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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
... forests in the Amazon has been estimated to be undergoing a persistent decline, 23 driven by an increase in tree mortality, associated with environmental change [8][9][10] . The 24 ...
... old-growth Amazon forest may thus continue to lose its climate change mitigation role 25 by absorbing less carbon from the atmosphere in the future [8][9][10] . 26 ...
... Finally, we 1 calculated the multi-model mean and standard deviation statistics. In order to assess 2 the old-growth sink simulated by the DGVMs, we compared it against RAINFOR 3 inventory based estimates 8,9,34 for the common period (2010-2015) by using a Welch's 4 t-test to test whether the averages over the same period were significantly different. 5 ...
The Amazon is the largest continuous tropical forest in the world and plays a key role in the global carbon cycle. Human-induced disturbances and climate change have impacted the Amazon carbon balance. Here we conduct a comprehensive analysis of state-of-the-art estimates of the contemporary land carbon fluxes in the Amazon. Over the whole Amazon region bottom-up methodologies suggest a small average carbon sink over 2010-2020, in contrast with a carbon small source simulated by top-down inversions (2010-2018). However, these estimates are not significantly different from one another when accounting for their large individual uncertainties, highlighting remaining knowledge gaps, and urgent need to reduce such uncertainties. Nevertheless, both methodologies agreed on an Amazon net carbon source during recent climate extremes and that south-eastern Amazon was a net land carbon source over the whole study period (2010-2020). Overall, our results point to increasing human-induced disturbances (deforestation and forest degradation by wildfires) and reduction in the old-growth forest sink during drought. If the current trends in deforestation and forest degradation and regional drying continue, it will have negative implications for reducing carbon emissions and maintaining globally important natural carbon stocks, as part of the requirements for achieving the Paris Agreement goals.
... Our predicted declines in equilibrium AGB and tropical carbon stocks generally agree with observed trends in carbon losses attributed to climate change, particularly droughts [22][23][24] . In intact forests, for instance, field-based observations and predictions indicate recent or near-term declines in biomass accumulation during episodic droughts [25][26][27] . The reduction in carbon sequestration in these intact forests was associated with extreme droughts 23,26 , when air temperature was often substantially higher than historical values. ...
... CO 2 fertilization is the main process accounting for these differences between our empirical approach and ESMs. The debate about CO 2 fertilization is still ongoing, with some observational evidence of CO 2 fertilization increasing tropical forest carbon stocks 25,26 while recent field-based studies suggest that the rate of carbon gain is slowing 12,25,26 . Moreover, other processes that reduce the vegetation carbon sink are frequently misrepresented in ESMs, including nutrient limitation, drought vulnerability, plant mortality, biomass turnover and fire disturbance 11,14,15,37,38,39,40 . ...
... CO 2 fertilization is the main process accounting for these differences between our empirical approach and ESMs. The debate about CO 2 fertilization is still ongoing, with some observational evidence of CO 2 fertilization increasing tropical forest carbon stocks 25,26 while recent field-based studies suggest that the rate of carbon gain is slowing 12,25,26 . Moreover, other processes that reduce the vegetation carbon sink are frequently misrepresented in ESMs, including nutrient limitation, drought vulnerability, plant mortality, biomass turnover and fire disturbance 11,14,15,37,38,39,40 . ...
Tropical ecosystems store over half of the world’s aboveground live carbon as biomass, and water availability plays a key role in its distribution. Although precipitation and temperature are shifting across the tropics, their effect on biomass and carbon storage remains uncertain. Here we use empirical relationships between climate and aboveground biomass content to show that the contraction of humid regions, and expansion of those with intense dry periods, results in substantial carbon loss from the neotropics. Under a low emission scenario (Representative Concentration Pathway 4.5) this could cause a net reduction of aboveground live carbon of ~14.4–23.9 PgC (6.8–12%) from 1950–2100. Under a high emissions scenario (Representative Concentration Pathway 8.5) net carbon losses could double across the tropics, to ~28.2–39.7 PgC (13.3–20.1%). The contraction of humid regions in South America accounts for ~40% of this change. Climate mitigation strategies could prevent half of the carbon losses and help maintain the natural tropical net carbon sink.
... Historically, up to 200 petagrams of carbon (200,000,000,000 tonnes) has been stored in the Amazon, in above and below ground biomass and soils (Li et al, 2022;Brienen et al, 2015;Ritchie et al, 2022). Due to increased fires, climate change, agricultural conversion, and broader land use pressures, parts of the Amazon are now a significant source of carbon emissions. ...
... Estimates of Amazon carbon stocks range between 100-200 petagrams of Carbon (100,000,000,000 to 200,000,000,000 tonnes), this equates to 367-733 GtCO2 (gigatons of CO 2 ) stored in the Amazon (Brienen et al, 2015;Gatti et al, 2021). ...
... LOOK LIKE? (Boulton et al, 2022) find evidence of rising dieback in more than three-quarters of the Amazon forest, since the early 2000s, consistent with a loss of resilience. Exploring past growth rates in trees from their rings, has also revealed that rates of growth (measured via net above-ground biomass) have declined by one-third during the past decade, compared to the 1990s (Brienen et al, 2015). This is a consequence of tree growth rate levelling off in recent years, as moisture has become a growth limiting factor, and tree longevity has shortened. ...
... Global carbon emissions have impacted Amazon's most remote forests by changing the atmospheric composition and air temperature. The accumulation of atmospheric CO2 has contributed to the increased growth of primary forests and mortality rates in the mid-2000s (Brienen et al. 2015). Although this likely CO2 effect has ultimately promoted forest carbon (C) gains, especially during the 1990s, carbon accumulation rates are now slowing down. ...
... However, the rate of carbon accumulation has sharply declined over the past two decades. One important reason for this reduction is significant droughts causing widespread reductions in tree growth and increases in tree mortality, especially the larger, carbon-rich ones, as shown in Figure 23.2 (Brienen et al. 2015;Brando et al. 2019a). Another potential cause for the reduction is the increase in atmospheric CO2, promoting higher forest turnover rates (McDowell et al. 2018). ...
... Another potential cause for the reduction is the increase in atmospheric CO2, promoting higher forest turnover rates (McDowell et al. 2018). As a combined result of these changes, the carbon accumulation capacity of undisturbed forests is getting weaker for both the Amazon and tropical Africa, with the possibility of forests becoming global carbon sources (Hubau et al. 2020;Brienen et al. 2015;Gatti et al. 2021). Chapter 23: Impacts of Deforestation and Climate Change on Biodiversity, Ecological Processes, and Environmental Adaptation ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Overall, the processes of woody biomass creation and tree mortality have not been in balance in recent decades, leading to a net biomass carbon sink, equivalent to positive Net Biome Productivity (NBP). Data are extrapolated to the area of the Amazon forest biome using values provided in Malhi et al. (2016) and Brienen et al. (2015). Malhi et al. (2009a). ...
... The net carbon balance of a mature terra firme Amazonian forest could be expected to be zero from ecological first principles, as the uptake of carbon through photosynthesis is compensated by releases of carbon through heterotrophic and autotrophic respiration. However, long term inventories suggest a net rate of increase of vegetation biomass of 0.6 Mg C ha -1 y -1 (where Mg is 10 6 grams) (see below), equivalent to about 2% of photosynthesis (Brienen et al. 2015). ...
... 95% C.I.) Pg C year -1 if extrapolated over the Amazon forest biome in the 2000s (Brienen et al. 2015) (Figure 6.4). This accumulation seems to stop in drought years (Phillips et al. 2009) and seems to be declining over time (Brienen et al. 2015). Increasing length of the dry season may lead to the intact forests of the Amazon becoming a carbon source in the near future (see Chapter 19). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Overall, the processes of woody biomass creation and tree mortality have not been in balance in recent decades, leading to a net biomass carbon sink, equivalent to positive Net Biome Productivity (NBP). Data are extrapolated to the area of the Amazon forest biome using values provided in Malhi et al. (2016) and Brienen et al. (2015). Malhi et al. (2009a). ...
... The net carbon balance of a mature terra firme Amazonian forest could be expected to be zero from ecological first principles, as the uptake of carbon through photosynthesis is compensated by releases of carbon through heterotrophic and autotrophic respiration. However, long term inventories suggest a net rate of increase of vegetation biomass of 0.6 Mg C ha -1 y -1 (where Mg is 10 6 grams) (see below), equivalent to about 2% of photosynthesis (Brienen et al. 2015). ...
... 95% C.I.) Pg C year -1 if extrapolated over the Amazon forest biome in the 2000s (Brienen et al. 2015) (Figure 6.4). This accumulation seems to stop in drought years (Phillips et al. 2009) and seems to be declining over time (Brienen et al. 2015). Increasing length of the dry season may lead to the intact forests of the Amazon becoming a carbon source in the near future (see Chapter 19). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Recent studies have suggested that faster forest growth (NPP) leads to higher tree mortality at local and regional scales, particularly in tropical forests 10,11 . This has been recently demonstrated across spatial scales in boreal forests using tree-ring datasets 12 and is consistent with ESM projections across forest biomes 13 . ...
... The data are from largely unmanaged forest plots, because management implies distinct LOSS patterns, and management/forestry is not incorporated in models. Our approach is motivated by the positive heuristic relationships (Supplementary Figs. 2 and 3) between historical LOSS and projected NPP and HR carbon fluxes in DGVMs, in line with the known pattern of faster growth and higher mortality [10][11][12][13] and the couplings of growth, mortality and respiration at long-term and broad spatial scales 20,21 . We used LOSS also because: (1) it can be directly measured in forest inventory datasets 13 with high accuracy relative to remote sensing; (2) LOSS remains less studied relative to NPP and LOSS is unrealistically represented (i.e., as a proportion of NPP) in DGVMs 13 . ...
... Drivers of LOSS. Mean annual temperature (MAT), aridity index (the ratio of precipitation to potential evapotranspiration), and precipitation seasonality were identified as the dominant predictors of LOSS across continents ( Supplementary Fig. 7a), with positive relationships with LOSS ( Fig. 3a) 10,36 . In contrast to local-scale studies 40,41 , wood density, forest stand density, and soil conditions were poor predictors of LOSS when all data were used. ...
Considerable uncertainty and debate exist in projecting the future capacity of forests to sequester atmospheric CO2. Here we estimate spatially explicit patterns of biomass loss by tree mortality (LOSS) from largely unmanaged forest plots to constrain projected (2015–2099) net primary productivity (NPP), heterotrophic respiration (HR) and net carbon sink in six dynamic global vegetation models (DGVMs) across continents. This approach relies on a strong relationship among LOSS, NPP, and HR at continental or biome scales. The DGVMs overestimated historical LOSS, particularly in tropical regions and eastern North America by as much as 5 Mg ha−1 y−1. The modeled spread of DGVM-projected NPP and HR uncertainties was substantially reduced in tropical regions after incorporating the field-based mortality constraint. The observation-constrained models show a decrease in the tropical forest carbon sink by the end of the century, particularly across South America (from 2 to 1.4 PgC y−1), and an increase in the sink in North America (from 0.8 to 1.1 PgC y−1). These results highlight the feasibility of using forest demographic data to empirically constrain forest carbon sink projections and the potential overestimation of projected tropical forest carbon sinks. Here the authors use broad-scale tree mortality data to estimate biomass loss, constraining uncertainty of projected forest net primary productivity in 6 models, finding weaker tropical forest carbon sinks with climate change.
... 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.
... Such speculative grilagem practices have long been seen as a major driver for deforestation in the Amazon. 54 'Even before approval, a land grab draft law is already destroying the Amazon', Institutio Socioambiental (27 Mat 2021), accessible at < https://www.socioambiental.org/en/noticias-socioambientais/even-before-approval-aland-grab-draft-law-is-already-destroying-the-amazon >. ...
... Given that the values stated above for Amazon carbon sequestration are based on an estimated area of intact forests in tropical South America of 6.29 x 10 8 ha 54 , based on the Global Land Cover map 200054,55 , the mean sequestration rate for the Amazon is 2.45 -3.78 x 10 -9 GtCO2 ha -1 (= 2.45 -3.78 tCO2 ha -1 ). We estimate that an average of 3,985 km 2 (= 398,500 ha) of deforestation was attributable to Bolsonaro in each of the first two years of his tenure (362,000 and 435,000 ha in 2019 and 2020, respectively). ...
... Additional CO2 is expected to buffer the effect of water stress by increasing plant water-use efficiency and accelerating tree growth (section 22.5.3). Elevated atmospheric CO2 may be the cause of the increase in woody biomass and productivity observed across Amazonian forests (Brienen et al. 2015), favoring fast-growth species (Esquivel-Muelbert et al., 2019). However, elevated atmospheric CO2 driven accelerations of tree growth have come at the cost of decreasing tree longevity across the basin, further contributing to increased tree mortality rates (Brienen et al. 2015;Hubau et al. 2020). ...
... Elevated atmospheric CO2 may be the cause of the increase in woody biomass and productivity observed across Amazonian forests (Brienen et al. 2015), favoring fast-growth species (Esquivel-Muelbert et al., 2019). However, elevated atmospheric CO2 driven accelerations of tree growth have come at the cost of decreasing tree longevity across the basin, further contributing to increased tree mortality rates (Brienen et al. 2015;Hubau et al. 2020). The acceleration of the system via CO2 fertilization may allow trees to reach the canopy earlier and be more vulnerable to death , and particularly vulnerable to water deficits (Oliveira et al. 2021). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Inventories from long-term forest plot networks (e.g., RAIN-FOR), many beginning in the 1980s, provide data on carbon dynamics for intact, mature forests at nearly 300 sites. These individual plots, scaled to the total forested area, indicate that intact forests are a net sink for carbon, although the rate of carbon uptake has decreased over the past three decades, mainly due to increases in mortality (Brienen et al. 2015;Phillips and Brienen, 2017;Hubau et al. 2020) (see Chapter 6). The carbon sink or uptake (i.e., carbon removal from the atmosphere, reported here with a negative sign) estimated for mature upland forests, scaled to an area of 7.25 x 10 6 km 2 , results in an estimate of mean net carbon uptake in intact forests for the 1990s of -0.59 ± 0.18 Pg C y -1 . ...
... For the last decade (2010 through 2019), bottom-up studies indicate that mature forests are carbon sinks of -0.22 ± 0.30 Pg C y -1(Brienen et al. 2015;Phillips and Brienen, 2017;Hubau et al. 2020), and secondary forests -0.10 ± 0.02 Pg C y -1 . Carbon emissions include forest fires of 0.20 ± 0.20 Pg C y -1 (van derWerf et al. 2010;van der Laan-Luijkx et al. 2015;Baccini et al. 2017;Aragão et al. 2018;, forest degradation, deforestation, and other carbon emissions of 0.32 ± 0.10 Pg C y -1(Aguiar et al. 2016;Assis et al. 2020;Smith et al. 2020;Silva Junior et al. 2020), where fire emissions from deforestation are 0.05 ± 0.01 Pg C y -1(Aguiar et al. 2016;Assis et al. 2020), representing 14% of total fires, included in the total fire emission estimate. ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Based on a study in China, forest-stored carbon is 32%, 300%, and 150% higher than that of grassland, shrubland, and cropland, respectively [9]. An observation from tropical Amazon shows that carbon sequestration in tropical forests starts to decline because of an increase in tree mortality [10,11]. From 1983 to 2011, carbon sequestration in the Amazon tropical forest decreased at a rate of −0.034 Mg C ha −1 year −2 [11]. ...
... An observation from tropical Amazon shows that carbon sequestration in tropical forests starts to decline because of an increase in tree mortality [10,11]. From 1983 to 2011, carbon sequestration in the Amazon tropical forest decreased at a rate of −0.034 Mg C ha −1 year −2 [11]. Meanwhile, shrubs have been found to grow faster than trees and play a strategic role in carbon sequestration [12]. ...
Climatic conditions and land cover play crucial roles in influencing the process of carbon uptake through vegetation. This study aimed to analyze the effect of climate variability on carbon uptake of four different land covers in Jambi Province, Indonesia. The four land cover types studied were: forest, shrub, grass, and irrigated soybean, based on Community Land Model version 5. Forest was found to have the highest net primary production (NPP) compared to the other land covers. Seasonal climate variability showed no major effect on NPP and gross primary production (GPP). However, GPP and NPP experienced significant declines during El Ni Southern Oscillation (ENSO), particularly in 2015. Carbon use efficiency (CUE=NPP/GPP) was also affected by ENSO, where CUE decreased during El Ni, particularly in October and November with an increased number of days without rainfall. In addition, the difference between latent (LE) and sensible heat (H) flux, denoted as (LE-H), decreased from August to November. This difference was highly correlated with NPP. This result indicates that when water supply is low, stomata will close, thereby reducing photosynthesis and transpiration, and allocating more of the available energy to sensible heat flux rather than latent heat flux.
... Inventories from long-term forest plot networks (e.g., RAIN-FOR), many beginning in the 1980s, provide data on carbon dynamics for intact, mature forests at nearly 300 sites. These individual plots, scaled to the total forested area, indicate that intact forests are a net sink for carbon, although the rate of carbon uptake has decreased over the past three decades, mainly due to increases in mortality (Brienen et al. 2015;Phillips and Brienen, 2017;Hubau et al. 2020) (see Chapter 6). The carbon sink or uptake (i.e., carbon removal from the atmosphere, reported here with a negative sign) estimated for mature upland forests, scaled to an area of 7.25 x 10 6 km 2 , results in an estimate of mean net carbon uptake in intact forests for the 1990s of -0.59 ± 0.18 Pg C y -1 . ...
... For the last decade (2010 through 2019), bottom-up studies indicate that mature forests are carbon sinks of -0.22 ± 0.30 Pg C y -1(Brienen et al. 2015;Phillips and Brienen, 2017;Hubau et al. 2020), and secondary forests -0.10 ± 0.02 Pg C y -1 . Carbon emissions include forest fires of 0.20 ± 0.20 Pg C y -1 (van derWerf et al. 2010;van der Laan-Luijkx et al. 2015;Baccini et al. 2017;Aragão et al. 2018;, forest degradation, deforestation, and other carbon emissions of 0.32 ± 0.10 Pg C y -1(Aguiar et al. 2016;Assis et al. 2020;Smith et al. 2020;Silva Junior et al. 2020), where fire emissions from deforestation are 0.05 ± 0.01 Pg C y -1(Aguiar et al. 2016;Assis et al. 2020), representing 14% of total fires, included in the total fire emission estimate. ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... • The elevated atmospheric CO 2 had a strong positive influence on gross primary productivity (GPP) and also offset deforestation, when native forest was converted to grasses • Land use change also had a negative effect on evaporation and most intense effects of climate change (as temperature increasing) were on deforested areas • Uncertainties were found in the outputs of the models and in the climatic forcings. Divergences were also observed among the models Furthermore, the Amazon rainforest is an important sink and reservoir for carbon (Brienen et al., 2015;Pan et al., 2011). Estimates based on forest inventories in the Amazon basin showed that undisturbed tropical forests act as a strong carbon sink with an estimated annual uptake of 0.42-0.65 ...
... Estimates based on forest inventories in the Amazon basin showed that undisturbed tropical forests act as a strong carbon sink with an estimated annual uptake of 0.42-0.65 PgCyr −1 for 1990-2007, around 25% of the residual terrestrial carbon sink (Brienen et al., 2015). This sink is probably driven by increasing atmospheric CO 2 via the downstream effects of increased photosynthesis (fertilization) and intrinsic water use efficiency (WUE; Fleischer et al., 2019;Ueyama et al., 2020;Walker et al., 2020). ...
Recent publications indicate that the Amazon may be acting more as a carbon source than a sink in some regions. Moreover, the Amazon is a source of moisture for other regions in the continent, and deforestation over the years may be reducing this function. In this work, we analyze the impacts of elevated CO2 (eCO2) and land use change (LUC) on gross primary productivity (GPP) and evaporation in the southern Amazon (7°S 14°S, 66°W 51°W), which suffered strong anthropogenic influence in the period of 1981‒2010. We ran four dynamic global vegetation models (DGVMs), isolating historical CO2, constant CO2, LUC, and potential natural vegetation scenarios with three climate variable data sets: precipitation, temperature, and shortwave radiation. We compared the outputs to five “observational” data sets obtained through eddy covariance, remote sensing, meteorological measurements, and machine learning. The results indicate that eCO2 may have offset deforestation, with GPP increasing by ∼13.5% and 9.3% (dry and rainy seasons, respectively). After isolating the LUC effect, a reduction in evaporation of ∼4% and ∼1.2% (dry and rainy seasons, respectively) was observed. The analysis of forcings in subregions under strong anthropogenic impact revealed a reduction in precipitation of ∼15 and 30 mm, and a temperature rise of 1°C and 0.6°C (dry and rainy seasons, respectively). Differences in the implementation of plant physiology and leaf area index in the DGVMs introduced some uncertainties in the interpretation of the results. Nevertheless, we consider that it was an important exercise given the relevance.
... 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. ...
... Elevated forest mortality related to extreme storms in the central Amazon was found in the La Niña wet year of 1990, La Niña year of 1999 followed by prolonged warmer temperatures and drought in the previous years, and in the drought year of 2005 34 . The relationship between extreme storms and tree mortality also implies that increasing frequency of convective storms 36 may contribute to the observed increase in tree mortality and a weakening of the carbon sink across Amazonia [37][38][39] . ...
Forest mortality caused by convective storms (windthrow) is a major disturbance in the Amazon. However, the linkage between windthrows at the surface and convective storms in the atmosphere remains unclear. In addition, the current Earth system models (ESMs) lack mechanistic links between convective wind events and tree mortality. Here we find an empirical relationship that maps convective available potential energy, which is well simulated by ESMs, to the spatial pattern of large windthrow events. This relationship builds connections between strong convective storms and forest dynamics in the Amazon. Based on the relationship, our model projects a 51 ± 20% increase in the area favorable to extreme storms, and a 43 ± 17% increase in windthrow density within the Amazon by the end of this century under the high-emission scenario (SSP 585). These results indicate significant changes in tropical forest composition and carbon cycle dynamics under climate change. The authors link the frequency of convective storms in the Amazon basin to the density of large forest mortality events (windthrows) and project an increase in forest disturbance from these dynamics due to climate warming over this century.
... Amazon forests cover 5.3 million km 2 , representing 40% of the global tropical area (Marengo et al., 2018). The forests hold a large carbon stock but show a long-term decreasing trend of carbon accumulation (Brienen et al., 2015) due to climate change, degradation and deforestation (Brando et al., 2014;Trondoli Matricardi et al., 2020;Barlow et al., 2016). However, some research argues that Amazon forests could be more resilient to disturbance than expected. ...
Vegetation optical depth (VOD) is seasonally sensitive to plant water content and aboveground biomass. This index has a strong penetrability within the vegetation canopy and is less impacted by atmosphere aerosol contamination effects, clouds and sun illumination than optical vegetation indices. VOD is thus increasingly applied in ecological applications, e.g., carbon stock, phenology and vegetation monitoring. However, VOD retrieval over dense forests is subject to uncertainties caused by the thick canopy and complex multiple scattering effects. Thus, a comprehensive evaluation of VOD products over dense forests is needed for effective and accurate applications. This study evaluated the seasonal variations of eight recently developed/reprocessed VOD products at different frequencies (e.g., Ku-, X-, C-and L-band) over Amazon intact forests, supported by the ORCHIDEE-CAN-NHA model-simulated vegetation water content. Furthermore, we also explored the potential causes of VOD retrieval issues, in terms of retrieval algorithm uncertainties. We first confirmed that soil water availability dominated seasonal dynamics of vegetation water content over Amazon intact forests. This was verified by model-simulated vegetation water content and by C-band radar backscatter observations. Generally, evening or midday vegetation water content shows higher correlations with soil moisture than morning or midnight vegetation water content. In terms of ability of morning or midnight VOD products to follow the seasonality of soil moisture, active microwave ASCAT-IB C-VOD (median seasonal correlation with soil moisture (R) ~ 0.50) outperforms the passive microwave VOD products, followed by passive microwave AMSR2 X-VOD (R ~ 0.26) and VODCA X-VOD (R ~ 0.16). However, SMOS-IC L-VOD (R ~ − 0.15) and AMSR2 C1-VOD (R ~ − 0.20) show obviously negative seasonal correlations with soil moisture across most pixels. This implausible behavior is likely to be caused by the inappropriate setting of time-invariant scattering effects in the passive microwave VOD retrieval algorithms, which could lead to an overestimation of the VOD amplitude during dry seasons. Thus, we recommend that the seasonal scattering effects be considered in the passive microwave VOD retrieval algorithms. These findings can contribute to the improvement of VOD retrieval algorithms and help with the development of their ecological applications over Amazon dense forests.
... Decades of deforestation have damaged more than 50% of all tropical forests (Gibbs et al. 2010;Jacobson et al. 2019). Such deforestation followed by agricultural usage significantly depletes the nitrogen (N) and carbon (C) levels in the soil (Amazonas et al. 2011;Brienen et al. 2015;Groppo et al. 2015;Powers and Marín-Spiotta 2017), presumably damaging the soil microbial communities associated with the C and N cycles, reducing the capacity of the soils to serve as C and N sinks (Bardgett and van der Putten 2014;Mendes et al. 2015;Eaton et al. 2019Eaton et al. , 2021a. Reforestation strategies are being implemented to remediate the damage done to these forests and their soils (Aide et al. 2013;Locatelli et al. 2015;Philipson et al. 2020;Poorter et al. 2021). ...
Aims
This study was designed to determine if planting the leguminous tree Inga punctata in previously cleared former tropical premontane wet forests changed the Nitrogen (N)-fixer and Lignin Degrader community compositions resulting in increased accumulation of soil carbon (C) and N components.
Methods
Soils were collected near the base of old growth (> 50 years old), 4, 8 and 11-year-old I. punctata trees, and assessed for differences in various soil C and N metrics, and the mean proportion of sequences (MPS, as “relative abundance” via 16S rRNA V3, V4 sequencing), composition, stability and evenness of the N-fixer and Lignin Degrader community genera.
Results
The N-fixer MPS decreased, and Lignin Degraders increased, while evenness and stability of both increased in soils along the tree age gradient. The Lignin Degrader MPS were positively correlated with TN, NO3⁻, TOC, and Biomass C, and negatively correlated with N-fixer MPS and NH4⁺. The N-fixer MPS were negatively correlated with TN, NO3⁻, TOC, Biomass-C and Lignin Degrader MPS, and positively correlated with NH4⁺. Evenness, stability, and dissimilarity increased for both groups in soils along the tree age gradient.
Conclusions
This is the first evidence that I. punctata facilitates changes in tree-soil N-fixer and Lignin Degrader communities over time by increasing the dissimilarity, evenness and stability of both groups, and increases the accumulation of tree soil C and N. This suggests I. punctata facilitates soil recovery such that it can serve as C and N sinks and support its future use in reforestation management strategy.
... Intuitively, the R S first increased and then decreased with afforestation age (Fig. 3a). Afforestation age can influence stand productivity and SOC inputs (Brienen et al., 2015). In the early afforestation stage, low stand productivity and poor understory vegetation, leading to less organic matter entered into the soil and low R S (Tatsumi, 2020). ...
Mixed plantation and pure plantation are two afforestation modes in practice, which make great contributions to carbon sinks of forests ecosystem. However, the difference in SOC response to the two kinds of afforestation modes (mixed plantation and pure plantation) remained controversial at present. This study conducted a synthesis to estimate afforesta-tion modes effect on SOC sequestrations based on 218 filed observations in China. The results showed that mixed plantations preserved more SOC sequestrations than pure plantations in China. The SOC sequestration rates (R S) in 0-20 cm layer of mixed and pure plantations were 0.89 and 0.32 Mg ha −1 yr −1 , respectively. Particularly, the R S of arbor-shrub mixtures (0.97 Mg ha −1 yr −1) was the highest among all mixed plantations. Generally , the R S was increased first and then decreased since afforestation, with the peaking value of 1.20 Mg ha −1 yr −1 during 6-10 years. Moreover, afforestations on cropland had a higher R S compared to that on barren lands or woodlands, and reforestations on woodlands usually led to SOC loss. Compared with high-temperature and high-precipitation environments (C-rich regions), afforestation in low-temperature and low-precipitation environments (C-deficit regions) had the higher R S. Overall, conducting mixed plantations, especially arbor-shrub mixtures, was more beneficial to promote SOC sequestration than pure plantations. The findings suggest that mixed plantations should be taken into accounting in future afforestation projects in the view of improving the carbon benefits of the ecosystem.
... Forests remove carbon continuously from the atmosphere and are currently estimated to provide a sink of −7.6 ± 49 Gt CO2e per year, with 30 percent from tropical and subtropical forests, 47 percent from temperate forests, and 21 percent from boreal forests (Harris et al., 2021). However, this sink has been declining due to emissions from forest loss and degradation, interacting with increasing impacts from climate change (Raupach et al., 2014;Brienen et al., 2015;2017, Gatti et al.;, Zhu et al., 2021Anderegg et al., 2022). It is therefore critical to conserve forest biodiversity and related ecological processes to help maintain their sink capacity. ...
... The ongoing Amazon rainforest deforestation is a global concern due to its profound negative impacts on soil biochemical cycles, which contribute to regional and global climate change BRIENEN et al., 2015;NAVARRETE et al., 2016;JIA et al., 2019;VELDKAMP et al., 2020). Our results are in agreement with previous research on CH4 fluxes turnover in the Amazon region, where soils go from being a sink to a source of atmospheric CH4 after forest-to-pasture conversion (STEUDLER et al., 1996;VERCHOT et al., 2000;. ...
Methane (CH4) constitutes the second most important greenhouse gas after CO2, and accounts for up to 2030% of global warming. Significant accumulation of CH4 in the atmosphere (~44%) is associated with land-use change. In soil, CH4 production and oxidation rates are intrinsically linked, and driven by methanogens (archaea) and methanotrophs (bacteria) which are, at the same time, shaped by edaphic and environmental conditions. This arises as a relevant issue due to the increasing intensification of agriculture, particularly in the context of climate change. This thesis focused on the characterization of methanogenic and methanotrophic communities and their response to land-use change in tropical and temperate forests. The thesis consists of three chapters presented in scientific manuscript format. The study in Chapter 1 was addressing the impact of forest-to-pasture conversion on CH4-cycling communities in Rondonia, Brazil, through metagenomic sequencing and high-resolution taxonomic and functional analysis, exploring biotic and abiotic factors influencing these microbial groups. Chapter 2 delves deeper into the study of forest-to-pasture conversion in another region of the Amazon Basin (Pará, Brazil) to identify the abiotic drivers of methanogenic and methanotrophic communities in forest and pasture soils. In this chapter, CH4 fluxes and edaphic parameters were measured in two seasons (wet and dry), two soil types (sandy and clayey) and four soil depths. The analyses included ~280 samples of 16S rRNA sequencing, the isotopic composition of CH4 samples, and soil physical and chemical properties. The study in Chapter 3, performed in Ontario, Canada, aims to compare the structure and activity of methanogens and methanotrophs in five riparian buffer systems with contrasting plant coverage in an agricultural landscape. Soils samples were collected during CH4 emissions hotspots, and DNA and cDNA samples were sequenced using nPCR-amplicons from pmoA gene (methanotrophs) and archaeal 16S rRNA (methanogens). Overall, our results provide strong evidence of the transformation of CH4-cycling communities due to land-use change, and identifies key abiotic drivers behind these microbial changes
... This regulatory capacity, associated with the year-round level of solar radiance, keeps the rainforest operating at a near optimum for photosynthesis (approximately 16% of global terrestrial GPP), resulting in a significant annual carbon sink of 0.38 (0.28-0.49 95% C.I.) Pg C year-1 (Beer et al. 2010;Brienen et al. 2015; see also Chapter 6). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Some limited use of emission avoidance credit-like instruments may persist after global net zero is achieved, perhaps as a means for facilitating abatement financing by countries with net negative emissions toward countries that still have net positive emissions, but they will by definition not be useable for making compensation claims. While nature-based removal carbon credits will continue to play an important role throughout the net zero transition, they face several constraints including limited land area in competition for food and fibre production, and the impact of global warming itself which is likely to substantially weaken, if not reverse, many biospheric carbon sinks (Brienen et al. 2015;Lowe and Bernie 2018). Again, within the context of those risks, these underlying activities will need to be maximally scaled in order to preserve ecosystem integrity, to preserve the ongoing capacity of nature to absorb carbon, and to deliver critical non-carbon co-benefits (Girardin et al. 2021). ...
Interest in carbon offsetting is resurging among companies and institutions, but the vast majority of existing offerings fail to enable a credible transition to a durable net zero emission state. A clear definition of what makes an offsetting product “net zero compliant” is needed. We introduce the “proset”, a new form of composite carbon credit in which the fraction of carbon allocated to geological-timescale storage options increases progressively, reaching 100% by the target net zero date, generating predictable demand for effectively permanent CO2 storage while making the most of the near-term opportunities provided by nature-based climate solutions, all at an affordable cost to the purchaser.
... While global estimates are important to have an overall carbon pool estimate (CHAVE et al., 2014;BRIENEN et al., 2015;PHILLIPS et al., 2016;POORTER et al., 2016), local estimates and factors which affect soil carbon dynamics at specific sites are also very important in this scenario (MELLO et al., 2018). Detailed knowledge of the spatial variability of the soil attributes is of great relevance for the sustainable management of natural or recovering ecosystems (SONG;WANG, 2014). ...
This study aimed to explore the physical and chemical attributes of the soil and to spatialize the soil organic carbon stock in a stretch of Atlantic Forest by evaluating four soil layers and the interrelationships of physical and chemical attributes as well as the spatialization of soil organic carbon stock by applying cokriging interpolation. Thus, 12 soil samples were collected in a soil layer, and the nutrient content, soil density, texture, soil organic carbon content and the soil carbon stock were determined. A Principal Component Analysis (PCA) grouped the most similar plots in terms of physical and chemical characteristics. Based on the spatial autocorrelation of the soil attributes, the digital elevation model data (altitude and slope) for the studied site were combined to explore the coordinate relationship between the terrain parameters and the soil organic carbon stock. We verified an increase in the soil fertility parallel to the increase in the organic matter content in the soil, helping to understand the differences and similarities of the identified sites in the field. There is a spatial difference in the soil organic carbon stock, with the largest being observed in areas of lower slope and altitude. The physical and chemical attributes of the soil in the Atlantic Forest varied according to the sampled points, being strongly related to the relief. The spatial variability altered soil organic carbon stocks in the forest under study.
... An extensive literature examines the role of increasing CO 2 in driving an increasing degree of plant/ecosystem scale nutrient limitation 2,3,77 : plants are getting increased supply of carbon but increasingly less nutrients as more and more nutrients are locked up in plant biomass. The resulting progressive nutrient limitation has fueled the fear of a saturating land carbon sink 4 due to the inability of the ecosystem to fix additional carbon 3,5,7 . Our analyses thus suggest plants can potentially invest an increasing amount of their photosynthates to tap into the previously under-exploited soil nutrient pool as the plant cost-benefit equation is being shifted by global warming and rising CO 2 . ...
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Recent studies of plant fine roots have greatly advanced our understanding of their geometric properties and symbiotic relationships, but knowledge of how these roots are spatially distributed across the soil matrix lags far behind. An improved understanding of broad-scale variability in root vertical distribution is critical for understanding plant-soil-atmosphere interactions and their influence on the land carbon sink. Here we analyze a continental-scale dataset of plant roots reaching 2-meters depth, spanning 19 ecoclimatic domains ranging from Alaskan tundra to Puerto Rican neotropical forest. Contrary to the common expectation that fine root abundance decays exponentially with increasing soil depth, we found surprising root bimodality at ~20% of 44 field sites —a secondary peak of fine root biomass far beneath the soil surface. All of the secondary root peaks were observed deeper than 60cm (with 33% below 1m), far deeper than the sampling depth commonly used in ecosystem studies and forestry surveys. We demonstrate that root bimodality is more likely in places with relatively low total fine root biomass, and is more frequently associated with shrubland vegetation but less with grassland. Further statistical analyses revealed that the secondary peak of root biomass coincided with unexpected high soil nitrogen contents at depth. By linking roots and nutrient distributions, we further demonstrate that deep soil nutrients tend to be underexploited by plant rooting systems, yet root bimodality offers a unique mechanism by which fine roots can tap into soil resources in the deep. Our findings suggest that empirical practices have often systematically overlooked root dynamics in deep soils, and as a result the current-generation global climate and vegetation models have relied on overly simplistic assumptions for plant rooting distribution.
... Global warming is leading to an increase in the frequency and intensity of droughts (Marengo et al. 2018). As a consequence, Amazonian forests are experiencing a reduction in water availability for plants (Pascolini-Campbell et al. 2021), and higher tree mortality and biomass loss (Phillips et al. 2009, Brienen et al. 2015, Berenguer et al. 2021. Therefore, it is crucial to assess the influence of local hydrological conditions on forest diversity, and on taxonomic and functional composition. ...
... Global warming is leading to an increase in the frequency and intensity of droughts (Marengo et al. 2018). As a consequence, Amazonian forests are experiencing a reduction in water availability for plants (Pascolini-Campbell et al. 2021), and higher tree mortality and biomass loss (Phillips et al. 2009, Brienen et al. 2015, Berenguer et al. 2021. Therefore, it is crucial to assess the influence of local hydrological conditions on forest diversity, and on taxonomic and functional composition. ...
Tree diversity and composition in Amazonia are known to be strongly determined by the water supplied by precipitation. Nevertheless, within the same climatic regime, water availability is modulated by local topography and soil characteristics (hereafter referred to as local hydrological conditions), varying from saturated and poorly drained to well‐drained and potentially dry areas. While these conditions may be expected to influence species distribution, the impacts of local hydrological conditions on tree diversity and composition remain poorly understood at the whole Amazon basin scale. Using a dataset of 443 1‐ha non‐flooded forest plots distributed across the basin, we investigate how local hydrological conditions influence 1) tree alpha diversity, 2) the community‐weighted wood density mean (CWM‐wd) – a proxy for hydraulic resistance and 3) tree species composition. We find that the effect of local hydrological conditions on tree diversity depends on climate, being more evident in wetter forests, where diversity increases towards locations with well‐drained soils. CWM‐wd increased towards better drained soils in Southern and Western Amazonia. Tree species composition changed along local soil hydrological gradients in Central‐Eastern, Western and Southern Amazonia, and those changes were correlated with changes in the mean wood density of plots. Our results suggest that local hydrological gradients filter species, influencing the diversity and composition of Amazonian forests. Overall, this study shows that the effect of local hydrological conditions is pervasive, extending over wide Amazonian regions, and reinforces the importance of accounting for local topography and hydrology to better understand the likely response and resilience of forests to increased frequency of extreme climate events and rising temperatures.
... Korner (2017) reported that the carbon storage potential for the forest ecosystems is controlled by the tree longevity rather than the growth rate. Size distributions are shifted toward trees with larger girth classes by high carbon stocks (Brienen et al., 2015). In the present study, the low density of mature tree individuals was recorded in lower and middle girth classes 18% and contributed only 2% of the biomass. ...
... T he Amazon rainforest has historically been one of the largest carbon pools on Earth, storing up to 200 petagrams of carbon (PgC) 1 . Furthermore, the Amazon rainforest has acted as a strong carbon sink, whereby from 1990-2007 the rainforest had an annual carbon uptake of 0.42-0.65 ...
Earth System Models project a wide range of rainfall changes in the Amazon rainforest, and hence changes in soil moisture and evapotranspiration. Hydrological changes are heterogeneous , meaning local measurements are too sparse to constrain projections of large-scale hydrological change. Here we show that changes in the amplitude of the temperature seasonal cycle are strongly correlated with annual mean evaporative fraction (surface latent heat flux as a fraction of surface net radiation) changes, across reanalyses and Earth System Model projections. We find an increase in annual temperature amplitude of 1°C is associated with a reduction in evaporative fraction of up to 0.04. The observed temperature seasonal cycle amplitude increase (0.4°C) over the last three decades implies Amazon drying, determined in the absence of soil or energy flux measurements, matches Earth System Model simulations of the recent past. Additionally, Earth System Models predict further temperature seasonal cycle amplitude increases, suggesting drying will continue with future climate change.
... Small changes in their growth and mortality rates can substantially affect their carbon balance, with a global impact on the growth rate of atmospheric CO 2 (2). The El Niño-Southern Oscillation leads to droughts impacting highly productive tropical forests, compounded with fires and increased pathogens and insect attacks (3), which enhance tree mortality and reduce carbon storage, weakening the tropical forest carbon sink (4,5). Previous observational and modeling studies reported that tropical regions switched from a carbon sink to source as a result of drought associated with the severe El Niño event in 2015 to 2016 (6)(7)(8). ...
The 2015/16 El Niño brought severe drought and record-breaking temperatures in the tropics. Here, using satellite-based L-band microwave vegetation optical depth, we mapped changes of above-ground biomass (AGB) during the drought and in subsequent years up to 2019. Over more than 60% of drought-affected intact forests, AGB reduced during the drought, except in the wettest part of the central Amazon, where it declined 1 y later. By the end of 2019, only 40% of AGB reduced intact forests had fully recovered to the predrought level. Using random-forest models, we found that the magnitude of AGB losses during the drought was mainly associated with regionally distinct patterns of soil water deficits and soil clay content. For the AGB recovery, we found strong influences of AGB losses during the drought and of [Formula: see text]. [Formula: see text] is a parameter related to canopy structure and is defined as the ratio of two relative height (RH) metrics of Geoscience Laser Altimeter System (GLAS) waveform data-RH25 (25% energy return height) and RH100 (100% energy return height; i.e., top canopy height). A high [Formula: see text] may reflect forests with a tall understory, thick and closed canopy, and/or without degradation. Such forests with a high [Formula: see text] ([Formula: see text] ≥ 0.3) appear to have a stronger capacity to recover than low-[Formula: see text] ones. Our results highlight the importance of forest structure when predicting the consequences of future drought stress in the tropics.
... Since trees are among the most important means for capturing and storing carbon dioxide so that it does not contribute to further warming, when trees burn, not only are those carbon sinks lost but also the carbon they held is immediately released into the atmosphere. For just one prominent example, the Amazon rainforest is crucial as a carbon sink (i.e., captures CO 2 that would otherwise join existing CO 2 in the atmosphere and accelerate global heating), and it contributes to the predictability of the water cycle and ocean currents [17,18]. It also contains much of the planet's biomass and biodiversity. ...
The climate crisis provides a critical new lens through which health and health behaviors need to be viewed. This paper has three goals. First, it provides background on the climate crisis, the role of human behavior in creating this crisis, and the health impacts of climate change. Second, it proposes a multilevel, translational approach to investigating health behavior change in the context of the climate crisis. Third, it identifies specific challenges and opportunities for increasing the rigor of behavioral medicine research in the context of the climate crisis. The paper closes with a call for behavioral medicine to be responsive to the climate crisis.
... Field data were curated and accessed via the Fores tPlots.net database (Lopez-Gonzalez et al., 2011) and subject to strict quality control to identify possible measurement or annotation errors, as described by Brienen et al. (2015). ...
Aim
Water availability is the major driver of tropical forest structure and dynamics. Most research has focused on the impacts of climatic water availability, whereas remarkably little is known about the influence of water table depth and excess soil water on forest processes. Nevertheless, given that plants take up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water conditions.
Location
Lowland Amazonian forests.
Time period
1971–2019.
Methods
We used 344 long‐term inventory plots distributed across Amazonia to analyse the effects of long‐term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil‐water and edaphic properties.
Results
Water supplied by both precipitation and groundwater affects forest structure and dynamics, but in different ways. Forests with a shallow water table (depth <5 m) had 18% less above‐ground woody productivity and 23% less biomass stock than forests with a deep water table. Forests in drier climates (maximum cumulative water deficit < −160 mm) had 21% less productivity and 24% less biomass than those in wetter climates. Productivity was affected by the interaction between climatic water deficit and water table depth. On average, in drier climates the forests with a shallow water table had lower productivity than those with a deep water table, with this difference decreasing within wet climates, where lower productivity was confined to a very shallow water table.
Main conclusions
We show that the two extremes of water availability (excess and deficit) both reduce productivity in Amazon upland ( terra‐firme ) forests. Biomass and productivity across Amazonia respond not simply to regional climate, but rather to its interaction with water table conditions, exhibiting high local differentiation. Our study disentangles the relative contribution of those factors, helping to improve understanding of the functioning of tropical ecosystems and how they are likely to respond to climate change.
... This regulatory capacity, associated with the year-round level of solar radiance, keeps the rainforest operating at a near optimum for photosynthesis (approximately 16% of global terrestrial GPP), resulting in a significant annual carbon sink of 0.38 (0.28-0.49 95% C.I.) Pg C year-1 (Beer et al. 2010;Brienen et al. 2015; see also Chapter 6). ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
As Florestas Estacionais Sazonalmente Secas (FESS) ocorrentes no Cerrado são caracterizadas pela presença de espécies arbóreas com diferentes níveis de caducifólia nos períodos de estação seca e variam na composição florística dependendo da sua localização geográfica. O presente trabalho tem como objetivo assumir que os padrões florístico-estruturais destas florestas podem ser marcantes, devido às condições ambientais impostas nos ambientes e proximidade com bacias hidrográficas distintas. Foram utilizados levantamentos fitossociológicos realizados em um hectare para 17 fragmentos de Floresta Estacional Semidecidual (FES), onde aferiu-se todos os indivíduos arbóreos a circunferência a altura do peito (CAP) de 1,30cm ≥ 15cm. A avaliação foi feita por meio de uma ordenação por Análise de Componente Principal incluindo variáveis abióticas e estruturais de cada floresta. Para análise de similaridade, foram utilizados dados florísticos em uma matriz de presença-ausência utilizando os dados de ocorrência das espécies identificadas em cada localidade. Para determinar as semelhanças, utilizou-se o coeficiente de similaridade de Sorensen, o índice de Bray-Curtis e o método de agrupamento das médias não ponderadas (UPGMA). Para explorar padrões de abundância, foi feito o Escalonamento Multidimensional Não Métrico (nMDS). Os padrões florísticos-estruturais apontaram a presença de dois grupos florísticos distintos, um menor grupo formando diferentes áreas das bacias hidrográficas do Rio Araguaia e Rio Paraguai, e outro grande grupo formado por áreas da bacia do Paraná, e outras desta mesma bacia, porém mais dissimilares do que as demais. A formação de grupos florísticos reflete que as comunidades analisadas possuem diversas espécies generalistas, pouco exigentes e que se adaptam bem a novas condições, com ocorrência para áreas de florestas estacionais no Cerrado e Mata Atlântica, formando duas províncias distintas situadas, sobretudo na bacia do Araguaia e Paraná.
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.
Droughts have recurrently impacted the Amazon rainforests, undermining the forest biomass carbon sink capacity due to a quicker increase of biomass mortality compared to growth. Most global land surface models used for assessments of the Global Carbon Budget and future climate projections have not incorporated drought-induced tree mortality. Their prediction of biomass dynamics are therefore subject to large uncertainties, as a result of (1) lack of explicit simulation of hydraulic transportin the continuum from soil to leaves; (2) lack of process-based equations connecting the impairment of the hydraulic transport system of trees to mortality; (3) lack of representation of mortality across trees sizes. To address these critical research gaps, I improved plant hydraulic representation in ORCHIDEECAN. This model was re-calibrated and evaluated over rainforests in Amazon basin, and applied to simulate the future evolution of biomass dynamics facing droughts. Firstly, I implemented a mechanistic hydraulic architecture that was designed by E. Joetzjer, and a hydraulic-failure related tree mortality module that I designed into ORCHIDEE-CAN. The model was calibrated against the world’s longest running drought manipulation experiment of Caxiuana in the eastern Amazon. Our model produced comparable annual tree mortality rates than the observation andcaptured biomass dynamics. This work provides a basis for further research in assimilating experimental observation data to parameterize the hydraulic failure induced tree mortality. Secondly, I applied ORCHIDEE-CAN-NHA over the Amazon intact rainforest. The model reproduced the drought sensitivity of aboveground biomass (AGB) growth and mortality observed atnetworks of forest inventory plots across Amazon intact forests for the two recent mega-droughts of 2005 and 2010. We predicted a more negative sensitivity of the net biomass carbon sink to water deficits for the recent 2015/16 El Nino, which was the most severe drought in the historical record. In the model, even if climate change with droughts becoming more severe tended to intensify tree mortality, increased CO2 concentration contributed to attenuate the C loss due to mortality by suppressing transpiration.Lastly, I used the ORCHIDEE-CAN-NHA model for future simulations of biomass carbondynamics. Most climate models (ISIMIP2 program) consistently predict a drier trend in northeastern Amazon. The simulation forced by the HadGEM climate model in the RCP8.5 scenario shows the most pronounced drying in eastern and northeastern Amazon, with a cross-over point at which the carbon sink turned to a carbon source in the Guiana Shield and East-central Amazon in the middle of the 21st century. This study sheds light on predicting the future evolution of Amazon rainforest biomass dynamics with an improved process-based model able to reproduce climate-change induced mortality.In the conclusion and outlook sections, future developments and research priorities are proposed, which would improve the reliability and performances of the process-based model presented in this dissertation, allowing to better capture mechanisms that control the evolution of forest biomass dynamics in the face of more frequent drought risks.
During the last two decades, inventory data show that droughts have reduced biomass carbon sink of the Amazon forest by causing mortality to exceed growth. However, process‐based models have struggled to include drought‐induced responses of growth and mortality, and have not been evaluated against plot data. A process‐based model, ORCHIDEE‐CAN‐NHA, including forest demography with tree cohorts, plant hydraulic architecture and drought‐induced tree mortality, was applied over Amazonia rainforests forced by gridded climate fields and rising CO2 from 1901 to 2019. The model reproduced the decelerating signal of net carbon sink and drought sensitivity of aboveground biomass (AGB) growth and mortality observed at forest plots across selected Amazon intact forests for 2005 and 2010. We predicted a larger mortality rate and a more negative sensitivity of the net carbon sink during the 2015/16 El Niño compared to the former droughts. 2015/16 was indeed the most severe drought since 1901 regarding both AGB loss and area experiencing a severe carbon loss. We found that even if climate change did increase mortality, elevated CO2 contributed to balance the biomass mortality, since CO2‐induced stomatal closure reduces transpiration thus offsets increased transpiration from CO2‐induced higher foliage area.
Mongolian Scots pine has been used for vegetation restoration and windbreaks in Horqin Sandy land, Northern China, where climate change is the principal factor limiting tree survival and growth. To investigate the effect of annual precipitation and annual temperature variables on stem biomass and carbon stock of Mongolian Scots pine healthy (HP), sub healthy (SHP), stress (STP), and shrink (SRP) plantation. We used climate sensitive allometric model to find out accurate biomass along climatic factors from 1965 to 2019. The result show that, stem biomass and carbon stock of Mongolian Scots pine, HP, SHP, STP and SRP plantation, have strong correlations with annual PP and annual (Tmax) (R² = 0.88, R² = 0.84, R² = 0.82, R² = 0.61) and (R² = 0.86, R² = 0.82, R² = 0.72, R² = 0.60). While, annual average (Tmini) and annual (Tmean) have a slightly positive correlations with the Mongolian Scots pine, HP and SHP, plantation (R² = 0.73, R² = 0.70) and (R² = 0.76, R² = 0.71). However, negative correlations (R² = 0.49, R² = 0.29) and (R² = 0.40, R² = 0.39) were found with STP, and SRP, plantation. Mongolian Scots pine, afforestation on reclamation sites brings important environmental and production benefits. Mongolian Scots pine has a strong adaptive nature with climate change and hence can survive under stress conditions of Horqin sandy land China.
The observed global net land carbon sink is captured by current land models. All models agree that atmospheric CO2 and nitrogen deposition driven gains in carbon stocks are partially offset by climate and land-use and land-cover change (LULCC) losses. However, there is a lack of consensus in the partitioning of the sink between vegetation and soil, where models do not even agree on the direction of change in carbon stocks over the past 60 years. This uncertainty is driven by plant productivity, allocation, and turnover response to atmospheric CO2 (and to a smaller extent to LULCC), and the response of soil to LULCC (and to a lesser extent climate). Overall, differences in turnover explain ~70% of model spread in both vegetation and soil carbon changes. Further analysis of internal plant and soil (individual pools) cycling is needed to reduce uncertainty in the controlling processes behind the global land carbon sink.
Forest ecosystems depend on their capacity to withstand and recover from natural and anthropogenic perturbations (that is, their resilience)1. Experimental evidence of sudden increases in tree mortality is raising concerns about variation in forest resilience2, yet little is known about how it is evolving in response to climate change. Here we integrate satellite-based vegetation indices with machine learning to show how forest resilience, quantified in terms of critical slowing down indicators3–5, has changed during the period 2000–2020. We show that tropical, arid and temperate forests are experiencing a significant decline in resilience, probably related to increased water limitations and climate variability. By contrast, boreal forests show divergent local patterns with an average increasing trend in resilience, probably benefiting from warming and CO2 fertilization, which may outweigh the adverse effects of climate change. These patterns emerge consistently in both managed and intact forests, corroborating the existence of common large-scale climate drivers. Reductions in resilience are statistically linked to abrupt declines in forest primary productivity, occurring in response to slow drifting towards a critical resilience threshold. Approximately 23% of intact undisturbed forests, corresponding to 3.32 Pg C of gross primary productivity, have already reached a critical threshold and are experiencing a further degradation in resilience. Together, these signals reveal a widespread decline in the capacity of forests to withstand perturbation that should be accounted for in the design of land-based mitigation and adaptation plans.
The recovery of soil conditions is crucial for successful ecosystem restoration and, hence, for achieving the goals of the UN Decade on Ecosystem Restoration. Here, we assess how soils resist forest conversion and agricultural land use, and how soils recover during subsequent tropical forest succession on abandoned agricultural fields. Our overarching question is how soil resistance and recovery depend on local conditions such as climate, soil type, and land-use history. For 300 plots in 21 sites across the Neotropics, we used a chonosequence approach in which we sampled soils from two depths in old-growth forests, agricultural fields (i.e., crop fields and pastures), and secondary forests that differ in age (1-95 years) since abandonment. We measured six soil properties using a standardized sampling design and lab analyses.
Soil resistance strongly depended on local conditions. Croplands and sites on high-activity clay (i.e. high fertility) show strong increases in bulk density, and decreases in pH, carbon (C) and nitrogen (N) during deforestation and subsequent agricultural use. Resistance is lower in such sites probably because of a sharp decline in fine root biomass in croplands in the upper soil layers, and a decline in litter input from formerly productive old-growth forest (on high-activity clays). Soil recovery also strongly depended on local conditions. During forest succession, high-activity clays and croplands decreased most strongly in bulk density and increased in C and N, possibly because of strongly compacted soils with low C and N after cropland abandonment, and because of rapid vegetation recovery in high-activity clays leading to greater fine root growth and litter input. Furthermore, sites at low precipitation decreased in pH, whereas sites at high precipitation increased in N and decreased in C:N ratio. Extractable phosphorus (P) did not recover during succession, suggesting increased P limitation as forests age. These results indicate that no single solution exists for effective soil restoration, and that local site conditions should determine the restoration strategies.
• Here we describe a new network of researchers and long-term,
in situ, measurements that will characterize the changing socio-ecology of the woodlands of southern Africa. These woodlands encompass the largest savanna in the world, but are chronically understudied, with few long-term measurements.
• A network of permanent sample plots (PSPs) is required to: (a) address management issues, particularly related to sustainable harvesting for energy and timber;
(b) understand how the woodlands are responding to a range of global and local drivers, such as climate change, CO2 fertilization, and harvesting; and (c) answer basic questions about biogeography, ecosystem function, and the role humans play in shaping the ecology of the region.
• We draw on other successful networks of PSPs and adapt their methods to the specific challenges of working in southern African woodlands. In particular we suggest divergences from established forest monitoring protocols that are needed to (a) adapt to a high level of ecosystem structural diversity (from open savanna to
dry forest); (b) quantify the chronic disturbances by people, fire, and herbivores; (c) quantify the diversity and function of the understory of grasses, forbs, and shrubs; (d) understand the life histories of resprouting trees; and (e) conduct work in highly utilized, human-dominated landscapes.
• We conclude by discussing how the SEOSAW network will integrate with remote sensing and modeling approaches. Throughout, we highlight the challengesinherent to integrating work by forest and savanna ecologists, and the wide range of skills needed to fully understand the socio-ecology of the southern African
woodlands.
Rapid changes in climate and disturbance regimes, including droughts and hurricanes, are likely to influence tropical forests, but our understanding of the compound effects of disturbances on forest ecosystems is extremely limited. Filling this knowledge gap is necessary to elucidate the future of these ecosystems under a changing climate.
We examined the relationship between hurricane response (damage, mortality, and resilience) and four hydraulic traits of 13 dominant woody species in a wet tropical forest subject to periodic hurricanes.
Species with high resistance to embolisms (low P 50 values) and higher safety margins () were more resistant to immediate hurricane mortality and breakage, whereas species with higher hurricane resilience (rapid post‐hurricane growth) had high capacitance and P 50 values and low . During 26 yr of post‐hurricane recovery, we found a decrease in community‐weighted mean values for traits associated with greater drought resistance (leaf turgor loss point, P 50 , ) and an increase in capacitance, which has been linked with lower drought resistance.
Hurricane damage favors slow‐growing, drought‐tolerant species, whereas post‐hurricane high resource conditions favor acquisitive, fast‐growing but drought‐vulnerable species, increasing forest productivity at the expense of drought tolerance and leading to higher overall forest vulnerability to drought.
Fossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO2) abundance by about 50% since the beginning of the industrial age. The atmospheric CO2 growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO2. As these CO2 emissions grew, uptake by the ocean increased in response to increases in atmospheric CO2 partial pressure (pCO2). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO2 uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid‐ and high‐latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship‐based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean‐atmosphere fluxes and interior ocean carbon storage on policy‐relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO2 in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.
Cette évaluation du service écosystémique de séquestration du carbone in situ à l’échelle de la France s’inscrit dans le cadre du programme EFESE (Évaluation Française des Écosystèmes et des Services Écosystémiques). Il s’agit de la première évaluation unifiée
du cycle du carbone à l’échelle française conduite dans l’optique d’améliorer sa prise en compte dans la décision. La méthode utilisée repose sur une caractérisation de ce service pour différents types d’écosystèmes couvrant l’ensemble du territoire français.
Les données collectées permettent de formuler des ordres de grandeur pertinents qui aident à prendre la mesure des enjeux associés à l’échelle nationale. Ces mêmes données sont mobilisées pour proposer des valeurs de référence utiles au niveau local afin d’améliorer la prise en compte de ce service écosystémique dans les décisions susceptibles d’affecter les écosystèmes, notamment pour les évaluations socio-économiques des projets et des investissements publics.
Drought-associated woody-plant mortality has been increasing in most regions with multi-decadal records and is projected to increase in the future, impacting terrestrial climate forcing, biodiversity and resource availability. The mechanisms underlying such mortality, however, are debated, owing to complex interactions between the drivers and the processes. In this Review, we synthesize knowledge of drought-related tree mortality under a warming and drying atmosphere with rising atmospheric CO2. Drought-associated mortality results from water and carbon depletion and declines in their fluxes relative to demand by living tissues. These pools and fluxes are interdependent and underlay plant defences against biotic agents. Death via failure to maintain a positive water balance is particularly dependent on soil-to-root conductance, capacitance, vulnerability to hydraulic failure, cuticular water losses and dehydration tolerance, all of which could be exacerbated by reduced carbon supply rates to support cellular survival or the carbon starvation process. The depletion of plant water and carbon pools is accelerated under rising vapour pressure deficit, but increasing CO2 can mitigate these impacts. Advancing knowledge and reducing predictive uncertainties requires the integration of carbon, water and defensive processes, and the use of a range of experimental and modelling approaches. Enhanced drought frequency and magnitude have impacted tree mortality, leading to multiple examples of regional-scale dieback. This Review outlines the mechanisms leading to mortality, including carbon starvation and hydraulic failure.
The resilience of the Amazon rainforest to climate and land-use change is crucial for biodiversity, regional climate and the global carbon cycle. Deforestation and climate change, via increasing dry-season length and drought frequency, may already have pushed the Amazon close to a critical threshold of rainforest dieback. Here, we quantify changes of Amazon resilience by applying established indicators (for example, measuring lag-1 autocorrelation) to remotely sensed vegetation data with a focus on vegetation optical depth (1991–2016). We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.
Tree mortality is a major control over tropical forest carbon stocks globally but the strength of associations between abiotic drivers and tree mortality within forested landscapes is poorly understood. Here, we used repeat drone photogrammetry across 1500 ha of forest in Central Panama over 5 years to quantify spatial variation in canopy disturbance rates and its predictors. We identified 11,153 canopy disturbances greater than 25 m2 in area, including treefalls, large branchfalls and standing dead trees, affecting 1.9% of area per year. Soil type, forest age and topography explained up to 46%–67% of disturbance rate variation at spatial grains of 58–64 ha, with higher rates in older forests, steeper slopes and local depressions. Furthermore, disturbance rates predicted the proportion of low canopy area across the landscape, and mean canopy height in old growth forests. Thus abiotic factors drive variation in disturbance rates and thereby forest structure at landscape scales. We used repeat drone photogrammetry across 1500 ha of forest in Central Panama over 5 years to quantify spatial variation in canopy disturbance rates and its predictors. Soil type, forest age and topography explained disturbance rate variation, with higher rates in older forests, steeper slopes and local depressions. Furthermore, disturbance rates predicted the proportion of low canopy area across the landscape, and mean canopy height in old growth forests.
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 (CO<sub>2</sub>) 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 CO<sub>2</sub> from fossil fuel combustion and cement production were 9.5 ± 0.5 PgC yr<sup>−1</sup> 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 CO<sub>2</sub> 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<sup>−1</sup> in 2011. The global atmospheric CO<sub>2</sub> concentration is measured directly and reached 391.38 ± 0.13 ppm at the end of year 2011, increasing 1.70 ± 0.09 ppm yr<sup>−1</sup> or 3.6 ± 0.2 PgC yr<sup>−1</sup> in 2011. Estimates from four ocean models suggest that the ocean CO<sub>2</sub> sink was 2.6 ± 0.5 PgC yr<sup>−1</sup> in 2011, implying a global residual terrestrial CO<sub>2</sub> sink of 4.1 ± 0.9 PgC yr<sup>−1</sup>. 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<sup>−1</sup> (range 6.6 to 112.4) to 8.0 Mg ha<sup>−1</sup> (−2.5 to 23.0). For all plots, aboveground live biomass was −52.2 Mg ha<sup>−1</sup> (−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 km<sup>2</sup> 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.