No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Long-term decline of the Amazon carbon sink
Abstract
Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades1, 2, with a substantial fraction of this sink probably located in the tropics3, particularly in the Amazon4. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity5. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale1, 2, and is contrary to expectations based on models6
... Carbon loss represents the amount of live biomass (with a diameter > 10 cm) that is transferred to the woody litter pool due to tree mortality, resulting from events of continuous competition-induced mortality (killing small trees) and events regarding pulses of drought-induced mortality (killing large trees). Then we aggregate the grid-level carbon gain and carbon loss to the basin level, following the approach used by Brienen et al. (2015). Observational time series of carbon gains, losses, and the net carbon balance for Amazonian forests are obtained from Brienen et al. (2015). ...
... Then we aggregate the grid-level carbon gain and carbon loss to the basin level, following the approach used by Brienen et al. (2015). Observational time series of carbon gains, losses, and the net carbon balance for Amazonian forests are obtained from Brienen et al. (2015). To gain a deeper insight into how eCO 2 impacts carbon loss, we examined changes in both competition-induced tree mortality (self-thinning (CIM)) and drought-induced tree mortality (DIM) as distinct components. ...
The Amazon rainforest plays a crucial role in global carbon storage, but a minor destabilization of these forests could result in considerable carbon loss. Among the external factors affecting vegetation, elevated CO2 (eCO2) levels have long been anticipated to have positive impacts on vegetation, including the direct enhancement of both photosynthesis and productivity and increasing water use efficiency. However, the overall impact of eCO2 on the net carbon balance, especially concerning tree-mortality-induced carbon loss and recovery following extreme drought events, has remained elusive. Here, we use a process-based model that couples physiological CO2 effects with demography and both drought mortality and resistance processes. The model was previously calibrated to reproduce observed drought responses of Amazon forest sites. The model results, based on factorial simulations with and without eCO2, reveal that eCO2 enhances forest growth and promotes competition between trees, leading to more natural self-thinning of forest stands. This occurs following a growth–mortality trade-off response, although the growth outweighs the tree loss. Additionally, eCO2 provides water-saving benefits, reducing the risk of tree mortality during drought episodes. However, extra carbon losses could still occur due to an eCO2-induced increase in background biomass density, leading to “more carbon available to lose” when severe droughts happen. Furthermore, we found that eCO2 accelerates drought recovery and enhances drought resistance and resilience. By delving into the less-explored aspect of tree mortality response to eCO2, the model improvements advance our understanding of how carbon balance responds to eCO2, particularly regarding mechanisms of continuous competition-induced carbon loss vs. pulses of drought-induced carbon loss. These findings provide valuable insights into the intricate ways in which rising CO2 influences forest carbon dynamics and vulnerability, offering a critical understanding of the Amazon rainforest's evolution amidst more frequent and intense extreme climate events.
... Measurements from long-term inventory plots suggest that Amazonian forests have contributed a major carbon sink for decades but that this carbon sink has been declining since the early 1990s (ref. 7), and may cease before 2040 (ref. 8). ...
... Field data were checked against rules to identify potential errors, identically for all 123 plots, consistent with previous large-scale analyses 7,8,44,48 . We assessed trees that increased in diameter >40 mm per year or shrunk >5 mm over an interval, to determine if they could have been inaccurately measured in the field. ...
The tropical forest carbon sink is known to be drought sensitive, but it is
unclear which forests are the most vulnerable to extreme events. Forests with
hotter and drier baseline conditions may be protected by prior adaptation, or
more vulnerable because they operate closer to physiological limits. Here we
report that forests in drier South American climates experienced the greatest
impacts of the 2015–2016 El Niño, indicating greater vulnerability to extreme
temperatures and drought. The long-term, ground-measured tree-by-tree
responses of 123 forest plots across tropical South America show that the
biomass carbon sink ceased during the event with carbon balance becoming
indistinguishable from zero (−0.02 ± 0.37 Mg C ha−1 per year). However,
intact tropical South American forests overall were no more sensitive to the
extreme 2015–2016 El Niño than to previous less intense events, remaining a
key defence against climate change as long as they are protected
... These intense changes include a significant reduction in precipitation, an increase in temperature and in the frequency of intense drought and flood events (Erfanian et al. 2017;Matricardi et al. 2020;Assis et al. 2022;Marengo et al. 2022;Smith et al. 2023), directly affecting the productivity of small-scale agriculture and extractivism and the composition and diversity of species in these ecosystems. Recent studies indicate that both the structure and composition of the tree flora in the Amazon have undergone adaptations to a drier and hotter climate (Brienen et al. 2015;Esquivel-Muelbert et al. 2019). ...
... However, the adaptations of biological communities are not able to keep up with the rapid pace of climate change, which is leading to large-scale tree species mortality events (Esquivel-Muelbert et al. 2020) and consequent reduction in forest productivity (Brienen et al. 2015). These effects vary between Amazonian regions, being more intense in the southern and eastern portions of the biome (Marengo et al. 2022). ...
... The Amazon basin in South America is an emblematic region in the global environmental discussion due to its extensive ecosystems 1,2 , its diverse biodiversity 1,3,4 , its climate regulation and forcing 1,5,6 , and its benefits to people 4,7 . The South American Amazon forests contain between 95 and 200 Pg of carbon stored in living biomass [8][9][10] . ...
... The science of the global carbon (C) cycle has continuously evolved, leading to important advances in estimating the fossil fuel component of the cycle. This highlights the urgency of addressing the critical and constant increase in greenhouse gas concentrations in the atmosphere 6,13 . The non-fossil fuel portion of the global C cycle carries great uncertainty. ...
The Amazon Forest, the largest contiguous tropical forest in the world, stores a significant fraction of the carbon on land. Changes in climate and land use affect total carbon stocks, making it critical to continuously update and revise the best estimates for the region, particularly considering changes in forest dynamics. Forest inventory data cover only a tiny fraction of the Amazon region, and the coverage is not sufficient to ensure reliable data interpolation and validation. This paper presents a new forest above-ground biomass map for the Brazilian Amazon and the associated uncertainty both with a resolution of 250 meters and baseline for the satellite dataset the year of 2016 (i.e., the year of the satellite observation). A significant increase in data availability from forest inventories and remote sensing has enabled progress towards high-resolution biomass estimates. This work uses the largest airborne LiDAR database ever collected in the Amazon, mapping 360,000 km² through transects distributed in all vegetation categories in the region. The map uses airborne laser scanning (ALS) data calibrated by field forest inventories that are extrapolated to the region using a machine learning approach with inputs from Synthetic Aperture Radar (PALSAR), vegetation indices obtained from the Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite, and precipitation information from the Tropical Rainfall Measuring Mission (TRMM). A total of 174 field inventories geolocated using a Differential Global Positioning System (DGPS) were used to validate the biomass estimations. The experimental design allowed for a comprehensive representation of several vegetation types, producing an above-ground biomass map varying from a maximum value of 518 Mg ha⁻¹, a mean of 174 Mg ha⁻¹, and a standard deviation of 102 Mg ha⁻¹. This unique dataset enabled a better representation of the regional distribution of the forest biomass and structure, providing further studies and critical information for decision-making concerning forest conservation, planning, carbon emissions estimate, and mechanisms for supporting carbon emissions reductions.
... Measurements from long-term inventory plots suggest that Amazonian forests have contributed a major carbon sink for decades but that this carbon sink has been declining since the early 1990s (ref. 7), and may cease before 2040 (ref. 8). ...
... Field data were checked against rules to identify potential errors, identically for all 123 plots, consistent with previous large-scale analyses 7,8,44,48 . We assessed trees that increased in diameter >40 mm per year or shrunk >5 mm over an interval, to determine if they could have been inaccurately measured in the field. ...
The tropical forest carbon sink is known to be drought sensitive, but it is unclear which forests are the most vulnerable to extreme events. Forests with hotter and drier baseline conditions may be protected by prior adaptation, or more vulnerable because they operate closer to physiological limits. Here we report that forests in drier South American climates experienced the greatest impacts of the 2015–2016 El Niño, indicating greater vulnerability to extreme temperatures and drought. The long-term, ground-measured tree-by-tree responses of 123 forest plots across tropical South America show that the biomass carbon sink ceased during the event with carbon balance becoming indistinguishable from zero (−0.02 ± 0.37 Mg C ha⁻¹ per year). However, intact tropical South American forests overall were no more sensitive to the extreme 2015–2016 El Niño than to previous less intense events, remaining a key defence against climate change as long as they are protected.
... Decreased water leads to increased tree death, directly through carbon starvation and hydraulic failure (Hartmann et al. 2015) and indirectly by exposing trees to insect outbreaks. Even in well-watered regions, extra implications of climate change, such as increased competition among trees (Luo and Chen 2015) or potentially shortened lifespans (Brienen et al. 2015), can still lead to increased mortality. Notably, these climate-driven increases in tree death translate to significant losses in woodland biomass (Lewis et al. 2011). ...
The ramifications of climate change permeate every facet of our contemporary lives, representing a universally acknowledged and significant global concern. In recent years, there has been a notable surge in exploring the potential of nature-based solutions, underscoring the importance of natural ecosystems and agroforestry in combatting climate change effects. These solutions endeavor to tackle diverse challenges such as climate change mitigation, ensuring food security, managing water resources, and mitigating disaster risks by harnessing the inherent capabilities of natural systems. This chapter extensively analyzes various approaches to alleviating climate change impacts, explicitly focusing on forests and agroforestry. The pivotal role of forests and agroforestry in the climate change discourse is a subject of intense debate, given their involvement in both carbon sequestration and emission processes. Agroforestry notably enhances farmers’ resilience to climate change while offering many ecological, social, and economic benefits. As the halfway point of the 2030 Agenda approaches, it becomes increasingly evident that current efforts are insufficient to meet climate targets. Nature-based solutions necessitate further exploration of the ecosystem benefits of forests across different settings, including natural environments, semi-natural areas, and urban spaces. These benefits extend beyond resource provision to encompass activities related to regulation, maintenance, and cultural services. Forests and agroforestry emerge as pivotal players in climate regulation, carbon sequestration, and the enhancement of air, soil, and water quality while mitigating the impact of natural disasters. Besides, they offer avenues for recreation, spiritual enrichment, and aesthetic enjoyment, thereby contributing to human well-being. This chapter advocates for studies addressing ecological, climate-related, and social aspects, fostering dialogue among scientists and stakeholders, and suggesting ways to implement forests as nature-based solutions. Such efforts are crucial for aiding stakeholders in decision-making processes to mitigate climate change’s impacts.
... A reasonable first-order assumption. This may not be accurate, as carbon density increases each year after the last episode of deforestation or disturbance and carbon density of undisturbed forest is falling over time as a result of global warming (Hubau et al. 2020;Brienen et al. 2015). Our method will be upgraded to reflect this. ...
This document describes the methodology developed by the Cambridge Center for Carbon Credits for estimating the number of credits to be issued to an avoided deforestation project in the tropical moist forest biome.
... However, Amazon intact forests are under pressure 10 and have experienced a persistent decline in their sink capacity in the past decades 11 , potentially attributable to drought-induced increases in tree mortality 12,13 . Climate change, including the increasing intensity and severity of extreme events, may play an important role in this progressive shift of intact Amazon forests from a carbon sink to a carbon source, as extreme productivity and mortality anomalies notably occur during or directly after extremely hot and dry events such as the large-scale drought of 2015/2016 14,15 . ...
In the Amazon, the dry season of 2023 as well as the beginning of the wet season in 2024 were marked by unprecedented high temperatures and large precipitation deficits. While the tropical forests in the Amazon play a crucial role in the global carbon cycle and are a biodiversity hotspot, they were also shown to suffer from El-Niño related droughts in the past, leading to legitimate concerns about the ecological consequences of the recent climate conditions. To this day, while there is a growing effort to make remote sensing products available close to real-time, land surface models that are critical tools to understand the interactions between the biosphere and the environment have lagged behind the present due to the complexity to run and process large model ensembles. In this study, we employed advanced machine learning models trained on state-of-the-art remote sensing and dynamic global vegetation model estimates of gross primary productivity (GPP). The models provide near real-time GPP estimates, revealing significant productivity reductions during the 2023/2024 drought. Negative GPP anomalies were more widespread across the Amazon than during any other recent major drought event. The Climate-GPP relationships that emerged from the models suggest that future temperature increases and changes in precipitation will severely challenge Amazon forest resilience.
... Future tree mortality is impossible to observe, but a new model reveals why tropical tree traits matter more than climate change variability for predicting hydraulic failure Climate change-induced atmospheric warming and regional declines in precipitation are likely to intensify losses of forests (Allen et al., 2010) over-and above the already decades-long background rates of mortality (van Mantgem et al., 2009) and declines in carbon sinks (Brienen et al., 2015). Consequently, there is enormous interest in identifying the variables needed to understand how forests respond to changing climate. ...
This article is a Commentary on Robbins et al. (2024), 244: 2239–2250.
... Case study: Equilibrium conditions. The overall Neotropical forest productivity is increasing, a phenomenon attributed to secular changes in local climate, ambient CO 2 concentration, or nutrient conditions (80)(81)(82)(83)(84). Differences in growth responses of lianas and trees associated with such productivity increases may have instigated the observed liana proliferation (1,31). ...
Extending and safeguarding tropical forest ecosystems is critical for combating climate change and biodiversity loss. One of its constituents, lianas, is spreading and increasing in abundance on a global scale. This is particularly concerning as lianas negatively impact forests’ carbon fluxes, dynamics, and overall resilience, potentially exacerbating both crises. While possibly linked to climate-change-induced atmospheric CO 2 elevation and drought intensification, the reasons behind their increasing abundance remain elusive. Prior research shows distinct physiological differences between lianas and trees, but it is unclear whether these differences confer a demographic advantage to lianas with climate change. Guided by extensive datasets collected in Panamanian tropical forests, we developed a tractable model integrating physiology, demography, and epidemiology. Our findings suggest that CO 2 fertilization, a climate change factor promoting forest productivity, gives lianas a demographic advantage. Conversely, factors such as extreme drought generally cause a decrease in liana prevalence. Such a decline in liana prevalence is expected from a physiological point of view because lianas have drought-sensitive traits. However, our analysis underscores the importance of not exclusively relying on physiological processes, as interactions with demographic mechanisms (i.e., the forest structure) can contrast these expectations, causing an increase in lianas with drought. Similarly, our results emphasize that identical physiological responses between lianas and trees still lead to liana increase. Even if lianas exhibit collinear but weaker responses in their performance compared to trees, a temporary liana prevalence increase might manifest driven by the faster response time of lianas imposed by their distinct life-history strategies than trees.
... Despite recent efforts to quantify the carbon losses and gains from forest degradation and recovery, the estimates remain highly variable (12,13,44). Field inventory data, which are often limited to intact forests (45,46) and rarely designed to cover areas with human disturbance (34,47), provide a limited sample of plots due to accessibility and cost (48). Satellite-based approaches, despite their wider coverage, suffer from coarse resolution that makes it difficult to quantify the extent and intensity of forest degradation because the signal of selective logging and fires fades away between cloud-free observations due to regeneration (49,50). ...
The Amazon forest contains globally important carbon stocks, but in recent years, atmospheric measurements suggest that it has been releasing more carbon than it has absorbed because of deforestation and forest degradation. Accurately attributing the sources of carbon loss to forest degradation and natural disturbances remains a challenge because of the difficulty of classifying disturbances and simultaneously estimating carbon changes. We used a unique, randomized, repeated, very high-resolution airborne laser scanning survey to provide a direct, detailed, and high-resolution partitioning of aboveground carbon gains and losses in the Brazilian Arc of Deforestation. Our analysis revealed that disturbances directly attributed to human activity impacted 4.2% of the survey area while windthrows and other disturbances affected 2.7% and 14.7%, respectively. Extrapolating the lidar-based statistics to the study area (544,300 km ² ), we found that 24.1, 24.2, and 14.5 Tg C y ⁻¹ were lost through clearing, fires, and logging, respectively. The losses due to large windthrows (21.5 Tg C y ⁻¹ ) and other disturbances (50.3 Tg C y ⁻¹ ) were partially counterbalanced by forest growth (44.1 Tg C y ⁻¹ ). Our high-resolution estimates demonstrated a greater loss of carbon through forest degradation than through deforestation and a net loss of carbon of 90.5 ± 16.6 Tg C y ⁻¹ for the study region attributable to both anthropogenic and natural processes. This study highlights the role of forest degradation in the carbon balance for this critical region in the Earth system.
... In intact tropical forests, the foremost threats remain ongoing deforestation and degradation, which are the primary causes of the declining carbon sink (Extended Data Fig. 1). More-intense and frequent droughts have also killed millions of trees, contributing to a weaker carbon sink in the Amazon 37,40 . Given that the combined sink in intact and regrowth forest is stable, the sign of the net sink for tropical forests as a whole is determined largely by the rate of deforestation emissions. ...
... Further, a recent trend of increasing drought has also been shown to reduce primary productivity in tropical forests (Zhang et al., 2016). This is supported by recent site-level studies which have shown that the carbon storage potential of these forests has declined in recent years due to an increase in mortality rates that may offset future gains in productivity owing to warmer temperatures, CO 2 fertilization, and reforestation (Brienen et al., 2015). ...
Future climate presents conflicting implications for forest biomass. We evaluate how plant hydraulic traits, elevated CO2 levels, warming, and changes in precipitation affect forest primary productivity, evapotranspiration, and the risk of hydraulic failure.
We used a dynamic vegetation model with plant hydrodynamics (FATES‐HYDRO) to simulate the stand‐level responses to future climate changes in a wet tropical forest in Barro Colorado Island, Panama. We calibrated the model by selecting plant trait assemblages that performed well against observations. These assemblages were run with temperature and precipitation changes for two greenhouse gas emission scenarios (2086–2100: SSP2‐45, SSP5‐85) and two CO2 levels (contemporary, anticipated).
The risk of hydraulic failure is projected to increase from a contemporary rate of 5.7% to 10.1–11.3% under future climate scenarios, and, crucially, elevated CO2 provided only slight amelioration. By contrast, elevated CO2 mitigated GPP reductions. We attribute a greater variation in hydraulic failure risk to trait assemblages than to either CO2 or climate.
Our results project forests with both faster growth (through productivity increases) and higher mortality rates (through increasing rates of hydraulic failure) in the neo‐tropics accompanied by certain trait plant assemblages becoming nonviable.
... In intact tropical forests, the foremost threats remain ongoing deforestation and degradation, which are the primary causes of the declining carbon sink (Extended Data Fig. 1). More-intense and frequent droughts have also killed millions of trees, contributing to a weaker carbon sink in the Amazon 37,40 . Given that the combined sink in intact and regrowth forest is stable, the sign of the net sink for tropical forests as a whole is determined largely by the rate of deforestation emissions. ...
The uptake of carbon dioxide (CO2) by terrestrial ecosystems is critical for moderating climate change¹. To provide a ground-based long-term assessment of the contribution of forests to terrestrial CO2 uptake, we synthesized in situ forest data from boreal, temperate and tropical biomes spanning three decades. We found that the carbon sink in global forests was steady, at 3.6 ± 0.4 Pg C yr⁻¹ in the 1990s and 2000s, and 3.5 ± 0.4 Pg C yr⁻¹ in the 2010s. Despite this global stability, our analysis revealed some major biome-level changes. Carbon sinks have increased in temperate (+30 ± 5%) and tropical regrowth (+29 ± 8%) forests owing to increases in forest area, but they decreased in boreal (−36 ± 6%) and tropical intact (−31 ± 7%) forests, as a result of intensified disturbances and losses in intact forest area, respectively. Mass-balance studies indicate that the global land carbon sink has increased², implying an increase in the non-forest-land carbon sink. The global forest sink is equivalent to almost half of fossil-fuel emissions (7.8 ± 0.4 Pg C yr⁻¹ in 1990–2019). However, two-thirds of the benefit from the sink has been negated by tropical deforestation (2.2 ± 0.5 Pg C yr⁻¹ in 1990–2019). Although the global forest sink has endured undiminished for three decades, despite regional variations, it could be weakened by ageing forests, continuing deforestation and further intensification of disturbance regimes¹. To protect the carbon sink, land management policies are needed to limit deforestation, promote forest restoration and improve timber-harvesting practices1,3.
... However, Amazon intact forests are under pressure 10 and have experienced a persistent decline in their sink capacity in the past decades 11 , potentially attributable to drought-induced increases in tree mortality 12,13 . Climate change, including the increasing intensity and severity of extreme events, may play an important role in this progressive shift of intact Amazon forests from a carbon sink to a carbon source, as extreme productivity and mortality anomalies notably occur during or directly after extremely hot and dry events such as the large-scale drought of 2015/2016 14,15 . ...
In the Amazon, the dry season of 2023 as well as the beginning of the wet season in 2024 were marked by unprecedented high temperatures and large precipitation deficits. While the tropical forests in the Amazon play a crucial role in the global carbon cycle and are a biodiversity hotspot, they were also shown to suffer from El-Niño related droughts in the past, leading to legitimate concerns about the ecological consequences of the recent climate conditions. To this day, while there is a growing effort to make remote sensing products available close to real-time, land surface models that are critical tools to understand the interactions between the biosphere and the environment have lagged behind the present due to the complexity to run and process large model ensembles. In this study, we employed advanced machine learning models trained on state-of-the-art remote sensing and dynamic global vegetation model estimates of gross primary productivity (GPP). The models provide near real-time GPP estimates, revealing significant productivity reductions during the 2023/2024 drought. Negative GPP anomalies were more widespread across the Amazon than during any other recent major drought event. The Climate-GPP relationships that emerged from the models suggest that future temperature increases and changes in precipitation will severely challenge Amazon forest resilience.
... The rainforests of the Amazon region are already directly affected by climate change. Satellite data and on-site measurements have shown that increasing droughts are transforming the Amazon forest from a carbon sink into a carbon source (Brienen et al., 2015). Already today, parts of the tree populations are not able to cope with the new climate conditions and are dying. ...
With current policies the Earth is on track to a warming of around 3 °C above preindustrial temperatures, a level of heat our planet has not seen for millions of years. Ecosystems, human society and infrastructure are not adapted to these temperatures. Due to non-linear effects, the impacts will be much more severe than just three times as bad as after 1 °C of warming. Land areas will continue to warm much more than the global average, many regions twice as much or even more. Extreme heat will become far more frequent and a major cause of human mortality, making large parts of the tropical land area essentially too hot to live. In addition, extreme rainfall and flooding, droughts, wildfires and harvest failures will increase in frequency and severity. The destructive power of tropical cyclones will also increase. Sea-level rise will accelerate further, and the destabilization of ice sheets will commit our descendants to loss of coastal cities and island nations. The risk of crossing devastating and irreversible tipping points of climate and biosphere will rise to a high level. This 3-degree world is not an inevitable fate, but action to prevent it must be swift and decisive.
... Tropical forests contain high functional biodiversity and sequester large amounts of carbon in primary and secondary forests (Pan et al., 2011;Brienen et al., 2015;Chazdon, 2016;Friedlingstein et al., 2022). The size of the future carbon sink in tropical forests may depend on soil nutrient availability (Wieder et al., 2015;Fleischer et al., 2019;Terrer et al., 2019). ...
Nutrient limitation may constrain the ability of recovering and mature tropical forests to serve as a carbon sink. However, it is unclear to what extent trees can utilize nutrient acquisition strategies – especially root phosphatase enzymes and mycorrhizal symbioses – to overcome low nutrient availability across secondary succession.
Using a large‐scale, full factorial nitrogen and phosphorus fertilization experiment of 76 plots along a secondary successional gradient in lowland wet tropical forests of Panama, we tested the extent to which root phosphatase enzyme activity and mycorrhizal colonization are flexible, and if investment shifts over succession, reflective of changing nutrient limitation. We also conducted a meta‐analysis to test how tropical trees adjust these strategies in response to nutrient additions and across succession.
We find that tropical trees are dynamic, adjusting investment in strategies – particularly root phosphatase – in response to changing nutrient conditions through succession. These changes reflect a shift from strong nitrogen to weak phosphorus limitation over succession. Our meta‐analysis findings were consistent with our field study; we found more predictable responses of root phosphatase than mycorrhizal colonization to nutrient availability.
Our findings suggest that nutrient acquisition strategies respond to nutrient availability and demand in tropical forests, likely critical for alleviating nutrient limitation.
... Model performance and fit were evaluated using fit values (R 2 ) and root mean square error (RSME) (Chave et al. 2005b(Chave et al. , 2014Pinto and Cuesta, 2019). To estimate C stocks and sequestration rates at the landscape scale, we used the bootstrapping resampling method to construct 95% confidence intervals and estimate the means of the carbon storage and sequestration rates from the 11 plots installed on each park (Brienen et al. 2015;Duque et al. 2021). Then, we multiplied the calculated means and confidence intervals by the SMP and GMP surface area to obtain estimates of AGC storage and annual sequestration. ...
Despite the importance of urban forests as important carbon sinks, studies in Ecuador have yet to assess their potential to store carbon. We assessed the carbon stored in the aboveground biomass (AGB) and annual rates of AGB accumulation in the Guangüiltagua Metropolitan Park (GMP) and the Southern Metropolitan Park (SMP). We installed 11 plots per park of 0.063 ha, where we surveyed all stems with a diameter at breast height (DBH) ≥2.5 cm. To estimate annual increments in AGB, we installed dendrometer bands on 10% of the total stems recorded in each plot (only in stems with ≥10 cm DBH). We measured the dendrometer band segment increase every 4 months from September 2019 to October 2020. Our results show that the GMP stores 171 ± 96 Mg C ha−1, significantly higher than the amount of carbon storage recorded in the SMP (100 ± 41 Mg C ha−1). In contrast, the GMP sequestered 3.30 ± 1.71 Mg C ha year−1, while the SMP sequestered an average of 4.45 ± 2.63 Mg C ha year−1. At the landscape scale, the SMP contains 0.072 Tg C (0.058–0.091, 95% CI), while the GMP contains a reservoir of 0.096 Tg C (0.067–0.13, 95% CI). Likewise, the AGB in the SMP 3,165 Mg C year−1 (2209–4297, 95% CI), while that in the GMP sequestered 1859 Mg year−1 (1361–2430, 95% CI). Our results show that the metropolitan parks of Quito are important carbon sinks and constitute essential elements in mitigating climate change in urban spaces.
... Although some climate-change effects (e.g. rising CO 2 , warming, extended growing season) can be positive, because of resource limitations and maladaptation to rapid climate shift, forests may not benefit from these positive impacts (Brienen et al., 2015;Luo et al., 2019). In addition, although there is evidence of local genetic adaptation to climate (Savolainen et al., 2007), whether most natural populations of trees will be able to adapt to rapid climate change is questionable. ...
... However, it is known that at least part of the anthropogenic CO 2 emission is buffered by an increased uptake by photosynthesis and via increased C sequestration of the terrestrial vegetation (IPCC, 2021), which cannot be explained by an increase in storage of non-structural C compounds (NSC) alone. A recent synthesis (Walker et al., 2021) shows that a range of evidence supports a C sink increase related to terrestrial vegetation with increased CO 2 concentration as forest inventories show an increase in wood biomass production (Brienen et al., 2015;Yu et al., 2019;Hubau et al., 2020). If true, these global findings were explicable either with a general CO 2 limitation of tree growth or a CO 2alleviated release of other limitations (Walker et al., 2021). ...
A conceptual understanding on how the vegetation's carbon (C) balance is determined by source activity and sink demand is important to predict its C uptake and sequestration potential now and in the future. We have gathered trajectories of photosynthesis and growth as a function of environmental conditions described in the literature and compared them with current concepts of source and sink control. There is no clear evidence for pure source or sink control of the C balance, which contradicts recent hypotheses. Using model scenarios, we show how legacy effects via structural and functional traits and antecedent environmental conditions can alter the plant's carbon balance. We, thus, combined the concept of short‐term source–sink coordination with long‐term environmentally driven legacy effects that dynamically acclimate structural and functional traits over time. These acclimated traits feedback on the sensitivity of source and sink activity and thus change the plant physiological responses to environmental conditions. We postulate a whole plant C‐coordination system that is primarily driven by stomatal optimization of growth to avoid a C source–sink mismatch. Therefore, we anticipate that C sequestration of forest ecosystems under future climate conditions will largely follow optimality principles that balance water and carbon resources to maximize growth in the long term.
... Las parcelas permanentes de muestreo (PPM) son una herramienta para el manejo e investigación de la dinámica de los bosques (naturales y bajo manejo) a diferentes escalas espaciales y temporales (Phillips et al., 2009;Brienen et al., 2015). Su propósito es conocer su dinámica a través del tiempo (Brenes, 2002) y, a su vez obtener información esencial que permita tomar decisiones futuras para su manejo y/o control (BOLFOR y PROMABOSQUE, 1999). ...
El libro es un documento de campo dirigido a actores locales y técnicos forestales que puede ayudar en la toma de decisiones para el manejo y control de plantas parásitas en bosques naturales y bajo manejo
... Tropical forests are the main global terrestrial carbon (C) sink, with an estimated uptake of 1.2 Pg C year −1 from 1990-2007 (Pan et al. 2011). The forests in the Amazon basin alone contribute around 25% to the global terrestrial C sink (Phillips et al. 2009, Pan et al. 2011, Feldpausch et al. 2012), but their sink strength seems to decline, mainly caused by a sustained long-term increase in tree mortality due to rising temperatures and greater drought frequency (Brienen et al. 2015, Hubau et al. 2020. This surge in extreme climate events is predicted to increase dead wood stocks; subsequently, the decomposition of woody material could strongly alter the forest's C balance (Seidl et al. 2017. ...
In the Amazon basin, approximately 60% of rainforest thrives on geologically old and highly weathered soils, thus decomposition represents an important mechanism for recycling nutrients from organic matter. Although dead logs and branches constitute up to 14% of the carbon stored in terrestrial ecosystems, woody debris decomposition and mainly the effect of direct nutrient cycling by plant root interaction is poorly studied and often overlooked in ecosystem carbon and nutrient budgets. Here we monitored the decomposition of five different local woody species covering a range of wood density by conducting a long‐term wood decomposition experiment over two years with factorial root presence and phosphorous (P) addition treatments in a central Amazonian rainforest. We hypothesized that woody debris decomposition is accelerated by colonizing fine roots mining for nutrients, possibly strongly affecting wood debris with lower density and higher nutrient concentration (P). We found that root colonization and P addition separately increased wood decay rates, and although fine root colonization increased when P was added, this did not result in a change in wood decay. Nutrient loss from wood was accelerated by P addition, whereas a root presence effect on nutrient mobilization was only detectable at the end of the experiment. Our results highlight the role of fine roots in priming wood decay, although direct nutrient acquisition by plants seems to only occur in more advanced stages of decomposition. On the other hand, the positive effect of P addition may indicate that microbial nutrient mobilization in woody material is driven mainly by wood stoichiometry rather than priming by root activity.
... A reasonable first-order assumption. This may not be accurate, as carbon density increases each year after the last episode of deforestation or disturbance and carbon density of undisturbed forest is falling over time as a result of global warming (Hubau et al. 2020;Brienen et al. 2015). Our method will be upgraded to reflect this. ...
This draft document describes the methodology developed by the Cambridge Center for Carbon Credits (4C) for estimating the number of credits to be issued to a project in the tropical moist forest (TMF) biome. It expands on the methodology outlined in (Swinfield and Balmford, 2023). We welcome comments and suggestions in the associated online document at https://tinyurl.com/cowgreport.
... A reasonable first-order assumption. This may not be accurate, as carbon density increases each year after the last episode of deforestation or disturbance and carbon density of undisturbed forest is falling over time as a result of global warming (Hubau et al. 2020;Brienen et al. 2015). Our method will be upgraded to reflect this. ...
This draft document describes the methodology developed by the Cambridge Center for Carbon Credits (4C) for estimating the number of credits to be issued to a project in the tropical moist forest (TMF) biome. It expands on the methodology outlined in (Swinfield and Balmford, 2023). We welcome comments and suggestions in the associated online document at https://tinyurl.com/cowgreport.
... When ecologies are in a pseudo-equilibrium, biomass growth is balanced by biomass turnover (e.g., mortality, needle casting), heterotrophic respiration, and wildfire removing C from above and belowground C pools (Ameray et al., 2021;Harmon et al., 2011). External perturbations of the equilibrium can increase biomass turnover rates (Brienen and al., 2015); or dampen or stimulate biomass growth relative to heterotrophic respiration, with wildfire playing a key role in fire adapted ecosystems (Harmon et al., 2011). ...
Wildfire futures and aboveground carbon (C) dynamics associated with forest restoration programs that integrate resource objective wildfire as part of a larger treatment strategy are not well understood. Using simulation modeling, we examined alternative forest and fuel management strategies on a 237,218-ha study area within a 778,000-ha landscape that is a high priority target for federal restoration programs. We simulated two wildfire management scenarios combined with three levels of conventional forest restoration treatments over 64 years using a detailed landscape disturbance and succession model developed in prior work. We found accelerated forest restoration used in concert with resource objective wildfire was the most effective at returning old growth forest structure, while stabilizing aboveground C stocks and restoring the fire return interval to its historic range of variation. In scenarios without forest restoration, the continued practice of resource objective wildfires during shoulder fire seasons reduced summer emissions in a negative feedback loop. In the short term, scenarios without forest restoration increased live tree C, but also increased the likelihood of C loss during wildfire activity driven by extreme fire weather. We found scenarios most effective at restoring fire-excluded pine forests to their historical old growth conditions came at a short-term cost of lost C, but with the long-term benefit of substantially increasing fire-resistant live tree C. Our results inform how local decision making can best balance competing goals of sequestering C, and stabilizing C stocks in frequent-fire pine forests using the principles of local fire ecology to restore and maintain old growth forest structure.
... The Amazon basin is a region of many different tropical forest ecological systems and high biodiversity (although not considered a biodiversity hotspot, (Myers et al., 2000)). It is a key Earth system component (Armstrong McKay et al. , 2022) , regulating regional and even global climates by cycling enormous amounts of water vapour and latent heat between land and atmosphere, by storing around 150-200 Pg carbon above and below ground, though this is in decline (Brienen et al. , 2015) . As such, it is perhaps better to see the Amazon basin as a combined ecological-climatic system. ...
The avoidance of hitting tipping points is often considered a key benefit of Solar Radiation Modification (SRM) techniques, however, the physical science underpinning this has thus far not been comprehensively assessed. This review assesses the available evidence for the interaction of SRM with a number of earth system tipping elements in the cryosphere, the oceans, the atmosphere and the biosphere , with a particular focus on the impact of SAI. We review the scant available literature directly addressing the interaction of SRM with the tipping elements or for closely related proxies to these elements. However, given how limited this evidence is, we also identify and describe the drivers of the tipping elements, and then assess the available evidence for the impact of SRM on these. We then briefly assess whether SRM could halt or reverse tipping once feedbacks have been initiated. Finally, we suggest pathways for further research. We find that SRM mostly reduces the risk of hitting tipping points relative to same emission pathway scenarios without SRM, although this conclusion is not clear for every tipping element, and large uncertainties remain.
... The massive extent of archaeological sites and widespread human-modified forests across Amazonia is critically important for establishing an accurate understanding of interactions between human societies, Amazonian forests, and Earth's climate (37). Considering the widespread extent of locations modified by pre-Columbian management and cultivation practices, Amazonia can be viewed as an ancient social-ecological system, with long-term responses to climate change (46), more similar to old secondary forests than pristine climax ecosystems (10). ...
... The massive extent of archaeological sites and widespread human-modified forests across Amazonia is critically important for establishing an accurate understanding of interactions between human societies, Amazonian forests, and Earth's climate (37). Considering the widespread extent of locations modified by pre-Columbian management and cultivation practices, Amazonia can be viewed as an ancient social-ecological system, with long-term responses to climate change (46), more similar to old secondary forests than pristine climax ecosystems (10). ...
Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected
pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species
significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery
that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state
... The initial stock is completely renewed over a period of 50 to 100 years (Galbraith et al. 2013: 3-4, Table 1). The decomposition period of the necro-mass in the Amazon Forest is a maximum of 13 years and often less than ten (Brienen et al. 2015: Table 2). In the African equatorial and sub-equatorial domain, most dead trees do not last long as their wood decomposes quickly. ...
North China is one of China’s most severely warming and drying regions, and understanding the dynamics of forest carbon sinks in North China is critical for forest management in response to climate change. This study examined the spatial and temporal dynamics of forest carbon sinks in North China from 2000 to 2020 using carbon cycle process and soil respiration data, and explored the relationship between the sinks’ spatial and temporal dynamics and changes in major climatic factors, particularly the effects of droughts on the forest sinks. The results showed that forest net ecosystem productivity (NEP) in North China increased significantly at 7.0 gC·m⁻²·yr⁻¹ over the last 21 years, mainly concentrated along Yanshan (e.g. Hebei Province) and Qinling (e.g. south-central Shaanxi Province) area. Shaanxi had the fastest NEP growth rate, while Henan had the slowest. The spatial distribution of forest NEP in North China decreased with increasing latitude, and the increase in NEP from 2000 to 2010 attained 115 gC·m⁻² was higher than that from 2010 to 2020. Moisture is the main climatic factor affecting forest carbon sinks in North China, but there is some spatial heterogeneity in the response patterns to precipitation, drought, and temperature in different regions. Drought levels have dramatically impacted forests in North China, and drought losses and post-drought recovery for NEP increased as drought levels increased. Extreme drought had the greatest impact on the forest NEP, with a loss of up to 93.46 gC m⁻², but the recovery from drought was much greater than the loss from drought, the entire increase might be as high as 120 gC·m⁻². Forest carbon sinks in North China have superior drought resistance, recovery, and resilience. This study illustrates the impact of conservation measures like afforestation in North China through the dynamic distribution of carbon sinks and also highlights the impacts of drought events with varying severity on forest carbon sinks.
Plain Language Summary
The Amazon rainforest (ARF) is Earth's most biodiverse ecosystem, crucial for regulating global and regional climate through water recycling and carbon uptake. Several studies suggest that ongoing deforestation, land‐use changes, and climate change induced shifts in rainfall patterns could trigger an abrupt regime shift from the current rainforest to a low‐treecover state. Here, we investigate the resilience of the ARF vegetation based on remotely sensed Vegetation Optical Depth, particularly useful in high‐biomass areas such as the ARF. The main feedback mechanism, essential for potential tipping, is moisture recycling. The trade winds bring in moisture from the Atlantic Ocean to South America's east, where it precipitates. Much of this moisture re‐enters the atmosphere via evapo‐transpiration and is transported further west, thereby establishing a moisture regime supporting the rainforest. The induced spatial coupling results in the spatial correlation being a reliable indicator of resilience. We compare changes in the spatial correlation to changes in the two classic indicators. The greatest resilience loss is detected in the southwestern Amazon, which has been identified as a highly‐coupled sub‐system since it is reliant on recycled moisture from upstream the trade winds, hence making the spatial correlation a particularly suitable and trustworthy resilience indicator there.
-Strong droughts in the Amazon have been increasing in frequency and intensity, from four in a century to four in less than 25 years, in concert with increasing deforestation and global warming. The synergy of droughts, deforestation, fire, and forest degradation have the potential to drive the Amazon to a tipping point where this globally important ecosystem may significantly reduce its capacity to provide critical services such as water recycling, carbon storage, and provision of goods for human well-being.
-Droughts increase tree mortality, and thus biomass loss, imperiling the functioning of the carbon sink provided by tree growth. Droughts also increase animal mortality, especially when river levels decrease abruptly and when forests are disturbed by fire and forest degradation.
• Droughts increase the risk of fires, with direct impacts such as carbon emissions and the loss of biodiversity and ecosystem services, while also threatening human health and food security and feedbacking to global warming.
• The socioeconomic impacts of droughts are large, and result in social, cultural and economic vulnerability. The impacts include threats to water security and quality, food security, public health, human rights, local-to-large scale economies, mobility, energy production, river bank stability, and human migrations.
• The impacts of droughts vary in nature and intensity across social communities (e.g., Indigenous, afro-descendant, ribeirinhos, caboclos, etc.), predominant economic activities (e.g., fishing, farming, extractivism, urban services), gender, age, and the regional differences between countries and the Amazon regions (e.g., lowlands, Amazonian Andes, and foothills).
• There are critical gaps to the knowledge required for planning future and immediate responses to climate crises. These include the lack of comprehensive monitoring of Amazonian forests, climate, and hydrology to inform adaptation programs, and the lack of social, economic, cultural, and demographic data at local and regional scales, especially concerning vulnerable populations.
Thermophilization is the directional change in species community composition towards greater relative abundances of species associated with warmer environments. This process is well-documented in temperate and Neotropical plant communities, but it is uncertain whether this phenomenon occurs elsewhere in the tropics. Here we extend the search for thermophilization to equatorial Africa, where lower tree diversity compared to other tropical forest regions and different biogeographic history could affect community responses to climate change. Using re-census data from 17 forest plots in three mountain regions of Africa, we find a consistent pattern of thermophilization in tree communities. Mean rates of thermophilization were +0.0086 °C·y⁻¹ in the Kigezi Highlands (Uganda), +0.0032 °C·y⁻¹ in the Virunga Mountains (Rwanda-Uganda-Democratic Republic of the Congo) and +0.0023 °C·y⁻¹ in the Udzungwa Mountains (Tanzania). Distinct from other forests, both recruitment and mortality were important drivers of thermophilzation in the African plots. The forests studied currently act as a carbon sink, but the consequences of further thermophilization are unclear.
Tropical forest productivity is increasingly reported to be nutrient limited, which may affect its response to seasonal droughts. Yet experimental evidence on nutrient limitation from Afrotropical forests remains rare. We conducted an ecosystem-scale, full factorial nitrogen (N)–phosphorus (P)–potassium (K) addition experiment in a moist forest in Uganda to investigate nutrient controls on fine litter production and foliar chemistry. The eight factorial treatments were replicated four times in 32 plots of 40 × 40 m each. During the three-year nutrient additions, we found K and P limitations on leaf litter production, exhibiting strong links to ecosystem responses to seasonal drought. Specifically, leaf litterfall consistently decreased in dry seasons with K additions, whereas P additions caused a reduction only during prolonged drought in the first year. Leaf litterfall was not significantly affected by N additions. Furthermore, K additions delayed the timing of leaf litterfall peak, underscoring the crucial role of K in regulating stomatal aperture and signalling during water-stress conditions and suggesting a prolonged leaf lifespan. Foliar N increased with N and P additions whereas K was the most resorbed nutrient. We conclude that the productivity and resilience of tropical forests, particularly under drier conditions, may depend on terrestrial K and P availability.
As temperature rises, net carbon uptake in tropical forests decreases, but the underlying mechanisms are not well understood. High temperatures can limit photosynthesis directly, for example by reducing biochemical capacity, or indirectly through rising vapor pressure deficit (VPD) causing stomatal closure.
To explore the independent effects of temperature and VPD on photosynthesis we analyzed photosynthesis data from the upper canopies of two tropical forests in Panama with Generalized Additive Models.
Stomatal conductance and photosynthesis consistently decreased with increasing VPD, and statistically accounting for VPD increased the optimum temperature of photosynthesis (Topt) of trees from a VPD‐confounded apparent Topt of c. 30–31°C to a VPD‐independent Topt of c. 33–36°C, while for lianas no VPD‐independent Topt was reached within the measured temperature range. Trees and lianas exhibited similar temperature and VPD responses in both forests, despite 1500 mm difference in mean annual rainfall.
Over ecologically relevant temperature ranges, photosynthesis in tropical forests is largely limited by indirect effects of warming, through changes in VPD, not by direct warming effects of photosynthetic biochemistry. Failing to account for VPD when determining Topt misattributes the underlying causal mechanism and thereby hinders the advancement of mechanistic understanding of global warming effects on tropical forest carbon dynamics.
Societal Impact Statement
Global climate models that incorporate carbon sources and sinks usually consider that forest uptake of carbon is in a state of equilibrium. Both historical and paleoecological records suggest that this is commonly not the case for Amazonia. Here, the impacts of colonial practices on Amazonian Indigenous peoples and forests are reviewed. Human activities affect forests' successional stages, trajectories, and species composition. By increasing the spatial coverage of paleoecological records that focus on pre‐ and post‐Columbian periods, the long‐term interactions between humans and Amazonian forests and their role in affecting Earth's climate may be better understood.
Summary
Legacy effects left by the activities of Indigenous people in Amazonia are well known. Although severe, widespread, and recently occurring, the impacts left post‐1492 CE have been less investigated. We review the impact of colonial practices on Indigenous peoples and Amazonian forests. We suggest that forests comprise the sum of their past events, in a mosaic of different cumulative successional trajectories depending on the type, frequency, intensity, and timing of human influence. In regions with a history of minimal human influence, old‐growth species sensitive to fire would be the dominant landscape. In regions with high pre‐Columbian and low colonial influence, old‐growth forests carrying pre‐Columbian ecological legacies would be prevalent. Regions occupied by Indigenous groups post‐1492 CE would also carry similar ecological legacies. In regions influenced by the Jesuits, mid‐successional forests are expected to be enriched with cacao trees. In regions of latex extraction during the rubber boom, mid‐growth forests would present high abundances of early and mid‐successional species and depletion of some species. In deforested areas, we expect early successional forests with influence of exotic useful species. This patchwork of history probably plays a large role in shaping today's forests, and the biodiversity and carbon dynamics documented within them. Paleoecological work focusing on the last millennium, although scarce, has the potential to detect these mosaics of past human influence, and they should be considered when estimating forest ages and successional stages across the basin.
How are rainforest photosynthesis and turbulent fluxes influenced by clouds? To what extent are clouds affected by local processes driven by rainforest energy, water and carbon fluxes? These interrelated questions were the main drivers of the intensive field experiment CloudRoots-Amazon22 which took place at the ATTO/Campina supersites in the Amazon rainforest during the dry season, in August 2022. CloudRoots-Amazon22 collected observational data to derive cause-effect relationships between processes occurring at the leaf-level up to canopy scales in relation to the diurnal evolution of the clear-to-cloudy transition. First, we studied the impact of cloud and canopy radiation perturbations on the sub-diurnal variability of stomatal conductance. Stoma opening is larger in the morning, modulated by the cloud optical thickness. Second, we combined 1 Hz-frequency measurements of the stable isotopologues of carbon dioxide and water vapor with measurements of turbulence to determine carbon dioxide and water vapor sources and sinks within the canopy. Using scintillometer observations, we inferred 1-minute sensible heat flux that responded within minutes to the cloud passages. Third, collocated profiles of state variables and greenhouse gases enabled us to determine the role of clouds in vertical transport. We then inferred, using canopy and upper-atmospheric observations and a parameterization, the cloud cover and cloud mass flux to establish causality between canopy and cloud processes. This shows the need of comprehensive observational set to improve weather and climate model representations. Our findings contribute to advance our knowledge of the coupling between cloudy boundary layers and primary carbon productivity of the Amazon rainforest.
The stable carbon isotope composition (δ¹³C) of plant components such as plant wax biomarkers is an important tool for reconstructing past vegetation. Plant wax δ¹³C is mainly controlled by photosynthetic pathways, allowing for the differentiation of C4 tropical grasses and C3 forests. Proxy interpretations are however complicated by additional factors such as aridity, vegetation density, elevation, and the considerable δ¹³C variability found among C3 plant species. Moreover, studies on plant wax δ¹³C in tropical soils and plants have focused on Africa, while structurally different South American savannas, shrublands and rainforests remain understudied. Here, we analyze the δ¹³C composition of long‐chain n‐alkanes and fatty acids from tropical South American soils and leaf litter to assess the isotopic variability in each vegetation type and to investigate the influence of climatic features on δ¹³C. Rainforests and open vegetation types show distinct values, with rainforests having a narrow range of low δ¹³C values (n‐C29 alkane: −34.4−0.7+0.9 ‰ Q2575 ; Suess‐effect corrected). This allows for the detection of even minor incursions of savanna (δ¹³C n‐C29 alkane −29.2−2.1+3.7 ‰) into rainforests. While Cerrado savannas and semi‐arid Caatinga shrublands grow under distinctly different climates, they can yield indistinct δ¹³C values for most compounds. Cerrado soils and litter show pronounced isotopic spreads between the n‐C33 and n‐C29 alkanes, while Caatinga shrublands show consistent values across the two homologs, thereby enabling the differentiation of these vegetation types. The same multi‐homolog isotope analysis can be extended to differentiate African shrublands from savannas.
Dissolved inorganic carbon (DIC) sources, transportation, and transition in inland water bodies have been intensively studied due to their important role in the global carbon cycle. While glacier‐fed lakes play a crucial role in global carbon cycling, related studies are limited. In this study, we investigated the spatiotemporal variability of DIC in the maritime glacier‐fed lakes of the southeastern Tibetan Plateau, identifying the carbon sources and potential controlling factors of DIC pathways The results revealed significant temporal variations in DIC and δ¹³C‐DIC, with averages of 7.29 ± 0.45 mg C L⁻¹ and –8.6 ± 0.2‰ in summer, and 3.40 ± 0.54 mg C L⁻¹ and –7.4 ± 0.6‰ in winter, respectively. Temporal variations in DIC and δ¹³C‐DIC were mainly controlled by carbonates weathering and silicate weathering processes. The chemical weathering reactions facilitate the consumption of dissolved CO2. Undersaturated pCO2 (120.02 ± 29.18 μatm) relative to atmospheric equilibrium suggests considerable capacity for CO2 uptake within glacier‐fed lakes system. We estimated that the maritime glacier‐fed lakes in the southeastern Tibetan Plateau absorb a total of 9.6 ± 2.7 × 10⁻³ Tg C‐CO2 yr⁻¹, highlighting their significant contribution to the global carbon budget. The distinctive landscape of the glacier‐fed system and the vulnerable weathering environment result in seasonal and spatial variations of DIC concentration and δ¹³C‐DIC values, as well as the chemical weathering‐induced CO2 sink in glacier regions. Given the accelerated glacier retreat observed in this area, further studies on the temporal variability of DIC in the water column are urgently needed to identify the mechanisms driving the biogeochemical reactions inside glacier‐fed lake. Our study highlights the unrecognized role of maritime glacier‐fed lakes as CO2 sinks and emphasizes their significance in regional carbon budgets.
Between 1954 and the mid-1980s, about 50,000 ha of native montane rainforest on the island of Hawai'i experienced a decline in canopy trees ("'ōhi'a dieback"), leading to great concern about the future of Hawai'i's rainforests. Dieback symptoms particularly affected the dominant tree species, the endemic Metrosideros polymorpha. Early hypotheses postulated that the forest decline was caused by a virulent pathogen or a combination of biotic disease and pest agents. This was ruled out after a decade of intensive disease research in the 1970s. Instead, it turned out that dieback patterns were significantly related to the physical environment, particularly the slope, topography, relative position on the hill slope, annual rainfall, and the type of substrate. Thus, an alternative hypothesis proposed that dieback is initiated by climate anomalies that manifest through soil moisture regimes under certain conditions of forest stand demography. Ironically, scientific perception of this interdisciplinary groundbreaking research that stimulated a global perspective on forest decline vanished while the awareness of climate change and its potential impact on the world's forests started to grow, rapidly becoming a major focus of research in recent years. In this paper, we reinforce memory of the world's first complex discussion on the natural causes of forest dieback as a showcase for the complexity of modern forest mortality research. This case demonstrates the need to rigorously identify, quantify, and fully understand all drivers of tree mortality to realistically project future climate-driven and other risks to forest ecosystem functions and services. Moreover, we summarize recent findings on forest mortality and climate change in the Pacific islands and beyond.
This article is a Commentary on Kullberg et al. (2024), 241: 1447–1463.
Aim
A unique risk faced by nocturnally migrating birds is the disorienting influence of artificial light at night (ALAN). ALAN originates from anthropogenic activities that can generate other forms of environmental pollution, including the emission of fine particulate matter (PM 2.5 ). PM 2.5 concentrations can display strong seasonal variation whose origin can be natural or anthropogenic. How this variation affects seasonal associations with ALAN and PM 2.5 for nocturnally migrating bird populations has not been explored.
Location
Western Hemisphere.
Time Period
2021
Major Taxa Studied
Nocturnally migrating passerine (NMP) bird species.
Methods
We combined monthly estimates of PM 2.5 and ALAN with weekly estimates of relative abundance for 164 NMP species derived using observations from eBird. We identified groups of species with similar associations with monthly PM 2.5 . We summarized their shared environmental, geographical, and ecological attributes.
Results
PM 2.5 was lowest in North America, especially at higher latitudes during the boreal winter. PM 2.5 was highest in the Amazon Basin, especially during the dry season (August–October). ALAN was highest within eastern North America, especially during the boreal winter. For NMP species, PM 2.5 associations reached their lowest levels during the breeding season (<10 μg/m ³ ) and highest levels during the nonbreeding season, especially for long‐distance migrants that winter in Central and South America (~20 μg/m ³ ). Species that migrate through Central America in the spring encountered similarly high PM 2.5 concentrations. ALAN associations reached their highest levels for species that migrate (~12 nW/cm ² /sr) or spend the nonbreeding season (~15 nW/cm ² /sr) in eastern North America.
Main Conclusions
We did not find evidence that the disorienting influence of ALAN enhances PM 2.5 exposure during stopover in the spring and autumn for NMP species. Rather, our findings suggest biomass burning in the Neotropics is exposing NMP species to consistently elevated PM 2.5 concentrations for an extended period of their annual life cycles.
Seasonal Forests (FE) occurring in the Cerrado, are characterized by the presence of tree species with different deciduous levels on dry seasons and vary in floristic composition depending on their geographic location. The present work has as premise that the floristic-structural patterns of these forests can be remarkable, due to the environmental conditions imposed by the environments and proximity to different watersheds. We used sample data of 17 fragments of Semideciduous Seasonal Forest (FE) in the Cerrado. For each sampling site to be inventoried an area of one hectare where the circunference of all the trees were measured at 1.30cm ≥ 15cm were included. An Principal Component Analysis - PCA, including abiotic and structural variables of each forest were made. For similarity analysis we used the floristic data in an absence-presence matrix of species and a number of trees of each species data. To determine floristic patters we use the Sorensen and Bray-Curtis similarity and made a cluster with the Unweighted Average Grouping Method (UPGMA). To explore the patterns of abundance performed in the Non-Metric multidimensional Scale (nMDS). The floristic-structural patterns indicated the presence of two distinct floristic groups, a smaller group formed different areas of the Araguaia and Paraguay River watersheds, and another large group formed by areas of the Paraná basin, and other others, even basin, more dissimilar than too much. The formation of floristic groups reflects that, as analyzed communities, there are several generalist species that are not very demanding and that adapt to new conditions, occurring in non-Cerrado and Atlantic Forest seasonal forest areas, forming two diverse tests located mainly in the Araguaia basin and Paraná.
Keywords
Seasonally Dry Forests; Diversity; Phytosociology; Environmental variables
Carbon dioxide (CO2) and methane (CH4) emissions from freshwater ecosystems are predicted to increase under climate warming. However, freshwater ecosystems in glacierized regions differ critically from those in non-glacierized regions. The potential emissions of CO2 and CH4 from glacierized environments in the Tibetan Plateau (TP) were only recently recognized. Here, the first direct measurement of CO2 and CH4 emission fluxes and isotopic composition during spring of 2022 in 13 glacial lakes of the TP revealed that glacial lakes were the previously overlooked CO2 sinks due to chemical weathering in glacierized regions. The daily average CO2 flux was -5.1±4.4 mmol m-1 d-1, and the CO2 consumption could reach 38.9 Gg C-CO2 yr-1 by all glacial lakes in the TP. This consumption might be larger during summer when glaciers experience intensive melting, highlighting the importance of CO2 uptake by glacial lake on the global carbon cycle. However, the studied glacial lakes were CH4 sources with total emission flux ranging from 4.4±3.3 to 4082.5±795.6 µmol m-2 day-1. The large CH4 range was attributed to ebullition found in three of the glacial lakes. The low dissolved organic carbon concentrations and CH4 oxidation might be responsible for low CH4 diffusive fluxes of glacial lakes without ebullition. In addition, groundwater input could alter CO2 and CH4 emissions from glacial lakes. CH4 in glacial lakes probably had a thermogenic source; whereas CO2 was influenced mainly by atmospheric input, as well as organic matter remineralization and CH4 oxidation. Overall, glacial lakes in the TP play an important role in global carbon cycle and budget, and more detailed isotopic and microbial studies are needed to constrain the contributions of different pathways to CO2 and CH4 production, consumption and emissions.
Gross primary production is the basis of global carbon uptake. Gross primary production losses are often related to hydroclimatic extremes such as droughts and heatwaves, but the trend of such losses driven by hydroclimatic extremes remains unclear. Using observationally-constrained and process-based model data from 1982-2016, we show that drought-heat events, drought-cold events, droughts and heatwaves are the dominant drivers of gross primary production loss. Losses associated with these drivers increase in northern midlatitude ecosystem but decrease in pantropical ecosystems, thereby contributing to around 70% of the variability in total gross primary production losses. These asymmetric trends are caused by an increase in the magnitude of gross primary production losses in northern midlatitudes and by a decrease in the frequency of gross primary production loss events in pantropical ecosystems. Our results suggest that the pantropics may have become less vulnerable to hydroclimatic variability over recent decades whereas gross primary production losses and hydroclimatic extremes in northern midlatitudes have become more closely entangled.
Forest biodiversity is critical for many ecosystem functions and services. Yet, it remains uncertain how plant functional diversity influences ecosystem functioning across environmental gradients and contiguous larger areas. We integrated remote sensing and terrestrial biosphere modeling to explore functional diversity–productivity relationships at multiple spatial scales for a heterogeneous forest ecosystem in Switzerland. We initialized forest structure and composition in the ecosystem demography model (ED2) through a combination of ground‐based surveys, airborne laser scanning and imaging spectroscopy for forest patches at 10 × 10‐m spatial grain. We derived morphological and physiological forest traits and productivity from model simulations at patch‐level to relate morphological and physiological aspects of functional diversity to the average productivity from 2006 to 2015 at 20 × 20 to 100 × 100‐m spatial extent. We did this for model simulations under observed and experimental conditions (mono‐soils, mono‐cultures and mono‐structures). Functional diversity increased productivity significantly (p < 0.001) across all simulations at 20 × 20 to 30 × 30 m scale, but at 100 × 100‐m scale positive relationships disappeared under homogeneous soil conditions potentially due to the low beta diversity of this forest and the saturation of functional richness represented in the model. Although local functional diversity was an important driver of productivity, environmental context underpinned the variation of productivity (and functional diversity) at larger spatial scales. In this study, we could show that the integration of remotely sensed information on forest composition and structure into terrestrial biosphere models is important to fill knowledge gaps about how plant biodiversity affects carbon cycling and biosphere feedbacks onto climate over large contiguous areas.
Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (H). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions: 1. What is the best H-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? 2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? 3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates? The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- andWeibull-H models provided the greatest reduction in uncertainty, with regional Weibull-H models preferred because they reduce uncertainty in smaller-diameter classes (�40 cm D) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8Mgha−1 (range 6.6 to 112.4) to 8.0Mgha−1 (−2.5 to 23.0). For all plots, aboveground live biomass was −52.2 Mgha−1 (−82.0 to −20.3 bootstrapped 95%CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H. After accounting for variation in H, total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in eastcentral
Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span
1668 million km2 and store 285 Pg C (estimate including H), then applying our regional relationships implies that carbon storage is overestimated by 35 PgC (31–39 bootstrapped 95%CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation.
Description Fit linear and generalized linear mixed-effects models. The models and their components are represented using S4 classes and methods. The core computational algorithms are implemented using the 'Eigen' C++ library for numerical linear algebra and 'RcppEigen' ``glue''.
(1) Mortality over a 13-year period was determined for all stems (⩾ 10-cm dbh) on 12.4 ha of primary lowland wet tropical forest at La Selva, Costa Rica. Altogether 23.2% of 5623 trees and lianas present in the initial inventory had died by the time of the subsequent inventory. (2) Mortality rates were independent of size among individuals ⩾ 10-cm dbh, and did not differ between buttressed and non-buttressed stems. (3) Of the dead individuals, 26% died standing, 31% had fallen, 7% were found buried under treefalls, and 37% had decomposed entirely, leaving no trace. (4) Mortality was nearly balanced by recruitment into the 10-cm dbh class; there was a net loss of 1.7% of stems in 13 years. (5) La Selva appears to be among the most dynamic of tropical forests studied to date, with an annual loss of stems of 2.03% and a consequent stand half-life of 34 years.
In the nineteen seventies, Jurečková and Jaeckel proposed rank estimation for linear models. Since that time, several authors have developed inference and diagnostic methods for these estimators. These rank-based estimators and their associated inference are highly efficient and are robust to outliers in response space. The methods include estimation of standard errors, tests of general linear hypotheses, confidence intervals, diagnostic procedures including stu-dentized residuals, and measures of influential cases. We have developed an R package, Rfit, for computing of these robust procedures. In this paper we highlight the main features of the pack-age. The package uses standard linear models syntax and includes many of the main inference and diagnostic functions.
Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate. Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain. The Amazon basin stores a vast amount of carbon, and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades. Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 ± 0.18 petagrams of carbon per year (Pg C yr(-1)) during the dry year but was carbon neutral (0.06 ± 0.1 Pg C yr(-1)) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 ± 0.14 Pg C yr(-1), which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 ± 0.10 Pg C yr(-1) previously estimated from forest censuses. Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists, the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought.
Earth system models project that the tropical land carbon sink will decrease in size in response to an increase in warming and drought during this century, probably causing a positive climate feedback. But available data are too limited at present to test the predicted changes in the tropical carbon balance in response to climate change. Long-term atmospheric carbon dioxide data provide a global record that integrates the interannual variability of the global carbon balance. Multiple lines of evidence demonstrate that most of this variability originates in the terrestrial biosphere. In particular, the year-to-year variations in the atmospheric carbon dioxide growth rate (CGR) are thought to be the result of fluctuations in the carbon fluxes of tropical land areas. Recently, the response of CGR to tropical climate interannual variability was used to put a constraint on the sensitivity of tropical land carbon to climate change. Here we use the long-term CGR record from Mauna Loa and the South Pole to show that the sensitivity of CGR to tropical temperature interannual variability has increased by a factor of 1.9 ± 0.3 in the past five decades. We find that this sensitivity was greater when tropical land regions experienced drier conditions. This suggests that the sensitivity of CGR to interannual temperature variations is regulated by moisture conditions, even though the direct correlation between CGR and tropical precipitation is weak. We also find that present terrestrial carbon cycle models do not capture the observed enhancement in CGR sensitivity in the past five decades. More realistic model predictions of future carbon cycle and climate feedbacks require a better understanding of the processes driving the response of tropical ecosystems to drought and warming.
Future climate change and increasing atmospheric CO2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510-758 ppm of CO2), vegetation carbon increases by 52-477 Pg C (224 Pg C mean), mainly due to CO2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended.
A directional change in tropical-forest productivity, a large component in the global carbon budget, would affect the rate of increase in atmospheric carbon dioxide ([CO2]). One current hypothesis is that “CO2 fertilization” has been increasing tropical forest productivity. Some lines of evidence instead suggest climate-driven productivity declines. Relevant direct field observations remain extremely limited for this biome. Using a unique long-term record of annual field measurements, we assessed annual aboveground net primary productivity (ANPP) and its relation to climatic factors and [CO2] in a neotropical rainforest through 1997–2009. Over this 12 year period, annual productivity did not increase, as would be expected with a dominant CO2 fertilization effect. Instead, the negative responses of ANPP components to climatic stress far exceeded the small positive responses associated with increasing [CO2]. Annual aboveground biomass production was well explained (73%) by the independent negative effects of increasing minimum temperatures and greater dry-season water stress. The long-term records enable a first field-based estimate of the [CO2] response of tropical forest ANPP: 5.24 g m2 yr -1 yr -1 (the summed [CO2]-associated increases in two of the four production components; the largest component, leaf litterfall, showed no [CO2] association). If confirmed by longer data series, such a small response from a fertile tropical rainforest would indicate that current global models overestimate the benefits from CO2 fertilization for this biome, where most forests’ poorer nutrient status more strongly constrains productivity responses to increasing [CO2]. Given the rapidly intensifying warming across tropical regions, tropical forest productivity could sharply decline through coming decades.
How tropical forest carbon stocks might alter in response to changes in climate and atmospheric composition is uncertain. However, assessing potential future carbon loss from tropical forests is important for evaluating the efficacy of programmes for reducing emissions from deforestation and degradation. Uncertainties are associated with different carbon stock responses in models with different representations of vegetation processes on the one hand1, 2, 3, and differences in projected changes in temperature and precipitation patterns on the other hand4, 5. Here we present a systematic exploration of these sources of uncertainty, along with uncertainty arising from different emissions scenarios for all three main tropical forest regions: the Americas (that is, Amazonia and Central America), Africa and Asia. Using simulations with 22 climate models and the MOSES–TRIFFID land surface scheme, we find that only in one 5 of the simulations are tropical forests projected to lose biomass by the end of the twenty-first century—and then only for the Americas. When comparing with alternative models of plant physiological processes1, 2, we find that the largest uncertainties are associated with plant physiological responses, and then with future emissions scenarios. Uncertainties from differences in the climate projections are significantly smaller. Despite the considerable uncertainties, we conclude that there is evidence of forest resilience for all three regions.
Accurate assessments of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties. We discuss changes compared to previous estimates, consistency within and among components, and methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics, while emissions from Land-Use Change (ELUC), including deforestation, are based on combined evidence from land cover change data, fire activity in regions undergoing deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. Finally, the global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms. For the last decade available (2002-2011), EFF was 8.3 ± 0.4 PgC yr-1, ELUC 1.0 ± 0.5 PgC yr-1, GATM 4.3 ± 0.1PgC yr-1, SOCEAN 2.5 ± 0.5 PgC yr-1, and SLAND 2.6 ± 0.8 PgC yr-1. For year 2011 alone, EFF was 9.5 ± 0.5 PgC yr -1, 3.0 percent above 2010, reflecting a continued trend in these emissions; ELUC was 0.9 ± 0.5 PgC yr-1, approximately constant throughout the decade; GATM was 3.6 ± 0.2 PgC yr-1, SOCEAN was 2.7 ± 0.5 PgC yr-1, and SLAND was 4.1 ± 0.9 PgC yr-1. GATM was low in 2011 compared to the 2002-2011 average because of a high uptake by the land probably in response to natural climate variability associated to La Niña conditions in the Pacific Ocean. The global atmospheric CO2 concentration reached 391.31 ± 0.13 ppm at the end of year 2011. We estimate that EFF will have increased by 2.6% (1.9-3.5%) in 2012 based on projections of gross world product and recent changes in the carbon intensity of the economy. All uncertainties are reported as ±1 sigma (68% confidence assuming Gaussian error distributions that the real value lies within the given interval), reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. This paper is intended to provide a baseline to keep track of annual carbon budgets in the future.
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties. We discuss changes compared to previous estimates, consistency within and among components, and methodology and data limitations. Based on energy statistics, we estimate that the global emissions of CO2 from fossil fuel combustion and cement production were 9.5 ± 0.5 PgC yr−1 in 2011, 3.0 percent above 2010 levels. We project these emissions will increase by 2.6% (1.9–3.5%) in 2012 based on projections of Gross World Product and recent changes in the carbon intensity of the economy. Global net CO2 emissions from Land-Use Change, including deforestation, are more difficult to update annually because of data availability, but combined evidence from land cover change data, fire activity in regions undergoing deforestation and models suggests those net emissions were 0.9 ± 0.5 PgC yr−1 in 2011. The global atmospheric CO2 concentration is measured directly and reached 391.38 ± 0.13 ppm at the end of year 2011, increasing 1.70 ± 0.09 ppm yr−1 or 3.6 ± 0.2 PgC yr−1 in 2011. Estimates from four ocean models suggest that the ocean CO2 sink was 2.6 ± 0.5 PgC yr−1 in 2011, implying a global residual terrestrial CO2 sink of 4.1 ± 0.9 PgC yr−1. All uncertainties are reported as ±1 sigma (68% confidence assuming Gaussian error distributions that the real value lies within the given interval), reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. This paper is intended to provide a baseline to keep track of annual carbon budgets in the future.
All carbon data presented here can be downloaded from the Carbon Dioxide Information Analysis Center ( doi:10.3334/CDIAC/GCP_V2012 ).
The year 2010 featured a widespread drought in the Amazon rain forest, which was more severe than the “once-in-a-century” drought of 2005. Water levels of major Amazon tributaries fell drastically to unprecedented low values, and isolated the floodplain population whose transportation depends upon on local streams which completely dried up. The drought of 2010 in Amazonia started in early austral summer during El Niño and then was intensified as a consequence of the warming of the tropical North Atlantic. An observed tendency for an increase in dry and very dry events, particularly in southern Amazonia during the dry season, is concomitant with an increase in the length of the dry season. Our results suggest that it is by means of a longer dry season that warming in the tropical North Atlantic affects the hydrology of the Amazon Rivers at the end of the recession period (austral spring). This process is, sometimes, further aggravated by deficient rainfall in the previous wet season.
Unknowns in future global warming are usually assumed to arise from uncertainties either in the amount of anthropogenic greenhouse gas emissions or in the sensitivity of the climate to changes in greenhouse gas concentrations. Characterizing the additional uncertainty in relating CO2 emissions to atmospheric concentrations has relied on either a small number of complex models with diversity in process representations, or simple models. To date, these models indicate that the relevant carbon cycle uncertainties are smaller than the uncertainties in physical climate feedbacks and emissions. Here, for a single emissions scenario, we use a full coupled climate–carbon cycle model and a systematic method to explore uncertainties in the land carbon cycle feedback. We find a plausible range of climate–carbon cycle feedbacks significantly larger than previously estimated. Indeed the range of CO2 concentrations arising from our single emissions scenario is greater than that previously estimated across the full range of IPCC SRES emissions scenarios with carbon cycle uncertainties ignored. The sensitivity of photosynthetic metabolism to temperature emerges as the most important uncertainty. This highlights an aspect of current land carbon modelling where there are open questions about the potential role of plant acclimation to increasing temperatures. There is an urgent need for better understanding of plant photosynthetic responses to high temperature, as these responses are shown here to be key contributors to the magnitude of future change.
Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height ( H ). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions:
1. What is the best H -model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass?
2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots?
3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates?
The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- and Weibull- H models provided the greatest reduction in uncertainty, with regional Weibull- H models preferred because they reduce uncertainty in smaller-diameter classes (≤40 cm D ) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8 Mg ha−1 (range 6.6 to 112.4) to 8.0 Mg ha−1 (−2.5 to 23.0). For all plots, aboveground live biomass was −52.2 Mg ha−1 (−82.0 to −20.3 bootstrapped 95% CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H . After accounting for variation in H , total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in east-central Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span 1668 million km2 and store 285 Pg C (estimate including H ), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31–39 bootstrapped 95% CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation.
One of the greatest sources of uncertainty for future climate predictions is the response of the global carbon cycle to climate change. Although approximately one-half of total CO(2) emissions is at present taken up by combined land and ocean carbon reservoirs, models predict a decline in future carbon uptake by these reservoirs, resulting in a positive carbon-climate feedback. Several recent studies suggest that rates of carbon uptake by the land and ocean have remained constant or declined in recent decades. Other work, however, has called into question the reported decline. Here we use global-scale atmospheric CO(2) measurements, CO(2) emission inventories and their full range of uncertainties to calculate changes in global CO(2) sources and sinks during the past 50 years. Our mass balance analysis shows that net global carbon uptake has increased significantly by about 0.05 billion tonnes of carbon per year and that global carbon uptake doubled, from 2.4 ± 0.8 to 5.0 ± 0.9 billion tonnes per year, between 1960 and 2010. Therefore, it is very unlikely that both land and ocean carbon sinks have decreased on a global scale. Since 1959, approximately 350 billion tonnes of carbon have been emitted by humans to the atmosphere, of which about 55 per cent has moved into the land and oceans. Thus, identifying the mechanisms and locations responsible for increasing global carbon uptake remains a critical challenge in constraining the modern global carbon budget and predicting future carbon-climate interactions.
1 The methods commonly used to estimate stem turnover rates (i.e. mortality and recruitment) in species rich tropical forests suffer from a previously unrecognized artefact. The estimated rate is not independent of the census period. 2 An average rate estimate will decrease with time if the sample population cannot be characterized as homogeneous. This artefact may have considerable significance for comparisons between permanent plot studies that have used different census periods. 3 We present a theoretical consideration of this census effect. The artefact will be severe when a fraction of the population has a very much higher mortality rate than the average. 4 Using a simple formulation we provide a mathematical proof that rate estimates will decline with increasing census periods for all but perfectly uniform populations. 5 The phenomenon of apparent rate decrease may be used to provide ecologically significant information about the diversity and dynamics of the population as it is related to th
Understanding the interplay between climate and land-use dynamics is a fundamental concern for assessing the vulnerability of Amazonia to climate change. In this study, we analyse satellite-derived monthly and annual time series of rainfall, fires and deforestation to explicitly quantify the seasonal patterns and relationships between these three variables, with a particular focus on the Amazonian drought of 2005. Our results demonstrate a marked seasonality with one peak per year for all variables analysed, except deforestation. For the annual cycle, we found correlations above 90% with a time lag between variables. Deforestation and fires reach the highest values three and six months, respectively, after the peak of the rainy season. The cumulative number of hot pixels was linearly related to the size of the area deforested annually from 1998 to 2004 (r2=0.84, p=0.004). During the 2005 drought, the number of hot pixels increased 43% in relation to the expected value for a similar deforested area (approx. 19 000 km2). We demonstrated that anthropogenic forcing, such as land-use change, is decisive in determining the seasonality and annual patterns of fire occurrence. Moreover, droughts can significantly increase the number of fires in the region even with decreased deforestation rates. We may expect that the ongoing deforestation, currently based on slash and burn procedures, and the use of fires for land management in Amazonia will intensify the impact of droughts associated with natural climate variability or human-induced climate change and, therefore, a large area of forest edge will be under increased risk of fires.
The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory
data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg
C year–1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year–1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year–1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year–1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year–1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the
terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.
Stand structure dynamics during early secondary forest succession were related to mortality, growth and recruitment rates, and the dependence of these demographic processes on fallow age and initial stand structure attributes was evaluated. In 11 secondary tropical rain-forest sites (1.5-19 y) in Chiapas, Mexico, one plot of 1.0 x 50 m was established. Diameter and height were measured for all trees >= 1 cm dbh, and their survival, growth and recruitment was monitored over a 2-y period. Changes in stand structure were especially fast in the first 5 y of succession, and decreased rapidly afterwards. which resulted from similar stand-level changes in relative mortality, growth and recruitment rates. Demographic processes were negatively related with initial stand basal area, but independent of initial tree density. Basal area was a better explanatory variable of the among-stand variability in these rates than fallow age. Results suggest that asymmetric competition and resulting patterns of tree-thinning are major driving forces determining secondary forest successional pathways. Fallow age per se is a compound variable reflecting community organization at a certain point along the successional axis, while community structure drives succession. Sudden mass mortality among dominant species in some stands showed that early secondary forest succession is not always a gradual and unidirectional process.
The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon-climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr(-1) is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon-climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr(-1) is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
Amazon forests are a key but poorly understood component of the global carbon cycle. If, as anticipated, they dry this century, they might accelerate climate change through carbon losses and changed surface energy balances. We used records from multiple long-term monitoring plots across Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events. Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 x 10(15) to 1.6 x 10(15) grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the potential for large carbon losses to exert feedback on climate change.
Wood performs several essential functions in plants, including mechanically supporting aboveground tissue, storing water and other resources, and transporting sap. Woody tissues are likely to face physiological, structural and defensive trade-offs. How a plant optimizes among these competing functions can have major ecological implications, which have been under-appreciated by ecologists compared to the focus they have given to leaf function. To draw together our current understanding of wood function, we identify and collate data on the major wood functional traits, including the largest wood density database to date (8412 taxa), mechanical strength measures and anatomical features, as well as clade-specific features such as secondary chemistry. We then show how wood traits are related to one another, highlighting functional trade-offs, and to ecological and demographic plant features (growth form, growth rate, latitude, ecological setting). We suggest that, similar to the manifold that tree species leaf traits cluster around the 'leaf economics spectrum', a similar 'wood economics spectrum' may be defined. We then discuss the biogeography, evolution and biogeochemistry of the spectrum, and conclude by pointing out the major gaps in our current knowledge of wood functional traits.
We determined the reproductive response of 19-year-old loblolly pine (Pinus taeda) to 4 years of carbon dioxide (CO2) enrichment (ambient concentration plus 200 microliters per liter) in an intact forest. After 3 years of CO2 fumigation, trees were twice as likely to be reproductively mature and produced three times as many cones and seeds as trees at ambient CO2 concentration. A disproportionate carbon allocation to reproduction under CO2 enrichment results in trees reaching maturity sooner and at a smaller size. This reproductive response to future increases in atmospheric CO2 concentration is expected to change loblolly dispersal and recruitment patterns.
The net ecosystem exchange of carbon dioxide was measured by eddy covariance methods for 3 years in two old-growth forest
sites near Santarém, Brazil. Carbon was lost in the wet season and gained in the dry season, which was opposite to the seasonal
cycles of both tree growth and model predictions. The 3-year average carbon loss was 1.3 (confidence interval: 0.0 to 2.0)
megagrams of carbon per hectare per year. Biometric observations confirmed the net loss but imply that it is a transient effect
of recent disturbance superimposed on long-term balance. Given that episodic disturbances are characteristic of old-growth
forests, it is likely that carbon sequestration is lower than has been inferred from recent eddy covariance studies at undisturbed
sites.
Tropical forests hold large stores of carbon, yet uncertainty remains regarding their quantitative contribution to the global carbon cycle. One approach to quantifying carbon biomass stores consists in inferring changes from long-term forest inventory plots. Regression models are used to convert inventory data into an estimate of aboveground biomass (AGB). We provide a critical reassessment of the quality and the robustness of these models across tropical forest types, using a large dataset of 2,410 trees >or= 5 cm diameter, directly harvested in 27 study sites across the tropics. Proportional relationships between aboveground biomass and the product of wood density, trunk cross-sectional area, and total height are constructed. We also develop a regression model involving wood density and stem diameter only. Our models were tested for secondary and old-growth forests, for dry, moist and wet forests, for lowland and montane forests, and for mangrove forests. The most important predictors of AGB of a tree were, in decreasing order of importance, its trunk diameter, wood specific gravity, total height, and forest type (dry, moist, or wet). Overestimates prevailed, giving a bias of 0.5-6.5% when errors were averaged across all stands. Our regression models can be used reliably to predict aboveground tree biomass across a broad range of tropical forests. Because they are based on an unprecedented dataset, these models should improve the quality of tropical biomass estimates, and bring consensus about the contribution of the tropical forest biome and tropical deforestation to the global carbon cycle.
Millions of trees live and grow all around us, and we all recognize the vital role they play in the world’s ecosystems. Publicity campaigns exhort us to plant yet more. Yet until recently comparatively little was known about the root causes of the physical changes that attend their growth. Since trees typically increase in size by three to four orders of magnitude in their journey to maturity, this gap in our knowledge has been a crucial issue to address. Here at last is a synthesis of the current state of our knowledge about both the causes and consequences of ontogenetic changes in key features of tree structure and function.
During their ontogeny, trees undergo numerous changes in their physiological function, the structure and mechanical properties of their wood, and overall architecture and allometry. This book examines the central interplay between these changes and tree size and age. It also explores the impact these changes can have, at the level of the individual tree, on the emerging characteristics of forest ecosystems at various stages of their development. The analysis offers an explanation for the importance of discriminating between the varied physical properties arising from the nexus of size and age, as well as highlighting the implications these ontogenetic changes have for commercial forestry and climate change. This important and timely summation of our knowledge base in this area, written by highly respected researchers, will be of huge interest, not only to researchers, but also to forest managers and silviculturists.