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Introduction: Since 1990, there has been a global decline in forest areas. Between 2010 and 2020, the greatest annual net loss of forests was on the African continent. Despite South African indigenous forests and trees being protected under the National Forests Act of 1998 (Act No. 84 of 1998), the country has also shown an increased annual net loss of forests. Although the Vhembe District Municipality in South Africa has lost forest owing to humaninduced deforestation and other land use activities, sacred forests have not been affected. According to traditional beliefs, exploitation of such indigenous patches of sacred forests is taboo. This study aims to explore the role of taboos in the protection of the remaining patches of sacred forest. Methods: The study relies on data collected between December 2022 and December 2023. Semi-structured interviewswere conductedwith key informants (n = 61) and local communities in Tshidzivhe and Duthuni villages (n = 60). Observations were used as a further data collection tool. The interview questions were prepared to assess the role of taboos in the protection and management of sacred forests. Data collected through interviews were analysed using thematic content analysis, while field observations helped to corroborate the results from the interviews. Results and discussion: The study identified two main taboos - one that restricts entry into the sacred forests (i.e. preventing entry into the sacred forests, and harvesting, hunting and hiking in these areas), and another that prohibits noise or activities that disrespect sacred forests. The study found that believers and nonbelievers alike, for fear of retribution by the spirits, still obey these taboos and their relatedmyths. This has allowed these areas to develop dense stands of closed-canopy evergreen forest that support more diverse flora and fauna than found in surrounding areas. Although sacred forests are not meant for biodiversity conservation, they offer opportunities to be integrated into global conservation targets of "30x30" and "Half-Earth" by 2030. They also offer the opportunity of serving as carbon sinks which is key to climate change mitigation. Recommendations for protecting sacred forests and associated taboos are drawn up based on these results. [ABSTRACT FROM AUTHOR]

Tropical forest productivity represents an important global carbon sink, but many tropical forests grow on infertile soils. Efficient nutrient cycling by litterfall has long been assumed to maintain tropical tree growth, but there is no direct evidence that the nutrients cycled in litterfall are essential for tropical forest productivity.To test whether nutrient cycling by litterfall maintains tropical forest above‐ground productivity, we established large‐scale long‐term litter removal (L−) and litter addition (L+) treatments in a mature lowland tropical forest. We hypothesised that the removal of nutrients in litter would reduce tree growth, survival and litter production in L− plots. By contrast, the addition of nutrients in litter would enhance tree growth, survival and litter production in L+ plots. To test our hypotheses, we recorded tree growth and survival every 2 years, and measured litterfall monthly during 17 years of treatments.Tree growth and litterfall declined over time in L− plots, with consistently lower growth rates compared to controls after 8 years, and lower litter production after 4 years of treatments. By contrast, although litterfall was higher in the L+ plots relative to the controls, there was only a minor transient increase in tree growth immediately after the start of treatments. Tree survival declined over time in all treatments but was not affected by litter manipulation.The long‐term decline in tree growth and litterfall in the L− plots provides the first empirical evidence that nutrient cycling by litterfall plays a key role in maintaining above‐ground productivity in this tropical forest. By contrast, the transient increase in growth in the L+ plots can be attributed to the large inputs of nutrients with the addition of the entire litter standing crop at the start of treatments. The addition of nutrients in litter over the long term was nonetheless sufficient to enhance litter production, possibly by accelerating leaf turnover.Synthesis: Efficient nutrient cycling by litterfall makes an important contribution to the annual nutrient requirements of mature tropical forest trees, compensating for infertile soils. Disturbances that disrupt this finely balanced cycle could therefore reduce biomass carbon sequestration in tropical forests. [ABSTRACT FROM AUTHOR]

Carbon sequestration constitutes a vital ecological function executed by ecosystems to mitigate global warming due to the burgeoning sustained anthropogenic activities which release greenhouse gases (carbon dioxide, methane, carbon monoxide, etc.). The current study evaluates carbon dynamics in forest ecosystems through the InVest model with temporal land use analyses using remote sensing data from 1973 to 2021 in the Chikamagaluru district of Karnataka. Land use dynamics were assessed using temporal remote sensing data through a machinelearning-based supervised Random Forest algorithm, which shows a decline in forest cover of 28.98%, an increase in agricultural area by 5.31%, and horticulture by 42.52% in the last five decades, which has led to the depletion of carbon stock by 30683.81 Gg. Land use changes have a long-term effect on climatic variables, leading to changes in local temperature, annual rainfall, and number of rainy days in the study area. [ABSTRACT FROM AUTHOR]

Background: The European Union (EU) has committed to achieve climate neutrality by 2050. This requires a rapid reduction of greenhouse gas (GHG) emissions and ensuring that any remaining emissions are balanced through CO2 removals. Forests play a crucial role in this plan: they are currently the main option for removing CO2 from the atmosphere and additionally, wood use can store carbon durably and help reduce fossil emissions. To stop and reverse the decline of the forest carbon sink, the EU has recently revised the regulation on land use, land-use change and forestry (LULUCF), and set a target of − 310 Mt CO2e net removals for the LULUCF sector in 2030. Results: In this study, we clarify the role of common concepts in forest management – net annual increment, harvest and mortality – in determining the forest sink. We then evaluate to what extent the forest sink is on track to meet the climate goals of the EU. For this assessment we use data from the latest national GHG inventories and a forest model (Carbon Budget Model). Our findings indicate that on the EU level, the recent decrease in increment and the increase in harvest and mortality are causing a rapid drop in the forest sink. Furthermore, continuing the past forest management practices is projected to further decrease the sink. Finally, we discuss options for enhancing the sinks through forest management while taking into account adaptation and resilience. Conclusions: Our findings show that the EU forest sink is quickly developing away from the EU climate targets. Stopping and reversing this trend requires rapid implementation of climate-smart forest management, with improved and more timely monitoring of GHG fluxes. This enhancement is crucial for tracking progress towards the EU's climate targets, where the role of forests has become – and is expected to remain – more prominent than ever before. [ABSTRACT FROM AUTHOR]

Forests play a critical role in global carbon cycling, and continuous forest destruction together with other factors has accelerated global warming. Furthermore, continued decline of forest areas will critically hinder the accomplishment of carbon neutrality goals. Although the geographical location of deforestation can now be rapidly and accurately detected with remote sensing technology, current forest change products are still not fine-grained, especially from the perspective of carbon trading. Here, we used a deep learning method to detect deforestation in large regions based on 2 m high-resolution optical remote sensing images. Firstly, we proposed a new deforestation detection dataset, which was generated from 11 provincial regions in the Yangtze River Economic Zone of China, containing a total number of 8330 samples (the size of each sample being 512 × 512 pixels). Then, a new deforestation detection model, SiamHRnet-OCR, was designed, based on this dataset. Compared with other deep learning models, SiamHRnet-OCR achieves better results in terms of precision, F1-score, and OA indicator: 0.6482, 0.6892, and 0.9898, respectively. Finally, two large-scale scenarios of deforestation experiments in Southern China were further tested; the deforestation detection results demonstrate that SiamHRnet-OCR can not only detect deforestation effectively but also capture the accurate boundary of the changing area. [ABSTRACT FROM AUTHOR]

Amazon forest dieback is seen as a potential tipping point under climate change. These concerns are partly based on an early coupled climate–carbon cycle simulation that produced unusually strong drying and warming in Amazonia. In contrast, the fifth-generation Earth system models (Phase 5 of the Coupled Model Intercomparison Project, CMIP5) produced few examples of Amazon dieback under climate change. Here we examine results from seven sixth-generation models (Phase 6 of the Coupled Model Intercomparison Project, CMIP6), which include interactive vegetation carbon and in some cases interactive forest fires. Although these models typically project increases in area-mean forest carbon across Amazonia under CO2 -induced climate change, five of the seven models also produce abrupt reductions in vegetation carbon, which indicate localised dieback events. The northern South America (NSA) region, which contains most of the rainforest, is especially vulnerable in the models. These dieback events, some of which are mediated by fire, are preceded by an increase in the amplitude of the seasonal cycle in near-surface temperature, which is consistent with more extreme dry seasons. Based on the ensemble mean of the detected dieback events we estimate that 7±5 % of the NSA region will experience abrupt downward shifts in vegetation carbon for every degree of global warming past 1.5 ∘ C. [ABSTRACT FROM AUTHOR]

Background: Countries seeking to mitigate climate change through forests require suitable modelling approaches to predict carbon (C) budget dynamics in forests and their responses to disturbance and management. The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) is a feasible and comprehensive tool for simulating forest C stock dynamics across broad levels, but discrepancies remain to be addressed in China. Taking Guizhou as the case study, we customised the CBM-CFS3 model according to China's context, including the modification of aboveground biomass C stock algorithm, addition of C budget accounting for bamboo forests, economic forests, and shrub forests, improvement of non-forest land belowground slow dead organic matter (DOM) pool initialisation, and other model settings. Results: The adequate linear relationship between the estimated and measured C densities (R2 = 0.967, P < 0.0001, slope = 0.904) in the model validation demonstrated the high accuracy and reliability of our customised model. We further simulated the spatiotemporal dynamics of forest C stocks and disturbance impacts in Guizhou for the period 1990–2016 using our customised model. Results shows that the total ecosystem C stock and C density, and C stocks in biomass, litter, dead wood, and soil in Guizhou increased continuously and significantly, while the soil C density decreased over the whole period, which could be attributed to deforestation history and climate change. The total ecosystem C stock increased from 1220 Tg C in 1990 to 1684 Tg C in 2016 at a rate of 18 Tg C yr−1, with significant enhancement in most areas, especially in the south and northwest. The total decrease in ecosystem C stock and C expenditure caused by disturbances reached 97.6 Tg C and 120.9 Tg C, respectively, but both represented significant decreasing trends owing to the decline of disturbed forest area during 1990–2016. Regeneration logging, deforestation for agriculture, and harvest logging caused the largest C stock decrease and C expenditure, while afforestation and natural expansion of forest contributed the largest increases in C stock. Conclusions: The forests in Guizhou were a net carbon sink under large-scale afforestation throughout the study period; Our customised CBM-CFS3 model can serve as a more effective and accurate method for estimating forest C stock and disturbance impacts in China and further enlightens model customisation to other areas. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Chinese government has made a strategic decision to reach 'carbon neutrality' before 2060. China's terrestrial ecosystem carbon sink is currently offsetting 7–15% of national anthropogenic emissions and has received widespread attention regarding its role in the 'carbon neutrality' strategy. We provide perspectives on this question by inferring from the fundamental principles of terrestrial ecosystem carbon cycles. We first elucidate the basic ecological theory that, over the long-term succession of ecosystem without regenerative disturbances, the carbon sink of a given ecosystem will inevitably approach zero as the ecosystem reaches its equilibrium state or climax. In this sense, we argue that the currently observed global terrestrial carbon sink largely emerges from the processes of carbon uptake and release of ecosystem responding to environmental changes and, as such, the carbon sink is never an intrinsic ecosystem function. We further elaborate on the long-term effects of atmospheric CO2 changes and afforestation on China's terrestrial carbon sink: the enhancement of the terrestrial carbon sink by the CO2 fertilization effect will diminish as the growth of the atmospheric CO2 slows down, or completely stops, depending on international efforts to combat climate change, and carbon sinks induced by ecological engineering, such as afforestation, will also decline as forest ecosystems become mature and reach their late-successional stage. We conclude that terrestrial ecosystems have nonetheless an important role to play to gain time for industrial emission reduction during the implementation of the 'carbon neutrality' strategy. In addition, science-based ecological engineering measures including afforestation and forest management could be used to elongate the time of ecosystem carbon sink service. We propose that the terrestrial carbon sink pathway should be optimized, by addressing the questions of 'when' and 'where' to plan afforestation projects, in order to effectively strengthen the terrestrial ecosystem carbon sink and maximize its contribution to the realization of the 'carbon neutrality' strategy. [ABSTRACT FROM AUTHOR]

Future land use and cover change (LUCC) simulations play an important role in providing fundamental data to reveal the carbon cycle response of forest ecosystems to LUCC. Subtropical forests have great potential for carbon sequestration, yet their future dynamics under natural and human influences are unclear. Zhejiang Province in China is an important distribution area for subtropical forests. For forest management, it is of great significance to explore the future dynamic changes of subtropical forests in Zhejiang. As a popular LUCC spatial simulation model, the cellular automata (CA) model coupled with machine learning and LUCC quantitative demand models such as system dynamics (SD) can achieve effective LUCC simulation. Therefore, we first integrated a back propagation neural network (BPNN), a CA, and a SD model as a BPNN_CA_SD (BCS) coupled model for future LUCC simulation and then designed a slow development scenario (SD_Scenario), a harmonious development scenario (HD_Scenario), a baseline development scenario (BD_Scenario), and a fast development scenario (FD_Scenario), combining climate change and human disturbance. Thirdly, we obtained future land-use patterns in Zhejiang Province from 2014 to 2084 under multiple scenarios, and finally, we analyzed the temporal and spatial changes of land use and discussed the subtropical forest dynamics of the future. The results showed the following: (1) The overall accuracy was approximately 0.8, the kappa coefficient was 0.75, and the figure of merit (FOM) value was over 28% when using the BCS model to predict LUCC, indicating that the model could predict the consistent change of LUCC accurately. (2) The future evolution of the LUCC under different scenarios varied, with the growth of bamboo forests and the decline of coniferous forests in the FD_Scenario being prominent among the forest dynamics changes. Compared with 2014, the bamboo forest in 2084 will increase by 37%, while the coniferous forest will decrease by 25%. (3) Comparing the area and spatial change of the subtropical forests, the SD_Scenario was found to be beneficial for the forest ecology. These results can provide an important decision-making reference for land-use planning and sustainable forest development in Zhejiang Province. [ABSTRACT FROM AUTHOR]

Gross primary productivity (GPP) is the largest flux in the global carbon cycle and satellite‐based GPP estimates have long been used to study the trends and interannual variability of GPP. With recent updates to geostationary satellites, we can now explore the diurnal variability of GPP at a comparable spatial resolution to polar‐orbiting satellites and at temporal frequencies comparable to eddy covariance (EC) tower sites. We used observations from the Advanced Baseline Imager on the Geostationary Operational Environmental Satellite‐R series (GOES‐R) to test the ability of subdaily satellite data to capture the shifts in the diurnal course of GPP at an oak savanna EC site in California, USA that is subject to seasonal soil moisture declines. We compared three methods to estimate GPP: (a) a light‐use efficiency model, (b) a linear relationship between the product of near‐infrared reflectance of vegetation and photosynthetically active radiation (LIN‐NIRvP) and EC tower GPP, and (c) a light response curve (LRC‐NIRvP) between NIRvP and EC GPP. The LRC‐NIRvP achieved the lowest mean absolute error for winter (2 µmol CO2 m−2 s−1), spring (2.51 µmol CO2 m−2 s−1), summer (1.43 µmol CO2 m−2 s−1), and fall (1.35 µmol CO2 m−2 s−1). The ecosystem experienced the largest shift in daily peak GPP in relation to the peak of incoming solar radiation toward the morning hours during the dry summers. The LRC‐NIRvP and the light‐use efficiency model were in agreement with these patterns of a shift in peak daily GPP toward the morning hours during summer. Our results can help develop diurnal estimates of GPP from geostationary satellites that are sensitive to fluctuating environmental conditions during the day. Plain Language Summary: Gross primary productivity (GPP) quantifies the drawdown of atmospheric CO2 through ecosystem‐scale photosynthesis. Large‐scale estimates of GPP are a crucial component of carbon cycle science and can be estimated using satellites. Motivated by the recent advances in the spectral coverage and spatial resolution of geostationary ("weather") satellites, we demonstrate how the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite‐R series can provide satellite‐based, half‐hourly GPP estimates at the Tonzi Ranch Ameriflux eddy covariance site in California, USA. We found that a light response curve is able to achieve the best agreement between ABI‐based estimates of GPP and GPP partitioned from gas exchange measurements at the eddy covariance site. Previous research has demonstrated that the diurnal peak of GPP shifts increasingly toward the morning at Tonzi Ranch as the year progresses into the dry season. We found that ABI can capture this characteristic seasonal shift of peak diurnal GPP, which highlights its ability to measure ecosystem dynamics in addition to the weather patterns that help cause them. Key Points: The Geostationary Operational Environmental Satellite‐R Series can estimate gross primary productivity every half hourA light response curve provides the best agreement with gross primary productivity estimated at an Ameriflux oak savanna siteDiurnal satellite‐based estimates of gross primary productivity follow the shift toward the mornings during the dry summers at the site [ABSTRACT FROM AUTHOR]

Climate change has substantially increased the frequency of extreme droughts in the Amazon basin, generating concern about impacts on the world's largest tropical forest, which contributes about one‐seventh of the global vegetation carbon sink. Most research to understand drought impacts has focused on the immediate influences of such events, neglecting post‐drought effects on ecosystems recovery. Since ecological processes are influenced by antecedent conditions, we analyzed whether extreme droughts affect vegetation growth (i.e., net primary productivity, NPP) recovery. Here, we evaluated the NPP in the Amazon basin from 2003 to 2020, a period in which drought frequency was almost double the decadal incidence of the last century. We show that NPP does respond to the coupled impacts of individual droughts and the post‐drought impacts during ecosystem recovery. In particular, our results reveal that the ecosystems undergoing recovery show NPP about 13% lower than reference values based on the pre‐drought state or in areas undisturbed by drought. NPP deficits have consistently increased with the extreme droughts of 2005, 2010, and 2015 due to the combined effects of disturbances magnitude and the length of recovery. If the expected increase in drought frequency and intensity does occur, reduced recovery may lead the Amazon Forest to an alternative ecosystem state with lower carbon uptake, contributing to a warming global climate. Plain Language Summary: Extreme droughts cause significant impacts on forest systems. Although drought disturbances are widely quantified, few studies address the impacts of post‐drought effects during the recovery period. In this work, we show that forests undergoing post‐drought recovery show lower levels of productivity than undisturbed systems. Recovery debts vary with drought intensity and the recovery time after each event. Global warming is projected to increase drought intensity and frequency worldwide and recovery debts may promote a decrease in forests carbon uptake. Key Points: Forests undergoing post‐drought recovery show lower levels of productivity than undisturbed systemsRecovery debts vary not only with the degree of intensity of the drought but also with the recovery time after each event [ABSTRACT FROM AUTHOR]

Background: The contribution of EU forests to climate change mitigation in 2021–2025 is assessed through the Forest Reference Levels (FRLs). The FRL is a projected country-level benchmark of net greenhouse gas emissions against which the future net emissions will be compared. The FRL models the hypothetical development of EU forest carbon sink if the historical management practices were continued, taking into account age dynamics. The Member States' FRLs have been recently adopted by the European Commission with the delegated Regulation (EU) 2021/268 amending the Regulation (EU) 2018/841. Considering the complexity of interactions between forest growth, management and carbon fluxes, there is a need to understand uncertainties linked to the FRL determination. Results: We assessed the methodologies behind the modelled FRLs and evaluated the foreseen impact of continuation of management practices and age dynamics on the near-future EU27 + UK forest carbon sink. Most of the countries implemented robust modelling approaches for simulating management practices and age dynamics within the FRL framework, but faced several challenges in ensuring consistency with historical estimates. We discuss that the projected 16% increase in harvest in 2021–2025 compared to 2000–2009, mostly attributed to age dynamics, is associated to a decline of 18% of forest sink (26% for living biomass only). Conclusions: We conclude that the FRL exercise was challenging but improved the modelling capacity and data availability at country scale. The present study contributes to increase the transparency of the implementation of forest-related EU policies and provides evidence-based support to future policy development. [ABSTRACT FROM AUTHOR]

Forest ecosystems play a central role in global water and carbon cycles, yet the impact of global climate change, in particular drought, on trees and forests is poorly understood. Therefore, there is an urgent need for forest‐scale experiments in improving our understanding of trees' responses to extreme drought events and subsequent recovery under field conditions. Here, we present the design and efficacy of a novel throughfall exclusion experiment with retractable roofs in a mature forest allowing for flexible drought and recovery periods. A total of 12 plots (144 ± 26 m2 on average) with 3–7 European beech and Norway spruce trees each were established by root trenching to a depth of one meter, four years prior to the experiment. Subsequent installation of roofs (n = 6) allowed for the removal of throughfall precipitation and almost a complete non‐availability of soil water in the upper 70 cm during five subsequent growing seasons, that is, 2014–2018. This reduction in available soil water resulted in pre‐dawn leaf water potentials down to −1.8 MPa in mature trees. Stem diameter growth decreased by 30% in beech and 70% in spruce, and fine root abundance was reduced by 57% in beech and 73% in spruce compared with controls. After only one growing season, the mycorrhizal community composition changed in response to drought. Careful watering of hydrophobic forest soils in early summer of 2019 resulted in recovered pre‐dawn leaf water potentials of drought‐stressed trees within one week. Recovery of stem diameter growth, however, did not occur within the same growing season and remained reduced by 33% in beech and 69% in spruce compared with controls. The implemented throughfall exclusion system imposed recurrent seasonal drought events on a mature beech/spruce forest with high efficacy. Shifts in community composition of mycorrhizae in parallel to tree growth decline advocate for a more holistic view on forest‐scale drought and watering experiments, particularly in light of more frequently predicted drought events in future. The perennial nature of mature trees and their subsequent slow recovery from drought, that is, over multiple growing seasons, argues for more long‐term experiments that span several years. [ABSTRACT FROM AUTHOR]

Summary: Plant traits are increasingly being used to improve prediction of plant function, including plant demography. However, the capability of plant traits to predict demographic rates remains uncertain, particularly in the context of trees experiencing a changing climate.Here we present data combining 17 plant traits associated with plant structure, metabolism and hydraulic status, with measurements of long‐term mean, maximum and relative growth rates for 176 trees from the world's longest running tropical forest drought experiment.We demonstrate that plant traits can predict mean annual tree growth rates with moderate explanatory power. However, only combinations of traits associated more directly with plant functional processes, rather than more commonly employed traits like wood density or leaf mass per area, yield the power to predict growth. Critically, we observe a shift from growth being controlled by traits related to carbon cycling (assimilation and respiration) in well‐watered trees, to traits relating to plant hydraulic stress in drought‐stressed trees.We also demonstrate that even with a very comprehensive set of plant traits and growth data on large numbers of tropical trees, considerable uncertainty remains in directly interpreting the mechanisms through which traits influence performance in tropical forests. [ABSTRACT FROM AUTHOR]

Although the effect of pollution on forest health and decline received much attention in the 1980s, it has not been considered to explain the 'Divergence Problem' in dendroclimatology; a decoupling of tree growth from rising air temperatures since the 1970s. Here we use physical and biogeochemical measurements of hundreds of living and dead conifers to reconstruct the impact of heavy industrialisation around Norilsk in northern Siberia. Moreover, we develop a forward model with surface irradiance forcing to quantify long‐distance effects of anthropogenic emissions on the functioning and productivity of Siberia's taiga. Downwind from the world's most polluted Arctic region, tree mortality rates of up to 100% have destroyed 24,000 km2 boreal forest since the 1960s, coincident with dramatic increases in atmospheric sulphur, copper, and nickel concentrations. In addition to regional ecosystem devastation, we demonstrate how 'Arctic Dimming' can explain the circumpolar 'Divergence Problem', and discuss implications on the terrestrial carbon cycle. [ABSTRACT FROM AUTHOR]

During the strong El Niño event of 2015–2016 large‐scale dieback of mangrove forests was observed in the Gulf of Carpentaria region of northern Australia. These and other intertidal communities are also extensive along the 7,400 km coastline of north‐eastern Australia. Determination of their floristic composition, potential carbon (C) store and sequestration capacity, and vulnerability to climate extremes is required for their effective conservation management and was the aim of this study.Standardized, state‐wide quantitative classification methods identified five mangrove forest and three saltmarsh communities covering 2,604 km2 along this coastline.Estuarine and oceanic mangrove forests were mapped separately. Carbon storage and sequestration capacity of the intertidal communities and their vulnerability to strong El Niño events were estimated using published data and GIS analyses.An estimated potential 126.2 (± 27.3 SEM) Tg C and 8.3 (±0.4 SD) Tg C were stored in the mangrove forests and saltmarshes, respectively. Comparatively, the rainforests of the region stored an estimated equivalent amount of C but covered three times the area, and the most widespread woodlands (Eucalyptus tetrodonta) of the region stored an estimated 1.5 times the C but covered 16 times the area. The C stored in the intertidal communities was estimated as equivalent to 493.47 Tg of CO2, valued at AU$6.8 billion on the Australian carbon market in December 2018. Annual C sequestration potential was 0.18–0.34 Tg C/year, valued between AU$8.9 and $17 million.Approximately 360 ha of mangrove forest was estimated as lost because of dieback during the 2015–16 El Niño event. Three types of mangrove forest were identified as potentially vulnerable to dieback from El Niño‐driven climate events.This study highlights the national and global significance of these intertidal systems and our findings need to be incorporated in future conservation and development planning of northern Australia. [ABSTRACT FROM AUTHOR]

Global warming with the burgeoning anthropogenic greenhouse gas (GHG) emissions (400 parts per million from 280 ppm CO2 emissions of pre-industrial era) has altered climate, eroding the ecosystem productivity and sustenance of water, affecting the livelihood of people. The anthropogenic activities such as burning fossil fuel, power generation, agriculture, industry, polluting water bodies and urban activities are responsible for increasing GHG footprint of which 72% constitute CO2. GHG footprint needs to be in balance with sequestration of carbon to sustain ecosystem functions. Forests are the major carbon sinks (about 45%) that aid in mitigating global warming. The current research focusses on the carbon budgeting through quantification of emissions and sinks in the forest ecosystems and changes in climatic conditions of Western Ghats. This would help in evolving appropriate mitigation strategies toward sustainable management of forests and mitigate impacts of global warming. The land-use land-cover (LULC) dynamics are the prime driver of climate change due to the loss of carbon sequestration potential as well as emissions. The Western Ghats are one among 36 global biodiversity hotspots and forests in this region sequester atmospheric carbon, which aid in moderating the global climate and sustaining water to ensure water and food security in the peninsular India. Assessment of LULC dynamics using temporal remote sensing data shows the decline of evergreen forest by 5% with an increase in agriculture, plantations and built-up area. The interior or intact forests have declined by 10%, and they are now confined to protected areas. The simulation of likely changes indicates that the region will have only 10% evergreen cover and 17% agriculture, 40% plantations and 5% built-up. Quantification of carbon reveals that the WG forest ecosystem holds 1.23 MGg (million gigagrams or Gt) in vegetation and soils. The annual incremental carbon is about 37,507.3 Gg, (or 37.5 million tons, Mt) and the highest in the forests of Karnataka part of WG. Simulation of the likely changes in carbon content indicates the loss of 0.23 MGg (2018–2031) carbon sequestration potential under business as usual scenario. The conservation scenario depicts an increase in carbon sequestration potential of WG forests with the protection. Sequestered carbon in WG is about INR 100 billion ($1.4 billion) at carbon trading of INR 2142 ($30) per tonne. Large-scale land-cover changes leading to deforestation has contributed to an increase in mean temperature by 0.5°C and decline in rainy days, which necessitates evolving prudent landscape management strategies involving all stakeholders for conservation of ecologically fragile WG. This will enhance the ability of forests to sequester atmospheric carbon and climate moderation, with the sustenance of ecosystem goods and services. [ABSTRACT FROM AUTHOR]

• Mangrove forests of the Western Irrawaddy River Delta decreased dramatically by 45.35% in the past 35 years, and the seaward progradation of mangrove forests can compensate for the loss of 2,812.32 ha. • The rate of mangrove forest prograde seaward in the Western Irrawaddy River Delta is higher than the rate of sea level rise at present. • Human activities are the main driver of landward mangrove forest loss, while sustained large waves exceeding 1 m in height may be a crucial factor in shaping the mangrove forest shoreline in the western Irrawaddy River Delta. Mangrove forests serve as a significant carbon sink and provide effective shoreline protection against devastating winds. However, these forests are facing an unprecedented decline in tropical and subtropical large deltas due to human activities and climate change. This study focuses on quantifying the dynamic changes of mangrove forests in the Western Irrawaddy River Delta (WIDR), which is part of Myanmar's largest delta in Southeast Asia, Remote sensing images from 1988 to 2022 were utilized alongside a machine learning approach to analyze these changes. The findings demonstrate a significant decline of mangrove forests within the WIRD, with a reduction in area by 45.35% over the past 35 years. Additionally, the patches of mangrove forests have become increasingly fragmented. Losses predominantly occurred in the inland regions, while gains were observed along the seaward edges, suggesting progradation towards the sea, which compensated for a net loss of 2,812.32 ha during the study period. The intensification of human activities, specifically deforestation and aquaculture pond utilization, appears to be the leading cause of catastrophic internal degradation within the WIRD's mangrove forests. Contrary to the influence of local sea level rise or variations in suspended sediment discharge into the WIRD, this study suggests that the persistent retreat of mangrove forest fringes is controlled by large waves generated by the southwest monsoon. Estuarine barriers situated in the WIRD act as buffers, dissipating wave energy and facilitating seaward growth. of mangrove forests. Our study reveals a significant pattern in the WIRD, where landward mangrove forest loss coincided with seaward mangrove forest gain. This work underscores the importance of addressing landward mangrove forest loss and recognizing the emergence of seaward gains in the WIRD, providing valuable insights for fostering successful and sustainable mangrove management and protection initiatives. [ABSTRACT FROM AUTHOR]

Under drought conditions, even tropical rainforests might turn from carbon sinks to sources, and tree species composition might be altered by increased mortality. We monitored stem diameter variations of 40 tree individuals with stem diameters above 10 cm belonging to eleven different tree genera and three tree life forms with high-resolution dendrometers from July 2007 to November 2010 and additionally March 2015 to December 2017 in a tropical mountain rainforest in South Ecuador, a biodiversity hotspot with more than 300 different tree species belonging to different functional types. Although our study area receives around 2200 mm of annual rainfall, dry spells occur regularly during so-called "Veranillo del Niño" (VdN) periods in October-November. In climate change scenarios, droughts are expected with higher frequency and intensity as today. We selected dry intervals with a minimum of four consecutive days to examine how different tree species respond to drought stress, raising the question if some species are better adapted to a possible higher frequency and increasing duration of dry periods. We analyzed the averaged species-specific stem shrinkage rates and recovery times during and after dry periods. The two deciduous broadleaved species Cedrela montana and Handroanthus chrysanthus showed the biggest stem shrinkage of up to 2 mm after 10 consecutive dry days. A comparison of daily circumference changes over 600 consecutive days revealed different drought responses between the families concerning the percentage of days with stem shrinkage/increment, ranging from 27.5 to 72.5% for Graffenrieda emarginata to 45–55% for Podocarpus oleifolius under same climate conditions. Moreover, we found great difference of recovery times after longer-lasting (i.e., eight to ten days) VdN drought events between the two evergreen broadleaved species Vismia cavanillesiana and Tapirira guianensis. While Vismia replenished to pre-VdN stem circumference after only 5 days, Tapirira needed 52 days on average to restore its circumference. Hence, a higher frequency of droughts might increase inter-species competition and species-specific mortality and might finally alter the species composition of the ecosystem. [ABSTRACT FROM AUTHOR]

• Compound hot extremes did not exacerbate tree growth across 70% of the forests. • Compound hot extremes have started to exacerbate tree growth decline in forests in dry regions. • Growth reduction by compound hot extremes showed a significant increase over the past decades. Under climate warming, the adverse effects of daytime or nighttime hot extremes on forest productivity have been widely reported. However, the impact of compound hot extremes (i.e., combination of daytime and nighttime hot extremes) on tree growth remains unclear. Combining long-term and large-scale tree-ring width and remote-sensing datasets between 1949 and 2020, we examined and compared the effects of individual and compound hot extremes on tree growth and forest productivity in the Northern Hemisphere. Here we showed that compound hot extremes did not exacerbate tree growth and productivity decline compared with individual daytime hot extremes across 70% of the forested area. However, we observed a stronger adverse effect of compound hot extremes on tree growth and productivity compared with individual daytime hot extremes in dry regions. Due to the increased severity and frequency of compound hot extremes, we predicted that compound hot extremes may impose a greater threat to forest productivity and global carbon cycling as compared to individual hot extremes under future climate change. Our results call for effective policies and actions to mitigate the rapidly growing adverse impact of compound hot extremes on forest ecosystems and carbon cycling. [Display omitted] Compound hot extremes generally exacerbate tree growth decline compared with daytime hot extremes in forests in dry regions but not in humid regions across the Northern Hemisphere, possibly due to the counterbalancing effects of daytime and nighttime hot extremes on water availability. [ABSTRACT FROM AUTHOR]

• We examined effects of tree-size and canopy structural complexity on GPP in forests. • MINoSGI model showed that more complex canopy structures increase GPP. • Proper values for biome-specific foliage shape reduce uncertainty in GPP estimates. • Increased GPP is attributed to an increase in diffuse light fraction within canopy. • MINoSGI is useful to clarify one possible mechanism of complexity-GPP relationships. Late-successional unmanaged forests (or old-growth forests) are important terrestrial carbon sinks. Their structurally complex features have been hypothesized to strongly affect forest productivity. However, the mechanisms through which structural complexity influences forest productivity remain unresolved. Here, we report a set of idealised simulations in boreal, sub-boreal, cool-temperate, warm-temperate and tropical forests using a dynamic model of atmosphere and vegetation interactions (Multilayered Integrated Numerical Model of Surface Physics–Growing Plants Interaction, MINoSGI). We aimed to elucidate the effects of tree–size and canopy structural complexity on stand-scale gross primary productivity (GPP) of old-growth forests over 300-year time series. We assumed the tree-size structures of mature old-growth forests as the initial conditions of the simulations. We focused on three different developmental phases of the forests: 29–48 years (phase I), 77–96 years (phase II) and 277–296 years (phase III) from the start of the simulations. Phase I corresponds to an old-growth forest because of our settings of the initial conditions of the simulations, and phase III to a long-term resultant forest without recruitment or mortality. We show that, for a given biome-specific leaf area index (LAI) and individual foliage shape (η), the greatest difference in GPP (ΔGPP) between forests with the most and least structurally complex canopies was 263 g C m−2 year−1 in phase I and II when old-growth forests with the most complex canopy structures sustained their complexity, equivalent to almost 13 % of the annual GPP. By contrast, the maximum difference in ΔGPP was reduced to 153 g C m−2 year−1 in phase III, equivalent to 8 % of the annual GPP total because the complex canopy structures of old-growth forests without recruitment or mortality approached less multi-layered ones similar to those of less complex and managed forests. Our simulation results indicate that greater tree–size and canopy structural complexity is associated with a broader vertical distribution of foliage, supporting the localisation of leaves in multiple layers. This increases the efficacy of light usage, particularly for shaded leaves receiving only diffuse light within the canopy. As a consequence, for all forest biomes, an increase in in-canopy diffuse light increases GPP in forests with complex canopy structures due to an enhancement of light use efficiency (LUE) of shaded leaves. Overall, our results quantify one of the mechanisms underlying the effects of canopy structural complexity on forest productivity. Moreover, differences in foliage shape between forest biomes can add to uncertainties when predicting GPP based on simulation models. We, therefore, suggest that precise values of the biome-specific factors associated with canopy structure should be employed into simulation models of global carbon budgets. [ABSTRACT FROM AUTHOR]

Climate change is expected to drive increased tree mortality through drought, heat stress, and insect attacks, with manifold impacts on forest ecosystems. Yet, climate-induced tree mortality and biotic disturbance agents are largely absent from process-based ecosystem models. Using data sets from the western USA and associated studies, we present a framework for determining the relative contribution of drought stress, insect attack, and their interactions, which is critical for modeling mortality in future climates. We outline a simple approach that identifies the mechanisms associated with two guilds of insects - bark beetles and defoliators - which are responsible for substantial tree mortality. We then discuss cross-biome patterns of insect-driven tree mortality and draw upon available evidence contrasting the prevalence of insect outbreaks in temperate and tropical regions. We conclude with an overview of tools and promising avenues to address major challenges. Ultimately, a multitrophic approach that captures tree physiology, insect populations, and tree-insect interactions will better inform projections of forest ecosystem responses to climate change. [ABSTRACT FROM AUTHOR]

Climate change alters the regional precipitation pattern and causes seasonal droughts that affect forest growth and belowground carbon cycling. This is expected to create greater oscillations in soil moisture that affect the stability of the soil organic carbon (SOC) pool. This study examined the effects of the precipitation decline on the SOC dynamics by experimentally controlling the throughfall in a Pinus massoniana plantation in subtropical region of China. Soil physicochemical properties were analyzed in topsoil (0–5cm depth) during the dry-cool and the wet-warm season after five consecutive years of ~30% throughfall reduction. We also assessed the SOC stock and its stability, as indicated by the easily oxidizable carbon (EOC) pool, SOC mineralization rates, soil aggregate size distributions and fine root biomass in relation to soil microbial community structure. The throughfall reduction reduced the soil moisture by 15–20% between sampling dates, with an average 18% during the five-year experiment. With throughfall reduction, topsoil SOC stocks significantly increased by 0.18 kg C m-2 or 10%, but fine root biomass, EOC content, and the micro-aggregate fraction were significantly higher, suggesting less stable SOC. The abundance of bacterial r-strategists (e.g. Bacteroidetes, Betaproteobacteria, and Gammaproteobacteria) increased significantly while K-strategists (e.g. Planctomycetes) decreased. Both SOC and EOC mineralization were positively correlated with the abundance of r-strategists, but negatively correlated with the K-strategists abundance. We posit that micro-aggregates, fine root biomass, and altered microbial strategist ratios are associated with the decline in SOC stability in forests with less throughfall. • Five-year ~30% throughfall reduction increased topsoil SOC stock by 10%. • Throughfall reduction reduced SOC biostability by increasing easily oxidizable C. • Fine root biomass and abundance of soil bacterial r-strategists were increased. • Soil microbial community shifted to optimize use of the accumulated SOC. [ABSTRACT FROM AUTHOR]

• New energy balance method predicts surface heating following land cover change • This method can simulate temperature change with different environmental conditions • Shrub encroachment and post-drought piñon mortality heat the surface up to 2oC • Shrub encroachment heating is dominated by reduced albedo and canopy conductance • Aerodynamic conductance explains surface temperature increase after piñon mortality The increase in large-scale land cover change (LCC) in recent decades, particularly in response to climate-driven disturbances, has potential to impact local and regional changes in climate due to modification of carbon sources and sinks, albedo, surface roughness and energy fluxes. Using observational data, we predict the impact of two of the most extensive LCCs occurring in the Southwestern US: drought-induced tree mortality and shrub encroachment into grasslands, on surface temperature. We developed a new energy balance method that extracts the biophysical responses to environmental conditions, to predict how structural changes in albedo, surface roughness and canopy conductance following LCC will alter surface temperature. This method allows us not only to explain the observed differences in surface temperature between two non-adjacent study sites with different environmental conditions, but also to separate the contribution of biophysical and non-biophysical properties to surface temperature. Our results suggest that changes in biophysical properties due to shrub encroachment and tree mortality in the Southwestern US (independent of changes in other environmental properties) can potentially lead to an increase in midday surface temperature (11AM to 2PM) of 1 to 2 degrees Celsius, comparable to changes in surface temperature following deforestation. Although the average surface temperature increase in response to both shrub encroachment and tree mortality is similar, the biophysical properties driving the temperature change are different in each scenario. Change in aerodynamic conductance following tree mortality is the largest contributor to heating, while reduced albedo and canopy conductance drive the increase in surface temperature following shrub encroachment. We also show how this increase in daytime surface temperature could be further intensified with future climate, especially with the expected reduction in soil water availability in the Southwest. [ABSTRACT FROM AUTHOR]

• We explored how subtropical forests respond to changing macro-climate patterns. • Subtropical forests were more sensitive to climate than expected. • Drought limitations were consistent across species and environments. • Drought sensitivity seemed largely related to large-scale climate variability. • Chinese subtropical karst ecosystems could face serious threats by increased warming and drying. Subtropical forests are an important but still poorly understood component of the global carbon cycle and global biodiversity. If climate continues to change as anticipated, increasing drought may affect the composition and structure of many subtropical forests. Understanding the environmental conditions that determine drought sensitivity across subtropical ecosystems and trees species will help accurately predict their response to climate change and inform the best mitigation and protection strategies. To identify the broad-scale drivers of drought sensitivity, we collected a large network of ring-width chronologies along a broad climate gradient that spans from east to west of the Yunnan-Guizhou Plateau (YGP), in southwestern China. Our network includes growth data from 10 trees species in 28 old growth subtropical coniferous sites. We used tree ring analyses, Redundancy Analysis (RDA), and linear mixed effects models to assess how drought responses varied geographically, climatically, and taxonomically. We found that aridity exerted the strongest limitation in our study area, implying that subtropical forest responses to drought may be more complex than commonly assumed. Moreover, we found that drought intensity during dry season, proxied by aridity index, is a stronger driver of drought sensitivity than stand characteristics and microenvironment. Further increases in drought frequency and dry season drought intensity in the region associated with climate change may pose a larger-than-expected threat to the growth, and ultimately persistence, of many subtropical coniferous forests. [ABSTRACT FROM AUTHOR]

Global warming and enhanced [CO2] challenge forests performance, forcing species to adapt in response and acclimate to a new environment. The functional processes involved in carbon and water forest dynamics need to be modelled to understand how forests will respond to global change. Warming could be beneficial for certain species, particularly where species dynamics are limited by temperature. Yet there are multiple examples of forest decline and accelerated mortality in many locations worldwide, triggered by an enhancement in vulnerability to water stress particularly of the least drought-tolerant species. Although increasing [CO2] could counterbalance the negative effect of water stress under certain conditions, the net response of trees to the interaction [CO2] x climate most likely will be negative and dominated by water stress limitations in drought-limited environments. Models need to include the different forcing factors governing plant dynamics at different spatio-temporal scales. In addition they need to simultaneously address hypotheses related to species vulnerability such as 'carbon starvation' and 'hydraulic failure', which are very much linked both to carbon sink and carbon source limitations. Dendrochronological data combine a large temporal (from intra-annual to multicentennial) and spatial coverage. These data have proved very useful to improve our understanding on how both climate and [CO2] interact to determine forest productivity and performance, and to produce more reliable, robust and realistic models. Dendrochronological data can help understand variability in carbon allocation in response to fast and abrupt changes in climate under an atmosphere with unprecedented high [CO2] levels. It is important that models include biologically meaningful non-linear response thresholds to key environmental factors. I will show some applications of different types of dendrochronological data and different forest models, and discuss their use to understand key coupled processes determining forest productivity and water use efficiency on a changing world. This will include examples from classic annual individual growth indices and carbon stable isotopes to stand-based allometric estimates of aboveground woody biomass, combined with other data sources needed to study the C and water cycles in forests. To understand variability in carbon allocation to the stem it is necessary to link other traits and plant processes including leaf and cambial phenology, net photosynthesis and transpiration. We are still far from perfectly addressing the mechanisms determining plant functioning in models, particularly under expected scenarios of high temperatures and [CO2] projected for the next century. For this reason there is much potential in using abundant dendrochronological data combined with other multiproxy data sources to improve models, but there are also different issues that need to be properly discussed given limitations in data and metadata. Discussion is encouraged to overcome shortcomings of current modelling approaches and propose future directions to improve model-data fusion using dendrochronological data to better understand the functional processes that will determine forest dynamics on a changing world. [ABSTRACT FROM AUTHOR]

Two major threats to semi-natural grasslands in temperate zones are 1) the increase of extreme drought events, and 2) nutrient loading due to agricultural fertilization and pollution. These threats may cause shifts in species diversity and abundance and also affect water and carbon ecosystem budgets. Therefore, it is pivotal to understand the impact of drought stress and nutrient addition on ecosystem carbon and water fluxes. Here, we experimentally investigated the combined effect of nitrogen addition (N) and simulated extreme drought (D) on the water and carbon fluxes of a semi-natural temperate grassland, located in Freiburg (South Germany). The semi-natural grassland was exposed to four different treatments: I) control C, II) nitrogen addition N, III) simulated extreme drought CD, IV) and the combination of nitrogen addition and simulated extreme drought ND. In order to study the response of the grassland, we combined eddy covariance techniques with open gas exchange systems and laser-based spectroscopy of water isotopologues, which are powerful tools to partition evapotranspiration and to trace water movements in plants, communities and ecosystems. Vegetation parameters were described by species richness, species abundance and leaf area index. Our results suggest that grassland communities, strongly changed in their species composition by nitrogen addition, can substantially lose their function as carbon sink during dry periods, while simulated extreme drought even increased this effect. This effect was linked to a loss in forb species (–25%) and to a strong dominance of grass species due to nitrogen loading. The grass dominated community suffered from a strong above-ground dieback in the dry summer months caused by a lower water use efficiency and weaker adaptations to drought of the community. Over the vegetation period (April-September) the carbon sequestration in our system was relative to the control group reduced by more than 60 % as a consequence to nitrogen addition, in combination with simulated extreme drought even by 73 %. Eutrophication can substantially decrease the carbon sink function of grassland communities, in particular when drought periods will increase under future climate conditions. Future management plans should stress on reducing human caused nitrogen input into grassland systems and tackle other threats to species richness. [ABSTRACT FROM AUTHOR]