森林的肥料、火灾及病虫害管理,以薪材替代化石燃料等.同时探讨了中国的森林管理存在的优势和不足.目前中国森林生态系统主要是植被碳库,在全球碳循环过程中扮演着“碳汇”的角色,但其“碳汇”功能较小.因此,如何加强对新建人工林的抚育、病虫害和火灾管理,增强中国森林的“碳汇”功能,充分发挥其在CO₂减排中的作用,是我们面临的重要工作     

Net change in carbon emissions with increased wood energy use in the United States

Use of wood biomass for energy results in carbon (C) emissions at the time of burning and alters C stocks on the land because of harvest, regrowth, and changes in land use or management. This study evaluates the potential effects of expanded woody biomass energy use (for heat and power) on net C emissions over time. A scenario with increased wood energy use is compared with a dynamic business-as-usual scenario where wood energy use is driven by its historical relationship with gross domestic product. At the national level, we projected that up to 78% of increased cumulative C emissions from increased wood burning and up to 80% of increased cumulative radiative forcing would be offset over 50 years by change in forest area loss, biomass regrowth on land, C storage in harvested wood products, and C in logging slash left in forests. For example, forest area is projected to decline in both scenarios, but 3.5 million hectares more are retained in the high wood energy-use case. Projected C offsets over a 50 year period differed substantially by US region (16% in the North, 50% in the West, and 95% in the South) not only because of differences in forest regrowth and induced investment in retaining and planting forest, but also because of shifts in competitive advantage among regions in producing various wood products. If wood systems displace coal systems that have 75% of the C emissions of wood energy systems per unit energy, then the nationwide net C emissions offset would be reduced to 71–74%. If displacing natural gas systems that have 40% of the level of wood bioenergy emissions per unit energy, the nationwide net C emissions offset would be 46–52%.     

A system-wide assessment of forest biomass production,markets, and carbon

This study examines the effects of supplying forest biomass on forest ecosystem services and goods with a dynamic systems model. This unique analysis models dynamic trade and investments in forestry, thereby capturing price changes from increased forest biomass demand on current and future flows of forest ecosystem services and natural capital stocks. Forests across the globe are interconnected through timber and forest biomass markets, which influence forest management decisions, land rents, and policy responses. Results indicate that expanding forest biomass consumption, even at relatively low levels, will have important impacts on ecosystem services, particularly the benefits of terrestrial carbon sequestration and timber outputs. Increased forest biomass production can be achieved with smaller impacts on ecosystem services through policies targeting natural forest preservation. However, policies that encourage residual biomass use for energy or discourage forest plantation expansion could potentially compromise carbon benefits.     

Effects of climate change and management on net climate impacts of production and utilization of energy biomass in Norway spruce with stable age‐class distribution

We studied the effects of climate change and forest management scenarios on net climate impacts (radiative forcing) of production and utilization of energy biomass, in a Norway spruce forest area over an 80‐year simulation period in Finnish boreal conditions. A stable age‐class distribution was used in model‐based analyses to identify purely the management effects under the current and changing climate (SRES B1 and A2 scenarios). The radiative forcing was calculated based on an integrated use of forest ecosystem model simulations and a life cycle assessment (LCA) tool. In this work, forest‐based energy was used to substitute coal, and current forest management (baseline management) was used as a reference management. In alternative management scenarios, the stocking was maintained 20% higher in thinning compared to the baseline management, and nitrogen fertilization was applied. Intensity of energy biomass harvest (e.g. logging residues, coarse roots and stumps) was varied in the final felling of the stands at the age of 80 years. Also, the economic profitability (NPV, 3% interest rate) of integrated production of timber and energy biomass was calculated for each management scenario. Our results showed that compared to the baseline management, climate benefits could be increased by maintaining higher stocking in thinning over rotation, using nitrogen fertilization and harvesting logging residues, stumps and coarse roots in the final felling. Under the gradually changing climate (in both SRES B1 and A2), the climate benefits were lower compared to the current climate. Trade‐offs between NPV and net climate impacts also existed.     

采伐木对森林碳储量的影响

森林是陆地生态系统中最大的碳库。在全球变暖背景下,有关林业管理对森林碳库的影响引起各国科学家的日益关注。目前国内大多数文献都将森林采伐木碳库视为当年排放,而实际上采伐木能长时间储存碳。本文根据利用方式和采伐习惯,将采伐木按使用方式分为:1)DBH≤6cm为采伐剩余物置于林内;2)DBH>6cm为实木产品和纸制产品。以长白山林区典型地带性植被阔叶红松林为对象,通过调查采伐前后乔木组成的变化,根据采伐木碳库实际排放情况,研究了采伐前后森林碳储量的动态变化。结果表明:留于林内采伐剩余物为1.1tC.hm-2,排放速度由大变小,全部排放时间80年;实木产品碳储量为20.56tC.hm-2,前80年累计排放20.07tC.hm-2(97.71%);纸制产品为3.63tC.hm-2,前7年累计排放3.45tC.hm-2(95.13%)。若将采伐木碳库视为当年排放,则碳库采伐后20年才能达到采伐前的水平;而考虑采伐木碳库实际排放速率,碳库储量则一直大于采伐前水平。因此,将采伐木碳库实际排放列入考虑,有利于合理估算我国森林碳储量,对正确评价我国森林碳汇功能具有积极意义。     

Potential effects of elevated carbon dioxide on leaf-feeding forest insects

The elevated concentration of atmospheric CO2 may result in a decline of leaf nutritional quality (especially N) and an increase in some kinds of defensive secondary components (such as phenolics). The changes in the phytochemistry of trees, combined with the effect of elevated CO2 per se, have a potential negative influence on insect herbivores. Here, we review the effect of elevated CO2 on the performance of leaf-feeding forest insects at individual-level and commu-nity-level. The elevated CO2 per se have little influence on the metabolism of insects. Over half of the tree-insect experimental systems show that the performance of individual insect become poorer under high-CO2 grown trees; but the others show that the insects have just little or no response to the treatments. The direction and magnitude of the changes in the performance of insects could be mediated by various factors. The effects of treatment are strongly species-dependent. The magni-tude of changes in the phytochemistry, the sensitivity and adaptive capacity of insects to the poorer leaf quality, the differences in plant growth conditions and experimental methods, and the mediated effects of other environmental factors (such as soil nutrient availability, light, temperature, O3) were all closely related to the final performance of insects. However, the larvae's consumption usually increased under enriched CO2 treatment, which was widely thought to be a compensa-tory response to poorer plant quality. The experiments on forest community-level found identically a reduction in herbivory, which was contrary to the results from small-scale experiments. The changes in insect popula-tion and the actual response of consumption by leaf-feeding forest insects under CO2 enrichment remain unclear, and more field-based experiments need to be conducted.     

Effects of mycorrhizal colonization on biomass production and nitrogen fixation of black locust (Robinia pseudoacacia) seedlings grown under elevated atmospheric carbon dioxide

Interactive effects of elevated atmospheric CO₂ and arbuscular mycorrhizal (AM) fungi on biomass production and N₂ fixation were investigated using black locust ( Robinia pseudoacacia ). Seedlings were grown in growth chambers maintained at either 350 μmol mol⁻¹ or 710 μmol mol⁻¹ CO₂. Seedlings were inoculated with Rhizobium spp. and were grown with or without AM fungi. The ¹⁵N isotope dilution method was used to determine N source partitioning between N₂ fixation and inorganic fertilizer uptake. Elevated atmospheric CO₂ significantly increased the percentage of fine roots that were colonized by AM fungi. Mycorrhizal seedlings grown under elevated CO₂ had the greatest overall plant biomass production, nodulation, N and P content, and root N absorption. Additionally, elevated CO₂ levels enhanced nodule and root mass production, as well as N₂ fixation rates, of non- mycorrhizal seedlings. However, the relative response of biomass production to CO₂ enrichment was greater in non-mycorrhizal seedlings than in mycorrhizal seedlings. This study provides strong evidence that arbuscular mycorrhizal fungi play an important role in the extent to which plant nutrition of symbiotic N₂-fixing tree species is affected by enriched atmospheric CO₂.     

Net climate impacts of forest biomass production and utilization in managed boreal forests

In this work, we studied the potentials offered by managed boreal forests and forestry to mitigate the climate change using forest‐based materials and energy in substituting fossil‐based materials (concrete and plastic) and energy (coal and oil). For this purpose, we calculated the net climate impacts (radiative forcing) of forest biomass production and utilization in the managed Finnish boreal forests (60°–70°N) over a 90‐year period based on integrated use forest ecosystem model simulations (on carbon sequestration and biomass production of forests) and life‐cycle assessment (LCA) tool. When studying the effects of management on the radiative forcing in a system integrating the carbon sink/sources dynamics in both biosystem and technosystem, the current forest management (baseline management) was used a reference management. Our results showed that the use of forest‐based materials and energy in substituting fossil‐based materials and energy would provide an effective option for mitigating climate change. The negative climate impacts could be further decreased by maintaining forest stocking higher over the rotation compared to the baseline management and by harvesting stumps and coarse roots in addition to logging residues in the final felling. However, the climate impacts varied substantially over time depending on the prevailing forest structure and biomass assortment (timber, energy biomass) used in substitution.     

Sorghum biomass production in the continental United States and its potential impacts on soil organic carbon and nitrous oxide emissions

National scale projections of bioenergy crop yields and their environmental impacts are essential to identify appropriate locations to place bioenergy crops and ensure sustainable land use strategies. In this study, we used the process‐based Daily Century (DAYCENT) model with site‐specific environmental data to simulate sorghum (Sorghum bicolor L. Moench) biomass yield, soil organic carbon (SOC) change, and nitrous oxide emissions across cultivated lands in the continental United States. The simulated rainfed dry biomass productivity ranged from 0.8 to 19.2 Mg ha^?1 year^?1, with a spatiotemporal average of  Mg ha^?1 year^?1, and a coefficient of variation of 35%. The average SOC sequestration and direct nitrous oxide emission rates were simulated as  Mg CO₂e ha^?1 year^?1 and  Mg CO₂e ha^?1 year^?1, respectively. Compared to field‐observed biomass yield data at multiple locations, model predictions of biomass productivity showed a root mean square error (RMSE) of 5.6 Mg ha^?1 year^?1. In comparison to the multi State (n = 21) NASS database, our results showed RMSE of 5.5 Mg ha^?1 year^?1. Model projections of baseline SOC showed RMSE of 1.9 kg/m² in comparison to a recently available continental SOC stock dataset. The model‐predicted N₂O emissions are close to 1.25% of N input. Our results suggest 10.2 million ha of cultivated lands in the Southern and Lower Midwestern United States will produce >10 Mg ha^?1 year^?1 with net carbon sequestration under rainfed conditions. Cultivated lands in Upper Midwestern states including Iowa, Minnesota, Montana, Michigan, and North Dakota showed lower sorghum biomass productivity (average: 6.9 Mg ha^?1 year^?1) with net sequestration (average: 0.13 Mg CO₂e ha^?1 year^?1). Our national‐scale spatially explicit results are critical inputs for robust life cycle assessment of bioenergy production systems and land use‐based climate change mitigation strategies.     

Pre-industrial particulate emissions and carbon sequestration from biomass burning in North America

Spatial trends in pre-industrial biomass burning emissions for eastern North America were reconstructed from sediment charcoal data. Petrographic thin sections were prepared from varved lake sediments along a transect of sites extending from NW Minnesota eastward to NE Maine. Results showed an exponential decline in charcoal abundance with distance east from the prairie/forest border. This result quantifies burning along the broad climate/vegetation gradient from xeric woodland to mesic eastern deciduous forest. Post-settlement charcoal accumulation showed no such geographic pattern, varying from site-to-site, likely reflecting local variability in land use and combustion sources. Results suggest the total emissions of large (> 10 m diameter) charcoal particles decreased by a factor of three during the twentieth century.     

黑龙江省温带森林火灾碳排放的计量估算

森林火灾干扰作为森林生态系统重要的干扰因子,剧烈地改变着森林生态系统的结构、功能、格局与过程,对区域乃至全球的碳循环与碳平衡产生重要影响。随着全球气候变暖,森林火灾干扰的频率和强度进一步加剧,其排放的含碳气体对大气中温室气体浓度的贡献率更大,进而加快气候变暖的速率。科学有效地对森林火灾碳排放及含碳气体排放量进行计量估算,对了解区域乃至全球的碳循环及碳平衡具有重要的理论价值和实践意义。根据黑龙江省温带森林1953—2012年火灾统计资料和森林调查数据,结合地理信息系统GIS技术,通过野外火烧迹地调查以及实验室的控制环境实验来确定森林火灾碳排放计量中的各种参数,在林分水平上,利用排放因子的方法,估算了黑龙江省温带森林60年间火灾碳排放量和含碳气体排放量。结果表明:黑龙江省温带森林60年间火灾碳排放量为5.88×107t,年均排放量为9.80×105t,约占全国年均森林火灾碳排放量的8.66%;含碳气体CO2、CO、CH4和非甲烷烃(nonmethane hydrocarbons,NMHC)的排放量分别为1.89×108、1.06×107、6.33×105和4.43×105t,含碳气体CO2、CO、CH4和NMHC的年均排放量分别为3.15×106、1.77×105、1.05×104和7.38×103t,分别占全国年均森林火灾各含碳气体排放量的7.74%、6.52%、9.42%和6.53%。研究发现针阔混交林型的森林火灾面积占总过火林地面积的57.54%,由于其燃烧效率较低,在森林火灾中的碳排放量仅占排放总量的38.57%;尤其是针阔混交林森林火灾面积占总过火林地面积的20.71%,而碳排放量仅占总排放量的9.67%;且CO2的排放因子较低,其CO2排放量仅占总排放量的8.95%。同时研究表明,黑龙江省温带森林年均的碳排放对该区域的碳循环与碳平衡产生重要影响,并针对研究结果提出了应对气候变化的森林经营可持续管理策略,亦提出了科学的林火管理策略及其合理化的林火管理路径。     

林地覆盖经营对雷竹生物量及土壤肥力的影响

以不同覆盖栽培年限(0、3、6、9和12年)雷竹林为研究对象,分析雷竹林退化过程中林分生长与土壤养分的变化趋势.结果表明:随着覆盖年限的增加,竹林地上及地下生物量均在覆盖3年时达到最大值,与对照相比增幅分别为14.6%和146.6%,差异显著;土壤养分含量受覆盖年限和土层深度的影响而出现差异性,并逐渐表现出上层富集的现象,土壤有机碳和全氮含量随覆盖年限的增加呈上升趋势,全磷含量在不同土层中均呈先降低后升高的变化趋势,在表层(0~20 cm)和底层(40~60 cm)土壤中覆盖6年时达到最低,亚表层(20~40 cm)土壤中覆盖3年时达到最低,全钾含量在表层土壤中持续增大,在亚表层和底层土壤中则表现为在覆盖0~3年下降、3~12年上升的变化趋势,试验雷竹林间差异显著.覆盖9年后,土壤肥力综合指数总体得到较大幅度的提高,亚表层土壤肥力优于表层和底层土,但不同覆盖年限间土壤肥力综合指数与雷竹各器官生物量均没有显著的相关性,而在亚表层中,土壤氮含量与竹叶生物量,以及钾含量与竹叶和鞭根生物量呈显著负相关.这表明长期覆盖及大量施用化肥导致的土壤养分过量积累已经对雷竹林的扩繁和生物量积累产生严重的抑制作用,加剧了竹林衰退趋势.     

Miscanthus biomass production for energy in Europe and its potential contribution to decreasing fossil fuel carbon emissions

Field trials throughout Europe over the past 15 years have confirmed the potential for high biomass production from Miscanthus, a giant perennial rhizomatous grass with C₄ photosynthesis. However, policies to promote the utilization of biomass crops require yield estimates that can be scaled up to regional, national and continental areas. The only way in which this information can be reliably provided is through the use of productivity models. Here, we describe MISCANMOD, a productivity model, which was used in conjunction with a GIS to plot potential, non‐water‐limited yields across Europe. Modelled rainfed yields were also calculated using a water balance approach based on FAO estimates of plant available water in the soil. The observed yields were consistent with modelled yields at 20 trial sites across Europe. We estimate that if Miscanthus was grown on 10% of suitable land area in the European Union (EU15), 231 TWh yr^?1 of electricity could be generated, which is 9% of the gross electricity production in 2000. Using the same scenario, the total carbon mitigation could be 76 Mt C yr^?1, which is about 9% of the EU total C emissions for the 1990 Kyoto Protocol baseline levels.     

中国能源消费碳排放的时空特征

选择联合国政府间气候变化专门委员会(IPCC)的部门方法和8大类能源,采用1990年至2009年的中国能源统计数据,按照自下而上的思路,对我国各省区的碳排放量进行估算,并从碳排放量、碳排放强度、人均碳排放量和碳排放密指标出发,深入分析了各省区碳排放的时空特征差异。以期对国内碳排放的时空特征分析,有助于决策者和能源分析家提高节能减排政策制定的有效性。     

武夷山毛竹天然林生物量与能量分配规律及其与人工林的比较研究

以武夷山国家自然保护区核心区天然毛竹林为研究对象,应用生物量优化模型对天然毛竹林生物量、能量的分配规律进行研究,结果表明:①毛竹天然林生物量按组分秆、枝、叶、竹蔸、鞭根的分配规律为5585.956、1120.456、387.453、1148.785、2827.099g·m~(-2),所占比例依次为50.46％、10.12％、3.50％、10.38％、25.54％,能量现存量按组分分别为112171.60、21694.0、7532.8、21796.8、52089.3kJ·m~(-2),所占比例依次为51.70％、10.00％、3.47％、10.05％、24.78％;②毛竹天然林生物量按龄级Ⅰ度、Ⅱ度、Ⅲ度、Ⅳ度、Ⅴ度及以上竹的分配规律为2151.845、1799.441、1184.757、1010.021、4923.684g·m~(-2),所占比例依次为19.44％、16.26％、10.70％、9.12％、44.48％。能量现存量按龄级分别为47465.97、40232.99、26502.84、17737.74、102488.8kJ·m~(-2),所占比例依次为20.25％、17.16％、11.30％、7.57％、43.72％。在此基础上,将毛竹天然林与人工林进行了比较分析。且为毛竹林的丰产培育提出了科学依据。     

Paired-tower measurements of carbon and energy fluxes following disturbance in the boreal forest

Disturbances by fire and harvesting are thought to regulate the carbon balance of the Canadian boreal forest over scales of several decades. However, there are few direct measurements of carbon fluxes following disturbances to provide data needed to refine mathematical models. The eddy covariance technique was used with paired towers to measure fluxes simultaneously at disturbed and undisturbed sites over periods of about one week during the growing season in 1998 and 1999. Comparisons were conducted at three sites: a 1‐y‐old burned jackpine stand subjected to an intense crown fire at the International Crown Fire Modelling Experiment site near Fort Providence, North‐west Territories; a 1‐y‐old clearcut aspen area at the EMEND project near Peace River, Alberta; and a 10‐y‐old burned, mixed forest near Prince Albert National Park, Saskatchewan. Nearby mature forest stands of the same types were also measured as controls. The harvested site had lower net radiation (R_n), sensible (H) and latent (LE) heat fluxes, and greater ground heat fluxes (G) than the mature forest. Daytime CO₂ fluxes were much reduced, but night‐time CO₂ fluxes were identical to that of the mature aspen forest. It is hypothesized that the aspen roots remained alive following harvesting, and dominated soil respiration. The overall effect was that the harvested site was a carbon source of about 1.6 gC m^?2 day^?1, while the mature site was a sink of about ?3.8 gC m^?2 day^?1. The one‐year‐old burn had lower R_n, H and LE than the mature jackpine forest, and had a continuous CO₂ efflux of about 0.8 gC m^–2 day^?1 compared to the mature forest sink of ? 0.5 g C m^?2 day^?1. The carbon source was likely caused by decomposition of fire‐killed vegetation. The 10‐y‐old burned site had similar H, LE, and G to the mature mixed forest site. Although the diurnal amplitude of the CO₂ fluxes were slightly lower at the 10‐y‐old site, there was no significant difference between the daily integrals (? 1.3 gC m^?2 day^?1 at both sites). It appears that most of the change in carbon flux occurs within the first 10 years following disturbance, but more data are needed on other forest and disturbance types for the first 20 years following the disturbance event.