Increase Carbon Storage Research Articles

Timber or carbon? Evaluating forest conservation strategies through a discrete choice experiment

There are growing concerns that timber harvesting in the tropics, even when done sustainably, can increase carbon emissions. Despite these concerns, few studies have addressed whether households that engage in timber harvesting would be willing to forgo property rights to receive payments for carbon sequestration. This study addresses this issue by examining the trade-off between timber production and carbon storage in the context of the Maya Biosphere Reserve forest concessions in Guatemala. We estimate willingness to increase carbon storage at the expense of timber harvesting through a discrete choice experiment administered to 716 households in the Maya Biosphere Reserve. Because many individuals have rights to harvest non-timber forest products and work in the tourism sector, we assess how rights for these activities would influence the willingness to participate in carbon contracts. Contract length and group or individual payment structures are also investigated. The results show that households prefer contracts that focus on carbon storage rather than timber harvesting, but access to forests so individuals can participate in non-timber forest product harvesting and tourism is critically important in this region.

Arginine-fed cultures generates triacylglycerol by triggering nitrogen starvation responses during robust growth in Chlamydomonas

Under nitrogen (N) starvation, certain microalgae increase carbon storage in the form of lipid droplets while also downregulating photosynthesis and eventually terminating growth. To improve lipid yield, we asked whether lipid droplets and N starvation responses can be induced without limiting growth or photosynthesis. In the chlorophyte Chlamydomonas reinhardtii, N starvation induces gametogenesis alongside lipid droplet accumulation, and gametogenesis has been observed in arginine-fed cultures wherein the arginine was provided as the sole N source. We therefore assessed whether arginine-fed cultures displayed N starvation responses other than gametogenesis in mixo- and phototrophic conditions, representing two primary modes of nutrition that may affect N starvation responses. We showed that arginine-fed cultures using two lab strains of C. reinhardtii supported normal mixotrophic growth, constitutively turned on N starvation-induced genes at the equivalent level to N-starved cells, and increased the triacylglycerol content of total fatty acids by 125–400% relative to ammonium-fed cultures. The lipid profile of triacylglycerol in these arginine-fed mixotrophic cultures exhibited 3 to 5.5-fold enrichment of saturated and monounsaturated fatty acids, a preferred characteristic of biodiesel precursors. Arginine-fed phototrophic cultures likewise turned on N starvation-induced genes, accumulated lipid droplets, and led to a 50% reduced growth rate per day while reaching a 3 to 6.5-fold more cell density at the stationary phase relative to ammonium-fed cultures. To test the applicability of our result to algae outside the green lineage, we conducted similar experiments with the diatom Phaeodactylum tricornutum, which also accumulated 2 to 7-fold more neutral lipids in arginine-fed phototrophic cultures without growth impairment relative to nitrate-fed cultures. We document a system wherein N starvation responses are induced without compromising photosynthesis or growth, thereby suited to the production of valuable chemicals and biofuel precursors without requiring stressors in microalgae.

Identifying priority management of Ecuadorian forests based on the environmental integrated assessment

Anthropogenic impacts, such as deforestation, soil erosion, and carbon dioxide emissions, have a negative influence over global warming due to the increase of CO2 levels in the atmosphere. The sustainable forest management is a way to mitigate climate change owing to the carbon storage capacity of forests. This study highlights the priority of forest management according to the integrated assessment of carbon storage under anthropogenic impacts in the administrative units of Ecuador. In the obtained map, the provinces Guayas, Esmeraldas, and Manabí showed the highest values of 25, 22.85 and 19.9, respectively, followed by two Amazon provinces, Morona Santiago and Sucumbíos. Therefore, we concluded that deforestation, soil erosion, and carbon dioxide emissions were more pronounced on the coast mainly due to agriculture and livestock activities and the forests in these provinces must have priority management. This analysis is useful for planning environmental practices in order to increase carbon storage as a strategy of mitigation for global warming.

Increasing carbon storage in subtropical forests over the Yangtze River basin and its relations to the major ecological projects

Forest carbon stocks has an important role in the global carbon budget. Based on the satellite-observed and LPJ model simulated aboveground biomass carbon (ABC) data, the spatial and temporal changes of subtropical forest carbon storage in the Yangtze River basin and its relations to the climate variation and human activities were analyzed by using the methods of cumulative curve analysis and climate sensitivity analysis during 1993–2012. The results revealed that: (1) In general, the forest ABC increased obviously in the Yangtze River basin during the past 20 years, and the ABC rose from 2563.91 Tg C in 1993 to 2893.17 Tg C in 2012, with a growth rate of 12.84%. The higher ABC distribution was mainly concentrated in the Jialing River basin and Hanjiang River basin and the significantly increasing trends could be found in most area of the Yangtze River basin; (2) The forest ABC was sensitive to the changes of temperature and precipitation. When the temperature increases by 1 °C, the ABC in the Yangtze River basin will increase by 3.32%, while it will decrease by −6.12% when the precipitation increases by 10%; (3) The forest ABC growth rate had accelerated from 3.15% in 1993–2000 to 8.01% in 2001–2012. The cumulative curve of the forest ABC was generally higher than the temperature or the precipitation after 2000. The total areas induced by climate variation and human activities accounted for 30.5% and 52.59% with an increases in ABC by 67.52 Tg C and 188.74 Tg C from 1993 to 2012, respectively. The implementation of major forestry projects might be the main reason for the rapid increase of forest ABC in the Yangtze River basin. This study suggested human activities such as ecological projects might contribute to the accelerated greening trend and highlighted the pivotal role of subtropical forest ABC in the carbon budget in China.

Carbon sequestration potential of forest vegetation in China from 2003 to 2050: Predicting forest vegetation growth based on climate and the environment

Abstract Over the past two decades, the burning of fossil fuels in China has been excessive, causing carbon emissions to increase. Surface temperatures and the occurrence of natural disasters have also increased. Considering the important role of forests in reducing emissions, China conducted a series of studies on carbon storage by forest vegetation that involved well-developed estimation methods. However, there are still uncertainties in predicting future changes in forest vegetation acting as a carbon sink. This study used data collected from 7801 national forest inventory (NFI) forest plots in 2003, 2008 and 2013 as well as related forest ecosystem biomass data. The dynamic growth, biomass and carbon storage of arbor, economic and shrubbery forests were studied. This study made a breakthrough in predicting forest biomass and carbon storage based on growth-related changes in forest vegetation in China, improved the accuracy of predicting arbor forest carbon storage and filled a gap in research on the carbon storage/sink properties of economic, shrubbery and bamboo forests. In the results of this study, from 2003 to 2050, the carbon storage, density and carbon sink of forest vegetation in China increased rapidly. Mature forests in China played a major role in the increase in carbon storage, and the quality of young, half-mature and mature forests steadily improved. China’s forest carbon storage was mainly concentrated in the southwestern and northeastern regions, between which the southwestern region had the highest carbon density. In addition, carbon storage and density increased faster in the southwestern region than in the northeastern region. The carbon storage and density of forest vegetation were greater in Tibet than in other areas. The carbon storage of forest vegetation in Tibet increased faster than that in other areas, and the carbon density of forest vegetation in Xinjiang increased faster than that in other areas. In addition, the carbon storage and carbon density of forest vegetation in Ningxia increased slower than those in other areas. From 2020 to 2050, China’s forest vegetation will absorb 22.14% of CO2 emissions from fossil fuel combustion, which will play an important role in slowing increases in greenhouse gases in the next 30 years.

An agricultural practise with climate and food security benefits: “Claying” with kaolinitic clay subsoil decreased soil carbon priming and mineralisation in sandy cropping soils

As the agricultural sector seeks to feed a growing global population, climate-smart agriculture offers opportunities to concurrently mitigate climate change by reducing greenhouse gas emissions and/or increasing carbon storage in soils. This study examined the potential for clay addition to reduce CO2 emissions from plant residues and soil organic matter in a sandy soil. Soils were sourced from a 15-year-old field trial where claying (200 t ha−1) had already demonstrated improvements in water infiltration, grain yield and profits. Isotopically labelled plant residues (wheat, canola, or pea) were used to separate residue-derived and soil-derived CO2 sources from a nil-clay control, a historically clayed, and two freshly created soils with either high (10%) or low (3%) subsoil clay additions. Laboratory incubations demonstrated that historically clayed soils released less CO2 from plant residues and soil organic matter. Clay addition also decreased the priming effect of adding fresh residue to soils. The results from clay experimentally added in the laboratory varied. Differences in chemical and biological indicators (pH, microbial biomass C and N, extractable organic C and N, NO3−, NH4+, abundance of bacterial, archaeal, fungal, LMCO, GH48 and CbhI genes) did not correlate with patterns of CO2 emissions across treatments. While claying practices have previously demonstrated benefits to crop productivity, this research demonstrates long-term changes in carbon-cycling that could promote greater carbon sequestration.

Effects of temperature on carbon circulation in macroalgal food webs are mediated by herbivores

Warming is one of the most dramatic aspects of climate change and threatens future ecosystem functioning. It may alter primary productivity and thus jeopardize carbon sequestration, a crucial ecosystem service provided by coastal environments. Fucus vesiculosus is an important canopy-forming macroalga in the Baltic Sea, and its main consumer is Idotea balthica. The objective of this study is to understand how temperature impacts a simplified food web composed of macroalgae and herbivores to quantify the effect on organic carbon storage. The organisms were exposed to a temperature gradient from 5 to 25 °C. We measured and modeled primary production, respiration, growth and epiphytic load on the surface of Fucus and respiration, growth and egestion of Idotea. The results show that temperature affects physiological responses of Fucus and Idotea separately. However, Idotea proved more sensitive to increasing temperatures than the primary producers. The lag between the collapse of the grazer and the decline of Fucus and epiphytes above 20 °C allows an increase of carbon storage of the primary productivity at higher temperatures. Therefore, along the temperature gradient, the simplified food web stores carbon in a non-monotonic way (reaching minimum at 20 °C). Our work stresses the need of considering the combined metabolic performance of all organisms for sound predictions on carbon circulation in food webs.

Environmental and management controls of soil carbon storage in grasslands of southwestern China

In order to predict the effects of climate change on the global carbon cycle, it is crucial to understand the environmental factors that affect soil carbon storage in grasslands. In the present study, we attempted to explain the relationships between the distribution of soil carbon storage with climate, soil types, soil properties and topographical factors across different types of grasslands with different grazing regimes. We measured soil organic carbon in 92 locations at different soil depth increments, from 0 to 100 cm in southwestern China. Among soil types, brown earth soils (Luvisols) had the highest carbon storage with 19.5 ± 2.5 kg m−2, while chernozem soils had the lowest with 6.8 ± 1.2 kg m−2. Mean annual temperature and precipitation, exerted a significant, but, contrasting effects on soil carbon storage. Soil carbon storage increased as mean annual temperature decreased and as mean annual precipitation increased. Across different grassland types, the mean carbon storage for the top 100 cm varied from 7.6 ± 1.3 kg m−2 for temperate desert to 17.3 ± 2.9 kg m−2 for alpine meadow. Grazing/cutting regimes significantly affected soil carbon storage with lowest value (7.9 ± 1.5 kg m−2) recorded for cutting grass, while seasonal (11.4 ± 1.3 kg m−2) and year-long (12.2 ± 1.9 kg m−2) grazing increased carbon storage. The highest carbon storage was found in the completely ungrazed areas (16.7 ± 2.9 kg m−2). Climatic factors, along with soil types and topographical factors, controlled soil carbon density along a soil depth in grasslands. Environmental factors alone explained about 60% of the total variation in soil carbon storage. The actual depth-wise distribution of soil carbon contents was significantly influenced by the grazing intensity and topographical factors. Overall, policy-makers should focus on reducing the grazing intensity and land conversion for the sustainable management of grasslands and C sequestration.

Carbon Sequestration in Coffee Agroforestry of Barbere District, Bale Zone, Southeastern Ethiopia: Implications for Climate Change Mitigation

Climate change has become one of the most challenges facing the global community today. Human activities, particularly the burning of fossil fuels and deforestation, have increased the level of greenhouse gases, major contributors to global warming in the atmosphere. In spite of this hard fact; there was a growing need to develop strategies that will reduce current levels of greenhouse gases in the atmosphere. One such mechanism is the sequestration of carbon by the agroforestry system. The objective of this study was to determine the above and below ground carbon sequestration potential of coffee agroforestry and indicating their contributions to climate change mitigation. The coffee agroforestry of the study area was divided into three-shade types: monoculture shade cover, intermediate shade covers and densely shaded grown comprises a total area of 261ha, of which 16 samples from the three-shade categories were chosen using lottery method. A total of 48 quadrant plots were laid to sample the coffee agroforestry system. Plot of size 400 m2 was used to measure the shade trees and coffee shrubs. Shade trees with >2.5 cm diameter at breast height were recorded, Coffee shrubs were measured in each 20m X 20m quadrant plot with stem diameter at 15 cm from the ground. Regression equations for estimation of AGB and BGB were established. Results indicate the coffee agroforestry production system that stores the most amount of carbon per hectare in its AGC and BGC was densely Shade (65.69+ 6.27Mg C ha-1), employing a variety of shade-tree species in three distinct layers. Conversely, the shaded monoculture with low structural complexity in its shade layer stores the least carbon (28.85+ 3.93 Mg C ha-1). The carbon-stock of the intermediate shade cover examined falls within this range. The study shows that the coffee agroforestry of Barbere district in southeastern Ethiopia plays a great role in the mitigation of climate change phenomenon by its good potential of carbon sequestration. This study recommends that the shade layer in coffee agroforestry be made denser for increased carbon storage and maintenance of biodiversity. Key Terms: - Agroforestry, Biomass, Barbere, Carbon stock, Mitigation DOI: 10.7176/CER/11-9-01 Publication date:October 31st 2019

Carbon Sequestration in Coffee Agroforestry of Barbere District, Bale Zone, Southeastern Ethiopia: Implications for Climate Change Mitigation

Climate change has become one of the most challenges facing the global community today. Human activities, particularly the burning of fossil fuels and deforestation, have increased the level of greenhouse gases, major contributors to global warming in the atmosphere. In spite of this hard fact; there was a growing need to develop strategies that will reduce current levels of greenhouse gases in the atmosphere. One such mechanism is the sequestration of carbon by the agroforestry system. The objective of this study was to determine the above and below ground carbon sequestration potential of coffee agroforestry and indicating their contributions to climate change mitigation. The coffee agroforestry of the study area was divided into three-shade types: monoculture shade cover, intermediate shade covers and densely shaded grown comprises a total area of 261ha, of which 16 samples from the three-shade categories were chosen using lottery method. A total of 48 quadrant plots were laid to sample the coffee agroforestry system. Plot of size 400 m2 was used to measure the shade trees and coffee shrubs. Shade trees with >2.5 cm diameter at breast height were recorded, Coffee shrubs were measured in each 20m X 20m quadrant plot with stem diameter at 15 cm from the ground. Regression equations for estimation of AGB and BGB were established. Results indicate the coffee agroforestry production system that stores the most amount of carbon per hectare in its AGC and BGC was densely Shade (65.69+ 6.27Mg C ha-1), employing a variety of shade-tree species in three distinct layers. Conversely, the shaded monoculture with low structural complexity in its shade layer stores the least carbon (28.85+ 3.93 Mg C ha-1). The carbon-stock of the intermediate shade cover examined falls within this range. The study shows that the coffee agroforestry of Barbere district in southeastern Ethiopia plays a great role in the mitigation of climate change phenomenon by its good potential of carbon sequestration. This study recommends that the shade layer in coffee agroforestry be made denser for increased carbon storage and maintenance of biodiversity. Key Terms: - Agroforestry, Biomass, Barbere, Carbon stock, Mitigation DOI: 10.7176/CER/11-9-01 Publication date:October 31st 2019

Simulating the impact of Grain-for-Green Programme on ecosystem services trade-offs in Northwestern Yunnan, China

One of the main manifestations of the Grain-for-Green Programme (GFGP) is land use change, which will affect the trade-off of ecosystem services. Since the implementation of the GFGP in Dali Autonomous Prefecture in 2000, land use/cover has undergone dramatic changes. This study used the CLUE-S model to simulate land use change in 2030, and explored the spatial pattern and relationship of different ecosystem services under the four scenarios of GFGP. The results show that, GFGP can help to improve indirect services of ecosystems, such as carbon storage and soil conservation. However, direct services of the ecosystem will decline, such as food production and water yield. Compared with 2010, the overall supply level of the four ecosystem services is the most balanced in the moderate GFGP scenario. In this scenario, total food production decreased by 179,000 tons and water yield decreased by 57 million cubic meters. Carbon storage and soil conservation continued to grow, increasing by 21.86 million tons and 17.87 million tons, respectively. The changes of ecosystem services in the strong GFGP scenario are extreme. The increases in carbon storage and soil conservation are at the expense of a significant reduction in food production and water yield. It can be concluded that GFGP may lead to intensifying ecosystem services trade-offs. Through comparing the changes of ecosystem services under different GFGP scenarios, it is found that the implementation intensity of GFGP should be deeply concerned in policy making.

Large-scale forest restoration stabilizes carbon under climate change in Southwest United States.

Higher tree density, more fuels, and a warmer, drier climate have caused an increase in the frequency, size, and severity of wildfires in western U.S. forests. There is an urgent need to restore forests across the western United States. To address this need, the U.S. Forest Service began the Four Forest Restoration Initiative (4FRI) to restore four national forests in Arizona. The objective of this study was to evaluate how restoration of ~400,000 ha under the 4FRI program and projected climate change would influence carbon dynamics and wildfire severity from 2010 to 2099. Specifically, we estimated forest carbon fluxes, carbon pools and wildfire severity under a moderate and fast 4FRI implementation schedule and compared those to status quo and no‐harvest scenarios using the LANDIS‐II simulation model and climate change projections. We found that the fast‐4FRI scenario showed early decreases in ecosystem carbon due to initial thinning/prescribed fire treatments, but total ecosystem carbon increased by 9–18% over no harvest by the end of the simulation. This increased carbon storage by 6.3–12.7 million metric tons, depending on the climate model, equating to removal of carbon emissions from 55,000 to 110,000 passenger vehicles per year until the end of the century. Nearly half of the additional carbon was stored in more stable soil pools. However, climate models with the largest predicted temperature increases showed declines by late century in ecosystem carbon despite restoration. Our study uses data from a real‐world, large‐scale restoration project and indicates that restoration is likely to stabilize carbon and the benefits are greater when the pace of restoration is faster.

Towards a model for circular renovation of the existing building stock: a preliminary study on the potential for CO2 reduction of bio-based insulation materials

In the context of strategies for mitigating the impacts of climate change within European cities, increasing attention is being paid worldwide to the use of urban green infrastructure which, in addition to the potential for improving the quality of the urban environment, allow significant amounts of CO2 to be removed from the air. However, considering the peculiarities of the dense European cities, most of the available surfaces in urban areas are the perimeter walls of buildings of considerable age that are in urgent need of measures to upgrade their energy performance. Based on this premise, this paper investigates the potential for CO2 storage resulting from the application of energy retrofit solutions using biogenic insulating materials. Starting from the analysis of the demand for insulation materials necessary for the energy requalification of the residential existing building stock in 28 European countries, following the renovation target fixed by EU, the research analyses, through the adoption of a dynamic LCA approach, the environmental benefits of bio-based materials compared to traditional solutions. The use of these materials, especially if they are fast-growing - as the study shows - offers several advantages in terms of climate change mitigation by reducing the energy needs and CO2 emissions of the existing building stock and increasing carbon storage capacity within cities. The results of this study are intended to provide a robust database on which to build a model of circular building renovation that takes into account the environmental long-term effects of measures for increasing energy efficiency of buildings.

Carbon accumulations by stock change approach in tropical highland forests of Chiapas, Mexico

Changes in forest biomass and soil organic carbon reserves have strong links to atmospheric carbon dioxide concentration. Human activities such as livestock grazing, forest fires, selective logging and firewood extraction are the common disturbances that affect the carbon dynamics of the forest ecosystems. Here, we hypothesized that such anthropogenic activities significantly reduce the carbon stocks and accumulation rates in the tropical highland forests of the Sierra Madre de Chiapas in Southern Mexico. We sampled the Pinus oocarpa Scheide dominated forests within the elevation range of 900 to 1100 m above sea level in 2010, 2014 and 2017. We measured the stand structural properties and used the reported allometric equations to calculate the tree carbon stocks. Stock change approach was used to calculate carbon accumulation rates. The results showed a gradual increase in carbon storage over the 7-year period from 2010 to 2017, but the rate of increase varied significantly between the study sites. The aboveground carbon stock was 107.25 ± 11.77 Mg ha−1 for the site with lower anthropogenic intensity, compared to 74.29 ± 16.85 Mg ha−1 for the site with higher intensity. The current annual increment for the forest with lower anthropogenic intensity was 7.81 ± 0.65 Mg ha−1 a−1, compared to 3.87 ± 1.03 Mg ha−1 a−1 in the site with high anthropogenic intensity. Although at varying rates, these forests are functioning as important carbon sinks. The results on carbon accumulation rates have important implications in greenhouse gas mitigations and forest change modelling in the context of changing global climate.

Future nitrogen availability and its effect on carbon sequestration in Northern Eurasia

Nitrogen (N) availability exerts strong control on carbon storage in the forests of Northern Eurasia. Here, using a process-based model, we explore how three factors that alter N availability—permafrost degradation, atmospheric N deposition, and the abandonment of agricultural land to forest regrowth (land-use legacy)—affect carbon storage in the region’s forest vegetation over the 21st century within the context of two IPCC global-change scenarios (RCPs 4.5 and 8.5). For RCP4.5, enhanced N availability results in increased tree carbon storage of 27.8 Pg C, with land-use legacy being the most important factor. For RCP8.5, enhanced N availability results in increased carbon storage in trees of 13.4 Pg C, with permafrost degradation being the most important factor. Our analysis reveals complex spatial and temporal patterns of regional carbon storage. This study underscores the importance of considering carbon-nitrogen interactions when assessing regional and sub-regional impacts of global change policies.

California's success in the socio-ecological practice of a forest carbon offset credit option to mitigate greenhouse gas emissions

The mitigation of climate change through the reduction in greenhouse gas emissions has become a central goal of international policy. An estimated 27 cap-and-trade programs to reduce carbon emissions exist worldwide. But only a small number of them use a forest carbon offset credit option. In 2012, California created a forest carbon offset credit option as part of its greenhouse gas cap-and-trade program. The offset credits have come primarily from US forests that meet requirements for additional, verifiable increases in carbon storage through improved forest management. California, with the help of its cap-and-trade program and modest carbon offset option, has met its initial goal for lower carbon emissions. This case study reveals a gap in socio-ecological practice research on a forest carbon offset credit option by identifying seven measures of success. These seven measures show how a forest carbon offset credit option can enhance a cap-and-trade program to reduce greenhouse gas emissions. Countries and regions that are using or contemplating the use of a forest carbon offset credit option can employ these seven measures to design, evaluate, or upgrade their forest carbon offset programs.

Large-scale integrated assessment of soil carbon and organic matter-related nitrogen fluxes in Saxony (Germany)

Changes in land-use, agricultural management and climate affect the turnover and storage of organic carbon in soils (SOC) as well as the nitrogen mobilization from soil organic matter (SOM), with potential side effects on nitrogen availability and leaching. When addressing the requests for increased carbon storage in soil as well as for the reduction of nitrogen losses, integrated approaches on regional scales are required that take into account the actual changes in agricultural management and climate. This study investigated the arable land (7345 km2) of Saxony (Germany) with regard to the following: (1) the trends of SOC storage and organic matter-related nitrogen fluxes, including their subregional and annual dynamics, (2) changes in the carbon input to arable soils and the turnover of organic matter, and (3) the contribution of different drivers (climate, crop production and fertilization, tillage system) to the simulated SOM changes for the period 1998–2014 on a 500 m grid. The model CANDY carbon balance (CCB) was specifically adapted for large-scale simulations of SOM turnover to link spatial data on soils and climate with regional statistics on agricultural management. This new ‘regional mode’ of CCB has been validated using data from 391 plots across different European locations. The initial SOC levels for Saxony assumed steady state conditions at the beginning of the simulation period and have been validated using data from 667 monitoring sites. The results showed an increase in the SOC stocks of the arable soils of Saxony of 785 × 103 t C (1.24‰ annually) during the simulation period. At the same time, the model simulated an average increase in organic nitrogen stored in SOM of approximately 7.5 kg N ha−1 a−1, with considerable differences between individual years and subregions. Both the increase in carbon inputs to soil (+8%) and the reduction of carbon turnover rates (−10%) had positive effects on SOC storage. While the increased use of conservation tillage was the most important driver for the overall increase in SOM storage in Saxony, climate variability and crop production and fertilization had the largest effect on its annual dynamics.

Towards a more complete quantification of the global carbon cycle

Abstract. The main components of global carbon budget calculations are the emissions from burning fossil fuels, cement production, and net land-use change, partly balanced by ocean CO2 uptake and CO2 increase in the atmosphere. The difference between these terms is referred to as the residual sink, assumed to correspond to increasing carbon storage in the terrestrial biosphere through physiological plant responses to changing conditions (ΔBphys). It is often used to constrain carbon exchange in global earth-system models. More broadly, it guides expectations of autonomous changes in global carbon stocks in response to climatic changes, including increasing CO2, that may add to, or subtract from, anthropogenic CO2 emissions. However, a budget with only these terms omits some important additional fluxes that are needed to correctly infer ΔBphys. They are cement carbonation and fluxes into increasing pools of plastic, bitumen, harvested-wood products, and landfill deposition after disposal of these products, and carbon fluxes to the oceans via wind erosion and non-CO2 fluxes of the intermediate breakdown products of methane and other volatile organic compounds. While the global budget includes river transport of dissolved inorganic carbon, it omits river transport of dissolved and particulate organic carbon, and the deposition of carbon in inland water bodies. Each one of these terms is relatively small, but together they can constitute important additional fluxes that would significantly reduce the size of the inferred ΔBphys. We estimate here that inclusion of these fluxes would reduce ΔBphys from the currently reported 3.6 GtC yr−1 down to about 2.1 GtC yr−1 (excluding losses from land-use change). The implicit reduction in the size of ΔBphys has important implications for the inferred magnitude of current-day biospheric net carbon uptake and the consequent potential of future biospheric feedbacks to amplify or negate net anthropogenic CO2 emissions.

Mangroves dramatically increase carbon storage after 3 years of encroachment

In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.

Understory ferns alter soil carbon chemistry and increase carbon storage during reforestation with native pine on previously degraded sites

Reforestation with native species and resulting understory succession can exert important influences on soil organic matter (SOM) storage and chemistry, but a mechanistic understanding of these effects is lacking. We studied different aged Masson pine (Pinus massoniana L.) plantations with and without the understory fern, Dicranopteris dichotoma (Thunb.) Berhn., in subtropical China to assess how SOM over a 30 year sequence of pine growth and fern expansion. To do this, we measured total SOM, lignin-derived phenols, soil carbon (total C and 13C), soil nitrogen (total N and 15N), and soil microbial community composition via phospholipid fatty acid (PLFA) analyses. We found that the accumulation of newly-formed SOM outweighed decomposition of old SOM, with the majority of this increase being derived from fern detrital inputs. Where ferns were present, ferns contributed 54–61% of total soil C storage in surface (0–10 cm depth) soils, which was 62–91% higher than pre-reforestation soil C storage. We found that the abundance of lignin-derived compounds was lower in fern dominated soils, perhaps because soils under ferns supported more soil fungi, the primary decomposers of the lignin in soil. Fern soils also showed higher ratios of syringyls to vanillyls and decreased δ13C values, an indicator that ferns altered the composition of SOM at the molecular level while contributing significantly to SOM accumulation. Reforestation especially when accompanied by fern expansion also improved soil N and phosphorus (P) status, with observed declines in soil δ15N in fern dominated soils aligning with increased nutrient retention and observed increases in soil C storage. Our study highlights the potentially important role of understory ferns in mediating SOM chemistry and soil C storage during ecosystem recovery.