Carbon Storage In Tropical Forests Research Articles

Experimental warming and drying increase older carbon contributions to soil respiration in lowland tropical forests

Tropical forests account for over 50% of the global terrestrial carbon sink, but climate change threatens to alter the carbon balance of these ecosystems. We show that warming and drying of tropical forest soils may increase soil carbon vulnerability, by increasing degradation of older carbon. In situ whole-profile heating by 4 °C and 50% throughfall exclusion each increased the average radiocarbon age of soil CO2 efflux by ~2–3 years, but the mechanisms underlying this shift differed. Warming accelerated decomposition of older carbon as increased CO2 emissions depleted newer carbon. Drying suppressed decomposition of newer carbon inputs and decreased soil CO2 emissions, thereby increasing contributions of older carbon to CO2 efflux. These findings imply that both warming and drying, by accelerating the loss of older soil carbon or reducing the incorporation of fresh carbon inputs, will exacerbate soil carbon losses and negatively impact carbon storage in tropical forests under climate change.

Land use intensity determines soil properties and biomass recovery after abandonment of agricultural land in an Amazonian biodiversity hotspot

There has been widespread clearance of tropical forests for agriculture, but in many cases the cultivation phase is only transient. The secondary forests recovering on these abandoned sites may contribute to mitigation of greenhouse gas emissions and protection of biodiversity, but the rates of recovery may be dependent on land-use intensity and changes in soil properties during cultivation. However fine-scale details on these changes are poorly known for many tropical forest locations. We quantified soil properties and recovery of woody biomass in 42 tropical forest fragments representing a chronosequence following two types of agricultural land-uses, and in 15 comparable reference old growth forests, between the Andes and the Amazon in Peru. Soil fertility, particularly base cation concentrations, responded negatively to increasing intensity of agricultural land-use, and either decreased or increased with time after abandonment dependent on prior land-use. The predicted mean recovery rate of woody biomass over the first 20 years following abandonment matched that predicted by a general model for the Neotropics, but recovery was three-fold higher on sites abandoned following traditional agriculture than on sites recovering from intensive agriculture. Estimated total biomass recovered to just above half that of reference old growth forests within 71 years. The inclusion of the biomass of lianas and smaller tree stems did not modify the apparent rate of ecosystem biomass recovery, however the proportion of the total biomass stored in small stems was greater following intensive than traditional agriculture, which suggests that patterns of stand structural development are sensitive to land-use history. We conclude that effects of historic land use on soil nutrient concentrations and their changes through time are required for a more complete interpretation of variation in biomass recovery rates at local scales. These results also highlight the critical importance of contemporary agricultural intensification for carbon storage in tropical forests.

Defaunation of large-bodied frugivores reduces carbon storage in a tropical forest of Southeast Asia

Recent studies have suggested that defaunation of large-bodied frugivores reduces above-ground carbon storage in tropical forests of South America and Africa, but not, or less so, in Southeast Asian tropical forests. Here we analyze the issue using the seed dispersal network (data of interaction between trees and animal seed dispersers) and forest composition of a 30-ha forest dynamics plot in central Thailand, where an intact fauna of primates, ungulates, bears and birds of all sizes still exists. We simulate the effect of two defaunation scenarios on forest biomass: 1) only primates extirpated (a realistic possibility in near future), and 2) extirpation of all large-bodied frugivores (LBF) including gibbons, macaques, hornbills and terrestrial mammals, the main targets of poachers in this region. For each scenario, we varied the population size reduction of the LBF dispersed tree species from 20% to 100%. We find that tree species dependent on seed dispersal by large-bodied frugivores (LBF) account for nearly one-third of the total carbon biomass on the plot, and that the community turnover following a complete defaunation would result in a carbon reduction of 2.4% to 3.0%, depending on the defaunation scenario and the model assumptions. The reduction was always greater than 1% when the defaunation intensity was at least 40%. These effect sizes are comparable to values reported for Neotropical forests, suggesting that the impact of defaunation on carbon deficit is not necessarily lower in Southeast Asian forests. The problem of defaunation in Asia, and the mutual benefits between biodiversity conservation and climate change mitigation, should therefore not be neglected by global policies to reduce carbon emissions.

Managing the invasion of guava trees to enhance carbon storage in tropical forests

Tropical forests account for a substantial percentage of the world’s carbon stocks, but the consequences to carbon storage of the rapid invasiveness of the guava tree in these forests is not known. Two different forest management strategies are practiced in a tropical forest in western Kenya: (1) a protection strategy where human entry is prohibited except for minimalistic human presence (e.g., research activities); and (2) a conservation strategy where human access to the forest and its resources are permitted. We assessed the effects of these management strategies and different levels of disturbance caused by the legacy effects of legal logging activities and the contemporary effects of unauthorized harvesting of forest products on the abundance of guava and non-guava trees and carbon storage in both plant biomass and soil in this forest. We found that guava trees were less likely to thrive and carbon storage in plants and soils was similar in sites with minimal disturbance under both the protection and conservation strategies. However, as disturbance increased, whether by the historical or contemporary effects of human activities, guava trees were more likely to thrive and carbon storage in plants shifted from non-guava trees to guava trees, but without an effect on more stable soil carbon. We conclude that regulations should be strictly enforced to prevent all logging activity, but the conservation strategy would provide similar effects on both forest plant and soil carbon to the protection strategy, while providing benefits to the surrounding community who rely on the forest for cultural and spiritual nourishment.

Defaunation affects carbon storage in tropical forests.

Carbon storage is widely acknowledged as one of the most valuable forest ecosystem services. Deforestation, logging, fragmentation, fire, and climate change have significant effects on tropical carbon stocks; however, an elusive and yet undetected decrease in carbon storage may be due to defaunation of large seed dispersers. Many large tropical trees with sizeable contributions to carbon stock rely on large vertebrates for seed dispersal and regeneration, however many of these frugivores are threatened by hunting, illegal trade, and habitat loss. We used a large data set on tree species composition and abundance, seed, fruit, and carbon-related traits, and plant-animal interactions to estimate the loss of carbon storage capacity of tropical forests in defaunated scenarios. By simulating the local extinction of trees that depend on large frugivores in 31 Atlantic Forest communities, we found that defaunation has the potential to significantly erode carbon storage even when only a small proportion of large-seeded trees are extirpated. Although intergovernmental policies to reduce carbon emissions and reforestation programs have been mostly focused on deforestation, our results demonstrate that defaunation, and the loss of key ecological interactions, also poses a serious risk for the maintenance of tropical forest carbon storage.

Evaluation of stem rot in 339 Bornean tree species: implications of size, taxonomy, and soil-related variation for aboveground biomass estimates

Abstract. Fungal decay of heart wood creates hollows and areas of reduced wood density within the stems of living trees known as stem rot. Although stem rot is acknowledged as a source of error in forest aboveground biomass (AGB) estimates, there are few data sets available to evaluate the controls over stem rot infection and severity in tropical forests. Using legacy and recent data from 3180 drilled, felled, and cored stems in mixed dipterocarp forests in Sarawak, Malaysian Borneo, we quantified the frequency and severity of stem rot in a total of 339 tree species, and related variation in stem rot with tree size, wood density, taxonomy, and species' soil association, as well as edaphic conditions. Predicted stem rot frequency for a 50 cm tree was 53 % of felled, 39 % of drilled, and 28 % of cored stems, demonstrating differences among methods in rot detection ability. The percent stem volume infected by rot, or stem rot severity, ranged widely among trees with stem rot infection (0.1–82.8 %) and averaged 9 % across all trees felled. Tree taxonomy explained the greatest proportion of variance in both stem rot frequency and severity among the predictors evaluated in our models. Stem rot frequency, but not severity, increased sharply with tree diameter, ranging from 13 % in trees 10–30 cm DBH to 54 % in stems ≥ 50 cm DBH across all data sets. The frequency of stem rot increased significantly in soils with low pH and cation concentrations in topsoil, and stem rot was more common in tree species associated with dystrophic sandy soils than with nutrient-rich clays. When scaled to forest stands, the maximum percent of stem biomass lost to stem rot varied significantly with soil properties, and we estimate that stem rot reduces total forest AGB estimates by up to 7 % relative to what would be predicted assuming all stems are composed strictly of intact wood. This study demonstrates not only that stem rot is likely to be a significant source of error in forest AGB estimation, but also that it strongly covaries with tree size, taxonomy, habitat association, and soil resources, underscoring the need to account for tree community composition and edaphic variation in estimating carbon storage in tropical forests.

Diversity enhances carbon storage in tropical forests

AbstractAimTropical forests store 25% of global carbon and harbour 96% of the world's tree species, but it is not clear whether this high biodiversity matters for carbon storage. Few studies have teased apart the relative importance of forest attributes and environmental drivers for ecosystem functioning, and no such study exists for the tropics.LocationNeotropics.MethodsWe relate aboveground biomass (AGB) to forest attributes (diversity and structure) and environmental drivers (annual rainfall and soil fertility) using data from 144,000 trees, 2050 forest plots and 59 forest sites. The sites span the complete latitudinal and climatic gradients in the lowland Neotropics, with rainfall ranging from 750 to 4350 mm year−1. Relationships were analysed within forest sites at scales of 0.1 and 1 ha and across forest sites along large‐scale environmental gradients. We used a structural equation model to test the hypothesis that species richness, forest structural attributes and environmental drivers have independent, positive effects on AGB.ResultsAcross sites, AGB was most strongly driven by rainfall, followed by average tree stem diameter and rarefied species richness, which all had positive effects on AGB. Our indicator of soil fertility (cation exchange capacity) had a negligible effect on AGB, perhaps because we used a global soil database. Taxonomic forest attributes (i.e. species richness, rarefied richness and Shannon diversity) had the strongest relationships with AGB at small spatial scales, where an additional species can still make a difference in terms of niche complementarity, while structural forest attributes (i.e. tree density and tree size) had strong relationships with AGB at all spatial scales.Main conclusionsBiodiversity has an independent, positive effect on AGB and ecosystem functioning, not only in relatively simple temperate systems but also in structurally complex hyperdiverse tropical forests. Biodiversity conservation should therefore be a key component of the UN Reducing Emissions from Deforestation and Degradation strategy.

Hunting alters seedling functional trait composition in a Neotropical forest.

Defaunation alters trophic interactions between plants and vertebrates, whichmay disrupt trophic cascades, thereby favoring a subset of plant species and reducing diversity. If particular functional traits characterize the favored plant species,.then defaunation may alter community-wide patterns of functional trait composition. Changes in plant functional traits occurring with defaunation may help identify the species interactions affected by defaunation and the potential for other cascading effects of defaunation. We tested the hypotheses that defaunation would (1) disrupt seed dispersal, thereby favoring species whose dispersal agents are not affected (e.g., small birds, bats, and abiotic agents), (2) reduce seed predation, thereby favoring larger-seeded species, and (3) reduce herbivory, thereby favoring species with lower leaf mass per area (LMA), leaf toughness, and wood density. We examined how these six traits responded to vertebrate defaunation caused by hunters or by experimental exclosures among more than-30 000 woody seedlings in a lowland tropical moist forest. Exclosures reduced terrestrial frugivores, granivores, and herbivores, while hunters also reduced volant and arboreal frugivores and granivores. The comparison of exclosures and hunting allowed us to parse the impacts of arboreal and volant species (reduced by hunters only) and terrestrial species (reduced by both hunters and exclosures). The loss of terrestrial vertebrates alone had limited effects on plant trait composition. The additional loss of volant and arboreal vertebrates caused significant shifts in plant species composition towards communities with more species dispersed abiotically, including lianas and low wood-density tree species, and fewer species dispersed by large vertebrates. In contrast to previous studies, community seed mass did not decline significantly in hunted sites. Our exclosure results suggest this is because reducing seed predators disproportionately benefits large-seeded species,.partially compensating for the reduction of seed dispersers at hunted sites. Our result9sdemonstrate that decreased seed dispersal and seed predation are important determinants of seedling community compositional change as a consequence of defaunation. Defaunation may also negatively impact carbon storage in tropical forests, by favoring lianas and low wood density tree species.

The relative importance of climate, stand variables and liana abundance for carbon storage in tropical forests

AbstractAimTo develop an integrative framework to evaluate variation in aboveground carbon storage (AGC). A model that can be applied to understand and predict how global‐change drivers influence tropical carbon sinks.LocationOld‐growth tropical forests world‐wide.MethodsUsing structural equation modelling (SEM), we propose an a priori model to evaluate the direct and indirect effects of climate, stand variables (basal area, tree diameter and wood density at plot level) and liana abundance onAGC. Our model indicated that stand variables increasedAGCwhile liana abundance decreasedAGCindirectly via negative effects on stand variables. We used a multigroupSEMto test the generality of our framework using a standardized dataset of 145 plots (0.1 ha) in dry, moist and wet tropical forests.ResultsOur model explained over 85% variation inAGCand showed a positive and consistent relationship between stand variables andAGCacross forests types. The effects of climate onAGCwere indirect rather than direct, with negative effects of temperature in all forests. Liana abundance reduced tree diameter and basal area in moist forests, but did not affectAGCin wet or dry forests.Main conclusionsOur results suggest that climate affectsAGCindirectly, via its direct influence on stand variables and liana abundance. The effects of lianas onAGCresult from reductions in stand variables and are as important as climate for moist forests, which harbour the greatest tropical carbon pools. Our model was consistent across forest types. This highlights the usefulness of an integrative framework to improve predictions of the effects of drivers of global change on tropical carbon sinks.

Amazonian functional diversity from forest canopy chemical assembly

Patterns of tropical forest functional diversity express processes of ecological assembly at multiple geographic scales and aid in predicting ecological responses to environmental change. Tree canopy chemistry underpins forest functional diversity, but the interactive role of phylogeny and environment in determining the chemical traits of tropical trees is poorly known. Collecting and analyzing foliage in 2,420 canopy tree species across 19 forests in the western Amazon, we discovered (i) systematic, community-scale shifts in average canopy chemical traits along gradients of elevation and soil fertility; (ii) strong phylogenetic partitioning of structural and defense chemicals within communities independent of variation in environmental conditions; and (iii) strong environmental control on foliar phosphorus and calcium, the two rock-derived elements limiting CO2 uptake in tropical forests. These findings indicate that the chemical diversity of western Amazonian forests occurs in a regionally nested mosaic driven by long-term chemical trait adjustment of communities to large-scale environmental filters, particularly soils and climate, and is supported by phylogenetic divergence of traits essential to foliar survival under varying environmental conditions. Geographically nested patterns of forest canopy chemical traits will play a role in determining the response and functional rearrangement of western Amazonian ecosystems to changing land use and climate.

Carbon storage in tropical forests correlates with taxonomic diversity and functional dominance on a global scale

AbstractAimWe examined (1) the relationships between aboveground tropical forestCstorage, biodiversity and environmental drivers and (2) how these relationships inform theory concerning ecosystem function and biodiversity. Experiments have shown that there is a positive relationship between biodiversity and ecosystem functioning, but intense debate exists on the underlying mechanisms. While some argue that mechanisms such as niche complementarity increase ecosystem function, others argue that these relationships are a selection effect.LocationEleven tropical forests in theAmericas,Africa andAsia.MethodsWe analysed the correlates of biodiversity and carbon storage in tropical forests using data from 59 1‐ha tree plots from a standardized global tropical forest biodiversity‐monitoring network. We examined taxonomic and functional diversity, abovegroundCstorage and environmental variables in order to determine the relationships between biodiversity and carbon storage in natural (non‐plantation) tropical forests.ResultsWe found that abovegroundCstorage in tropical forests increased with both taxonomic diversity and functional dominance, specifically the dominance of genera with large maximum diameters, after potential environmental drivers were accounted for (final modelR2 = 0.38,P < 0.001).Main conclusionsOur results suggest that niche complementarity and the selection effect are not mutually exclusive: they both play a role in structuring tropical forests. While previous studies have documented relationships between diversity andCstorage, these have largely been conducted on small scales in biomes that are relatively species poor compared with tropical forests (e.g. grasslands and temperate or boreal forests). Our results demonstrate that these positive biodiversity–ecosystem functioning relationships are also present in hyperdiverse systems on spatial scales relevant to conservation and management. This insight can be used to inform the conservation and management of tropical forests, which play a critical role in the global carbon cycle and are some of the biologically richest ecosystems on the planet.

Ecuación para estimar la biomasa arbórea en los bosques tropicales de Costa Rica

<p>Una de las medidas más relevantes para la mitigación del cambio climático es la conservación y regeneración del bosque en nuestros países. La cantidad de carbono que se almacena en la biomasa arbórea pasa a ser una medida relevante para la política pública. El presente trabajo analiza la asociación que tienen algunas variables dasométricas, fácilmente medibles, asociadas a la biomasa, con el propósito de estimarla indirectamente, dado que la medición directa de la biomasa arbórea es un trabajo complejo y tiene un costo muy elevado. El objetivo general del estudio fue hacer un análisis del comportamiento de las variables dasométricas fácilmente medibles para predecir biomasa arbórea con datos de dos bosques tropicales de Costa Rica, con el propósito de analizar su posible aplicación generalizada en los bosques tropicales de todo el país.</p> <p>Mediante una revisión bibliográfica, se determinaron cuatro posibles modelos que estiman biomasa en bosques tropicales. Se evaluaron 907 árboles con diámetro a la altura de pecho (dap) mayor a 10 cm en dos bosques tropicales de Costa Rica (Parque Nacional Corcovado en el suroeste y Fila Carbón en el sureste, vertiente del Caribe), generando una estimación de biomasa lo más precisa posible. Se realizó un análisis de las variables de los árboles (densidad específica de la madera, altura total y dap) y su biomasa, con el fin de desarrollar el modelo que facilitara la predicción de esta. El modelo final utiliza como variables independientes el dap y la densidad. Con el dap se da el hecho de que existe una alta correlación con la altura total, la cual es muy difícil de obtener en el campo, de modo que se decidió no utilizarla. La variable densidad es importante, ya que dos árboles con la misma estructura pero distinta densidad van a mostrar diferente cantidad de biomasa. Para la estimación de este modelo se utilizó una regresión segmentada (por la relación que tienen el dap y la altura total con la variable biomasa transformada) y cuadrados medios ponderados para resolver el problema de heterocedasticidad. El modelo final cumplió con los supuestos estadísticos de una regresión lineal general, evaluados por el comportamiento de los residuos y otras pruebas paramétricas, y obtiene un coeficiente de determinación de 0,992.</p> <p>Como conclusión, este estudio propone un enfoque metodológico para estimar la biomasa a nivel general en los bosques, lo cual se considera de utilidad para fundamentar la toma de decisiones sobre el almacenamiento a largo plazo del carbono en los bosques tropicales. Se espera que en estudios futuros se disponga de parcelas de otros bosques con mediciones de la biomasa real, para seguir calibrando el modelo propuesto para la estimación de la biomasa almacenada en los bosques tropicales.</p>

Whole-island carbon stocks in the tropical Pacific: Implications for mangrove conservation and upland restoration

Management of forest carbon (C) stocks is an increasingly prominent land-use issue. Knowledge of carbon storage in tropical forests is improving, but regional variations are still poorly understood, and this constrains forest management and conservation efforts associated with carbon valuation mechanisms (e.g., carbon markets). This deficiency is especially pronounced in tropical islands and low-lying coastal areas where climate change impacts are expected to be among the most severe. This study presents the first field estimate of island-wide carbon storage in ecosystems of Oceania, with special attention to the regional role of coastal mangroves, which occur on islands and coastal zones throughout the tropics. On two island groups of Micronesia (Yap and Palau), we sampled all above- and belowground C pools, including soil and vegetation, in 24 sites distributed evenly among the three major vegetation structural types: mangroves, upland forests, and open savannas (generally on degraded lands formerly forested). Total C stocks were estimated to be 3.9 and 15.2 Tg C on Yap and Palau, respectively. Mangroves contained by far the largest per-hectare C pools (830-1218 Mg C ha(-1)), with deep organic-rich soils alone storing more C (631-754 Mg C ha(-1)) than all pools combined in upland systems. Despite covering just 12-13% of land area, mangroves accounted for 24-34% of total island C stocks. Savannas (156-203 Mg C ha(-1)) contained significantly lower C stocks than upland forests (375-437 Mg C ha(-1)), suggesting that reforesting savannas where appropriate has high potential for carbon-based funding to aid restoration objectives. For mangroves, these results demonstrate the key role of these systems within the broader context of C storage in island and coastal landscapes. Sustainable management of mangrove forests and their large C stocks is of high importance at the regional scale, and climate change mitigation programs such as REDD+ could play a large role in avoiding deforestation of mangroves where this is a management objective.

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 1ha plots, the total carbon stock of the forest ecosystem was 303tCha−1. Living tree carbon stocks (both above- and belowground) ranged from 163 to 258tCha−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>70cm). The contributions of the shrub layer, herb layer, woody lianas, and fine litter each accounted for 1–2tCha−1 to the total carbon stock. The mineral soil C pools (top 100cm) ranged from 84 to 102tCha−1 and the C in woody debris from 5.6 to 12.5tCha−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.

Species Loss and Aboveground Carbon Storage in a Tropical Forest

Tropical forest biodiversity is declining, but the resulting effects on key ecosystem services, such as carbon storage and sequestration, remain unknown. We assessed the influence of the loss of tropical tree species on carbon storage by simulating 18 possible extinction scenarios within a well-studied 50-hectare tropical forest plot in Panama, which contains 227 tree species. Among extinction scenarios, aboveground carbon stocks varied by more than 600%, and biological insurance varied by more than 400%. These results indicate that future carbon storage in tropical forests will be influenced strongly by future species composition.

Elicitation of Expert Judgments of Climate Change Impacts on Forest Ecosystems

Detailed interviews were conducted with 11 leading ecologists to obtainindividualqualitative and quantitative estimates of the likely impact of a2 × [CO2] climate change onminimally disturbed forest ecosystems. Results display a much richer diversityof opinion thanis apparent in qualitative consensus summaries, such as those of the IPCC.Experts attachdifferent relative importance to key factors and processes such as soilnutrients, fire, CO2fertilization, competition, and plant-pest-predator interactions. Assumptionsand uncertaintiesabout future fire regimes are particularly crucial. Despite these differences,most of the expertsbelieve that standing biomass in minimally disturbed Northern forests wouldincrease and soilcarbon would decrease. There is less agreement about impacts on carbon storagein tropicalforests. Estimates of migration rates in northern forests displayed a rangeof more than fourorders of magnitude. Estimates of extinction rates and dynamic response showsignificantvariation between experts. A series of questions about research needs foundconsensus on theimportance of expanding observational and experimental work on ecosystemprocesses and ofexpanding regional and larger-scale observational, monitoring and modelingstudies. Results ofthe type reported here can be helpful in performing sensitivity analysis inintegrated assessmentmodels, as the basis for focused discussions of the state of currentunderstanding and researchneeds, and, if repeated over time, as a quantitative measure of progress inthis and other fieldsof global change research.

Effects of global change on carbon storage in tropical forests of South America

We used a process‐based model of ecosystem biogeochemistry (MBL‐GEM) to evaluate the effects of global change on carbon (C) storage in mature tropical forest ecosystems in the Amazon Basin of Brazil. We first derived a single parameterization of the model that was consistent with all the C stock and turnover data from three intensively studied sites within the Amazon Basin that differed in temperature, rainfall, and cloudiness. The range in temperature, soil moisture, and photosynthetically active radiation (PAR) among these sites is about as large as the anticipated changes in these variables in the tropics under CO2‐induced climate change. We then tested the parameterized model by predicting C stocks along a 2400‐km transect in the Amazon Basin. Comparison of predicted and measured vegetation and soil C stocks along this transect suggests that the model provides a reasonable approximation of how climatic and hydrologic factors regulate present‐day C stocks within the Amazon Basin. Finally, we used the model to predict and analyze changes in ecosystem C stocks under projected changes in atmospheric CO2 and climate. The central hypothesis of this exercise is that changes in ecosystem C storage in response to climate and CO2 will interact strongly with changes in other element cycles, particularly the nitrogen (N) and phosphorus (P) cycles. We conclude that C storage will increase in Amazonian forests as a result of (1) redistribution of nutrients from soil (with low C:nutrient ratios) to vegetation (with high C:nutrient ratios), (2) increases in the C:nutrient ratio of vegetation and soil, and (3) increased sequestration of external nutrient inputs by the ecosystem. Our analyses suggest that C:nutrient interactions will constrain increases in C storage to a maximum of 63 Mg/ha during the next 200 years, or about 16% above present‐day stocks. However, it is impossible to predict how much smaller the actual increase in C storage will be until more is known about the controls on soil P availability. On the basis of these analyses, we identify several topics for further research in the moist tropics that must be addressed to resolve these uncertainties.