Spatially explicit assessment of carbon stocks of a managed forest area in eastern Germany

The Kyoto-protocol permits the accounting of changes in forest carbon stocks due to forestry. Therefore, forest owners are interested in a reproducible quantification of carbon stocks at the level of forest management units and the impact of management to these stocks or their changes. We calculated the carbon stocks in tree biomass and the organic layer including their uncertainties for several forest management units (Tharandt forest, Eastern Germany, 5,500 ha) spatially explicit at the scale of individual stands by using standard forest data sources. Additionally, soil carbon stocks along a catena were quantified. Finally, carbon stocks of spruce and beech dominated stands were compared and effects of thinning intensity and site conditions were assessed. We combined forest inventory and data of site conditions by using the spatial unions of the shapes (i.e., polygons) in the stand map and the site map. Area weighted means of carbon (C) stocks reached 10.0 kg/m2 in tree biomass, 3.0 kg/m2 in the organic layer and 7.3 kg/m2 in mineral soil. Spatially explicit error propagation yielded a precision of the relative error of carbon stocks at the total studied area of 1% for tree biomass, 45% for the organic layer, and 20% for mineral soil. Mature beech dominated stands at the Tharandt forest had higher tree biomass carbon stocks (13.4 kg/m2) and lower organic layer carbon stocks (1.8 kg/m2) compared to stands dominated by spruce (11.6, 3.0 kg/m2). The difference of tree biomass stocks was mainly due to differences in thinning intensity. The additional effect of site conditions on tree carbon stocks was very small. We conclude that the spatially explicit combination of stand scale inventory data with data on site conditions is suited to quantify carbon stocks in tree biomass and organic layer at operational scale.     

Growth and carbon stocks of a spruce forest chronosequence in central Europe

Human induced changes in global environmental conditions are expected to influence or, as it is hypothesised in this study, have already influenced the biomass and growth of forest ecosystems. In this study, we reconstruct the history of tree growth and quantify the standing biomass along a chronosequence of six Norway spruce stands (Picea abies [L.] Karst; 16–142 years old) on acid soils in a mountainous region with high nitrogen deposition. The inventories of the study sites, as well as the historical stem growth of the sample trees were compared with common yield tables, representing growing conditions before 1960, to find out if and when significant changes in growth of trees had occurred. The growth at tree level (0.003–0.030 m³ yr⁻¹) was about 150–350% higher than predicted by the yield tables, independent of tree age. Because of low stand densities due to early thinning, the increase of stem growth at stand level (90% higher than yield table predictions) and the stand volume (35% higher than yield table predictions) were not as high as the increase of growth at tree level. Total biomass at stand level (including stems, branches, twigs, needles and roots) ranged between 35 and 180 t C ha⁻¹. Net primary productivity varied between 6 and 13 t C ha⁻¹ yr⁻¹. Intensive tree thinning activities probably stimulated growth of remaining trees, but the observed growth rates were beyond what would be expected from these activities exclusively. Thus it is assumed that the fertilisation effects of increased nitrogen deposition and CO₂ concentration, and improved climatic conditions due to ongoing climate change, have contributed to the observed changes in stem growth and that the thinning activities were synergetic with changing environmental conditions. The implications for carbon sinks as accountable under the Kyoto Protocol are probably small, because changes in environmental conditions are not accountable under the Kyoto Protocol and most of the observed changes in growth took place before 1990, the baseline for the Kyoto Protocol. Additionally, it is assumed that impacts on the carbon balance of forest stands due to changes in the thinning regime after 1990, which would be accountable according to article 3.4 of the Kyoto Protocol, are very small without any synergetic changes in environmental conditions.     

The effects of a thinning treatment on carbon stocks in a northern Arizona ponderosa pine forest

Vast areas of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest in the western United States have become unnaturally dense because of relatively recent land management practices that include fire suppression and livestock grazing. In many areas, thinning treatments can re-establish the natural ecological processes and help restore ecosystem structure and function. Precipitous global climate change has focused attention on the carbon storage in forests. An unintended consequence of fire suppression has been the increased storage of carbon in ponderosa stands. Thinning treatments reduce standing carbon stocks while releasing carbon through the combustion of fuel in logging machinery, burning slash, and the decay of logging slash and wood products. These reductions and releases of stored carbon must be compared to the risk of catastrophic fire burning through the stand and releasing large quantities of carbon to the atmosphere to more fully understand the costs and benefits – in carbon terms – of forest restoration strategies.     

Comparison of uncertainties in carbon sequestration estimates for a tropical and a temperate forest

We compare uncertainty through sensitivity and uncertainty analyses of the modelling framework CO2FIX V.2. We apply the analyses to a Central European managed Norway spruce stand and a secondary tropical forest in Central America. Based on literature and experience we use three standard groups to express uncertainty in the input parameters: 5%, 10% and 20%. Sensitivity analyses show that parameters exhibiting highest influence on carbon sequestration are carbon content, wood density and current annual increment of stems. Three main conclusions arise from this investigation: (1) parameters that largely determine model output are stem parameters, (2) depending on initial state of the model, perturbation can lead to multiple equilibrium, and (3) the standard deviation of total carbon stock is double in the tropical secondary forest for the wood density, and current annual increment. The standard deviation caused by uncertainty in mortality rate is more than 10-fold in the tropical forest case than in the temperate managed forest. Even in a case with good access to data, the uncertainty remains very high, much higher than what can reasonably be achieved in carbon sequestration through changes in forest management.     

Estimations of total ecosystem carbon pools distribution and carbon biomass current annual increment of a moist tropical forest

With increasing CO₂ in the atmosphere, there is an urgent need of reliable estimates of biomass and carbon pools in tropical forests, most especially in Africa where there is a serious lack of data. Information on current annual increment (CAI) of carbon biomass resulting from direct field measurements is crucial in this context, to know how forest ecosystems will affect the carbon cycle and also to validate eddy covariance flux measurements. Biomass data were collected from 25 plots of 13 ha spread over the different vegetation types and land uses of a moist evergreen forest of 772,066 ha in Cameroon. With site-specific allometric equations, we estimated biomass and aboveground and belowground carbon pools. We used GIS technology to develop a carbon biomass map of our study area. The CAI was estimated using the growth rates obtained from tree rings analysis. The carbon biomass was on average 264 ± 48 Mg ha⁻¹. This estimate includes aboveground carbon, root carbon and soil organic carbon down to 30 cm depth. This value varied from 231 ± 45 Mg ha⁻¹ of carbon in Agro-Forests to 283 ± 51 Mg ha⁻¹ of carbon in Managed Forests and to 278 ± 56 Mg ha⁻¹ of carbon in National Park. The carbon CAI varied from 2.54 ± 0.65 Mg ha⁻¹ year⁻¹ in Agro-Forests to 2.79 ± 0.72 Mg ha⁻¹ year⁻¹ in Managed Forests and to 2.85 ± 0.72 Mg ha⁻¹ year⁻¹ in National Park. This study provides estimates of biomass, carbon pools and CAI of carbon biomass from a forest landscape in Cameroon as well as an appropriate methodology to estimate these components and the related uncertainty.     

Effect of tree species on carbon stocks in forest floor and mineral soil and implications for soil carbon inventories

Forest soil organic carbon (SOC) and forest floor carbon (FFC) stocks are highly variable. The sampling effort required to assess SOC and FFC stocks is therefore large, resulting in limited sampling and poor estimates of the size, spatial distribution, and changes in SOC and FFC stocks in many countries. Forest SOC and FFC stocks are influenced by tree species. Therefore, quantification of the effect of tree species on carbon stocks combined with spatial information on tree species distribution could improve insight into the spatial distribution of forest carbon stocks.We present a study on the effect of tree species on FFC and SOC stock for a forest in the Netherlands and evaluate how this information could be used for inventory improvement. We assessed FFC and SOC stocks in stands of beech (Fagus sylvatica), Douglas fir (Pseudotsuga menziesii), Scots pine (Pinus sylvestris), oak (Quercus robur) and larch (Larix kaempferi).FFC and SOC stocks differed between a number of species. FFC stocks varied between 11.1 Mg C ha⁻¹ (beech) and 29.6 Mg C ha⁻¹ (larch). SOC stocks varied between 53.3 Mg C ha⁻¹ (beech) and 97.1 Mg C ha⁻¹ (larch). At managed locations, carbon stocks were lower than at unmanaged locations. The Dutch carbon inventory currently overestimates FFC stocks. Differences in carbon stocks between conifer and broadleaf forests were significant enough to consider them relevant for the Dutch system for carbon inventory.     

Above and below ground organic carbon stocks in a sub-tropical Pinus roxburghii Sargent forest of the Garhwal Himalayas

Accurate estimates of tree carbon,forest floor carbon and organic carbon in forest soils (SOC) are important in order to determine their contribution to global carbon (C) stocks.However,information about these carbon stocks is lacking.Some studies have investigated regional and continental scale patterns of carbon stocks in forest ecosystems;however,the changes in C storage in different components (vegetation,forest floor and soil) as a function of elevation in forest ecosystems remain poorly understood.In this study,we estimate C stocks of vegetation,forest floor and soils of a Pinus roxburghii Sargent forest in the Garhwal Himalayas along a gradient to quantify changes in carbon stock due to differences in elevation at three sites.The biomass of the vegetation changes drastically with increasing elevation among the three sites.The above-ground biomass (AGB) and below-ground biomass (BGB) were highest at site Ⅰ (184.46 and 46.386 t·ha-1 respectively) at an elevation of 1300 m followed by siteⅡ (173.99 and 44.057 t·ha-1 AGB and BGB respectively) at 1400 m and the lowest AGB and BGB were estimated at site Ⅲ(161.72 and 41.301 t·ha-1) at 1500 m.The trend for SOC stock was similar to that of biomass.Our results suggest that carbon storage (in both soil and biomass) is negatively correlated with elevation.     

Organic carbon stocks and stock changes of forest biomass in Belgium derived from forest inventory data in a spatially explicit approach

? Carbon sequestration in forest ecosystems is an important though still uncertain process in the global greenhouse gas balance.

? We computed biomass organic carbon (BOC) stocks of spatially explicit forested landscape units (LSU) in Belgium based on data collected in the regional forest inventories of 1984 (Wallonia region only) and 2000 (Wallonia and Flanders). C stock changes between 1984 and 2000 were estimated for Wallonia.

? The total BOC pool stored in Belgian forests in 2000 amounts to 57.8 Mt C in 6222 km², or 10.0 kg C m^?2 in broadleaf, 9.5 kg C m^?2 in coniferous and 8.7 kg C m^?2 in mixed forest. Based on previous soil organic carbon (SOC) analysis for the same LSU, BOC and SOC stock per LSU appeared only weakly correlated. The total BOC sequestration between 1984 and 2000 equals 5.7 Mt C over an area of 5 107 km², resulting in a flux of 0.07 kg C m^?2 y^?1. The BOC content of broadleaf forest in Wallonia increased with 6%, of coniferous forest with 32% and of mixed forest with 11%.

? The observed regional differences in BOC stocks and in BOC sequestration rates are explained by the forest age-class distribution and site productivity. The strength of the spatially explicit approach lies in the fact that BOC and SOC data originating from diverse sampling strategies can be combined for spatial or temporal comparison of C stocks.

     

Changes in soil carbon and nitrogen stocks after conversion of subtropical natural forest to loblolly pine plantations

Pinus plantations have increased in Brazil, and native forest areas have been converted for timber production. The clearing and the long-term loblolly pine (Pinus taeda L.) land-use effects on soil carbon and nitrogen stocks were evaluated in a natural broadleaved forest and in loblolly pine sites cultivated for 29, 35, 38 and 49 years, as well the soil contribution as ecosystem carbon pool. According to the exponential-decay model fitted to changes in carbon stock, the initial soil carbon stock of 200 Mg ha^?1 to a depth of 100 cm in the natural forest decreased by 36% over 49 years of pine cultivation (around 72.4 Mg ha^?1 of C). Around two-thirds of this decrease occurred in the top 30 cm of the soil and intensively in the first 12 years of cultivation, but slowly faded as carbon stock tended to reach a new steady state after approximately 49 years of cultivation. The soil nitrogen stock in the natural forest was 14.2 Mg ha^?1 to a depth of 100 cm and decreased by 36% over the 49 years. This decrease was linear according to the fitted model, especially in the top 30 cm where nitrogen decline was 83% and was proportionally more intense than the carbon decline. Despite the soil carbon decrease, soil remained the largest carbon reservoir in the ecosystem for the growing rotation time of loblolly pine in this region.

     

The impact of carbon trade on the management of short-rotation forest plantations

We extended the Hartman model to examine the optimal rotation, taking into consideration the economic benefits of wood and the dynamics of three carbon pools (aboveground biomass, dead organic matter, and harvested forest products). Chinese fir (Cunninghamia lanceolata) stands in Southern China were taken for a numerical example to analyze the effects of carbon price on the optimal management of short-rotation plantations. The results show that, with the current price of carbon, introducing the effects of harvesting on different carbon pools into the decision model would increase the optimal rotation age on poor (SI = 10) and medium (SI = 17) sites by one year, while it does not have any impact on the optimal rotation for good sites (SI = 21). Irrespective of site condition, the optimal rotation age is not sensitive to carbon price and interest rate. An increase in interest rate by 1% would reduce the optimal rotation age by one year. In conclusion, forest carbon trade could effectively enhance land owners' income from short-rotation forest plantations. However, it does not lead to any significant increase in forest carbon sink.     

Litter carbon inputs to the mineral soil of Japanese Brown forest soils: comparing estimates from the RothC model with estimates from MODIS

The level of organic carbon found in soil is the result of the balance between litter input to the soil and decomposition. Litter input to the soil is closely related to net primary production (NPP); at equilibrium, the NPP is equal to the litter input to soil. Plant litter input to a depth of 30 cm in the mineral soil was estimated for Japanese forest using the Rothamsted Carbon model (RothC) and an average value of soil organic carbon (SOC) content, and was compared with estimated litter inputs from the NPP dataset from Moderate Resolution Imaging Spectroradiometer (MODIS). A Monte Carlo uncertainty analysis of the input SOC was also conducted in order to reveal the sensitivity and uncertainty of the model to input SOC. The litter carbon input calculated using RothC and that derived from MODIS NPP were positively correlated, but the mean estimated litter input from RothC was 17.2% smaller than that estimated from MODIS. Mapping the normalized difference revealed spatial biases in the difference. The discrepancy was probably because of the different temperature controls for the MODIS algorithm and the RothC model, and also our simple assumption in the RothC calculation. This comparison reveals a close link between litter inputs estimated from SOC data and litter inputs estimated from satellite-based NPP data. The discrepancies between the estimates merit further study.     

The impact of windthrow on carbon sequestration in Switzerland: a model-based assessment

Carbon sequestered in biomass is not necessarily stored infinitely, but is exposed to human or natural disturbances. Storm is the most important natural disturbance agent in Swiss forests. Therefore, if forests are taken into account in the national carbon budget, the impact of windthrow on carbon pools and fluxes should be included. In this article the forest scenario model MASSIMO and the soil carbon model YASSO were applied to assess the effect of forest management and an increased storm activity on the carbon sequestration in Swiss forests. First, the soil model was adapted to Swiss conditions and validated. Second, carbon fluxes were assessed applying the two models under various forest management scenarios and storm frequencies. In particular, the influence of clearing after a storm event on the carbon budget was analyzed. The evaluation of the model results showed that the soil model reliably reproduces the amount of soil carbon at the test sites. The simulation results indicated that, within the simulated time period of 40 years, forest management has a strong influence on the carbon budget. However, forest soils only react slightly to changes in the above-ground biomass. The results also showed that a storm frequency increase of 30% has a small impact on the national carbon budget of forests. To develop effective mitigation strategies for forest management, however, longer time periods must be regarded.     

Long-term development of soil organic carbon and nitrogen stocks after shelterwood- and clear-cutting in a mountain forest in the Bavarian Limestone Alps

Forest soils store large stocks of soil organic matter (SOM) and are of vital importance for the ecosystem supply with nutrients and water. According to the available literature, depending on management regime and site properties, different negative and positive effects of forest management (particularly of forest thinnings and shelterwood cuttings) on soil organic carbon (SOC) and nitrogen (N) stocks are observed. To elucidate the long-term impact of different shelterwood systems and small clear-cuttings on the OC and N stocks of shallow calcareous soils in the Bavarian Alps, we conducted soil humus inventories on different plots of a mixed mountain forest management experiment started in 1976. The silvicultural multi-treatment experiment consists of a NW-exposed Main Experiment (ME) site with eight plots of different cutting intensity (two unthinned controls, two light shelterwood cuttings = 30 % of basal tree area removed, two heavy shelterwood cuttings = 50 % removed, and two clear-cuttings = 100 % removed) on Triassic dolostone. Additionally, plots were installed at a N-exposed dolostone (ND) site and two sites (FL, FH) on Flysch sandstone (each with one unthinned control and one heavy shelterwood cutting). The shelterwood cuttings from 1976 were repeated in 2003 to re-establish the overstorey basal area as produced by the first cutting in the different plots. Thirty-five years after the first treatments, forest floor SOC and N stocks were significantly decreased (up to ?70 %) at the different shelterwood and clear-cut treatments compared to the unthinned control at the ME site despite vigorous development of natural rejuvenation. Also significantly smaller topsoil (forest floor plus mineral soil 0–10 cm depth) OC stocks (between ?16 and ?20 %) were detected at the thinned compared to the control plots. Differences in topsoil N stocks were also considerable (between ?3 and ?14 %), but substantially smaller than OC stock changes. For the total soil down to 30 cm depth, OC stocks in the differently thinned plots were consistently smaller compared to the unthinned control plots. Comparable to our findings at the ME site, heavy shelterwood plots at the three other sites (ND, FL, and FH) showed significant losses of OC in the forest floor (up to 43 %), mineral soil (up to 38 %), topsoil (up to 38 %), and total soil (up to 34 %). Significant large absolute and relative SOC decreases coincided with sites characterized by large initial humus stocks. Moreover, significant effects of heavy shelterwood cuttings on SOC and N stocks (on average 23 % SOC loss and 13 % soil N loss for the forest floor plus the uppermost 10 cm mineral soil) were detected on a regional level. Our results show that different shelterwood systems are accompanied with a considerable long-term decrease in OC and N stocks in shallow calcareous forest soils of the Bavarian Alps. However, a comparison with a windthrown forest stand at a nearby similar site indicates that SOM losses after thinning operations are small compared to decreases following windthrow or other calamities with subsequent large soil erosion and increased mineralization processes.     

Changes in forest cover and carbon stocks of the coastal scarp forests of the Wild Coast,South Africa

Land-use intensification and declines in vegetative cover are considered pervasive threats to forests and biodiversity globally. The small extent and high biodiversity of indigenous forests in South Africa make them particularly important. Yet, relatively little is known about their rates of use and change. From analysis of past aerial photos we quantified rates of forest cover change in the Matiwane forests of the Wild Coast, South Africa, between 1942 and 2007, as well as quantified above and belowground (to 0.5?m depth) carbon stocks based on a composite allometric equation derived for the area. Rates of forest conversion were spatially variable, with some areas showing no change and others more noticeable changes. Overall, the net reduction was 5.2% (0.08% p.a.) over the 65-year period. However, the rate of reduction has accelerated with time. Some of the reduction was balanced by natural reforestation into formerly cleared areas, but basal area, biomass and carbon stocks are still low in the reforested areas. The total carbon stock was highest in intact forests (311.7 ± 23.7 Mg C ha^?1), followed by degraded forests (73.5 ± 12.3 Mg C ha^?1) and least in regrowth forests (51.2 ± 6.2 Mg C ha^?1). The greatest contribution to total carbon stocks was soil carbon, contributing 54% in intact forests, and 78% and 68% in degraded and regrowth forests, respectively. The Matiwane forests store 4.78 Tg C, with 4.7 Tg C in intact forests, 0.06 Tg C in degraded forests and 0.02 Tg C in regrowth forests. The decrease in carbon stocks within the forests as a result of the conversion of the forest area to agricultural fields was 0.19 Tg C and approximately 0.0003 Tg C was released through harvesting of firewood and building timber.     

National inventories of down and dead woody material forest carbon stocks in the United States: Challenges and opportunities

Concerns over the effect of greenhouse gases and consequent international agreements and regional/national programs have spurred the need for comprehensive assessments of forest ecosystem carbon stocks. Down and dead woody (DDW) materials are a substantial component of forest carbon stocks; however, few surveys of DDW carbon stocks have been conducted at national-scales around the world. This study uses the DDW survey of the United States as a case study to examine the challenges of inventorying DDW at a national scale, reviews how dead wood carbon pools are currently estimated in the National Greenhouse Gas Inventory (NGHGI), and suggests opportunities for improving such inventories. The US currently estimates national DDW carbon stocks using models with standing live tree attributes as predictor variables, calibrated using preliminary DDW field estimates. In recent years, implementation of a national DDW inventory has resulted in inventory-based DDW estimates. National field-based DDW estimates follow the national patterns of DDW carbon dispersion seen in earlier model-based estimates. Although the current DDW inventory provides fairly repeatable measurements within a statistically defensible national sample design for producing national estimates of DDW carbon stocks, improving numerous aspects of the DDW survey would may improve the accuracy and precision of C estimates reported in the NGHGI.     

Effects of fertilisation on phosphorus pools in the volcanic soil of a managed tropical forest

Acacia koa forests benefit from phosphorus fertilisation, but it is unknown if fertilisation is a short or long term effect on P availability. Past research suggests that P cycling in soils with high P sorption capacity, such as Andisols, was through organic pathways. We studied leaf P and soil P fractions in a tropical forest Andisol for 3 years after fertilisation with triple super phosphate. Leaf P concentration and labile P remained high after fertilisation. Fertilisation had increased all the inorganic P fractions over the length of the study, while organic P fractions had not. The results suggested that the organic P fractions had a reduced role as a source of labile P after fertilisation. The size and dynamics of the sodium hydroxide- and hydrochloric acid-extractable P pools would suggest that either pool could be major sources of labile P. Because of the high level of poorly crystalline minerals in Andisols (allophone and imogolite), it would be expected that applied P would quickly lead to strong P sorption onto mineral surfaces and thus a rapid decline in P availability. We propose that the high organic matter present in these soils had masked some of the Al and Fe sorption sites, which allowed the sorption and desorption when large amounts of addition P were applied.     

Risk assessment of ozone impact on the carbon absorption of Japanese representative conifers

A risk assessment of ozone (O₃) impact on the annual carbon absorption (ACA) of Japanese representative conifers was conducted based on the results of an experimental study, monitoring data of oxidant concentrations and vegetation surveys. The areas with high O₃-induced reduction in ACA did not necessarily correspond to the areas with relatively high O₃-exposure. Widespread distribution of O₃-sensitive tree species such as Pinus densiflora and Larix kaempferi, and high ACA were important factors that induced a high risk of O₃ impact on the ACA. Therefore, we concluded that not only the accumulated O₃-exposure but also the variety of tree habitat, the tree sensitivity to O₃ and the ACA among the tree species must be taken into account to assess the risk of O₃ impact on the ACA of Japanese conifers. The O₃-induced reduction in the total ACA of the three tree species in Japan was estimated to be 0.8%.     

Use of middle infrared radiation to estimate the leaf area index of a boreal forest

The leaf area index (LAI) of boreal forest can be estimated using reflected radiation recorded by satellite sensors. Measurements of visible and near infrared radiation are commonly used in the normalized difference vegetation index (NDVI) to estimate LAI. However, research, mainly in tropical forest, has demonstrated that LAI is related more closely to radiation of middle infrared wavelengths than of visible wavelengths. This paper derives a vegetation index, VI3, based on radiation from vegetation recorded at near and middle infrared wavelengths. For a boreal forest canopy, the relationship between VI3 and LAI was observed to be much stronger than that between NDVI and LAI. In addition, the LAI estimated using VI3 accounted for about 76% of the variation in field estimates of LAI, compared with about 46% when using the NDVI. We conclude that information provided by middle infrared radiation should be considered when estimating the leaf area index of boreal forest.     

Component carbon fluxes and their contribution to ecosystem carbon exchange in a pine forest: an assessment based on eddy covariance measurements and an integrated model

We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine forest (Pinus sylvestris L.) in eastern Finland (62 degrees 47' N, 30 degrees 58' E) over three climatically contrasting years (2000-2002). Eddy flux measurements showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m-2> year-1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss by respiration was 565, 629 and 640 g C m-2 year-1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and wood being 46-62, 27-44 and 9-10%, respectively. The wide range in daily net C uptake during the growing season was largely attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn, ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure deficit.     

全球森林管理的趋势及对碳储量的影响

全球森林日益受到土地利用变化、分散化、管理目标变化和退化的影响。运用管理强度描述全球森林动态变化趋势,并概述了与森林管理相关的全球碳库变化。讨论了对“管理”的不同解释,并强调了一些重要的核算和分析问题。全球森林面积自1990 年以来下降了3％,但全球各地人工林面积都有所增加,截止2010 年已占全球森林面积的近7％。由于人为因素造成的栖息地破碎和退化,使得占所有林地34％的原始森林面积正在下降,尤其是南美洲和非洲。同时,自然再生林面积也有所下降。由于管理强度的增加,1990 年以来,非施业林面积（通常被定义为缺乏人类管理计划或保护状态的土地）大幅度下降,截止2010 年仅占全球森林的21％,而用于水土保持、生物多样性保护和提供生态系统服务等非木质林产品用地面积大幅增加。从全球来看,木材生产自1990 年以来一直相对稳定,但非木质林产品用地面积越来越多,表明林业采伐面积占森林总面积的比例较小。根据管理森林和区域研究领域的发展趋势可知,历史上和现在的森林管理是当前碳储量的一个非常重要的决定因素。目前,已建成的森林抵消了来自使用化石燃料释放二氧化碳的约30％,而减少森林的砍伐可能会将陆地碳地面总吸收量从大约4.0 t 升至每年6.2 t。然而,研究结果表明,多样化使用森林土地可能对维持或提高目前的陆地碳汇有重大影响。未来,诸如大气二氧化碳的增加和气候变化等间接的人类影响,以及土地管理的直接影响和木材生物燃料的日益增长的需求,都将成为影响土地管理战略规划和森林生态系统全球碳循环的重要因素。