Ecosystem Carbon Sequestration Research Articles

Ecosystem carbon stocks of mangrove forest in Yingluo Bay, Guangdong Province of South China

Mangrove ecosystems could play important ecological, social and economic roles in addressing the mitigation of climate change through reduced deforestation. The present study aimed to estimate ecosystem carbon stocks (carbon accumulated in both biomass and soil) across the tidal gradient of mangroves in Yingluo Bay, Guangdong Province of South China. The ecosystem carbon storage, as well as vegetation biomass and soil organic carbon (SOC) storage, increased along with the tidal gradient of mangrove forests from the low intertidal zone to the high intertidal zone. The ecosystem carbon storage of the Avicennia marina, Sonneratia apetala, Aegiceras corniculatum+Kandelia obovata, Rhizophora stylosa and Bruguiera gymnorrhiza stands were 212.88t/ha, 262.03t/ha, 323.57t/ha, 443.13t/ha and 376.80t/ha, respectively and their vegetation carbon pools accounted for 11.65%, 29.79%, 19.19%, 37.76% and 25.94% of ecosystem carbon storage, respectively. Compared to the mangrove ecosystem, there was a much lower ecosystem carbon stock (97.32t/ha) at the bare mud flat. The relatively high vegetation biomass, which coupled with carbon-rich soils, resulted in the presence of larger ecosystem carbon stocks compared to other subtropical forests in the same latitude zone. A significant positive correlation was found between vegetation biomass and soil organic carbon concentration of the upper 0–50cm layers. This may indicate that the increase of vegetation biomass will raise the mangrove-derived SOC in the soil (especially the 0–50cm soil layers). Reforestation by using mangrove forests is an important way to increase ecosystem carbon sequestration in coastal areas.

The Environmental Price Tag on a Ton of Mountaintop Removal Coal

While several thousand square kilometers of land area have been subject to surface mining in the Central Appalachians, no reliable estimate exists for how much coal is produced per unit landscape disturbance. We provide this estimate using regional satellite-derived mine delineations and historical county-level coal production data for the period 1985–2005, and further relate the aerial extent of mining disturbance to stream impairment and loss of ecosystem carbon sequestration potential. To meet current US coal demands, an area the size of Washington DC would need to be mined every 81 days. A one-year supply of coal would result in ∼2,300 km of stream impairment and a loss of ecosystem carbon sequestration capacity comparable to the global warming potential of >33,000 US homes. For the first time, the environmental impacts of surface coal mining can be directly scaled with coal production rates.

Aircraft Regional-Scale Flux Measurements over Complex Landscapes of Mangroves, Desert, and Marine Ecosystems of Magdalena Bay, Mexico

AbstractNatural ecosystems are rarely structurally simple or functionally homogeneous. This is true for the complex coastal region of Magdalena Bay, Baja California Sur, Mexico, where the spatial variability in ecosystem fluxes from the Pacific coastal ocean, eutrophic lagoon, mangroves, and desert were studied. The Sky Arrow 650TCN environmental research aircraft proved to be an effective tool in characterizing land–atmosphere fluxes of energy, CO2, and water vapor across a heterogeneous landscape at the scale of 1 km. The aircraft was capable of discriminating fluxes from all ecosystem types, as well as between nearshore and coastal areas a few kilometers distant. Aircraft-derived average midday CO2 fluxes from the desert showed a slight uptake of −1.32 μmol CO2 m−2 s−1, the coastal ocean also showed an uptake of −3.48 μmol CO2 m−2 s−1, and the lagoon mangroves showed the highest uptake of −8.11 μmol CO2 m−2 s−1. Additional simultaneous measurements of the normalized difference vegetation index (NDVI) allowed simple linear modeling of CO2 flux as a function of NDVI for the mangroves of the Magdalena Bay region. Aircraft approaches can, therefore, be instrumental in determining regional CO2 fluxes and can be pivotal in calculating and verifying ecosystem carbon sequestration regionally when coupled with satellite-derived products and ecosystem models.

Biomasa vegetal en zonas degradadas por minería en un bosque pluvial tropical del Chocó Biogeográfico

The aim of this work was to study the changes of plant biomass in primary succession after a forest mining in the municipalities of Certegui and Union Panamericana, Department of Choco, Colombia. For which, was evaluated by the method of chronosequence, aboveground and belowground biomass of five zones with different periods of time (between 1.5 and 6 years) after mining. Equations were used to calculate the carbon biomass of the plots and used a growth model of von Bertalanffy model the change in plant biomass over time. Generally found in areas with degraded by mining various stages regeneration occurred biomass values between 104.83 g m 2 and 4115.46 g m 2 (equivalent to between 1.05 t ha -1 and 41.15 t ha -1 ). Plant biomass increased significantly over time. The modeling of plant biomass versus time showed that after the disturbances caused by mining colonizing vegetation of these soils takes over 1000 years to reach a similar average biomass than in primary forests of the region. In terms of global climate change is essential to the recovery of areas degraded by mining in the region as a strategy to increase ecosystem carbon sequestration and mitigate environmental problems.

Carbon benefits from protected areas in the conterminous United States.

BackgroundConversion of forests to other land cover or land use releases the carbon stored in the forests and reduces carbon sequestration potential of the land. The rate of forest conversion could be reduced by establishing protected areas for biological diversity and other conservation goals. The purpose of this study is to quantify the efficiency and potential of forest land protection for mitigating GHG emissions.ResultsThe analysis of related national-level datasets shows that during the period of 1992–2001 net forest losses in protected areas were small as compared to those in unprotected areas: -0.74% and −4.07%, respectively. If forest loss rates in protected and unprotected area had been similar, then forest losses in the protected forestlands would be larger by 870 km2/yr forests, that corresponds to release of 7 Tg C/yr (1 Tg=1012 g). Conversely, and continuing to assume no leakage effects or interactions of prices and harvest levels, about 1,200 km2/yr forests could have remained forest during the period of 1992–2001 if net area loss rate in the forestland outside protected areas was reduced by 20%. Not counting carbon in harvested wood products, this is equivalent to reducing fossil-fuel based carbon emissions by 10 Tg C/yr during this period. The South and West had much higher potentials to mitigate GHG emission from reducing loss rates in unprotected forests than that of North region. Spatially, rates of forest loss were higher across the coastal states in the southeastern US than would be expected from their population change, while interior states in the northern US experienced less forest area loss than would have been expected given their demographic characteristics.ConclusionsThe estimated carbon benefit from the reduced forest loss based on current protected areas is 7 Tg C/yr, equivalent to the average carbon benefit per year for a previously proposed ten-year $110 million per year tree planting program scenario in the US. If there had been a program that could have reduced forest area loss by 20% in unprotected forestlands during 1992–2001, collectively the benefits from reduced forest loss would be equal to 9.4% of current net forest ecosystem carbon sequestration in the conterminous US.

Assessing net carbon sequestration on urban and community forests of northern New England, USA

Urban and community forests play an important role in the overall carbon budget of the USA. Accurately quantifying carbon sequestration by these forests can provide insight for strategic planning to mitigate greenhouse gas effects on climate change. This study provides a new methodology to estimate net forest carbon sequestration (FCS) in urban and community lands of northern New England using ground based forest growth rates, housing density data, satellite derived land cover and tree canopy cover maps at the county level. We estimated that the region's urban and community forests sequestered 603,200tC/yr ($38.7million/yr value), contributing 8.2% of regional net forest ecosystem carbon sequestration. The contributions at the state level varied from 2.3% in Vermont to 16.6% in New Hampshire with substantial variation at the county level up to 73.3%. Spatially, contribution rates from urban and community forests at the county level were much higher and concentrated in southeast portion of NH and southwest portion of ME along the coast, and decreased toward inland areas. Our estimated net FCS compared reasonably with gross FCS in the region reported by a previous study. On average, the net FCS was 34.2% lower (varying from 41.9% lower in Vermont to 28.1% lower in Maine) than the corresponding gross FCS mainly because of a lower regional average net growth rate used in this study, compared to the national average gross carbon sequestration rate used in the previous study.

A tool for estimating impacts of woody encroachment in arid grasslands: Allometric equations for biomass, carbon and nitrogen content in Prosopis velutina

Regression equations were developed to estimate above ground biomass and carbon and nitrogen mass of foliage and stem size fractions from plant size dimensions (basal diameter, canopy area, height, canopy volume) for a tall shrub species (Prosopis velutina) that has increased in abundance in arid and semi-arid grasslands in the southwestern United States and northwestern Mexico. Regression equations were also developed to describe relationships among the dimensions of plant size. All equations were significant (p < 0.001); and all but two had r2 values >0.72. In addition to species-specific information, we found support for the global patterns of foliar biomass increasing to the ¾ power of stem biomass and height increasing to the ½ power of stem diameter. We provide a comprehensive report of all equations, which can support a variety of in situ (ground-based), modeling, and remote-sensing objectives related to quantifying changes in ecosystem function and carbon sequestration accompanying changes in woody plant abundance. We advocate that comprehensive reporting should become more common for arid and semi-arid woody species in order to support a broad spectrum of users while laying the foundation for the development of global generalizations similar to those available for forest trees.

Restoring ecosystem carbon sequestration through afforestation: A sub-tropic restoration case study

The long-term Forest Restoration Experimental Project (FREP) was established in 1991 on a sub-tropical, barren, degraded, red soil with a rolling terrain located in Taihe County, Jianxi province, China. The objective of the FREP was to evaluate the effects of restoration, through afforestation of various local climax species, on ecological functions to provide guidance for future restoration projects on severely deteriorated landscapes, which are very common in southern China. In this study, we selected five restoration forests: Chinese sweetgum (Liquidamber formosana), schima (Schima superb), masson’s pine (Pinus massoniana), slash pine (Pinus elliottii), Chinese sweetgum×slash pine mixtures, and one experimental control (natural recovery) to evaluate the differences in carbon storage and pool structures, including above- and below-ground carbon pools, forest floor litter, woody debris, and soil organic carbon (SOC). A similar assessment was also conducted on the species functional groups (coniferous forest, broad-leaved forest, and mixed-species forest – broad-leaved×coniferous species mixture) based on groupings of studied species. We also evaluated the recovery trajectory of FREP’s evergreen broad-leaved forest by comparing it with local ecosystems.Over the 19-year study period, the Total Ecosystem Carbon (TEC) stocks in the five restoration types were significantly higher than that in the control sites, but there were no significant differences in the TEC stock among the restoration types. The TEC was 119MgCha−1 for Chinese sweetgum, 118MgCha−1 for schima, 105MgCha−1 for masson’s pine, 104MgCha−1 for slash pine, and 124MgCha−1 for the mixture. However, there was a significant variation in the carbon pool structure among restoration functional groups. The SOC pool sizes of broad-leaved and mixed-species forest were 25% and 16% significantly higher than the coniferous forest, respectively. This difference may be explained by the recovery trajectory, which suggests that the evergreen forest (schima) in FREP is still in the early developmental stage, and its projected rate of growth is much slower than the average growth rate in the region. This study clearly demonstrated that active restoration can enhance ecosystem carbon sequestration. Clearly, a long-term monitoring program is critical for obtaining more information that will enable us to extrapolate our findings for broader restoration plans and to increase the carbon sequestration strength of restored forests.

Interannual and spatial impacts of phenological transitions, growing season length, and spring and autumn temperatures on carbon sequestration: A North America flux data synthesis

Understanding feedbacks of ecosystem carbon sequestration to climate change is an urgent step in developing future ecosystem models. Using 187 site-years of flux data observed at 24 sites covering three plant functional types (i.e. evergreen forests (EF), deciduous forests (DF) and non-forest ecosystems (NF) (e.g., crop, grassland, wetland)) in North America, we present an analysis of both interannual and spatial relationships between annual net ecosystem production (NEP) and phenological indicators, including the flux-based carbon uptake period (CUP) and its transitions, degree-day-derived growing season length (GSL), and spring and autumn temperatures. Diverse responses were acquired between annul NEP and these indicators across PFTs. Forest ecosystems showed consistent patterns and sensitivities in the responses of annual NEP to CUP and its transitions both interannually and spatially. The NF ecosystems, on the contrary, exhibited different trends between interannual and spatial relationships. The impact of CUP onset on annual NEP in NF ecosystems was interannually negative but spatially positive. Generally, the GSL was observed to be a likely good indicator of annual NEP for all PFTs both interannually and spatially, although with relatively moderate correlations in NF sites. Both spring and autumn temperatures were positively correlated with annual NEP across sites while this potential was greatly reduced temporally with only negative impacts of autumn temperature on annual NEP in DF sites. Our analysis showed that DF ecosystems have the highest efficiency in accumulating NEP from warmer spring temperature and prolonged GSL, suggesting that future climate warming will favor deciduous species over evergreen species, and supporting the earlier observation that ecosystems with the greatest net carbon uptake have the longest GSL.

Radiative forcing of natural forest disturbances

AbstractForest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate‐regulating properties of forests. Using both tower‐based and remotely sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO2 forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO2 forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane‐damaged mangrove forest in the subtropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will probably increase in the future under climate change, making it imperative to represent these processes accurately in global climate models.

Southern Ocean natural iron fertilization

Modeling and Synthesis of Southern Ocean Natural Iron Fertilization; Woods Hole, Massachusetts, 27–29 June 2011; For many years a major paradox in ocean science was the existence of regions where the major nutrients are present in nonlimiting concentrations yet phytoplankton biomass is low. Pioneering experiments in the 1990s firmly established that the likely cause of this high‐nutrient, low‐chlorophyll condition is a deficit of iron relative to other nutrients. Iron is required for numerous processes within the cell, including photosynthesis, respiration, and nutrient uptake, yet because of its chemical properties, in seawater it is present at vanishingly small concentration levels. Elucidating the role of iron in governing ecosystem functioning and carbon sequestration is in its infancy; however, one promising approach is to make observations in regions where landmasses act as point sources of iron. In 2004–2006, three separate expeditions targeted the southern Indian Ocean around the Crozet and Kerguelen Islands and in the southern Scotia Sea around the southern Drake Passage. Representatives from all three programs met recently to compare findings and identify critical gaps in existing knowledge.

Decomposition and nitrogen transformation rates in a temperate grassland vary among co-occurring plant species

Decomposition of organic matter varies depending upon interactions between the composition of the organic matter and the source of the microbial community, with differences in these interactions among vegetation types leading to the Home Field Advantage (HFA) hypothesis whereby decomposition of litters is faster in soils previously conditioned by them. It is possible that HFA operates on smaller scales within plant communities with ecosystem processes responding to subtle changes of plant community dominance. Using field measurements and laboratory incubations, we found a strong plant species effect on nitrogen availability and transformations and the relative importance of autotrophic and heterotrophic processes to nitrification. We found that the origin of the soil microbial community had little influence on litter decomposition when litter quality was high but was important with low-quality litter, most of which was root material. Our results demonstrate that plant species identity has a substantial impact on both litter decomposition and N cycling even within a single vegetation type and on an extremely local scale via both litter chemistry and specificity of the associated soil microbial community. Therefore, changes in botanical composition could alter decomposition and nutrient release altering ecosystem productivity and carbon sequestration potential.

A climatically extreme year has large impacts on C4species in tallgrass prairie ecosystems but only minor effects on species richness and other plant functional groups

Summary1. The occurrence and intensity of climate extremes, such as extremely warm years, are expected to continue to increase with increasing tropospheric radiative forcing caused by anthropogenic greenhouse gas emissions.2. Responses of terrestrial ecosystem processes and services – such as above‐ground net primary productivity (ANPP) and maintenance of plant species diversity – to these extreme years for multiple years post‐perturbation are poorly understood but can have significant feedback effects on net ecosystem CO2uptake and ecosystem carbon sequestration.3. We exposed six 12 000‐kg intact natural tallgrass prairie monoliths to an extremely warm year (+4 °C in 2003) in the second year of a 4‐year study (2002–2005) using the EcoCELL whole‐ecosystem controlled‐environment, gas exchange facility. Six control monoliths were not warmed in the second year but were maintained under average field conditions. Natural diel and seasonal patterns in air temperature were maintained in both treatments throughout the study. Thus, with the exception of the second year in the ‘warmed’ treatment, we created 4 years of nearly identical climate in all EcoCELLs.4. Interannual ANPP (10 cm clipping height) responses of the entire plant community to the extreme year were largely determined by responses of the dominant C4grasses. These included large decreases in ANPP in 2003 followed by complete recovery to levels observed in the control ecosystems in the year following warming. Species richness and productivity of the nitrogen‐fixing plant functional group appeared to play a role in defining overall plant community ANPP, however, even though this richness and productivity could not explain the decrease in community ANPP observed in warmed ecosystems in the second year (2003) of the study or its recovery in the year after (2004). Surprisingly, very few of the 67 species present in plant communities during the 4‐year study responded to the warm year at any time during or after the treatment.5. Synthesis. Results from this study indicate that as extreme climate years become more prevalent, their immediate and lagged impacts on collective ecosystem processes, such as whole‐community ANPP, may be very pronounced, but effects on component ecosystem processes may be limited to the dominant plant functional group (ANPP).

Carbon payments for mangrove conservation: ecosystem constraints and uncertainties of sequestration potential

Abstract Natural ecosystem change over time is an often unconsidered issue for PES and REDD+ schemes, and a lack of consideration of thermodynamic limitations has led to misconceptions and oversimplifications regarding ecosystem services, especially for tropical mangrove forests. Mangroves are non-linear, non-equilibrium systems uniquely adapted to a highly dynamic boundary where shorelines are continually evolving and sea-level ever changing, and rarely conform to classical concepts of forest development and succession. Not all mangroves accumulate carbon and rates of forest floor accretion are directly linked to the frequency of tidal inundation. Carbon payments in either a PES or REDD+ scheme are dependent on the rate of carbon sequestration, not the size of C stocks, so site selection must be ordinarily confined to the sea edge. Gas emissions and net ecosystem production (NEP) are linked to forest age, particularly for monospecific plantations. Planting of mixed-species forests is recommended to maximize biodiversity, food web connectivity and NEP. Old-growth forests are the prime ecosystems for carbon sequestration, and policy must give priority to schemes to maintain their existence. Large uncertainties exist in carbon sequestration potential of mangroves, and such limitations must be factored into the design, timeframe and execution of PES and REDD+ schemes.

Impact of two different types of El Nino events on the Amazon climate and ecosystem productivity

Aims The Amazon basin plays an important role in the global carbon budget. Interannual climate variability associated with El Nino can affect the Amazon ecosystem carbon balance. In recent years, studies have suggested that there are two different types of El Ninos: eastern-Pacific (EP) El Nino and central-Pacific (CP) El Nino. The impacts of two types of El Nino on the Amazon climate and Amazon ecosystem are analyzed in the study. Methods A composite method has been applied to highlight the common features for the EPand CP-El Nino events using observational data, IPCC-AR4 model output. Potential impacts of the two different types of El Nino on ecosystem carbon sequestration over the Amazon have been investigated using a process-based biogeochemical model, the Biome–BioGeochemical Cycles model (Biome–BGC). Important Findings Below-normal rainfall is observed year round in northern, central and eastern Amazonia during EP-El Nino years. During CP-El Nino years, negative rainfall anomalies are observed in most of the Amazon during the austral summer wet season, while there is average or above-average precipitation in other seasons. EPand CP-El Nino events produce strikingly different precipitation anomaly pattern in the tropical and subtropical Andes during the austral fall season: wetter conditions prevail during EP-El Nino years and drier conditions during CP-El Nino years. Temperatures are above-average year round throughout tropical South America during EP-El Nino events, especially during austral summer. During CP-El Nino events, average or slightly above-average temperatures prevail in the tropics, but these temperatures are less extreme than EP year’s temperature except in austral fall. These precipitation and temperature anomalies influence ecosystem productivity and carbon sequestration throughout the Amazon. Using the Biome–BGC model, we find that net ecosystem production (NEP) in the EP-El Nino years is below average, in agreement with most previous studies; such results indicate that the Amazon region acts as a net carbon source to the atmosphere during EP-El Nino years. In the CP-El Nino years, NEP does not differ significantly from its climatological value, suggesting that the Amazon forest remains a carbon sink for the atmosphere. Thus, even if CP-El Nino events increase in frequency or amplitude under global warming climate as predicted in some Global Climate Models, the Amazon rainforest may remain a carbon sink to the atmosphere during El Nino years in the near future.

Modeling to discern nitrogen fertilization impacts on carbon sequestration in a Pacific Northwest Douglas-fir forest in the first-postfertilization year

This study investigated how nitrogen (N) fertilization with 200 kg N ha−1 of urea affected ecosystem carbon (C) sequestration in the first-postfertilization year in a Pacific Northwest Douglas-fir (Pseudotsuga menziesii) stand on the basis of multiyear eddy-covariance (EC) and soil-chamber measurements before and after fertilization in combination with ecosystem modeling. The approach uses a data-model fusion technique which encompasses both model parameter optimization and data assimilation and minimizes the effects of interannual climatic perturbations and focuses on the biotic and abiotic factors controlling seasonal C fluxes using a prefertilization 9-year-long time series of EC data (1998–2006). A process-based ecosystem model was optimized using the half-hourly data measured during 1998–2005, and the optimized model was validated using measurements made in 2006 and further applied to predict C fluxes for 2007 assuming the stand was not fertilized. The N fertilization effects on C sequestration were then obtained as differences between modeled (unfertilized stand) and EC or soil-chamber measured (fertilized stand) C component fluxes. Results indicate that annual net ecosystem productivity in the first-post-N fertilization year increased by∼83%, from 302 ± 19 to 552 ± 36 g m−2 yr−1, which resulted primarily from an increase in annual gross primary productivity of∼8%, from 1938 ± 22 to 2095 ± 29 g m−2 yr−1 concurrent with a decrease in annual ecosystem respiration (Re) of∼5.7%, from 1636 ± 17 to 1543 ± 31 g m−2 yr−1. Moreover, with respect to respiration, model results showed that the fertilizer-induced reduction in Re (∼93 g m−2 yr−1) principally resulted from the decrease in soil respiration Rs (∼62 g m−2 yr−1).

Quantifying soil organic carbon in complex landscapes: an example of grassland undergoing encroachment of woody plants

AbstractThe invasion of woody plants into grass‐dominated ecosystems has occurred worldwide during the past century with potentially significant impacts on soil organic carbon (SOC) storage, ecosystem carbon sequestration and global climate warming. To date, most studies of tree and shrub encroachment impacts on SOC have been conducted at small scales and results are equivocal. To quantify the effects of woody plant proliferation on SOC at broad spatial scales and to potentially resolve inconsistencies reported from studies conducted at fine spatial scales, information regarding spatial variability and uncertainty of SOC is essential. We used sequential indicator simulation (SIS) to quantify spatial uncertainty of SOC in a grassland undergoing shrub encroachment in the Southern Great Plains, USA. Results showed that both SOC pool size and its spatial uncertainty increased with the development of woody communities in grasslands. Higher uncertainty of SOC in new shrub‐dominated communities may be the result of their relatively recent development, their more complex above‐ and belowground architecture, stronger within‐community gradients, and a greater degree of faunal disturbance. Simulations of alternative sampling designs demonstrated the effects of spatial uncertainty on the accuracy of SOC estimates and enabled us to evaluate the efficiency of sampling strategies aimed at quantifying landscape‐scale SOC pools. An approach combining stratified random sampling with unequal point densities and transect sampling of landscape elements exhibiting strong internal gradients yielded the best estimates. Complete random sampling was less effective and required much higher sampling densities. Results provide novel insights into spatial uncertainty of SOC and its effects on estimates of carbon sequestration in terrestrial ecosystem and suggest effective protocol for the estimating of soil attributes in landscapes with complex vegetation patterns.

Fire ignition patterns affect production of charcoal in southern forests

Although charcoal represents a relatively minor portion of available biomass burned in wildfires and prescribed burns, its recalcitrant properties confer residence times ranging from centuries to millennia, with significance for carbon sequestration in frequently burned forests. Here, we determined whether charcoal formation differed between the two most common prescribed fire spread patterns in southern forests: head (with the wind) and backing (against the wind). Pine wood samples were distributed randomly within a mesic flatwoods burn unit in north-central Florida, and subjected either to a head fire (n = 34) or a backing fire (n = 34). Backing fires formed more than twice as much charcoal as head fires (1.53 v. 0.38% of available biomass), presumably because of differences in residence times, oxygen availability and fire intensity between the two fire spread patterns. These results suggest that the contribution of charcoal to ecosystem carbon sequestration is greater when flatwoods forests are burned against the prevailing wind direction, and that further investigation of these trends is warranted.

Changes in soil carbon flux and carbon stock over a rotation of poplar plantations in northwest China

AbstractForest soil is a major component of terrestrial ecosystems for carbon sequestration and plays an important role in the global carbon cycle. Soil carbon flux and soil carbon pools were investigated in a poplar plantation chronosequence over a rotation in northwest China. Based on continuous field observation in 2007, the results showed that mean soil CO2 efflux rate was 5.54, 4.81, and 3.93 μmol CO2 m−2 s−1 for stands of 2‐, 8‐, and 15‐year‐old, respectively, during the growing season. Significant differences in soil respiration of three age classes were mainly because soil temperature, carbon allocation, and fine root growth changed greatly with stand age. Multiple regression analysis suggested that soil temperature and fine root biomass in the upper layer could explain 78–85% of the variation in soil respiration. Mineral soil C stock at 0–40 cm depth was 55.77, 55.09, and 58.14 t ha−1 in the 2‐, 8‐, and 15‐year‐old stands, respectively. The average rate of soil C sequestration was 0.13 t ha−1 year−1 following afforestation on former crop lands. Although the plantations had similar management practices and soil types since their establishment, many biotic and abiotic factors such as root biomass and turnover rate, soil condition of the plantations had undergone marked changes at different development stages, which could result in the remarkable differences in soil carbon flux and storage over a rotation. Our results highlight the importance of the development stage within a rotation of poplar plantation in assessment of soil carbon budget.

The influence of precipitation pulses on soil respiration – Assessing the “Birch effect” by stable carbon isotopes

Sudden pulse-like events of rapidly increasing CO 2 -efflux occur in soils under seasonally dry climates in response to rewetting after drought. These occurrences, termed “Birch effect”, can have a marked influence on the ecosystem carbon balance. Current hypotheses indicate that the “Birch” pulse is caused by rapidly increased respiration and mineralization rates in response to changing moisture conditions but the underlying mechanisms are still unclear. Here, we present data from an experimental field study using straight-forward stable isotope methodology to gather new insights into the processes induced by rewetting of dried soils and evaluate current hypotheses for the “Birch“-CO 2 -pulse. Two irrigation experiments were conducted on bare soil, root-free soil and intact vegetation during May and August 2005 in a semi-arid Mediterranean holm oak forest in southern Portugal. We continuously monitored CO 2 -fluxes along with their isotopic compositions before, during and after the irrigation. δ 13 C signatures of the first CO 2 -efflux burst, occurring immediately after rewetting, fit the hypothesis that the “Birch” pulse is caused by the rapid mineralization of either dead microbial biomass or osmoregulatory substances released by soil microorganisms in response to hypo-osmotic stress in order to avoid cell lyses. The response of soil CO 2 -efflux to rewetting was smaller under mild (May) than under severe drought (August) and isotopic compositions indicated a larger contribution of anaplerotic carbon uptake with increasing soil desiccation. Both length and severity of drought periods probably play a key role for the microbial response to the rewetting of soils and thus for ecosystem carbon sequestration.