Soil carbon dynamics under young tropical secondary forests on former pastures—A case study from Panama

Secondary forests are gaining increased importance in tropical landscapes and have recently been reported to act as potential belowground carbon sinks. While economic interest in the management of secondary forests to mitigate carbon emissions is rising, the dynamics of soil carbon stocks under these ecosystems remain poorly understood. Recent studies report conflicting results concerning soil carbon trends as well as multiple confounding factors (e.g. soil type, topography and land-use history) affecting these trends. In this study, organic carbon stocks were measured in the mineral soil up to 20 cm depth of at 24 active pastures, 5-8-year-old, and 12-15-year-old secondary forest sites on former pastures. Additionally, we estimated carbon stocks under a 100-year-old secondary forest and compared them to those of nearby mature forests. Abiotic conditions in the study area were homogenous, enabling us to isolate the effect of land-use change on soil organic carbon stocks. Contrary to our expectations, soil carbon stocks in the top 10 cm did not change with young secondary forest development. Pasture soils stored 24.8 ± 2.9 Mg ha⁻¹ carbon (mean ± standard error) in the top 10 cm, and no accumulation of soil carbon was apparent during the first 15 years of secondary succession. Soil carbon stocks under 100-year-old secondary forests, averaging 43.0 ± 7.9 Mg ha⁻¹ (mean ± standard error), were clearly higher than those recorded at younger sites and approached levels of soil carbon stocks under mature forests. These data indicate that soil carbon stocks in this region of Panama are not affected by the land-use transition from pasture to young secondary regrowth. However, an increase of soil carbon storage might be possible over a longer period of time. Our results support trends observed in other tropical areas and highlight the importance of environmental conditions such as soil properties rather than land-use transitions on soil carbon dynamics. While our understanding of organic carbon dynamics in tropical soils remains limited, these results underscore the challenges of undertaking short-term reforestation projects with the expectation of increasing soil carbon sequestration.     

Rapid carbon accumulation within an unmanaged,mixed, temperate woodland

Forest carbon stocks have increased in both Europe and North America in recent decades. National forest inventories are often used to indicate recent carbon dynamics, but the data from unmanaged forests are often incomplete. Here we calculate changing biomass carbon stocks for a mixed, unmanaged British woodland with two different management histories: (1) older growth stands untouched since 1902 and (2) younger growth stands clear felled in 1943 but have developed naturally since. Transects in the older growth have been monitored since 1945 and the younger growth since 1977. Separate estimates of tree carbon (C), soil C and dead wood C were obtained to verify how C is apportioned in these stands. Tree biomass C stocks had approximately doubled in the older growth stands since 1945 and 60% of C was stored in tree biomass, 38% was stored in soil and 2% stored in coarse woody debris. This study suggests that natural older growth stands are storing more C than typical managed forests, with tree biomass the most important compartment for C stores. If management is to be shifted from biomass production to increased C stores, due consideration should be given to the role of unmanaged, older growth forests.     

An Exploratory,Post-Harvest Comparison of Ecological and Economic Characteristics of Forest Stewardship Council Certified and Uncertified Northern Hardwood Stands∗

ABSTRACT

As more forest entities worldwide consider pursuing Forest Stewardship Council (FSC) certification, a critical question remains on whether stand-level management impacts differ between certified and uncertified forests. To begin to answer this question, we measured forest structure on three FSC-certified stands, three uncertified stands, and six adjacent unharvested reference stands (12 stands total) composed primarily of sugar maple (Acer saccharum) on non-industrial private properties in central Vermont, USA. The certified and uncertified partial harvests reduced total tree biomass and live tree carbon storage by one-third compared to reconstructed pre-harvest conditions. Both treatments also contained significantly lower densities of saplings and some mid-size trees compared to non-harvested references due to similar impacts from harvesting. The net present value of merchantable sugar maple over 10 year projections was consistently lower on certified than uncertified stands, but this difference was insignificant at discount rates from 4–8%. The certified stands contained significantly greater total residual volumes of coarse woody debris (standing and downed) than uncertified stands, although the debris was smaller than that found in unmanaged mature forests. Overall, our data suggest that FSC-certified harvested stands in northern hardwood forests have similar sugar maple timber value, aboveground live tree carbon storage value, similar live tree structure, and greater residual coarse woody debris than uncertified harvested stands.     

Ecosystem carbon storage and partitioning in a tropical seasonal forest in Southwestern China

Tropical forests play an important role in the global carbon cycle. Despite an increasing number of studies have addressed carbon storage in tropical forests, the regional variation in such storage remains poorly understood. Uncertainty about how much carbon is stored in tropical forests is an important limitation for regional-scale estimates of carbon fluxes and improving these estimates requires extensive field studies of both above- and belowground stocks. In order to assess the carbon pools of a tropical seasonal forest in Asia, total ecosystem carbon storage was investigated in Xishuangbanna, SW China. Averaged across three 1 ha plots, the total carbon stock of the forest ecosystem was 303 t C ha⁻¹. Living tree carbon stocks (both above- and belowground) ranged from 163 to 258 t C ha⁻¹. The aboveground biomass C pool is comparable to the Dipterocarp forests in Sumatra but lower than those in Malaysia. The variation of C storage in the tree layer among different plots was mainly due to different densities of large trees (DBH > 70 cm). The contributions of the shrub layer, herb layer, woody lianas, and fine litter each accounted for 1–2 t C ha⁻¹ to the total carbon stock. The mineral soil C pools (top 100 cm) ranged from 84 to 102 t C ha⁻¹ and the C in woody debris from 5.6 to 12.5 t C ha⁻¹, representing the second and third largest C component in this ecosystem. Our results reveal that a high percentage (70%) of C is stored in biomass and less in soil in this tropical seasonal forest. This study provides an accurate estimate of the carbon pool and the partitioning of C among major components in tropical seasonal rain forest of northern tropical Asia. Results from this study will enhance our ability to evaluate the role of these forests in regional C cycles and have great implications for conservation planning.     

Biomass and carbon pools of disturbed riparian forests

Quantification of carbon pools as affected by forest age/development can facilitate riparian restoration and increase awareness of the potential for forests to sequester global carbon. Riparian forest biomass and carbon pools were quantified for four riparian forests representing different seral stages in the South Carolina Upper Coastal Plain. Three of the riparian forests were recovering from disturbance (thermal pollution), whereas the fourth represents a mature, relatively undisturbed riparian forest. Above and belowground carbon pools were determined from linear transects established perpendicular to the main stream channels and spanning the width of the riparian area. The objective of this study was to quantify the biomass and carbon pools in severely disturbed, early successional bottomland hardwood riparian forests and to compare these values to those of a less disturbed, mature riparian forest.

Aboveground biomass in all four riparian forests increased during the 2.5-year investigation period. The total carbon pool in these South Carolina Coastal Plain riparian forests increased with forest age/development due to greater tree and soil carbon pools. The mature riparian forest stored approximately four times more carbon than the younger stands. The importance of the herbaceous biomass layer and carbon pool declined relative to total aboveground biomass with increasing forest age. As stands grew older fine root biomass increased, but an inverse relationship existed between percentages of fine root biomass to total biomass. The root carbon pool increased with forest age/development due to a combination of greater fine root biomass and higher root percent carbon.

Aboveground net primary production (NPP) in young riparian forests rapidly approached and exceeded NPP of the more mature riparian forest. As a woody overstory became established (after 8–10 years) annual litterfall rate as a function of NPP was independent of forest age and litterfall amount in the young riparian forests was comparable to mature riparian forests. Biomass in the riparian forest floor and carbon pool declined with increasing riparian forest development. Woody debris in these riparian forests comprised a relatively small carbon pool. An understanding of bottomland hardwood riparian forest carbon pools at different stages of succession allows us to assess how time since disturbance influences these pools, leading to a better understanding of the recovery processes.     

Carbon stocks and productivity of mangrove forests in Tanzania

Mangroves offer a number of ecosystem goods and services, including carbon (C) storage. As a carbon pool, mangroves could be a source of CO₂ emissions as a result of human activities such as deforestation and forest degradation. Conversely, mangroves may act as a CO₂ sink through biomass accumulation. This study aimed to determine carbon stocks, harvest removals and productivity of mangrove forests of mainland Tanzania. Nine species were recorded in mainland Tanzania, among them Avicennia marina (Forssk.) Vierh., Rhizophora mucronata Lam. (31%) and Ceriops tagal (Perr.) C.B.Rob. (20%) were dominant. The aboveground, dead wood, belowground and total carbon were 33.5 ± 5.8 Mg C ha^?1, 1.2 ± 1.1 (2% of total carbon), 30.0 ± 4.5 Mg C ha^?1 (46% of total carbon) and 64.7 ± 8.4 Mg C ha^?1 at 95% confidence level, respectively. Carbon harvest removals accounted for loss of about 4% of standing total carbon stocks annually. Results on the productivity of mangrove forests (using data from permanent sample plots monitored for four years [1995-1998]) showed an overall carbon increment of 5.6 Mg C ha^?1 y^?1 (aboveground carbon), 4.1 C ha^?1 y^?1 (belowground carbon) and 9.7 C ha^?1 y^?1 (total carbon) at 23%, 32% and 27% levels of uncertainty, respectively. Both natural death and tree cutting/harvest removals resulted in significant decline of annual carbon productivity. Findings from this study demonstrate that mangroves store large quantities of carbon and are more productive than other dominant forest formations in southern Africa. Both their deforestation and forest degradation, therefore, is likely to contribute to large quantities of emission and loss of carbon sink functionality. Therefore, mangroves need to be managed sustainably.     

Carbon stocks and soil respiration rates during deforestation, grassland use and subsequent Norway spruce afforestation in the Southern Alps, Italy

Changes in carbon stocks during deforestation, reforestation and afforestation play an important role in the global carbon cycle. Cultivation of forest lands leads to substantial losses in both biomass and soil carbon, whereas forest regrowth is considered to be a significant carbon sink. We examined below- and aboveground carbon stocks along a chronosequence of Norway spruce (Picea abies (L.) Karst.) stands (0-62 years old) regenerating on abandoned meadows in the Southern Alps. A 130-year-old mixed coniferous Norway spruce-white fir (Abies alba Mill.) forest, managed by selection cutting, was used as an undisturbed control. Deforestation about 260 years ago led to carbon losses of 53 Mg C ha(-1) from the organic layer and 12 Mg C ha(-1) from the upper mineral horizons (Ah, E). During the next 200 years of grassland use, the new Ah horizon sequestered 29 Mg C ha(-1). After the abandonment of these meadows, carbon stocks in tree stems increased exponentially during natural forest succession, levelling off at about 190 Mg C ha(-1) in the 62-year-old Norway spruce and the 130-year-old Norway spruce-white fir stands. In contrast, carbon stocks in the organic soil layer increased linearly with stand age. During the first 62 years, carbon accumulated at a rate of 0.36 Mg C ha(-1) year(-1) in the organic soil layer. No clear trend with stand age was observed for the carbon stocks in the Ah horizon. Soil respiration rates were similar for all forest stands independently of organic layer thickness or carbon stocks, but the highest rates were observed in the cultivated meadow. Thus, increasing litter inputs by forest vegetation compared with the meadow, and constantly low decomposition rates of coniferous litter were probably responsible for continuous soil carbon sequestration during forest succession. Carbon accumulation in woody biomass seemed to slow down after 60 to 80 years, but continued in the organic soil layer. We conclude that, under present climatic conditions, forest soils act as more persistent carbon sinks than vegetation that will be harvested, releasing the carbon sequestered during tree growth.     

Soil organic carbon stock in the Belgian Ardennes as affected by afforestation and deforestation from 1868 to 2005

The effects of historical land use changes on the global C cycle have mainly been studied by means of bookkeeping models. Here, we investigate with such models the impact of afforestation and deforestation on soil organic carbon (SOC) stocks. This approach, using field-based estimates of the response of SOC upon land use changes, is applied to a pilot area in the Belgian Ardennes over one and a half century (1868–2005). After a small initial decline during the 1868–1888 period due to deforestation for agricultural use, mean SOC stocks increased steadily up to 1990, due essentially to the conversion of deciduous to coniferous forests (in the study area, deciduous forests stored less SOC than coniferous) and the reclamation of heathland, which occurred both at the turn of the 19th and 20th centuries. Simulations showed that SOC stocks decreased recently (1990–2005) because of the slow down of sequestration in coniferous forests and a reversion of some of the coniferous plantations to deciduous forests. Over the entire period, afforestation resulted in a net sequestration of carbon (0.16 t C ha⁻¹ year⁻¹). Monte Carlo simulations demonstrated that the model was highly sensitive to its inputs (initial SOC stocks for each land use) both in term of predicted SOC stocks and rates of SOC stocks change. However, the sensitivity of the model was not large enough to revert the main trends of SOC changes observed. Compared to the amount of carbon sequestered in the biomass, the contribution of soils to the C sink in forest is small. Despite several sources of errors, a detailed reconstruction of land use changes combined with realistic SOC response curves upon land use conversion are required to be able to quantify the contribution of soils to terrestrial carbon fluxes.     

森林保护碳汇项目方法学研究

森林保护碳汇项目是林业行业减排增汇项目的重要组成,因其多重效益已被纳入应对气候变化的行动倡议和碳交易市场领域。文中基于我国温室气体自愿减排市场的需求,从计量碳库的选择、基线情景的确定、额外性论证及碳储量计量等方面研究出适合我国的森林保护碳汇项目方法学,提出将木质林产品、地上生物量、枯死木及枯落物作为计量碳库并采用蓄积法、生物量扩展因子法及衰减函数法计算碳储量的新碳汇项目方法学,以期为我国森林保护碳汇项目开发及全国碳交易市场建设提供理论参考。     

Do thinnings influence biomass and soil carbon stocks in Mediterranean maritime pinewoods?

The effects of silvicultural treatments on carbon sequestration are poorly understood, particularly in areas like the Mediterranean where soil fertility is low and climatic conditions can be harsh. In order to improve our understanding of these effects, a long-term thinning experiment in a stand of Mediterranean maritime pine (Pinus pinaster Ait.) was studied to identify the effects of thinning on soil carbon (forest floor and mineral soil), above and belowground biomass and fine and coarse woody debris. The study site was a 59-year-old pinewood, where three thinnings of differing intensities were applied: unthinned (control), moderate thinning and heavy thinning. The three thinning interventions (for the managed plots) involved whole-tree harvesting. The results revealed no differences between the different thinning treatments as regards the total soil carbon pool (forest floor + mineral soil). However, differences were detected in the case of living aboveground biomass and total dead wood debris between unthinned and thinned plots; the former containing larger amounts of carbon. The total carbon present in the unthinned plots was 317 Mg ha^?1; in the moderately thinned plots, it was 256 Mg ha^?1 and in the case of heavily thinned plots, 234 Mg ha^?1. Quantification of these carbon compartments can be used as an indicator of total carbon stocks under different forest management regimes and thus identify the most appropriate to mitigate the effects of global change. Our results indicated that thinning do not alter the total soil carbon content at medium term, suggesting the sustainability of these silvicultural treatments.     

Stocks and dynamics of soil organic carbon and coarse woody debris in three managed and unmanaged temperate forests

The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha^?1 in the unmanaged spruce forest and 23 and 30 Mg C ha^?1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha^?1) and greater in the spruce forest (36 Mg C ha^?1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O _e and O _a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.     

Description of a new procedure to estimate the carbon stocks of all forest pools and impact assessment of methodological choices on the estimates

Forest ecosystems play a major role in atmospheric carbon sequestration and emission. Comparable organic carbon stock estimates at temporal and spatial scales for all forest pools are needed for scientific investigations and political purposes. Therefore, we developed a new carbon stock (CS) estimation procedure that combines forest inventory and soil and litter geodatabases at a regional scale (southern Belgium). This procedure can be implemented in other regions and countries on condition that available external carbon soil and litter data can be linked to forest inventory plots. The presented procedure includes a specific CS estimation method for each of the following forest pools and subpools (in brackets): living biomass (aboveground and belowground), deadwood (dead trees and snags, coarse woody debris and stumps), litter, and soil. The total CS of the forest was estimated at 86 Tg (185 Mg ha^?1). Soil up to 0.2 m depth, living biomass, litter, and deadwood CSs account, respectively, for 48, 47, 4, and 1 % of the total CS. The analysis of the CS variation within the pools across ecoregions and forest types revealed in particular that: (1) the living biomass CS of broadleaved forests exceeds that of coniferous forests, (2) the soil and litter CSs of coniferous forest exceed those of broadleaved forests, and (3) beech stands come at the top in carbon stocking capacity. Because our estimates differ sometimes significantly from the previous studies, we compared different methods and their impacts on the estimates. We demonstrated that estimates may vary highly, from ?16 to +12 %, depending on the selected methods. Methodological choices are thus essential especially for estimating CO₂ fluxes by the stock change approach. The sources of error and the accuracy of the estimates were discussed extensively.     

Carbon uptake by secondary forests in Brazilian Amazonia

Estimating the contribution of deforestation to greenhouse gas emissions requires calculations of the uptake of carbon by the vegetation that replaces the forest, as well as the emissions from burning and decay of forest biomass and from altered emissions and uptakes by the soil. The role of regeneration in offsetting emissions from deforestation in the Brazilian Legal Amazon has sometimes been exaggerated. Unlike many other tropical areas, cattle pasture (rather than shifting cultivation) usually replaces forest in Brazilian Amazonia. Degraded cattle pastures regenerate secondary forests more slowly than do fallows in shifting cultivation systems, leading to lower uptake of carbon. The calculations presented here indicate that in 1990 the 410 × 10³ km² deforested landscape was taking up 29 × 10⁶ t of carbon (C) annually (0.7 t C ha⁻¹ year⁻¹). This does not include the emissions from clearing of secondary forests, which in 1990 released an estimated 27 × 10⁶ t C, almost completely offsetting the uptake from the landscape. Were the present land-use change processes to continue, carbon uptake would rise to 365 × 10⁶ t annually (0.9 t C ha⁻¹ year⁻¹) in 2090 in the 3.9 × 10⁶ km⁶ area that would have been deforested by that year. The 1990 rate of emissions from deforestation in the region greatly exceeded the uptake from regrowth of replacement vegetation.     

国外森林碳融资模式比较及其对我国的启示

林业在应对气候变化方面的作用和地位越来越为各国和国际社会所重视。与其他缓解气候变化的选择相比, 森林碳减排的成本相对较低。但是, 资金缺口目前已成为REDD和REDD+面临的主要挑战之一, 也成为各国政府、学术界和企业界共同关注的焦点。文中对国外森林碳融资模式进行归纳分析, 指出其发展趋势, 提出国外实践对我国发展森林碳融资的借鉴意义。     

Effects of harvest management practices on forest biomass and soil carbon in eucalypt forests in New South Wales,Australia: Simulations with the forest succession model LINKAGES

Understanding long-term changes in forest ecosystem carbon stocks under forest management practices such as timber harvesting is important for assessing the contribution of forests to the global carbon cycle. Harvesting effects are complicated by the amount, type, and condition of residue left on-site, the decomposition rate of this residue, the incorporation of residue into soil organic matter and the rate of new detritus input to the forest floor from regrowing vegetation. In an attempt to address these complexities, the forest succession model LINKAGES was used to assess the production of aboveground biomass, detritus, and soil carbon stocks in native Eucalyptus forests as influenced by five harvest management practices in New South Wales, Australia. The original decomposition sub-routines of LINKAGES were modified by adding components of the Rothamsted (RothC) soil organic matter turnover model. Simulation results using the new model were compared to data from long-term forest inventory plots. Good agreement was observed between simulated and measured above-ground biomass, but mixed results were obtained for basal area. Harvesting operations examined included removing trees for quota sawlogs (QSL, DBH >80 cm), integrated sawlogs (ISL, DBH >20 cm) and whole-tree harvesting in integrated sawlogs (WTH). We also examined the impact of different cutting cycles (20, 50 or 80 years) and intensities (removing 20, 50 or 80 m³). Generally medium and high intensities of shorter cutting cycles in sawlog harvesting systems produced considerably higher soil carbon values compared to no harvesting. On average, soil carbon was 2–9% lower in whole-tree harvest simulations whereas in sawlog harvest simulations soil carbon was 5–17% higher than in no harvesting.     

Carbon stocks in coffee agroforests and mixed dry tropical forests in the western highlands of Guatemala

Tree removal in Latin American coffee agroforestry systems has been widespread due to complex and interacting factors that include fluctuating international markets, government-supported agricultural policies, and climate change. Despite shade tree removal and land conversion risks, there is currently no widespread policy incentive encouraging the maintenance of shade trees for the benefit of carbon sequestration. In facilitation of such incentives, an understanding of the capacity of coffee agroforests to store carbon relative to tropical forests must be developed. Drawing on ecological inventories conducted in 2007 and 2010 in the Lake Atitlán region of Guatemala, this research examines the carbon pools of smallholder coffee agroforests (CAFs) as they compare to a mixed dry forest (MDF) system. Data from 61 plots, covering a total area of 2.24 ha, was used to assess the aboveground, coarse root, and soil carbon reservoirs of the two land-use systems. Results of this research demonstrate the total carbon stocks of CAFs to range from 74.0 to 259.0 Megagrams (Mg)?C ha^?1 with a mean of 127.6?±?6.6 (SE)?Mg?C ha^?1. The average carbon stocks of CAFs was significantly lower than estimated for the MDF (198.7?±?32.1?Mg?C?ha^?1); however, individual tree and soil pools were not significantly different suggesting that agroforest shade trees play an important role in facilitating carbon sequestration and soil conservation. This research demonstrates the need for conservation-based initiatives which recognize the carbon sequestration benefits of coffee agroforests alongside natural forest systems.     

Carbon pools and temporal dynamics along a rotation period in Quercus dominated high forest and coppice with standards stands

Carbon pools in two Quercus petraea (sessile oak) dominated chronosequences under different forest management (high forest and coppice with standards) were investigated. The objective was to study temporal carbon dynamics, in particular carbon sequestration in the soil and woody biomass production, in common forest management systems in eastern Austria along with stand development. The chronosequence approach was used to substitute time-for-space to enable coverage of a full rotation period in each system. Carbon content was determined in the following compartments: aboveground biomass, litter, soil to a depth of 50 cm, living root biomass and decomposing residues in the mineral soil horizons. Biomass carbon pools, except fine roots and residues, were estimated using species-specific allometric functions. Total carbon pools were on average 143 Mg ha⁻¹ in the high forest stand (HF) and 213 Mg ha⁻¹ in the coppice with standards stand (CS). The mean share of the total organic carbon pool (TOC) which is soil organic carbon (SOC) differs only marginally between HF (43.4%) and CS (42.1%), indicating the dominance of site factors, particularly climate, in controlling this ratio. While there was no significant change in O-layer and SOC stores over stand development, we found clear relationships between living biomass (aboveground and belowground) pools and C:N ratio in topsoil horizons with stand age. SOC pools seem to be very stable and an impact of silvicultural interventions was not detected with the applied method. Rapid decomposition and mineralization of litter, indicated by low O-horizon pools with wide C:N ratios of residual woody debris at the end of the vegetation period, suggests high rates of turnover in this fraction. CS, in contrast to HF benefits from rapid resprouting after coppicing and hence seems less vulnerable to conditions of low rainfall and drying topsoil.     

湖南主要森林类型碳汇功能及其经济价值评价

利用湖南省森林资源主要数据汇编(1999—2003年),依据不同森林类型生物量与蓄积量之间的回归方程,对湖南省几种主要森林类型的生物量和碳贮量进行了推算,分析了不同林龄结构的碳密度以及天然林与人工林的碳贮量,并对整个湖南省的森林经济价值进行估算。结果表明:湖南省主要森林类型的总碳贮量为94.935 Tgc,碳汇总经济价值为70 723.26万元,固定CO2的经济效益达259 554.36万元。阔叶树的碳汇能力最强,其次是杉木和马尾松;湖南省的天然林和人工林的碳贮量相差不大,不同龄组碳密度高低排序的基本规律是:过熟林>成熟林>近熟林>中龄林>幼龄林;而中龄林的碳贮量最多,过熟林碳贮量最少。     

Temporal dynamics and spatial variations of forest vegetation carbon stock in Liaoning Province,China

There are many uncertainties in the estimation of forest car- bon sequestration in China, especially in Liaoning Province where vari- ous forest inventory data have not been fully utilized. By using forest inventory data, we estimated forest vegetation carbon stock of Liaoning Province between 1993 and 2005. Results showed that forest biomass carbon stock increased from 68.91 Tg C in 1993 to 97.51 Tg C in 2005, whereas mean carbon density increased from 18.48 Mg·ha -1 C to 22.33 Mg·ha -1 C. The carbon stora...     

Forest structure and live aboveground biomass variation along an elevational gradient of tropical Atlantic moist forest (Brazil)

Live aboveground biomass (AGB) is an important source of uncertainty in the carbon balance from the tropical regions in part due scarcity of reliable estimates of live AGB and its variation across landscapes and forest types. Studies of forest structure and biomass stocks of Neotropical forests are biased toward Amazonian and Central American sites. In particular, standardized estimates of aboveground biomass stocks for the Brazilian Atlantic forest are rarely available. Notwithstanding the role of environmental variables that control the distribution and abundance of biomass in tropical lowland forests has been the subject of considerable research, the effect of short, steep elevational gradients on tropical forest structure and carbon dynamics is not well known. In order to evaluate forest structure and live AGB variation along an elevational gradient (0–1100 m a.s.l.) of coastal Atlantic Forest in SE Brazil, we carried out a standard census of woody stems ≥4.8 cm dbh in 13 1-ha permanent plots established on four different sites in 2006–2007. Live AGB ranged from 166.3 Mg ha⁻¹ (bootstrapped 95% CI: 144.4,187.0) to 283.2 Mg ha⁻¹ (bootstrapped 95% CI: 253.0,325.2) and increased with elevation. We found that local-scale topographic variation associated with elevation influences the distribution of trees >50 cm dbh and total live AGB. Across all elevations, we found more stems (64–75%) with limited crown illumination but the largest proportion of the live AGB (68–85%) was stored in stems with highly illuminated or fully exposed crowns. Topography, disturbance and associated changes in light and nutrient supply probably control biomass distribution along this short but representative elevational gradient. Our findings also showed that intact Atlantic forest sites stored substantial amounts of carbon aboveground. The live tree AGB of the stands was found to be lower than Central Amazonian forests, but within the range of Neotropical forests, in particular when compared to Central American forests. Our comparative data suggests that differences in live tree AGB among Neotropical forests are probably related to the heterogeneous distribution of large and medium-sized diameter trees within forests and how the live biomass is partitioned among those size classes, in accordance with general trends found by previous studies. In addition, the elevational variation in live AGB stocks suggests a large spatial variability over coastal Atlantic forests in Brazil, clearly indicating that it is important to consider regional differences in biomass stocks for evaluating the role of this threatened tropical biome in the global carbon cycle.