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Greenhouse gas (GHG) emissions from the Agriculture, Forest, and Other Land Use sector account for 23% of net global anthropogenic emissions. However, effective conservation agriculture practices can sequester carbon (C) up to 1 m in soil depth and vegetation biomass. Integrated Crop--Livestock--Forestry (ICLF) systems attempt to ensure sustainable agricultural production by combining various agricultural, livestock, and forestry production systems. This bibliographic review aims to present and discuss ICLF systems and their advantages and disadvantages compared with conventional systems, achieving a better understanding of the sources and sinks of GHGs (C[H.sub.4], [N.sub.2]O, and C[O.sub.2]). Integrated systems exist in tropical and temperate climates with different practices, arrangements, designs, and modalities. Intercropping species with different root structures provides more ecological interactions that enhance biodiversity, soil quality, and C sequestration while reducing GHG emissions. Yet, ICLF systems are complex and require technical assistance and support for being implemented, besides an extensive initial investment that increases the cost of operation. A relevant carbon sink in ICLF systems is carbon from tree biomass, where the wood can be used for various purposes. Timber for sawmills and general construction has a longer C immobilization time. Methane from enteric fermentation is the greatest contributor to GHG emissions in livestock and ICLF systems. Nitrous oxide is released primarily from synthetic fertilizers (when applied), manure deposited on pastures, and the decomposition of plant residues. Carbon dioxide is emitted to a lesser extent from the application of lime and urea. Many studies do not include all compartments in the C balance and often focus on only one GHG or compartment of C. Accordingly, more studies on the sources and sinks of C and their potential to ofset GHG emissions in terms of C[O.sub.2] equivalent are urged. Key words: agroforestry systems, carbon dioxide, nitrous oxide, methane, climate change, sustainable agriculture, 1. Introduction Anthropogenic activities have changed the greenhouse gas (GHG) concentrations in the atmosphere, with a 47% increase in carbon dioxide (C[O.sub.2]), 156% in methane (C[H.sub.4]), and 23% in nitrous [...]

We integrate a carbon net sink and stand-level wood production to analyze their simultaneous optimization as an economic problem. Carbon is included in living trees, wood products, and forest soil. Forestry is specified by a size-structured model for optimizing thinning timing and intensity, rotation period, and the optimal choice of rotation versus continuous cover forestry. The optimal inclusion of a carbon net sink increases the carbon pool mainly in living trees and forest soil, while the effect on the product carbon pool remains minor. With a 3% interest rate, increasing the C[O.sub.2] price to 40 [euro] per tC[O.sub.2] increases the total steady-state carbon pool by 131% and the soil carbon accounts for ca. 60% of the increased carbon storage. Omitting soil carbon, as in previous studies, leads to underestimates of the carbon sink, significantly decreasing the optimal total C[O.sub.2] net sink and achievable economic net gain from joint wood production and carbon management. The inclusion of soil carbon suggests that, in contrast to previous results, a higher C[O.sub.2] price does not necessarily favor continuous cover forestry. Key words: carbon sequestration, economic profitability, soil carbon, continuous cover forestry, rotation forestry, optimal rotation, 1. Introduction Climate change and the aim of limiting global warming have strongly increased the attention given to forests as carbon sinks (Shukla et al. 2019). Compared with the tropics, [...]

Coastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems.sup.1,2, primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates.sup.3. Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-first century.sup.4, but these carbon-climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion.sup.4,5. Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1 at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillar collapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space.sup.6 created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate-carbon modelling. Wetlands exposed to rapid sea-level rise over the late Holocene contain more soil carbon than those that experienced a long period of sea-level stability., Author(s): Kerrylee Rogers [sup.1] , Jeffrey J. Kelleway [sup.2] , Neil Saintilan [sup.2] , J. Patrick Megonigal [sup.3] , Janine B. Adams [sup.4] , James R. Holmquist [sup.3] , Meng [...]

Abstract. Scientific studies report decreases, increases, or negligible changes in soil organic carbon (C) stocks upon afforestation; however, these studies neglect the potential role of total nitrogen (N), tree species, [...]

Seagrass habitats provide invaluable ecosystem services, including the ability to sequester carbon through primary production. In the absence of significant grazing pressure, changes in seagrass biomass reflect net photosynthetic activity [...]

To better understand the potential impact of the invasive hemlock woolly adelgid (HWA, Adelges tsugae Annand) and presalvage activities on carbon (C) dynamics in northern stands of eastern hemlock (Tsuga canadensis (L.) Carr.), we used the Forest Vegetation Simulator and Forest Inventory and Analysis data to model C storage and successional pathways under four scenarios: presalvage harvesting; HWA-induced mortality; presalvage harvesting plus HWA-induced mortality; and no disturbance (control). Our simulation showed that all treatments differed in total C storage in the short term, with HWA-induced mortality providing the highest total C storage due to regeneration and ingrowth of replacement species combined with retention of standing and downed deadwood. At the end of the 150-year simulation, all disturbance scenarios had significantly lower total C than the control. The cumulative net C gain was lower for the two presalvage scenarios than for the HWA scenario, indicating that allowing HWA to progress naturally through a stand may result in the least impact to long-term C sequestration and net C storage. While differences were not significant on low hemlock density stands, impacts to the estimated 267 000 ha of northeastern forests where hemlock is dominant could result in conversion to red maple (Acerrubrum L.) and a net loss of over 4 million metric tons of potentially sequestered C over the next 150 years. Key words: Adelges tsugae, carbon sequestration, Forest Vegetation Simulator, FVS, Tsuga canadensis. Pour mieux comprendre l'impact potentiel du puceron lanigere de la pruche (PLP, Adelges tsugae Annand) et des activites de recuperation preventive sur la dynamique du carbone (C) dans les peuplements nordiques de pruche du Canada (Tsuga canadensis (L.) Carr.), nous avons utilise les donnees du simulateur de vegetation forestiere et de l'analyse et inventaire forestier pour modeliser le stockage de C et les sentiers successionnels en fonction de quatre scenarios : coupe de recuperation preventive; mortalite causee par le PLP; coupe de recuperation preventive plus mortalite causee par le PLP; et temoin non perturbe. Notre simulation a montre que tous les scenarios different du point du vue du stockage du C total a court terme et que la mortalite causee par le PLP permet d'emmagasiner la quantite la plus elevee de C total a cause de la regeneration et du recrutement des especes remplacantes combines a la retention du bois mort sur pied et au sol. A la fin de la simulation d'une duree de 150 ans, le C total etait significativement moins eleve dans tous les scenarios de perturbation que dans le temoin. Le gain cumulatif de C etait plus faible dans les deux scenarios de recuperation preventive que dans le scenario impliquant le PLP, ce qui indique que le fait de laisser le PLP progresser naturellement dans un peuplement pourrait etre l'approche qui a le moins d'impact sur la sequestration et le stockage de C a long terme. Bien que les differences ne soient pas significatives dans les peuplements ou la densite de la pruche est faible, les impacts sur les 267 000 ha de forets du nord-est ou l'on estime que la pruche estdominante pourraient entrainer la conversion vers l'erable rouge (Acerrubrum L.) etune perte nette de plus de quatre millions de tonnes metriques de C qui aurait pu etre sequestre au cours des 150 prochaines annees. [Traduit par la Redaction] Mots-cles: Adelges tsugae, sequestration du carbone, simulateur de vegetation forestiere, SVF, Tsuga canadensis., Introduction Forested ecosystems are the largest terrestrial sink that sequesters and stores atmospheric CO2 and thus play a prominent role in mitigating greenhouse gas emissions (Brown 2002; Davis et al. [...]

Converging evidence suggests that freshwater systems play an important role in the carbon cycles at both regional and global scales. In addition, there are serious concerns that ongoing and future changes to the environment could alter these dynamics. This is particularly important in the boreal forest biome, which contains a very high density of lakes. In this review, we synthesize the current state of research to provide a critical overview of (i) the role of boreal lakes as emitters versus sinks of carbon, (ii) their contribution to the regional carbon balance, (iii) knowledge gaps that may inhibit an accurate evaluation of the role of boreal lakes in a landscape context, and (iv) impacts of environmental perturbations on carbon dynamics in boreal lakes. Several recent studies indicate that boreal lakes are actively processing, emitting, and storing carbon rather than being passive transport conduits. Yet, generalizing the role of lake ecosystems for the overall carbon balance of the boreal forest biome is challenging because of the scarcity of studies on lake carbon budgets in a landscape context that can capture the potential temporal and spatial variability and uncertainties associated with the available estimates of carbon pools and fluxes. Further, environmental perturbations, such as climate change, acidic deposition, and nutrient enrichment, likely affect both carbon export to lakes and in-lake carbon processing in boreal regions. Predicting their overall impacts on lake carbon budgets is particularly difficult, not only because individual environmental stressors likely affect multiple processes involved in carbon cycling, but also because often multiple stressors act synergistically or antagonistically at the landscape level. Accordingly, long-term, system-wide approaches are required to accurately evaluate the importance of lakes for boreal carbon budgets in a changing environment. Key words: boreal forest, lakes, carbon budgets, C[O.sub.2] emission, environmental perturbations, climate change. Des preuves convergentes suggerent que les systemes d'eau douce jouent un role important dans le cycle du carbone a l'echelle regionale aussi bien que globale. De plus, il existe de serieuses preoccupations a l'effet que les changements actuels et a venir de l'environnement pourraient alterer ces processus dynamiques. Ceci est particulierement important en forets boreales lesquelles comportent une tres forte densite de lacs. Dans cette revue, les auteurs synthetisent l'etat actuel des recherches afin de proposer une vue critique de l'ensemble, incluant (i) le role des lacs boreaux comme emetteurs versus puits de carbone, (ii) leur contribution a la balance regionale du carbone, (iii) les manques de connaissances susceptibles d'inhiber l'evaluation precise du role des lacs boreaux a l'echelle du paysage et (iv) les impacts des perturbations environnementales sur la dynamique du carbone dans les lacs boreaux. Plusieurs etudes recentes indiquent que les lacs boreaux transforment, emettent et accumulent activement le carbone plutot que d'agir seulement comme des conduits de transport passifs. Cependant, la generalisation du role des ecosystemes lacustres a l'ensemble de la balance carbonee du biome forestier boreal constitue un defi, du a la rarete des etudes sur les budgets du carbone des lacs a l'echelle du paysage, pouvant tenir compte de la variabilite spatio-temporelle potentielle, ainsi que de la variabilite et des incertitudes associees avec les estimations disponibles sur les pools et les flux de carbone. De plus, les perturbations environnementales, comme le changement climatique, les depositions acides et l'enrichissement en nutriments, affectent vraisemblablement a la fois l'exportation du carbone vers les lacs et sa transformation dans ces lacs, en regions boreales. Il s'avere particulierement difficile d'en predire les impacts sur les budgets carbones des lacs, non seulement parce que les agents stressants environnementaux individuels sont susceptibles d'affecter plusieurs processus impliques dans le cyclage du carbone, mais aussi parce que souvent les multiples agents stressants agissent de facon synergique ou antagoniste a l'echelle du paysage. Consequemment, des approches a long terme et a l'echelle des systemes sont necessaires pour evaluer precisement l'importance des lacs dans les budgets du carbone dans un environnement en changement. [Traduit par la Redaction] Mots-cles: foret boreale, lacs, budget du carbone, emission de C[O.sub.2], perturbations environnementales, changement climatique., Introduction Boreal forests play a dominant role in the carbon cycle of the northern hemisphere, sequestering about 0.5 ± 0.1 Pg C [yr.sup.-1] over the past two decades, equaling 20%-22% [...]

Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence--although each with important uncertainties--lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments. The study of an iron-fertilized phytoplankton bloom dominated by diatoms, which takes up carbon dioxide from the atmosphere, shows that a substantial proportion of the bloom eventually sinks to the deep-sea floor, sequestering the carbon for timescales of centuries or more. Greening the seas The iron hypothesis proposes that the supply of iron-bearing dust to certain oceanic regions stimulates phytoplankton blooms that, by sinking out to the deep ocean when the organisms die, sequester carbon absorbed from exchange with the atmosphere. Experiments carried out to test the idea have provided clear evidence that iron addition generates phytoplankton blooms in waters with high -nutrient but low -chlorophyll concentrations, as proposed. But the fate of phytoplankton blooms and hence the extent of any carbon sequestration to the deep ocean has remained uncertain. This paper presents multiple lines of evidence, collected by aboard RV Polarstern in 2004 during the European Iron Fertilization Experiment (EIFEX), that suggest carbon is exported to the deep ocean as a result of iron fertilization, with at least half of the bloom biomass sinking to below 1,000 metres., Author(s): Victor Smetacek [sup.1] [sup.2] , Christine Klaas [sup.1] , Volker H. Strass [sup.1] , Philipp Assmy [sup.1] [sup.3] , Marina Montresor [sup.4] , Boris Cisewski [sup.1] [sup.5] , Nicolas [...]