碳同位素技术在森林生态系统碳循环研究中的应用

碳同位素技术对碳素在生态系统中的迁移动态具有很好的示踪作用,在生态学各领域研究中应用广泛。土壤、大气、植物是森林生态系统的重要碳库,植物是大气和土壤交换碳元素的重要介质。本文简要总结了碳同位素技术在研究碳元素在植物体内以及植物、土壤、大气碳库之间的迁移规律和生态学过程中的应用,展望了该技术在森林界面学中的应用前景。     

林火干扰对广东省桉树林生态系统碳密度的影响

林火作为森林非连续的生态因子,引起森林生态系统碳库碳储量与碳分配的变化,影响森林演替进程及固碳能力。以桉树林不同林火干扰强度的火烧迹地为对象,采用相邻样地比较法,以野外调查采样与室内试验分析相结合为主要手段,研究不同林火干扰强度对森林生态系统各碳库及生态系统碳密度变化和空间分布格局的影响,探讨林火干扰对生态系统碳密度与碳分布格局的影响机制。结果表明:林火干扰降低了植被碳密度(P<0.05),轻度、中度和重度林火干扰样地植被碳密度依次为67.88、35.68和15.50 t·hm^-2,相比对照分别下降了15.86%、55.78%和80.79%;在轻度、中度和重度林火干扰样地中,凋落物碳密度分别为1.43、0.94和0.81 t·hm^-2,相比对照分别降低了28.14%、52.76%和59.30%;不同林火干扰强度样地土壤有机碳密度均低于对照,且减少幅度随土壤剖面深度增加而逐渐变小,轻度、中度和重度林火干扰样地土壤有机碳密度分别为103.30、84.33和70.04 t·hm^-2,相比对照分别下降了11.67%、27....     

Generating carbon finance through avoided deforestation and its potential to create climatic, conservation and human development benefits

Recent proposals to compensate developing countries for reducing emissions from deforestation (RED) under forthcoming climate change mitigation regimes are receiving increasing attention. Here we demonstrate that if RED credits were traded on international carbon markets, even moderate decreases in deforestation rates could generate billions of Euros annually for tropical forest conservation. We also discuss the main challenges for a RED mechanism that delivers real climatic benefits. These include providing sufficient incentives while only rewarding deforestation reductions beyond business-as-usual scenarios, addressing risks arising from forest degradation and international leakage, and ensuring permanence of emission reductions. Governance may become a formidable challenge for RED because some countries with the highest RED potentials score poorly on governance indices. In addition to climate mitigation, RED funds could help achieve substantial co-benefits for biodiversity conservation and human development. However, this will probably require targeted additional support because the highest biodiversity threats and human development needs may exist in countries that have limited income potentials from RED. In conclusion, how successfully a market-based RED mechanism can contribute to climate change mitigation, conservation and development will strongly depend on accompanying measures and carefully designed incentive structures involving governments, business, as well as the conservation and development communities.     

Partitioning direct and indirect human-induced effects on carbon sequestration of managed coniferous forests using model simulations and forest inventories

Temperate forest ecosystems have recently been identified as an important net sink in the global carbon budget. The factors responsible for the strength of the sinks and their permanence, however, are less evident. In this paper, we quantify the present carbon sequestration in Thuringian managed coniferous forests. We quantify the effects of indirect human‐induced environmental changes (increasing temperature, increasing atmospheric CO₂ concentration and nitrogen fertilization), during the last century using BIOME‐BGC, as well as the legacy effect of the current age‐class distribution (forest inventories and BIOME‐BGC). We focused on coniferous forests because these forests represent a large area of central European forests and detailed forest inventories were available. The model indicates that environmental changes induced an increase in biomass C accumulation for all age classes during the last 20 years (1982–2001). Young and old stands had the highest changes in the biomass C accumulation during this period. During the last century mature stands (older than 80 years) turned from being almost carbon neutral to carbon sinks. In high elevations nitrogen deposition explained most of the increase of net ecosystem production (NEP) of forests. CO₂ fertilization was the main factor increasing NEP of forests in the middle and low elevations. According to the model, at present, total biomass C accumulation in coniferous forests of Thuringia was estimated at 1.51 t C ha^?1 yr^?1 with an averaged annual NEP of 1.42 t C ha^?1 yr^?1 and total net biome production of 1.03 t C ha^?1 yr^?1 (accounting for harvest). The annual averaged biomass carbon balance (BCB: biomass accumulation rate‐harvest) was 1.12 t C ha^?1 yr^?1 (not including soil respiration), and was close to BCB from forest inventories (1.15 t C ha^?1 yr^?1). Indirect human impact resulted in 33% increase in modeled biomass carbon accumulation in coniferous forests in Thuringia during the last century. From the forest inventory data we estimated the legacy effect of the age‐class distribution to account for 17% of the inventory‐based sink. Isolating the environmental change effects showed that these effects can be large in a long‐term, managed conifer forest.     

Linkages between phosphorus transformations and carbon decomposition in a forest soil

Phosphorus mineralization is chemically coupled with organic matter (OM) decomposition in surface horizons of a mixed-conifer forest soil from the Sierra Nevada, California, and is also affected by the disturbance caused by forest harvesting. Solution¹³C nuclear magnetic resonance (NMR) spectroscopy of NaOH extracts revealed a decrease of O-alkyl and alkyl-C fractions with increasing degree of decomposition and depth in the soil profile, while carbonyl and aromatic C increased. Solid-state¹³C-NMR analysis of whole soil samples showed similar trends, except that alkyl C increased with depth. Solution³¹P-NMR indicated that inorganic P (P₁) increased with increasing depth, while organic-P (P_o) fractions decreased. Close relationships between P mineralization and litter decomposition were suggested by correlations between P₁ and C fractions (r = 0.82, 0.81, –0.87, and –0.76 for carbonyl, aromatic, alkyl and O-alkyl fractions, respectively). Correlations for diester-P and pyrophosphate with O-alkyl (r = 0.63 and 0.84) and inverse correlations with aromatics (r = –0.74 and –0.72) suggest that mineralization of these P fractions coincides with availability of C substrate. A correlation between monoester P and alkyl C (r = 0.63) suggests mineralization is linked to breakdown of structural components of the plant litter. NMR analyses, combined with Hedley-P fractionation, suggest that post-harvest buildup of labile P in decomposed litter increases the potential for leaching of P during the first post-harvest season, but also indicates reduced biological activity that transports P from litter to the mineral soil. Thus, P is temporarily stored in decomposed litter, preventing its fixation by mineral oxides. In the mineral horizons,³¹P-NMR provides evidence of decline in biologically-available P during the first post-harvest season.     

Contemporary carbon stocks of mineral forest soils in the Swiss Alps

Soil organic carbon (SOC) has been identified as the main globalterrestrial carbon reservoir, but considerable uncertainty remains as toregional SOC variability and the distribution of C between vegetationand soil. We used gridded forest soil data (8–km × 8–km)representative of Swiss forests in terms of climate and forest typedistribution to analyse spatial patterns of mineral SOC stocks alonggradients in the European Alps for the year 1993. At stand level, meanSOC stocks of 98 t C ha^–1 (N = 168,coefficient of variation: 70%) were obtained for the entiremineral soil profile, 76 t C ha^–1 (N =137, CV: 50%) in 0–30 cm topsoil, and 62 t Cha^–1 (N = 156, CV: 46%) in0–20 cm topsoil. Extrapolating to national scale, we calculatedcontemporary SOC stocks of 110 Tg C (entire mineral soil, standarderror: 6 Tg C), 87 Tg C (0–30 cm topsoil, standarderror: 3.5 Tg C) and 70 Tg C (0–20 cm topsoil, standarderror: 2.5 Tg C) for mineral soils of accessible Swiss forests(1.1399 Mha). According to our estimate, the 0–20 cm layers ofmineral forest soils in Switzerland store about half of the Csequestered by forest trees (136 Tg C) and more than five times morethan organic horizons (13.2 Tg C).At stand level, regression analyses on the entire data set yielded nostrong climatic or topographic signature for forest SOC stocks in top(0–20 cm) and entire mineral soils across the Alps, despite thewide range of values of site parameters. Similarly, geostatisticalanalyses revealed no clear spatial trends for SOC in Switzerland at thescale of sampling. Using subsets, biotic, abiotic controls andcategorial variables (forest type, region) explained nearly 60%of the SOC variability in topsoil mineral layers (0–20 cm) forbroadleaf stands (N = 56), but only little of thevariability in needleleaf stands (N = 91,R ² = 0.23 for topsoil layers).Considerable uncertainties remain in assessments of SOC stocks, due tounquantified errors in soil density and rock fraction, lack of data onwithin-site SOC variability and missing or poorly quantifiedenvironmental control parameters. Considering further spatial SOCvariability, replicate pointwise soil sampling at 8–km × 8–kmresolution without organic horizons will thus hardly allow to detectchanges in SOC stocks in strongly heterogeneous mountain landscapes.     

在我国开展林业碳汇项目的利弊分析

因为CO2等温室气体的增加导致的全球气候变暖严重影响了世界各国社会和经济的发展,而森林具有吸收大气中的CO2,减缓气候变暖的作用,因此2001年的《波恩政治协议》和《马拉喀什协定》同意将造林、再造林等林业碳汇项目作为第一承诺期合格的清洁发展机制(CDM)项目。目前,国际上此类活动已相继展开,而我国还未展开此类活动。为了给我国是否可以开展林业碳汇项目提供参考,文章对我国开展林业碳汇项目的利与弊进行了比较详细的分析和比较,认为可以在我国适当开展林业碳汇项目,以促进我国经济和社会的可持续发展,并进一步加强我国在国际上的地位。     

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.     

13C natural abundance variations in carbonates and organic carbon from boreal forest wetlands

¹³C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated wetland with δ¹³C values as low as -97 ‰ in carbonate minerals found in floating peat mats. It is postulated that¹³C depleted CH₄ is oxidized in the mat and reacts with calcium ions to form calcite (identified through x-ray diffraction). Methane flux measurements during the summer of 1992 showed much lower fluxes in areas with floating peat mats relative to open water. Secondary carbonates in the basin peat have isotope compositions close to the δ¹³C values of the peat organic carbon (-25 ‰), indicating their origin from fermentation and possibly from sulfate-reduction. In the upland basin peat deposits, the δ¹³C_PDB values of organic C were constant with depth, while the permanently saturated mire had localities of¹³C enrichment in deeper layers of the peat. The¹³C enrichment may reflect areas of intense CH₄ production in which¹³C enriched residual substrate is left behind during the production of highly¹³C depleted CH₄.     

Biomass and carbon accumulation in a fire chronosequence of a seasonally dry tropical forest

Seasonally dry tropical forests (SDTF) are a widely distributed vegetation type in the tropics, characterized by seasonal rainfall with several months of drought when they are subject to fire. This study is one of the first attempts to quantify above- and belowground biomass (AGB and BGB) and above- and belowground carbon (AGC and BGC) pools to calculate their recovery after fire, using a chronosequence approach (six forests that ranged form 1 to 29 years after fire and mature forest). We quantified AGB and AGC pools of trees, lianas, palms, and seedlings, and BGB and BGC pools (Oi, Oe, Oa soil horizons, and fine roots). Total AGC ranged from 0.05 to nearly 72 Mg C ha⁻¹, BGC from 21.6 to nearly 85 Mg C ha⁻¹, and total ecosystem carbon from 21.7 to 153.5 Mg C ha⁻¹; all these pools increased with forest age. Nearly 50% of the total ecosystem carbon was stored in the Oa horizon of mature forests, and up to 90% was stored in the Oa-horizon of early successional SDTF stands. The soils were shallow with a depth of <20 cm at the study site. To recover values similar to mature forests, BGC and BGB required <19 years with accumulation rates greater than 20 Mg C ha⁻¹ yr⁻¹, while AGB required 80 years with accumulation rates nearly 2.5 Mg C ha⁻¹ yr⁻¹. Total ecosystem biomass and carbon required 70 and 50 years, respectively, to recover values similar to mature forests. When belowground pools are not included in the calculation of total ecosystem biomass or carbon recovery, we estimated an overestimation of 10 and 30 years, respectively.     

基于森林清查资料的江西和浙江森林植被固碳潜力

以我国江西、浙江两省的森林植被为研究对象,基于1999-2003年间第六次全国森林清查数据及收集的1030个亚热带森林样地文献资料,依据林分生长的经验方程,估算了两个地区森林2004-2013年的固碳潜力,并基于455个样点的调查数据研究了不同森林管理措施(纯林间种、间伐、施肥)对森林未来固碳潜力的影响.结果表明:第六次森林清查以来的10年(2004-2013)间,江西森林植被年均自然固碳潜力约11.37 Tg C·a-1(1Tg=1012g),而浙江省森林植被年均自然固碳潜力约4.34 Tg C·a-1.纯林间种对江西、浙江两省森林植被固碳潜力影响最大,其次为间伐抚育,施肥的影响最小,纯林间种、间伐和施肥3种森林管理措施使江西省森林植被固碳潜力分别提高(6.54±3.9)、(3.81±2.02)和(2.35±0.6) Tg C·a-1,浙江省森林植被固碳潜力分别提高(2.64±1.28)、(1.42±0.69)和(1.15±0.29) Tg C·a-1.     

Estimating carbon carrying capacity in natural forest ecosystems across heterogeneous landscapes: addressing sources of error

Evaluating contributions of forest ecosystems to climate change mitigation requires well‐calibrated carbon cycle models with quantified baseline carbon stocks. An appropriate baseline for carbon accounting of natural forests at landscape scales is carbon carrying capacity (CCC); defined as the mass of carbon stored in an ecosystem under prevailing environmental conditions and natural disturbance regimes but excluding anthropogenic disturbance. Carbon models require empirical measurements for input and calibration, such as net primary production (NPP) and total ecosystem carbon stock (equivalent to CCC at equilibrium). We sought to improve model calibration by addressing three sources of errors that cause uncertainty in carbon accounting across heterogeneous landscapes: (1) data‐model representation, (2) data‐object representation, (3) up‐scaling. We derived spatially explicit empirical models based on environmental variables across landscape scales to estimate NPP (based on a synthesis of global site data of NPP and gross primary productivity, n=27), and CCC (based on site data of carbon stocks in natural eucalypt forests of southeast Australia, n=284). The models significantly improved predictions, each accounting for 51% of the variance. Our methods to reduce uncertainty in baseline carbon stocks, such as using appropriate calibration data from sites with minimal human disturbance, measurements of large trees and incorporating environmental variability across the landscape, have generic application to other regions and ecosystem types. These analyses resulted in forest CCC in southeast Australia (mean total biomass of 360 t C ha^?1, with cool moist temperate forests up to 1000 t C ha^?1) that are larger than estimates from other national and international (average biome 202 t C ha^?1) carbon accounting systems. Reducing uncertainty in estimates of carbon stocks in natural forests is important to allow accurate accounting for losses of carbon due to human activities and sequestration of carbon by forest growth.     

Effects of nutrient additions on ecosystem carbon cycle in a Puerto Rican tropical wet forest

Wet tropical forests play a critical role in global ecosystem carbon (C) cycle, but C allocation and the response of different C pools to nutrient addition in these forests remain poorly understood. We measured soil organic carbon (SOC), litterfall, root biomass, microbial biomass and soil physical and chemical properties in a wet tropical forest from May 1996 to July 1997 following a 7‐year continuous fertilization. We found that although there was no significant difference in total SOC in the top 0–10 cm of the soils between the fertilization plots (5.42±0.18 kg m^?2) and the control plots (5.27±0.22 kg m^?2), the proportion of the heavy‐fraction organic C in the total SOC was significantly higher in the fertilized plots (59%) than in the control plots (46%) (P<0.05). The annual decomposition rate of fertilized leaf litter was 13% higher than that of the control leaf litter. We also found that fertilization significantly increased microbial biomass (fungi+bacteria) with 952±48 mg kg^?1soil in the fertilized plots and 755±37 mg kg^?1soil in the control plots. Our results suggest that fertilization in tropical forests may enhance long‐term C sequestration in the soils of tropical wet forests.     

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.     

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.     

Meeting Europe's climate change commitments: quantitative estimates of the potential for carbon mitigation by agriculture

Under the Kyoto Protocol, the European Union is committed to a reduction in CO₂ emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, land‐use/land‐management change and forestry activities that are shown to reduce atmospheric CO₂ levels can be included in the Kyoto targets. These activities include afforestation, reforestation and deforestation (article 3.3 of the Kyoto Protocol) and the improved management of agricultural soils (article 3.4). In this paper, we estimate the carbon mitigation potential of various agricultural land‐management strategies and examine the consequences of European policy options on carbon mitigation potential, by examining combinations of changes in agricultural land‐use/land‐management. We show that no single land‐management change in isolation can mitigate all of the carbon needed to meet Europe's climate change commitments, but integrated combinations of land‐management strategies show considerable potential for carbon mitigation. Three of the combined scenarios, one of which is an optimal realistic scenario, are by themselves able to meet Europe's emission limitation or reduction commitments. Through combined land‐management scenarios, we show that the most important resource for carbon mitigation in agriculture is the surplus arable land. We conclude that in order to fully exploit the potential of arable land for carbon mitigation, policies will need to be implemented to allow surplus arable land to be put into alternative long‐term land‐use. Of all options examined, bioenergy crops show the greatest potential for carbon mitigation. Bioenergy crop production also shows an indefinite mitigation potential compared to other options where the mitigation potential is finite. We suggest that in order to exploit fully the bioenergy option, the infrastructure for bioenergy production needs to be significantly enhanced before the beginning of the first Kyoto commitment period in 2008. It is not expected that Europe will attempt to meet its climate change commitments solely through changes in agricultural land‐use. A reduction in CO₂‐carbon emissions will be key to meeting Europe's Kyoto targets, and forestry activities (Kyoto Article 3.3) will play a major role. In this study, however, we demonstrate the considerable potential of changes in agricultural land‐use and ‐management (Kyoto Article 3.4) for carbon mitigation and highlight the policies needed to promote these agricultural activities. As all sources of carbon mitigation will be important in meeting Europe's climate change commitments, agricultural carbon mitigation options should be taken very seriously.     

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.