The tropical forest carbon cycle and climate change

Greenhouse gases emissions and global climate change: Examining the influence of CO2, CH4, and N2O

An in-depth analysis of the role of greenhouse gases (GHGs) in climate change is examined here along with their diverse sources, including the combustion of fossil fuels, agriculture, and industrial processes. Key GHG components such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are considered, along with data on emissions across various economic sectors. The consequences of climate change are also highlighted, ranging from more frequent and intense extreme weather events to rising sea levels and impacts on ecosystems and human health. The industrial revolution and unrestricted use of fossil fuels are key factors leading to an increase in GHG concentrations in the atmosphere. Global efforts to reduce emissions are considered, starting with the 1997 Kyoto Protocol and culminating in the 2015 Paris Agreement. The limited effectiveness of early initiatives is underscored, emphasizing the significant importance of the Paris Agreement that provides a global framework for establishing goals to reduce GHG emissions by country. The Green Climate Fund and other international financial mechanisms are also considered as essential tools for financing sustainable projects in developing countries. The global community faces the challenge and necessity for more ambitious efforts to achieve the set goals for reducing GHG emissions. Successful strategies are examined by Sweden, Costa Rica, and Denmark to achieve zero GHG emissions that integrate renewable energy sources and technologies. The importance of global cooperation for creating a sustainable future is also emphasized.

Impacts of elevated temperature and vapour pressure deficit on leaf gas exchange and plant growth across six tropical rainforest tree species

Elevated air temperature (Tair) and vapour pressure deficit (VPDair) significantly influence plant functioning, yet their relative impacts are difficult to disentangle. We examined the effects of elevated Tair (+6°C) and VPDair (+0.7 kPa) on the growth and physiology of six tropical tree species. Saplings were grown under well-watered conditions in climate-controlled glasshouses for 6 months under three treatments: (1) low Tair and low VPDair, (2) high Tair and low VPDair, and (3) high Tair and high VPDair. To assess acclimation, physiological parameters were measured at a set temperature. Warm-grown plants grown under elevated VPDair had significantly reduced stomatal conductance and increased instantaneous water use efficiency compared to plants grown under low VPDair. Photosynthetic biochemistry and thermal tolerance (Tcrit) were unaffected by VPDair, but elevated Tair caused Jmax25 to decrease and Tcrit to increase. Sapling biomass accumulation for all species responded positively to an increase in Tair, but elevated VPDair limited growth. This study shows that stomatal limitation caused by even moderate increases in VPDair can decrease productivity and growth rates in tropical species independently from Tair and has important implications for modelling the impacts of climate change on tropical forests.

Deforestation in Latin America in the 2000s predominantly occurred outside of typical mature forests

The role of tropical forests in the global carbon budget remains controversial, as carbon emissions from deforestation are highly uncertain. This high uncertainty arises from the use of either fixed forest carbon stock density or maps generated from satellite-based optical reflectance with limited sensitivity to biomass to generate accurate estimates of emissions from deforestation. New space missions aiming to accurately map the carbon stock density rely on direct measurements of the spatial structures of forests using lidar and radar. We found that lost forests are special cases, and their spatial structures can be directly measured by combining archived data acquired before and after deforestation by space missions principally aimed at measuring topography. Thus, using biomass mapping, we obtained new estimates of carbon loss from deforestation ahead of forthcoming space missions. Here, using a high-resolution map of forest loss and the synergy of radar and lidar to estimate the aboveground biomass density of forests, we found that deforestation in the 2000s in Latin America, one of the severely deforested regions, mainly occurred in forests with a significantly lower carbon stock density than typical mature forests. Deforestation areas with carbon stock densities lower than 20.0, 50.0, and 100.0 Mg C/ha accounted for 42.1%, 62.0%, and 83.3% of the entire deforested area, respectively. The average carbon stock density of lost forests was only 49.13 Mg C/ha, which challenges the current knowledge on the carbon stock density of lost forests (with a default value 100 Mg C/ha according to the Intergovernmental Panel on Climate Change Tier 1 estimates, or approximately 112 Mg C/ha used in other studies). This is demonstrated over both the entire region and the footprints of the spaceborne lidar. Consequently, our estimate of carbon loss from deforestation in Latin America in the 2000s was 253.0 ± 21.5 Tg C/year, which was considerably less than existing remote-sensing-based estimates, namely 400-600 Tg C/year. This indicates that forests in Latin America were most likely not a net carbon source in the 2000s compared to established carbon sinks. In previous studies, considerable effort has been devoted to rectify the underestimation of carbon sinks; thus, the overestimation of carbon emissions should be given sufficient consideration in global carbon budgets. Our results also provide solid evidence for the necessity of renewing knowledge on the role of tropical forests in the global carbon budget in the future using observations from new space missions.

Secretory Production of the Hericium erinaceus Laccase from Saccharomyces cerevisiae

Mushroom laccases play a crucial role in lignin depolymerization, one of the most critical challenges in lignin utilization. Importantly, laccases can utilize a wide range of substrates, such as toxicants and antibiotics. This study isolated a novel laccase, named HeLac4c, from endophytic white-rot fungi Hericium erinaceus mushrooms. The cDNAs for this enzyme were 1569 bp in length and encoded a protein of 523 amino acids, including a 20 amino-acid signal peptide. Active extracellular production of glycosylated laccases from Saccharomyces cerevisiae was successfully achieved by selecting an optimal translational fusion partner. We observed that 5 and 10 mM Ca2+, Zn2+, and K+ increased laccase activity, whereas 5 mM Fe2+ and Al3+ inhibited laccase activity. The laccase activity was inhibited by the addition of low concentrations of sodium azide and L-cysteine. The optimal pH for the 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt was 4.4. Guaiacylglycerol-β-guaiacyl ether, a lignin model compound, was polymerized by the HeLac4c enzyme. These results indicated that HeLac4c is a novel oxidase biocatalyst for the bioconversion of lignin into value-added products for environmental biotechnological applications.

Boosting Formate Electrooxidation by Heterostructured PtPd Alloy and Oxides Nanowires

Direct formate fuel cells (DFFCs) receive increasing attention as promising technologies for the future energy mix and environmental sustainability, as formate can be made from carbon dioxide utilization and is carbon neutral. Herein, heterostructured platinum-palladium alloy and oxides nanowires (PtPd-ox NWs) with abundant defect sites are synthesized through a facile self-template method and demonstrated high activity toward formate electrooxidation reaction (FOR). The electronic tuning arising from the heterojunction between alloy and oxides influence the work function of PtPd-ox NWs. The sample with optimal work function reveals the favorable adsorption behavior for intermediates and strong interaction in the d-p orbital hybridization between Pt site and oxygen in formate, favoring the FOR direct pathway with a low energy barrier. Besides the thermodynamic regulation, the heterostructure can also provide sufficient hydroxyl species to facilitate the formation of carbon dioxide due to the ability of combining absorbed hydrogen and carbon monoxide at adjacent active sites, which contributes to the improvement of FOR kinetics on PtPd-ox NWs. Thus, heterostructured PtPd-ox NWs achieve dual regulation of FOR thermodynamics and kinetics, exhibiting remarkable performance and demonstrating potential in practical systems.

Ecology: A few species dominate forest tree abundance pan-tropically

An analysis of over 1 million old-growth tropical forest trees reveals that ∼2.2% of species comprise 50% of the individuals in Africa, Amazonia, and Southeast Asia, suggesting that the ecological mechanisms underpinning tree community assembly are ubiquitous across the tropics.

A new circa 2007 biomass map for China differs significantly from existing maps

The forest area of China is the fifth largest of any country, and unlike in many other countries, in recent decades its area has been increasing. However, there are substantial differences in estimates of the amount of carbon this forest contains, ranging from 3.92 to 17.02 Pg C for circa 2007. This makes it unclear how the changes in China's forest area contribute to the global carbon cycle. We generate a circa 2007 aboveground biomass (AGB) map at a resolution of 50 m using optical, radar and LiDAR satellite data. Our estimates of total carbon stored in the forest in China was 9.52 Pg C, with an average forest AGB of 104 Mg ha-1. Compared with three existing AGB maps, our AGB map showed better correlation with a distributed set of forest inventory plots. In addition, our high resolution AGB map provided more details on spatial distribution of forest AGB, and is likely to help understand the carbon storage changes in China's forest.

Twenty-five years of Open-Top Chambers in tropical environments: where, how, and what are we looking at regarding flora response to climate change?

MAIN CONCLUSION

Open-Top Chambers should be more used in tropical ecosystems to study climate change effects in plants as they are still insufficient to extract plant response patterns in these ecosystems. Understanding flora response to climate change (CC) is critical for predicting future ecosystem dynamics. Open-Top Chambers (OTCs) have been widely used to study the effects of CC on plants and are very popular in temperate ecosystems but are still underused in tropical regions. In this systematic review, we aimed to discuss the use of OTCs in the study of the effects of different agents of climate change on tropical flora by presenting scientometric data, discussing the technical aspects of its use and enumerating some observations on plant response patterns to climatic alterations in the tropics. Our analysis indicated that the bottleneck in choosing an OTC shape is not strictly related to its purpose or the type of parameter modulated; instead, passive or active approaches seem to be a more sensitive point. The common critical point in using this technique in warmer regions is overheating and decoupling, but it can be overcome with simple adaptations and extra features. The most frequently parameter modulated was CO2, followed by O3 and temperature. The plant families with more representatives in the studies analyzed were Fabaceae, Myrtaceae, and Poaceae, and the most represented biome was tropical and subtropical moist broadleaf forests. In conclusion, OTCs are a valuable and feasible tool to study CC effects on various tropical ecosystems, regardless of structure, active/passive approach, or other technical features. One of the primary advantages of this methodology is its applicability for in situ use, eliminating the need for plant transplantation. We encourage studies using OTC experimental design for plant conservation in the tropics.

Cross-scale spatial variability and associations of carbon pools provide insight into regulating carbon sequestration in tropical montane rainforests

The spatial distribution of plant, soil, and microbial carbon pools, along with their intricate interactions, presents a great challenge for the current carbon cycle research. However, it is not clear what are the characteristics of the spatial variability of these carbon pools, particularly their cross-scale relationships. We investigated the cross-scale spatial variability of microbial necromass carbon (MNC), soil organic carbon (SOC) and plant biomass (PB), as well as their correlation in a tropical montane rainforest using multifractal analysis. The results showed multifractal spatial variations of MNC, SOC, and PB, demonstrating their adherence to power-law scaling. MNC, especially low MNC, exhibited stronger spatial heterogeneity and weaker evenness compared with SOC and PB. The cross-scale correlation between MNC and SOC was stronger than their correlations at the measurement scale. Furthermore, the cross-scale spatial variability of MNC and SOC exhibited stronger and more stable correlations than those with PB. Additionally, this research suggests that when SOC and PB are both low, it is advisable for reforestations to potentiate MNC formation, whereas when both SOC and PB are high some thinning can be advisable to favour MNC formation. Thus, these results support the utilization of management measures such as reforestation or thinning as nature-based solutions to regulate carbon sequestration capacity of tropical forests by affecting the correlations among various carbon pools.

Transition from positive to negative indirect CO2 effects on the vegetation carbon uptake

Although elevated atmospheric CO2 concentration (eCO2) has substantial indirect effects on vegetation carbon uptake via associated climate change, their dynamics remain unclear. Here we investigate how the impacts of eCO2-driven climate change on growing-season gross primary production have changed globally during 1982-2014, using satellite observations and Earth system models, and evaluate their evolution until the year 2100. We show that the initial positive effect of eCO2-induced climate change on vegetation carbon uptake has declined recently, shifting to negative in the early 21st century. Such emerging pattern appears prominent in high latitudes and occurs in combination with a decrease of direct CO2 physiological effect, ultimately resulting in a sharp reduction of the current growth benefits induced by climate warming and CO2 fertilization. Such weakening of the indirect CO2 effect can be partially attributed to the widespread land drying, and it is expected to be further exacerbated under global warming.

Shifts in internal stem damage along a tropical precipitation gradient and implications for forest biomass estimation

Woody biomass is a large carbon store in terrestrial ecosystems. In calculating biomass, tree stems are assumed to be solid structures. However, decomposer agents such as microbes and insects target stem heartwood, causing internal wood decay which is poorly quantified. We investigated internal stem damage across five sites in tropical Australia along a precipitation gradient. We estimated the amount of internal aboveground biomass damaged in living trees and measured four potential stem damage predictors: wood density, stem diameter, annual precipitation, and termite pressure (measured as termite damage in downed deadwood). Stem damage increased with increasing diameter, wood density, and termite pressure and decreased with increasing precipitation. High wood density stems sustained less damage in wet sites and more damage in dry sites, likely a result of shifting decomposer communities and their differing responses to changes in tree species and wood traits across sites. Incorporating stem damage reduced aboveground biomass estimates by > 30% in Australian savannas, compared to only 3% in rainforests. Accurate estimates of carbon storage across woody plant communities are critical for understanding the global carbon budget. Future biomass estimates should consider stem damage in concert with the effects of changes in decomposer communities and abiotic conditions.

Long-term warming increased carbon sequestration capacity in a humid subtropical forest

Tropical and subtropical forests play a crucial role in global carbon (C) pools, and their responses to warming can significantly impact C-climate feedback and predictions of future global warming. Despite earth system models projecting reductions in land C storage with warming, the magnitude of this response varies greatly between models, particularly in tropical and subtropical regions. Here, we conducted a field ecosystem-level warming experiment in a subtropical forest in southern China, by translocating mesocosms (ecosystem composed of soils and plants) across 600 m elevation gradients with temperature gradients of 2.1°C (moderate warming), to explore the response of ecosystem C dynamics of the subtropical forest to continuous 6-year warming. Compared with the control, the ecosystem C stock decreased by 3.8% under the first year of 2.1°C warming; but increased by 13.4% by the sixth year of 2.1°C warming. The increased ecosystem C stock by the sixth year of warming was mainly attributed to a combination of sustained increased plant C stock due to the maintenance of a high plant growth rate and unchanged soil C stock. The unchanged soil C stock was driven by compensating and offsetting thermal adaptation of soil microorganisms (unresponsive soil respiration and enzyme activity, and more stable microbial community), increased plant C input, and inhibitory C loss (decreased C leaching and inhibited temperature sensitivity of soil respiration) from soil drying. These results suggest that the humid subtropical forest C pool would not necessarily diminish consistently under future long-term warming. We highlight that differential and asynchronous responses of plant and soil C processes over relatively long-term periods should be considered when predicting the effects of climate warming on ecosystem C dynamics of subtropical forests.

Two centuries of biodiversity discovery and loss in Singapore

There is an urgent need for reliable data on the impacts of deforestation on tropical biodiversity. The city-state of Singapore has one of the most detailed biodiversity records in the tropics, dating back to the turn of the 19th century. In 1819, Singapore was almost entirely covered in primary forest, but this has since been largely cleared. We compiled more than 200 y of records for 10 major taxonomic groups in Singapore (>50,000 individual records; >3,000 species), and we estimated extinction rates using recently developed and novel statistical models that account for "dark extinctions," i.e., extinctions of undiscovered species. The estimated overall extinction rate was 37% (95% CI [31 to 42%]). Extrapolating our Singapore observations to a future business-as-usual deforestation scenario for Southeast Asia suggests that 18% (95% CI [16 to 22%]) of species will be lost regionally by 2100. Our extinction estimates for Singapore and Southeast Asia are a factor of two lower than previous estimates that also attempted to account for dark extinctions. However, we caution that particular groups such as large mammals, forest-dependent birds, orchids, and butterflies are disproportionately vulnerable.

Sustainable poverty alleviation through forests: Pathways and strategies

Forests are the most productive terrestrial ecosystems across the world. They can play both a direct and indirect role in global poverty alleviation through their social, economic and environmental functions. However, the potential of forests in poverty alleviation is underestimated to a great extent. Sustainability, the most essential advantage and characteristic of forests for poverty alleviation, has not been fully recognized. To that end, we propose the concept of sustainable poverty alleviation through forests (SPAF). This concept shifts the vision of poverty alleviation through forests from a narrow focus on subsistence and livelihood to a sustainable poverty alleviation that promotes all dimensions of human development. There is abundant evidence that forests can at least contribute to sustainable poverty alleviation through a synergy of seven pathways: subsistence materials, health, income, employment, women's empowerment, climate change mitigation and biodiversity, which are highly consistent with the United Nations Sustainable Development Goals. SPAF also faces enormous implementation challenges, so a sustainable global strategy is urgently needed to provide direction for worldwide poverty alleviation at the crossroads of nature and humanity.

Carbon sequestration and storage capacity of Chinese fir at different stand ages

In southern China, Chinese fir Cunninghamia lanceolata is one of the most important native conifer trees, widely used in afforestation programs. This area has the largest forestland atmospheric carbon sink, and a relatively young stand age characterizes these forests. However, how C. lanceolata forests evolved regarding their ability to sequester carbon remains unclear. Here we present data on carbon storage and sequestration capacity of C. lanceolata at six stand ages (5-, 10-, 15-, 20-, 30- and 60 - year-old stands). Results show that the carbon stock in trees, understory, vegetation, litter, soil, and ecosystem significantly increased with forest age. The total ecosystem carbon stock increased from 129.11 to 348.43 Mg ha-1 in the 5- and 60 - year-old stands. The carbon sequestration rate of C. lanceolata shows an overall increase in the first two stand intervals (5-10 and 10-15), peaks in the 15-20 stand intervals, and then decreases in the 20-30 and 30-60 stand intervals. Our result revealed that carbon sequestration rate is a matter of tree age, with the highest sequestration rates occurring in the middle age forest (15-20 - year-old). Therefore, this information may be useful for national climate change mitigation actions and afforestation programs, since forests are primarily planted for this purpose.

High vulnerability of coastal wetlands in Chile at multiple scales derived from climate change, urbanization, and exotic forest plantations

Coastal wetlands are considered one of the most vulnerable ecosystems worldwide; the ecosystem services they provide and the conservation of their biodiversity are threatened. Despite the high ecological and socioenvironmental value of coastal wetlands, regional and national vulnerability assessments are scarce. In this study we aimed to assess the vulnerability of coastal wetlands in Chile from 18°S to 42°S (n = 757) under a multiscale approach that included drivers associated with climate change and land cover change. We assessed multiple drivers of vulnerability at three spatial scales (10 m, 100 m, and 500 m) by analyzing multiple remote sensing data (16 variables) on land cover change, wildfires, climatic variables, vegetation functional properties, water surface and importance for biodiversity. We constructed a multifactorial vulnerability index based on the variables analyzed, which provided a map of coastal wetland vulnerability. Then we explored the main drivers associated with the vulnerability of each coastal wetland by performing a Principal Components Analysis with Agglomerative Hierarchical Clustering, which allowed us to group coastal wetlands according to the drivers analyzed. We found that 42.6 ± 9.2 % of the coastal wetlands evaluated have high or very high vulnerability, with higher vulnerability at the 500 m scale (51.4 %). We identified four groups of coastal wetlands: two located in central Chile, mainly affected by climate change-associated drivers (41.9 ± 2.1 %), and one in central Chile which is affected by land cover change (52.8 ± 6.2 %); the latter has a lower vulnerability level. The most vulnerable coastal wetlands were located in central Chile. Our results present novel findings about the current vulnerability of coastal wetlands, which could be validated by governmental institutions in field campaigns. Finally, we believe that our methodological approach could be useful to generate similar assessments in other world zones.

Aligning climate scenarios to emissions inventories shifts global benchmarks

Taking stock of global progress towards achieving the Paris Agreement requires consistently measuring aggregate national actions and pledges against modelled mitigation pathways1. However, national greenhouse gas inventories (NGHGIs) and scientific assessments of anthropogenic emissions follow different accounting conventions for land-based carbon fluxes resulting in a large difference in the present emission estimates2,3, a gap that will evolve over time. Using state-of-the-art methodologies4 and a land carbon-cycle emulator5, we align the Intergovernmental Panel on Climate Change (IPCC)-assessed mitigation pathways with the NGHGIs to make a comparison. We find that the key global mitigation benchmarks become harder to achieve when calculated using the NGHGI conventions, requiring both earlier net-zero CO2 timing and lower cumulative emissions. Furthermore, weakening natural carbon removal processes such as carbon fertilization can mask anthropogenic land-based removal efforts, with the result that land-based carbon fluxes in NGHGIs may ultimately become sources of emissions by 2100. Our results are important for the Global Stocktake6, suggesting that nations will need to increase the collective ambition of their climate targets to remain consistent with the global temperature goals.

Contribution of land use and cover change (LUCC) to the global terrestrial carbon uptake

Terrestrial carbon uptake is critical to the removal of greenhouse gases and mitigation of global warming, which are closely related to land use and cover change (LUCC). However, understanding terrestrial carbon uptake and the LUCC contribution remains unclear because of complex interactions with other drivers (particularly climate change). By proposing an innovative approach of "trajectory analysis", this study aimed to isolate the LUCC contribution to terrestrial carbon uptake over different scales. Methodologically, global land was first divided into sub-regions of land transformations and stable land trajectories. Then, the carbon uptake change in the stable land trajectory was taken as a synthetic influence of climate change, which was used as a reference to isolate the carbon uptake alternation generated from the LUCC contribution in the land transformation trajectories. Finally, future LUCC and the terrestrial carbon uptake response were predicted under different development pathways. The results showed the global mean net ecosystem production (NEP) was 27.44 ± 36.51 g C m-2 yr-1 in the past two decades (2001-2019), generating 3.15 ± 0.88 Pg C yr-1 of the total terrestrial carbon uptake. Both the NEP and total carbon uptake showed significant increasing trends. Specifically, the mean NEP increased from 17.96 g C m-2 yr-1 in 2001 to 37.37 g C m-2 yr-1 in 2019, with the trend written as y = 1.20× + 15.20 (R2 = 0.62, p < 0.01). Meanwhile, the total carbon uptake increased from 2.35 Pg C yr-1 in 2001 to 4.13 Pg C yr-1 in 2019, which could be written as y = 0.12× + 1.93 (R2 = 0.56, p < 0.01). Climate change acted as the dominant factor for the trends at the global scale, which contributed 21.26 g C m-2 yr-1 and 1.59 Pg C yr-1 of the mean NEP and total carbon uptake changes in the stable land trajectories (94.30 million km2 that covered 63.29 % of the global land area), and the historical LUCC contributed -6.30 g C m-2 yr-1 (-40.85 %) and - 0.046 Pg C yr-1 (-57.50 %) of the mean NEP and the total carbon uptake change in the land transformation trajectories (6.64 million km2 that covered 4.46 % of the global land area), respectively. The maximum LUCC contribution (-61.85 g C m-2 yr-1) to the mean NEP occurred in the land transformations from evergreen needleleaf forests to woody savannas, while the maximum contribution (-0.034 Pg C y-1) to total carbon uptake was in the deforested regions from evergreen broadleaf forests to woody savannas. Eight SSP-RCP scenarios predictions demonstrated that future terrestrial carbon uptake would increase by an average of 0.015 Pg C yr-1 in 2100 due to global afforestation. SSP4-3.4 and SSP5-3.4 had the greatest potential for increasing carbon uptake, which is expected to reach a maximum increase (0.045 Pg C yr-1) in 2100. In contrast, the minimum terrestrial carbon uptake would occur in SSP5-8.5, which had the highest CO2 emissions. In conclusion, although relatively limited at the global scale, LUCC (particularly forest change) exerted an unneglectable role on terrestrial carbon uptake in land transformation regions. The results of this study will help to clarify terrestrial carbon uptake dynamics and provide a basis for carbon neutral and climatic adaptation.

Estimating the spatial amplification of damage caused by degradation in the Amazon

The Amazon rainforests have been undergoing unprecedented levels of human-induced disturbances. In addition to local impacts, such changes are likely to cascade following the eastern-western atmospheric flow generated by trade winds. We propose a model of spatial and temporal interactions created by this flow to estimate the spread of effects from local disturbances to downwind locations along atmospheric trajectories. The spatial component captures cascading effects propagated by neighboring regions, while the temporal component captures the persistence of local disturbances. Importantly, all these network effects can be described by a single matrix, acting as a spatial multiplier that amplifies local forest disturbances. This matrix holds practical implications for policymakers as they can use it to easily map where the damage of an initial forest disturbance is amplified and propagated to. We identify regions that are likely to cause the largest impact throughout the basin and those that are the most vulnerable to shocks caused by remote deforestation. On average, the presence of cascading effects mediated by winds in the Amazon doubles the impact of an initial damage. However, there is heterogeneity in this impact. While damage in some regions does not propagate, in others, amplification can reach 250%. Since we only account for spillovers mediated by winds, our multiplier of 2 should be seen as a lower bound.

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis pathways

In the near future, climate change will cause enhanced frequency and/or severity of droughts in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with implications for carbon cycling and atmospheric chemistry that are challenging to predict. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission. To address this gap, we used position-specific 13C-pyruvate labeling to investigate leaf CO2 and VOC fluxes from four tropical species before and during a controlled drought in the enclosed rainforest of Biosphere 2 (B2). Overall, plants that were more drought-sensitive had greater reductions in daytime CO2 production. Although daytime CO2 production was always dominated by non-mitochondrial processes, the relative contribution of CO2 from the tricarboxylic acid cycle tended to increase under drought. A notable exception was the legume tree Clitoria fairchildiana R.A. Howard, which had less anabolic CO2 production than the other species even under pre-drought conditions, perhaps due to more efficient refixation of CO2 and anaplerotic use for amino acid synthesis. The C. fairchildiana was also the only species to allocate detectable amounts of 13C label to VOCs and was a major source of VOCs in B2. In C. fairchildiana leaves, our data indicate that intermediates from the mevalonic acid (MVA) pathway are used to produce the volatile monoterpene trans-β-ocimene, but not isoprene. This apparent crosstalk between the MVA and methylerythritol phosphate pathways for monoterpene synthesis declined with drought. Finally, although trans-β-ocimene emissions increased under drought, it was increasingly sourced from stored intermediates and not de novo synthesis. Unique metabolic responses of legumes may play a disproportionate role in the overall changes in daytime CO2 and VOC fluxes in tropical forests experiencing drought.

Broadening the focus of forest conservation beyond carbon

Two concurrent trends are contributing towards a much broader view of forest conservation. First, the appreciation of the role of forests as a nature-based climate solution has grown rapidly, particularly among governments and the private sector. Second, the spatiotemporal resolution of forest mapping and the ease of tracking forest changes have dramatically improved. As a result, who does and who pays for forest conservation is changing: sectors and people previously considered separate from forest conservation now play an important role and need to be held accountable and motivated or forced to conserve forests. This change requires, and has stimulated, a broader range of forest conservation solutions. The need to assess the outcomes of conservation interventions has motivated the development and application of sophisticated econometric analyses, enabled by high resolution satellite data. At the same time, the focus on climate, together with the nature of available data and evaluation methods, has worked against a more comprehensive view of forest conservation. Instead, it has encouraged a focus on trees as carbon stores, often leaving out other important goals of forest conservation, such as biodiversity and human wellbeing. Even though both are intrinsically connected to climate outcomes, these areas have not kept pace with the scale and diversification of forest conservation. Finding synergies between these 'co-benefits', which play out on a local scale, with the carbon objective, related to the global amount of forests, is a major challenge and area for future advances in forest conservation.

The effect of the vertical gradients of photosynthetic parameters on the CO2 assimilation and transpiration of a Panamanian tropical forest

Terrestrial biosphere models (TBMs) include the representation of vertical gradients in leaf traits associated with modeling photosynthesis, respiration, and stomatal conductance. However, model assumptions associated with these gradients have not been tested in complex tropical forest canopies. We compared TBM representation of the vertical gradients of key leaf traits with measurements made in a tropical forest in Panama and then quantified the impact of the observed gradients on simulated canopy-scale CO₂ and water fluxes. Comparison between observed and TBM trait gradients showed divergence that impacted canopy-scale simulations of water vapor and CO₂ exchange. Notably, the ratio between the dark respiration rate and the maximum carboxylation rate was lower near the ground than at the top-of-canopy, leaf-level water-use efficiency was markedly higher at the top-of-canopy, and the decrease in maximum carboxylation rate from the top-of-canopy to the ground was less than TBM assumptions. The representation of the gradients of leaf traits in TBMs is typically derived from measurements made within-individual plants, or, for some traits, assumed constant due to a lack of experimental data. Our work shows that these assumptions are not representative of the trait gradients observed in species-rich, complex tropical forests.

Designing an optimized landscape restoration with spatially interdependent non-linear models

Brazilian Atlantic Forest is a biodiversity hotspot drastically fragmented due to different land use practices. Our understanding on the impacts of fragmentation and restoration practices on ecosystem functionality significantly increased during the last decades. However, it is unknown to our knowledge how a precision restoration approach, integrated with landscape metrics, will affect the decision-making process of forest restoration. Here, we applied Landscape Shape Index and Contagion metrics in a genetic algorithm for planning forest restoration in watersheds at the pixel level. We evaluated how such integration may configure the precision of restoration with scenarios related to landscape ecology metrics. The genetic algorithm worked toward optimizing the site, shape, and size of forest patches across the landscape according to the results obtained in applying the metrics. Our results, obtained by simulations of scenarios, support aggregation of forest restoration zones as expected, with priority restoration areas indicated where most of the aggregation of forest patches occurs. Our optimized solutions for the study area (Santa Maria do Rio Doce Watershed) predicted an important improvement of landscape metrics (LSI = 44 %; Contagion/LSI = 73 %). Largest shifts are suggested based on LSI (i.e., three larger fragments) and Contagion/LSI (i.e., only one well-connected fragment) optimizations. Our findings indicate that restoration in an extremely fragmented landscape will promote a shift toward more connected patches and with reduction of the surface:volume ratio. Our work explores the use of genetic algorithms to propose forest restoration based on landscape ecology metrics in a spatially explicit innovative approach. Our results indicate that LSI and Contagion:LSI ratio may affect the choice concerning precise location of restoration sites based on forest fragments scattered in the landscape and reinforce the usefulness of genetic algorithms to yield an optimized-driven solution for restoration initiatives.

Responses of carbon, nitrogen, and phosphorus contents and stoichiometry in soil and fine roots to natural vegetation restoration in a tropical mountainous area, Southern China

The stoichiometry of key elements such as C, N, and P is an important indicator of ecosystem nutrient status and biogeochemical cycling. Nevertheless, the responses of soil and plant C:N:P stoichiometric characteristics to natural vegetation restoration remain poorly understood. In this study, we investigated C, N, and P contents and stoichiometry in soil and fine roots along vegetation restoration stages (grassland, shrubland, secondary forest, and primary forest) in a tropical mountainous area in southern China. We found that soil organic carbon, total N, C:P ratio, and N:P ratio significantly increased with vegetation restoration and significantly decreased with increasing soil depth, whereas there was no significant effect on soil total P and C:N ratio. Furthermore, vegetation restoration significantly increased the fine root N and P content and N:P ratio, whereas soil depth significantly decreased the fine root N content and increased the C:N ratio. The increasing average N:P ratio in fine roots from 17.59 to 21.45 suggested that P limitation increased with vegetation restoration. There were many significant correlations between C, N, and P contents and their ratios in soil and fine roots, indicating a reciprocal control of nutrient stoichiometric characteristics between them. These results contribute to our understanding of changes in soil and plant nutrient status and biogeochemical cycling during vegetation restoration and provide valuable information for restoration and management of tropical ecosystems.

Forest microbiome and global change

Forests influence climate and mitigate global change through the storage of carbon in soils. In turn, these complex ecosystems face important challenges, including increases in carbon dioxide, warming, drought and fire, pest outbreaks and nitrogen deposition. The response of forests to these changes is largely mediated by microorganisms, especially fungi and bacteria. The effects of global change differ among boreal, temperate and tropical forests. The future of forests depends mostly on the performance and balance of fungal symbiotic guilds, saprotrophic fungi and bacteria, and fungal plant pathogens. Drought severely weakens forest resilience, as it triggers adverse processes such as pathogen outbreaks and fires that impact the microbial and forest performance for carbon storage and nutrient turnover. Nitrogen deposition also substantially affects forest microbial processes, with a pronounced effect in the temperate zone. Considering plant-microorganism interactions would help predict the future of forests and identify management strategies to increase ecosystem stability and alleviate climate change effects. In this Review, we describe the impact of global change on the forest ecosystem and its microbiome across different climatic zones. We propose potential approaches to control the adverse effects of global change on forest stability, and present future research directions to understand the changes ahead.

Plant roots fuel tropical soil animal communities

Belowground life relies on plant litter, while its linkage to living roots had long been understudied, and remains unknown in the tropics. Here, we analysed the response of 30 soil animal groups to root trenching and litter removal in rainforest and plantations in Sumatra, and found that roots are similarly important to soil fauna as litter. Trenching effects were stronger in soil than in litter, with an overall decrease in animal abundance in rainforest by 42% and in plantations by 30%. Litter removal little affected animals in soil, but decreased the total abundance by 60% in rainforest and rubber plantations but not in oil palm plantations. Litter and root effects on animal group abundances were explained by body size or vertical distribution. Our study quantifies principle carbon pathways in soil food webs under tropical land use, providing the basis for mechanistic modelling and ecosystem-friendly management of tropical soils.

Recent decrease of the impact of tropical temperature on the carbon cycle linked to increased precipitation

The atmospheric CO₂ growth rate (CGR) variability is largely controlled by tropical temperature fluctuations. The sensitivity of CGR to tropical temperature [Formula: see text] has strongly increased since 1960, but here we show that this trend has ceased. Here, we use the long-term CO₂ records from Mauna Loa and the South Pole to compute CGR, and show that [Formula: see text] increased by 200% from 1960-1979 to 1979-2000 but then decreased by 117% from 1980-2001 to 2001-2020, almost returning back to the level of the 1960s. Variations in [Formula: see text] are significantly correlated with changes in precipitation at a bi-decadal scale. These findings are further corroborated by results from a dynamic vegetation model, collectively suggesting that increases in precipitation control the decreased [Formula: see text] during recent decades. Our results indicate that wetter conditions have led to a decoupling of the impact of the tropical temperature variation on the carbon cycle.

Spatio-Temporal Development of Vegetation Carbon Sinks and Sources in the Arid Region of Northwest China

Drylands, which account for 41% of Earth's land surface and are home to more than two billion people, play an important role in the global carbon balance. This study analyzes the spatio-temporal patterns of vegetation carbon sinks and sources in the arid region of northwest China (NWC), using the net ecosystem production (NEP) through the Carnegie-Ames-Stanford approach (CASA). It quantitatively evaluates regional ecological security over a 20-year period (2000-2020) via a remote sensing ecological index (RSEI) and other ecological indexes, such as the Normalized Difference Vegetation Index (NDVI), fraction of vegetation cover (FVC), net primary productivity (NPP), and land use. The results show that the annual average carbon capacity of vegetation in NWC changed from carbon sources to carbon sinks, and the vegetation NEP increased at a rate of 1.98 gC m-2 yr-1 from 2000 to 2020. Spatially, the annual NEP in northern Xinjiang (NXJ), southern Xinjiang (SXJ) and Hexi Corridor (HX) increased at even faster rates of 2.11, 2.22, and 1.98 gC m-2 yr-1, respectively. Obvious geographically heterogeneous distributions and changes occurred in vegetation carbon sinks and carbon sources. Some 65.78% of the vegetation areas in NWC were carbon sources during 2000-2020, which were concentrated in the plains, and SXJ, the majority carbon sink areas are located in the mountains. The vegetation NEP in the plains exhibited a positive trend (1.21 gC m-2 yr-1) during 2000-2020, but this speed has slowed since 2010. The vegetation NEP in the mountain exhibited only intermittent changes (2.55 gC m-2 yr-1) during 2000-2020; it exhibited a negative trend during 2000-2010, but this trend has reversed strongly since 2010. The entire ecological security of NWC was enhanced during the study period. Specifically, the RSEI increased from 0.34 to 0.49, the NDVI increased by 0.03 (17.65%), the FVC expanded by 19.56%, and the NPP increased by 27.44%. Recent positive trends in NDVI, FVC and NPP have enhanced the capacity of vegetation carbon sinks, and improved the eco-environment of NWC. The scientific outcomes of this study are of great importance for maintaining ecological stability and sustainable economic development along China's Silk Road Economic Belt.

Remote sensing technology for rapid extraction of burned areas and ecosystem environmental assessment

Forest fires are one of the significant disturbances in forest ecosystems. It is essential to extract burned areas rapidly and accurately to formulate forest restoration strategies and plan restoration plans. In this work, we constructed decision trees and used a combination of differential normalized burn ratio (dNBR) index and OTSU threshold method to extract the heavily and mildly burned areas. The applicability of this method was evaluated with three fires in Muli County, Sichuan, China, and we concluded that the extraction accuracy of this method could reach 97.69% and 96.37% for small area forest fires, while the extraction accuracy was lower for large area fires, only 89.32%. In addition, the remote sensing environment index (RSEI) was used to evaluate the ecological environment changes. It analyzed the change of the RSEI level through the transition matrix, and all three fires showed that the changes in RSEI were stronger for heavily burned areas than for mildly burned areas, after the forest fire the ecological environment (RSEI) was reduced from good to moderate. These results realized the quantitative evaluation and dynamic evaluation of the ecological environment condition, providing an essential basis for the restoration, decision making and management of the affected forests.

Towards carbon neutrality: what has been done and what needs to be done for carbon emission reduction?

Carbon emissions embodied in anthropogenic activities represent the major cause of global warming. Countries, regions, and cities have implemented comprehensive, multi-level and multi-scale measures to reduce emissions and move towards carbon neutrality. The demand for carbon emission reduction (CER) is made more challenging by different geographical locations, country-owned natural resources, and economic development stages. The main objectives of this paper are to conduct a bibliometric analysis to map the frontiers and directions of CER and to explore the paths and development models of CER from the perspective of spatio-temporal, multi-scale, multi-sectoral, and multi-responsible subjects. This study reveals that carbon emission evaluation and prediction, correlation and causal relationship analysis, and CER-related policy simulation and optimization are the most critical hotspots. Additionally, we point out the shortcomings of and future developments for the three study dimensions above. The bibliometric analysis also highlights the fact that a cooperative global value chain as well as amendable policies and mechanisms for CER will help with climate change mitigation and adaptation through the use of advanced carbon capture and storage technologies. We review the technical measures for and policy responses to CER adopted by different countries and industries at the theoretical and practical levels and provide new recommendations. Our work provides important information for climate actions in different countries and sectors and for developing more effective CER strategies and policies.

Spatiotemporal dynamic of subtropical forest carbon storage and its resistance and resilience to drought in China

Subtropical forests are rich in vegetation and have high photosynthetic capacity. China is an important area for the distribution of subtropical forests, evergreen broadleaf forests (EBFs) and evergreen needleleaf forests (ENFs) are two typical vegetation types in subtropical China. Forest carbon storage is an important indicator for measuring the basic characteristics of forest ecosystems and is of great significance for maintaining the global carbon balance. Drought can affect forest activity and may even lead to forest death and the stability characteristics of different forest ecosystems varied after drought events. Therefore, this study used meteorological data to simulate the standardized precipitation evapotranspiration index (SPEI) and the Biome-BGC model to simulate two types of forest carbon storage to quantify the resistance and resilience of EBF and ENF to drought in the subtropical region of China. The results show that: 1) from 1952 to 2019, the interannual drought in subtropical China showed an increasing trend, with five extreme droughts recorded, of which 2011 was the most severe one; 2) the simulated average carbon storage of the EBF and ENF during 1985-2019 were 130.58 t·hm^-2 and 78.49 t·hm^-2, respectively. The regions with higher carbon storage of EBF were mainly concentrated in central and southeastern subtropics, where those of ENF mainly distributed in the western subtropic; 3) The median of resistance of EBF was three times higher than that of ENF, indicating the EBF have stronger resistance to extreme drought than ENF. Moreover, the resilience of two typical forest to 2011 extreme drought and the continuous drought events during 2009 - 2011 were similar. The results provided a scientific basis for the response of subtropical forests to drought, and indicating that improve stand quality or expand the plantation of EBF may enhance the resistance to drought in subtropical China, which provided certain reference for forest protection and management under the increasing frequency of drought events in the future.

The road to recovery: a synthesis of outcomes from ecosystem restoration in tropical and sub-tropical Asian forests

Current policy is driving renewed impetus to restore forests to return ecological function, protect species, sequester carbon and secure livelihoods. Here we assess the contribution of tree planting to ecosystem restoration in tropical and sub-tropical Asia; we synthesize evidence on mortality and growth of planted trees at 176 sites and assess structural and biodiversity recovery of co-located actively restored and naturally regenerating forest plots. Mean mortality of planted trees was 18% 1 year after planting, increasing to 44% after 5 years. Mortality varied strongly by site and was typically ca 20% higher in open areas than degraded forest, with height at planting positively affecting survival. Size-standardized growth rates were negatively related to species-level wood density in degraded forest and plantations enrichment settings. Based on community-level data from 11 landscapes, active restoration resulted in faster accumulation of tree basal area and structural properties were closer to old-growth reference sites, relative to natural regeneration, but tree species richness did not differ. High variability in outcomes across sites indicates that planting for restoration is potentially rewarding but risky and context-dependent. Restoration projects must prepare for and manage commonly occurring challenges and align with efforts to protect and reconnect remaining forest areas. The abstract of this article is available in Bahasa Indonesia in the electronic supplementary material. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Implications of tropical cyclones on damage and potential recovery and restoration of logged forests in Vietnam

Many natural forests in Southeast Asia are degraded following decades of logging. Restoration of these forests is delayed by ongoing logging and tropical cyclones, but the implications for recovery are largely uncertain. We analysed meteorological, satellite and forest inventory plot data to assess the effect of Typhoon Doksuri, a major tropical cyclone, on the forest landscapes of central Vietnam consisting of natural forests and plantations. We estimated the return period for a cyclone of this intensity to be 40 years. Plantations were almost twice as likely to suffer cyclone damage compared to natural forests. Logged natural forests (9-12 years after cessation of government-licensed logging) were surveyed before and after the storm with 2 years between measurements and remained a small biomass carbon sink (0.1 ± 0.3 Mg C ha-1 yr-1) over this period. The cyclone reduced the carbon sink of recovering natural forests by an average of 0.85 Mg C ha-1 yr-1, less than the carbon loss due to ongoing unlicensed logging. Restoration of forest landscapes in Southeast Asia requires a reduction in unlicensed logging and prevention of further conversion of degraded natural forests to plantations, particularly in landscapes prone to tropical cyclones where natural forests provide a resilient carbon sink. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Multiscale predictors of small tree survival across a heterogeneous tropical landscape

Uncertainties about controls on tree mortality make forest responses to land-use and climate change difficult to predict. We tracked biomass of tree functional groups in tropical forest inventories across Puerto Rico and the U.S. Virgin Islands, and with random forests we ranked 86 potential predictors of small tree survival (young or mature stems 2.5-12.6 cm diameter at breast height). Forests span dry to cloud forests, range in age, geology and past land use and experienced severe drought and storms. When excluding species as a predictor, top predictors are tree crown ratio and height, two to three species traits and stand to regional factors reflecting local disturbance and the system state (widespread recovery, drought, hurricanes). Native species, and species with denser wood, taller maximum height, or medium typical height survive longer, but short trees and species survive hurricanes better. Trees survive longer in older stands and with less disturbed canopies, harsher geoclimates (dry, edaphically dry, e.g., serpentine substrates, and highest-elevation cloud forest), or in intervals removed from hurricanes. Satellite image phenology and bands, even from past decades, are top predictors, being sensitive to vegetation type and disturbance. Covariation between stand-level species traits and geoclimate, disturbance and neighboring species types may explain why most neighbor variables, including introduced vs. native species, had low or no importance, despite univariate correlations with survival. As forests recovered from a hurricane in 1998 and earlier deforestation, small trees of introduced species, which on average have lighter wood, died at twice the rate of natives. After hurricanes in 2017, the total biomass of trees ≥12.7 cm dbh of the introduced species Spathodea campanulata spiked, suggesting that more frequent hurricanes might perpetuate this light-wooded species commonness. If hurricane recovery favors light-wooded species while drought favors others, climate change influences on forest composition and ecosystem services may depend on the frequency and severity of extreme climate events.

Multiscale spatial analysis of headwater vulnerability in South-Central Chile reveals a high threat due to deforestation and climate change

Headwaters represent an essential component of hydrological, ecological, and socioeconomical systems, by providing constant water streams to the complete basin. However, despite the high importance of headwaters, there is a lack of vulnerability assessments worldwide. Identifying headwaters and their vulnerability in a spatially explicit manner can enable restauration and conservation programs. In this study, we assess the vulnerability of headwaters in South-Central Chile (38.4 to 43.2°S) considering multiple degradation factors related to climate change and land cover change. We analyzed 2292 headwaters, characterizing multiple factors at five spatial scales by using remote sensing data related to Land Use and Cover Change (LUCC), human disturbances, vegetation cover, climate change, potential water demand, and physiography. We then generated an index of vulnerability by integrating all the analyzed variables, which allowed us to map the spatial distribution of headwater vulnerability. Finally, to estimate the main drivers of degradation, we performed a Principal Components Analysis with an Agglomerative Hierarchical Clustering, that allowed us to group headwaters according to the analyzed factors. The largest proportion of most vulnerable headwaters are located in the north of our study area with 48.1 %, 62.1 %, and 28.1 % of headwaters classified as highly vulnerable at 0, 10, and 30 m scale, respectively. The largest proportion of headwaters are affected by Climate Change (63.66 %) and LUCC (23.02 %) on average across all scales. However, we identified three clusters, in which the northern cluster is mainly affected by LUCC, while the Andean and Coastal clusters are mainly affected by climate change. Our results and methods present an informative picture of the current state of headwater vulnerability, identifying spatial patterns and drivers at multiple scales. We believe that the approach developed in this study could be useful for new studies in other zones of the world and can also promote Chilean headwater conservation.

Role of space station instruments for improving tropical carbon flux estimates using atmospheric data

The tropics is the nexus for many of the remaining gaps in our knowledge of environmental science, including the carbon cycle and atmospheric chemistry, with dire consequences for our ability to describe the Earth system response to a warming world. Difficulties associated with accessibility, coordinated funding models and economic instabilities preclude the establishment of a dense pan-tropical ground-based atmospheric measurement network that would otherwise help to describe the evolving state of tropical ecosystems and the associated biosphere-atmosphere fluxes on decadal timescales. The growing number of relevant sensors aboard sun-synchronous polar orbiters provide invaluable information over the remote tropics, but a large fraction of the data collected along their orbits is from higher latitudes. The International Space Station (ISS), which is in a low-inclination, precessing orbit, has already demonstrated value as a proving ground for Earth observing atmospheric sensors and as a testbed for new technology. Because low-inclination orbits spend more time collecting data over the tropics, we argue that the ISS and its successors, offer key opportunities to host new Earth-observing atmospheric sensors that can lead to a step change in our understanding of tropical carbon fluxes.

Tree species richness as an important biotic factor regulates the soil phosphorus density in China's mature natural forests

Tree species richness has been recognized as an underlying driving factor for regulating soil phosphorus (P) status in many site-specific studies. However, it remains poorly understood whether this is true at broad scales where soil P strongly rely on climate, soil type and vegetation type. Here, based on the data of 946 mature natural forest sites from a nationwide field survey in China, we analyzed the impact of tree species richness on soil P density of China's mature natural forests (deciduous coniferous forest, DCF; evergreen coniferous forest, ECF; deciduous broad-leaved forest, DBF; evergreen broad-leaved forest, EBF; and mixed coniferous and broad-leaved forest, MF). Our results showed that tree species richness had a negative effect on soil P density in China's mature natural forests. The Random Forest regression model showed that the relative importance of tree species richness to soil P density was second only to the climate factors (mean annual temperature, MAT; mean annual precipitation, MAP). In addition, the structural equation model (SEM) results showed that the goodness fit of SEM increased when the tree species richness was included into the model. These results suggested that tree species richness was an important factor in regulating the China's mature natural forests soil P density. Furthermore, the SEM results showed that the decreased soil P density was related to the increase in ANPP and the decrease in litter P concentration induced by tree species richness. This result indicates that tree species richness could facilitate plant P absorption and inhibit plant P return into the soil, and thus reducing the soil P density in China's mature natural forests. In conclusion, we found tree species richness was an important biotic factor in regulating soil P density at broad scales, which should be fully considered in Earth models that represent P cycle.

A pantropical assessment of deforestation caused by industrial mining

Driven by rapidly increasing demand for mineral resources, both industrial mining and artisanal mining are intensifying across the tropical biome. A number of regional studies have analyzed mining-induced deforestation, but scope and patterns across all tropical countries have not yet been investigated. Focusing on industrial mining, we use geospatial data to quantify direct forest loss within mining sites in 26 countries. We also perform a statistical assessment to test whether industrial mining drives indirect deforestation in the mine surroundings. We show that direct deforestation concentrates only in a few countries, while industrial mining causes indirect deforestation in two-thirds of tropical countries. In order to preserve tropical forests, direct and indirect deforestation impacts of mining projects should be fully considered.

Growing demand for minerals continues to drive deforestation worldwide. Tropical forests are particularly vulnerable to the environmental impacts of mining and mineral processing. Many local- to regional-scale studies document extensive, long-lasting impacts of mining on biodiversity and ecosystem services. However, the full scope of deforestation induced by industrial mining across the tropics is yet unknown. Here, we present a biome-wide assessment to show where industrial mine expansion has caused the most deforestation from 2000 to 2019. We find that 3,264 km2 of forest was directly lost due to industrial mining, with 80% occurring in only four countries: Indonesia, Brazil, Ghana, and Suriname. Additionally, controlling for other nonmining determinants of deforestation, we find that mining caused indirect forest loss in two-thirds of the investigated countries. Our results illustrate significant yet unevenly distributed and often unmanaged impacts on these biodiverse ecosystems. Impact assessments and mitigation plans of industrial mining activities must address direct and indirect impacts to support conservation of the world’s tropical forests.

Feedback in tropical forests of the Anthropocene

Tropical forests are complex systems containing myriad interactions and feedbacks with their biotic and abiotic environments, but as the world changes fast, the future of these ecosystems becomes increasingly uncertain. In particular, global stressors may unbalance the feedbacks that stabilize tropical forests, allowing other feedbacks to propel undesired changes in the whole ecosystem. Here, we review the scientific literature across various fields, compiling known interactions of tropical forests with their environment, including the global climate, rainfall, aerosols, fire, soils, fauna, and human activities. We identify 170 individual interactions among 32 elements that we present as a global tropical forest network, including countless feedback loops that may emerge from different combinations of interactions. We illustrate our findings with three cases involving urgent sustainability issues: (1) wildfires in wetlands of South America; (2) forest encroachment in African savanna landscapes; and (3) synergistic threats to the peatland forests of Borneo. Our findings reveal an unexplored world of feedbacks that shape the dynamics of tropical forests. The interactions and feedbacks identified here can guide future qualitative and quantitative research on the complexities of tropical forests, allowing societies to manage the nonlinear responses of these ecosystems in the Anthropocene.

Facilitating Reforestation Through the Plant Microbiome: Perspectives from the Phyllosphere

Tree planting and natural regeneration contribute to the ongoing effort to restore Earth's forests. Our review addresses how the plant microbiome can enhance the survival of planted and naturally regenerating seedlings and serve in long-term forest carbon capture and the conservation of biodiversity. We focus on fungal leaf endophytes, ubiquitous defensive symbionts that protect against pathogens. We first show that fungal and oomycetous pathogen richness varies greatly for tree species native to the United States (n = 0-876 known pathogens per US tree species), with nearly half of tree species either without pathogens in these major groups or with unknown pathogens. Endophytes are insurance against the poorly known and changing threat of tree pathogens. Next, we review studies of plant phyllosphere feedback, but knowledge gaps prevent us from evaluating whether adding conspecific leaf litter to planted seedlings promotes defensive symbiosis, analogous to adding soil to promote positive feedback. Finally, we discuss research priorities for integrating the plant microbiome into efforts to expand Earth's forests.

Recent advances in CO2 capture and reduction

Given the continuous and excessive CO₂ emission into the atmosphere from anthropomorphic activities, there is now a growing demand for negative carbon emission technologies, which requires efficient capture and conversion of CO₂ to value-added chemicals. This review highlights recent advances in CO₂ capture and conversion chemistry and processes. It first summarizes various adsorbent materials that have been developed for CO₂ capture, including hydroxide-, amine-, and metal organic framework-based adsorbents. It then reviews recent efforts devoted to two types of CO₂ conversion reaction: thermochemical CO₂ hydrogenation and electrochemical CO₂ reduction. While thermal hydrogenation reactions are often accomplished in the presence of H₂, electrochemical reactions are realized by direct use of electricity that can be renewably generated from solar and wind power. The key to the success of these reactions is to develop efficient catalysts and to rationally engineer the catalyst-electrolyte interfaces. The review further covers recent studies in integrating CO₂ capture and conversion processes so that energy efficiency for the overall CO₂ capture and conversion can be optimized. Lastly, the review briefs some new approaches and future directions of coupling direct air capture and CO₂ conversion technologies as solutions to negative carbon emission and energy sustainability.

Human expansion into Asian highlands in the 21st Century and its effects

Most intensive human activities occur in lowlands. However, sporadic reports indicate that human activities are expanding in some Asian highlands. Here we investigate the expansions of human activities in highlands and their effects over Asia from 2000 to 2020 by combining earth observation data and socioeconomic data. We find that ∼23% of human activity expansions occur in Asian highlands and ∼76% of these expansions in highlands comes from ecological lands, reaching 95% in Southeast Asia. The expansions of human activities in highlands intensify habitat fragmentation and result in large ecological costs in low and lower-middle income countries, and they also support Asian developments. We estimate that cultivated land net growth in the Asian highlands contributed approximately 54% in preventing the net loss of the total cultivated land. Moreover, the growth of highland artificial surfaces may provide living and working spaces for ∼40 million people. Our findings suggest that highland developments hold dual effects and provide new insight for regional sustainable developments.

Most of the intensive human activities usually occur in lowlands. Here the authors report that human activity expansions also were widely distributed in Asian highlands in the 21st century and held dual effects, which provides new insights for regional human activity expansions.

Recurrent droughts increase risk of cascading tipping events by outpacing adaptive capacities in the Amazon rainforest

Tipping elements are nonlinear subsystems of the Earth system that have the potential to abruptly shift to another state if environmental change occurs close to a critical threshold with large consequences for human societies and ecosystems. Among these tipping elements may be the Amazon rainforest, which has been undergoing intensive anthropogenic activities and increasingly frequent droughts. Here, we assess how extreme deviations from climatological rainfall regimes may cause local forest collapse that cascades through the coupled forest-climate system. We develop a conceptual dynamic network model to isolate and uncover the role of atmospheric moisture recycling in such tipping cascades. We account for heterogeneity in critical thresholds of the forest caused by adaptation to local climatic conditions. Our results reveal that, despite this adaptation, a future climate characterized by permanent drought conditions could trigger a transition to an open canopy state particularly in the southern Amazon. The loss of atmospheric moisture recycling contributes to one-third of the tipping events. Thus, by exceeding local thresholds in forest adaptive capacity, local climate change impacts may propagate to other regions of the Amazon basin, causing a risk of forest shifts even in regions where critical thresholds have not been crossed locally.

Biobased plastic: A plausible solution toward carbon neutrality in plastic industry?

Biobased plastic exhibits unique benefits for achieving carbon neutrality, a key step toward reducing atmospheric greenhouse gases, due to its stability, high carbon content, and origin of carbon by photosynthesis. Herein we evaluate the role and potential of biobased plastic as an alternative carbon reservoir which is completely artificial, since most plastic polymers are synthetic and massively produced after the 1950 s. Model simulation indicates that plastic, under usage, burial, and littering, forms a growing carbon reservoir, sinking 6.82 gigatons of carbon (GtC) in 2020. Plastic-formed carbon is estimated to stack up to 19.4-23.2 GtC in 2060 under various production scenarios. However, only 18-40% of carbon stored in plastic is biobased carbon, equivalent to approximately 31-48 gigatons of carbon dioxide. Without any low carbon energy upgrade, carbon neutrality is difficult to achieve even with 90% biobased plastic substitution and 50% recycling ratio. Because extra GHG emissions are generated as a result of increasingly using incineration as a post-treatment strategy in response to increasing waste generation, the annual net GHG emission continues to rebound after the bio-based plastic substitution and plastic recycling approach their upper limits. Additional strategies are therefore needed to achieve complete carbon neutrality.

Simulating environmentally-sensitive tree recruitment in vegetation demographic models

Vegetation demographic models (VDMs) endeavor to predict how global forests will respond to climate change. This requires simulating which trees, if any, are able to recruit under changing environmental conditions. We present a new recruitment scheme for VDMs in which functional-type-specific recruitment rates are sensitive to light, soil moisture and the productivity of reproductive trees. We evaluate the scheme by predicting tree recruitment for four tropical tree functional types under varying meteorology and canopy structure at Barro Colorado Island, Panama. We compare predictions to those of a current VDM, quantitative observations and ecological expectations. We find that the scheme improves the magnitude and rank order of recruitment rates among functional types and captures recruitment limitations in response to variable understory light, soil moisture and precipitation regimes. Our results indicate that adopting this framework will improve VDM capacity to predict functional-type-specific tree recruitment in response to climate change, thereby improving predictions of future forest distribution, composition and function.

Climatic and biotic factors influencing regional declines and recovery of tropical forest biomass from the 2015/16 El Niño

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.

Urban development enhances soil organic carbon storage through increasing urban vegetation

Anthropogenic activities can lead to the loss of soil organic carbon (SOC) or improve its storage, hence they have the potential to exacerbate or help mitigate climate change. Urban expansion results in an initial loss of soil carbon, but long-term SOC changes during urban development are poorly understood. Herein, we studied SOC changes in the suburban and urban areas of cities with high levels of urbanization based on a long-term resampling campaign in Beijing, and a compilation of SOC content data from 21 other cities with high levels of urbanization across China over the past three decades. Our results revealed that the SOC of topsoils decreased by 17.2% in the suburban areas and increased by 104.4% in the urban areas of cities with high levels of urbanization. The changes in SOC were positively correlated with the changes in vegetation coverage and productivity. Partial least square method structural equation model analyses showed that changes in vegetation could directly affect SOC changes, and the changes in vegetation coverage and productivity were induced by human activities and climate changes in Beijing. The topsoils in the urban areas of cities with high levels of urbanization can act as carbon sinks due to the increase in vegetation. This study can help improve our understanding of the role of the SOC content of cities within the global C cycle and provide suggestions for achieving the goal of carbon neutrality in China.