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Location of the East Asian monsoon region. The red circle and inner blue lines represent the East Asian monsoon region. The yellow arrows represent the Western Pacific subtropical high, Siberian high and Indian Ocean high. The green region indicates the Tibetan Plateau (9).
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Understanding the location of carbon sources and sinks is essential for accurately predicting future changes in atmospheric carbon dioxide and climate. Mid- to high-latitude terrestrial ecosystems are well known to be the principal carbon sink regions, yet less attention has been paid to the mid- to low-latitude ecosystems. In this stu...
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... the location of carbon sources and sinks and the underlying driving forces at scales ranging from local to global is crucial for accurately predicting future changes in atmospheric carbon dioxide and climate, and is helpful for defining management options for the global carbon cycle (1). In the Northern Hemisphere, mid- to high-latitude (40 – 60°N) terrestrial ecosystems have been shown to be carbon sink regions (2, 3), with a high carbon uptake by the large areas of temperate and boreal forests that are distributed from North America to Asiatic Russia (4). Tropical (0 – 20°N) forests in the Neotropics (5) and Africa (6) are also found to be carbon sinks. Conversely, the mid- to low-latitudes (20 – 40°N) of the American, European, and African continents include large areas under the control of the subtropical anticyclone that prevailing desert, steppe, and shrub ecosystems, such as the Sahara Desert, the Sonoran Desert, and the North American Prairie. Interestingly, the subtropical anticyclone zone also contains distinctive subtropical forests in the southeastern United States and East Asian monsoon region. There are large areas of subtropical forests in the East Asian monsoon region that benefit from the uplift of the Tibetan Plateau and the water supply furnished by the East Asian monsoon ( SI Appendix , Fig. S1). The Tibetan Plateau (mean eleva- tion over 4,000 m), acting as a strong heat source in summer, generates upward airflow motions over its eastern flank that, combined with large amounts of moisture from the tropics, result in strong monsoons and wet climate in East Asia (7, 8). The approximate location of the East Asian monsoon region is latitude 20 – 40°N, longitude 100 – 145°E. This region includes the eastern part of China and the southern parts of Japan and Korea (9), and is characterized by wet, warm summer and dry, mild winter. The East Asian summer monsoon can bring large amounts of water vapor from the Pacific and Indian Oceans to the conti- nent in summer, and the East Asian winter monsoon, driven by the Siberian high, brings large amounts of cold air to the con- tinent in winter (Fig. 1). Forests in this region are typically com- posed of subtropical evergreen broad-leaved, deciduous broad- leaved, and mixed stands (10). Moderate resolution imaging spectroradiometer (MODIS) land-cover estimates indicate that the area of forest in the East Asian monsoon region increased from 2001 to 2010 ( SI Appendix , Fig. S2). Furthermore, nitrogen deposition in this region has increased significantly, and it has been predicted to be one of the areas with the largest future increase in nitrogen deposition (11) ( SI Appendix , Fig. S3). These changes are expected to cause a large carbon dioxide uptake by the forests in the East Asian monsoon region; however, there are limited data regarding the role of these forests in the global carbon cycle. Here, we present estimates of the forest net ecosystem productivity (NEP) in the East Asian monsoon region based on a compilation of field observations using the eddy covariance technique during the period of the 1990s and 2000s. We analyzed 467 NEP records of 106 forest sites from ChinaFlux, AsiaFlux, AmeriFlux, CarboEurope, and other networks, covering latitudes from 2° to 70°N and longitudes from 147°W to 143°E in the Northern Hemisphere ( SI Appendix , Fig. S4 and Table S1). To better understand the importance of low-latitude Asian forests to the Northern Hemisphere land carbon uptake, we further investigated the determinants of NEP in the region and evalu- ated their impacts on NEP by comparing our eddy-covariance estimates with the results of three process-oriented models [Lund-Potsdam-Jena (LPJ) (12), Organizing Carbon and Hy- drology In Dynamic Ecosystems (ORCHIDEE) (13), Commu- nity Land Model version 4-Carbon Nitrogen (CLM4CN) (14)] that have been used extensively in global terrestrial carbon flux evaluations ( Materials and Methods ). By analyzing the latitudinal distribution of gross primary productivity (GPP), ecosystem respiration (RE), and NEP (Fig. 2), we found that the East Asian monsoon forests from 20°N to 40°N had the highest average NEP (Fig. 2 B ). The NEP values from 20°N to 30°N and from 30°N to 40°N reached 341 ± 67 ( n = 4) and 368 ± 45 g C m − 2 yr − 1 ( n = 14) (mean ± 1 SE), respectively, which are significantly higher than the corresponding values at low latitudes (0 – 20°N, 63 ± 52 g C m − 2 yr − 1 , n = 5, P < 0.05) and high latitudes (50 – 70°N, 127 ± 34 g C m − 2 yr − 1 , n = 6, P < 0.05) in Asia (Fig. 2 and SI Appendix , Table S2). Compared with average forest NEP at the same latitudes, the NEP of the East Asian monsoon forests is significantly higher than that of the Europe – Africa ( n = 2, P < 0.05) (Fig. 3). The average NEP is close to the value measured in subtropical forests of the southeastern United States ( n = 3, P > 0.05 ) (Fig. 3), but the latter forests exhibit a larger spatial variation in NEP from available eddy covariance data (Fig. 3). The magnitude of NEP in the East Asian monsoon region is comparable to the average NEP measured in intensively managed Western European forests between 40°N and 60°N (392 ± 47 g C m − 2 yr − 1 , n = 19) but much higher than the average NEP of Asian (157 ± 28 g C m − 2 yr − 1 , n = 11) and North American forests (180 ± 33 g C m − 2 yr − 1 , n = 28) between 40°N and 60°N (Fig. 3). A deeper understanding of the driving forces underlying the high NEP values in the East Asian monsoon region is critical for understanding the mechanisms that control the terrestrial carbon cycle and the sustainability of the current carbon uptake. Previous studies indicated that recovery from past disturbance coupled to changes in disturbance regimes, plays an important role in controlling NEP variations (15 – 17). Because the age structure of a forest is a simple and direct proxy for time since disturbance, we analyzed how forest age affects NEP. Integrating site-level, directly observed NEP, and forest age data, we found that NEP shows a clearly decreasing relationship with increasing forest age, although variation occurred within the age bands (Fig. 4 A ). Maximum NEP is observed in forests of less than 50 y, a phe- nomenon that is most likely a result of the high level of photo- synthesis by young forests to produce biomass and structure that are consistently observed in tropical to boreal forests (18 – 20). In young forests, net primary productivity (NPP) exceeds heterotrophic respiration ( R h ), resulting in high NEP, whereas in older stands, NPP may decline while R h continues to increase because of the accumulation of detritus and soil organic matter from earlier production (21). Fig. 5 A illustrates that the average stand age in the East Asian monsoon forests with eddy-covariance measurements, is significantly younger than those forests measured at other latitudes. At the regional scale, intensive afforestation and reforestation indeed have been conducted in the East Asian monsoon region since the 1960s. In particular, the area of plantation forest increased to 38.22 Mha and the area ...
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... Subtropical forests, which often feature complex topography, encompass a quarter of China's land area [23,24], holding significant ecological importance. These forests are among the world's most productive ecosystems, playing crucial roles in regulating global and regional climates and biogeochemical cycles [25][26][27]. Additionally, the forests provide essential services like wood production and non-wood products, directly impacting human livelihoods. ...
Exploring the relationship between topography and forest multifunctionality enhances understanding of the mechanisms maintaining forest multifunctionality and proves beneficial for managing overall forest functions across different landscapes. Leveraging census data from a 20 ha subtropical forest plot, we investigated the topographic variations in individual functions, multifunctionality, and their interrelationships. Our results revealed that relative to lower elevations, higher elevations had higher woody productivity, sapling growth, and recruitment that drove higher average forest multifunctionality (FMA). However, forest multifunctionality at the 50% threshold level (FMt50) had no significant difference between high and low elevations. Compared with the valley and slope, higher woody productivity, higher sapling recruitment, and higher soil organic carbon stock drove higher forest multifunctionality (FMA and FMt50) in the ridge. These results indicate the ridge serves as a forest multifunctionality “hotspot” within the Tiantong 20 hm2 plot. Additionally, relative to the low elevation, the degree of synergy among functions at the high elevation was significantly lower, indicating difficulties in attaining high forest multifunctionality at the high elevation. Our work underscores the importance of topography in regulating subtropical forest multifunctionality and relationships between forest functions at a local scale, suggesting that future forest management strategies (such as regulating synergistic or trade-off relationships between functions) should give particular attention to topographic conditions.
... Our agecalibrated parameters increase NBP by an average of 50 gC m 2 yr 1 across all forests, especially in the BoNE type, the NBP increased by 118 gC m 2 yr 1 on average, increasing the estimate of the carbon sink in young forests. Such underestimation of NBP under SS assumption is also supported by Ge et al. (2018) and Yu et al. (2014). It should be noted that we did not calibrate the parameters affecting heterotrophic respiration, thus the NBP may be biased. ...
Many land surface models (LSMs) assume a steady‐state assumption (SS) for forest growth, leading to an overestimation of biomass in young forests. Parameters inversion under SS will potentially result in biased carbon fluxes and stocks in a transient simulation. Incorporating age‐dependent biomass into LSMs can simulate real disequilibrium states, enabling the model to simulate forest growth from planting to its current age, and improving the biased post‐calibration parameters. In this study, we developed a stepwise optimization framework that first calibrates “fast” light‐controlled CO2 fluxes (gross primary productivity, GPP), then leaf area index (LAI), and finally “slow” growth‐controlled biomass using the Global LAnd Surface Satellite (GLASS) GPP and LAI products, and age‐dependent biomass curves for the 25 forests. To reduce the computation time, we used a machine learning‐based model to surrogate the complex integrated biosphere simulator LSM during calibration. Our calibrated model led to an error reduction in GPP, LAI, and biomass by 28.5%, 35.3% and 74.6%, respectively. When compared with net biome productivity (NBP) using no‐age‐calibrated parameters, our age‐calibrated parameters increased NBP by an average of 50 gC m⁻² yr⁻¹ across all forests, especially in the boreal needleleaf evergreen forests, the NBP increased by 118 gC m⁻² yr⁻¹ on average, increasing the estimate of the carbon sink in young forests. Our work highlights the importance of including forest age in LSMs, and provides a novel framework for better calibrating LSMs using constraints from multiple satellite products at a global scale.
... First, evaluations of terrestrial ecosystem carbon are usually conducted at large scales, such as continents (Winkler et al. 2023), countries (Uchale et al. 2023) and provinces (Ran et al. 2023), and the resolution is often not high. Additionally, due to the use of different data sources and models, such as the Ecosystem process modelling method (He et al. 2019), the Atmospheric inversion method , the Eddy covariance method (Yu et al. 2014) and the Inventory method (Piao et al. 2009), the amount of carbon sink/ source in China still faces significant uncertainties; carbon sink values varied between 0.1 Pg C/yr and higher than 1.0 Pg C/yr (Chuai et al. 2018). For calculating anthropogenic carbon emissions, both the 'top-down' and 'bottom-up' methods are used, each with advantages and disadvantages. ...
Cities are main carbon emissions generators. Land use changes can not only affect terrestrial ecosystems carbon, but also anthropogenic carbon emissions. However, carbon monitoring at a spatial level is still coarse, and low-carbon land use encounters the challenge of being unable to adjust at the patch scale. This study addresses these limitations by using land-use data and various auxiliary data to explore new methods. The approach involves developing a high-resolution carbon monitoring model and investigating a patch-scale low-carbon land use model by integrating high carbon sink/source images with the Future Land Use Simulation model. Between 2000 and 2020, the results reveal an increasing trend in both carbon emissions and carbon sinks in the Shangyu district. Carbon sinks can only offset approximately 3% of the total carbon emissions. Spatially, the north exhibits net carbon emissions, while the southern region functions more as a carbon sink. A total of 14.5% of the total land area witnessed a change in land-use type, with the transfer-out of cropland constituting the largest area at 96.44 km², accounting for 50% of the total transferred area. Land-use transfer resulted in an annual increase of 77.72 × 10⁴ t in carbon emissions between 2000 and 2020. Through land-use structure optimisation, carbon emissions are projected to increase by only 7154 t C/year from 2000 to 2030, significantly lower than the amount between 2000 and 2020. Further low-carbon land optimisation at the patch scale can enhance the carbon sink by 129.59 t C/year. The conclusion drawn is that there is considerable potential to reduce carbon emissions through land use control. The new methods developed in our study can effectively contribute to high-resolution carbon monitoring in spatial contexts and support low-carbon land use, promoting the application of low-carbon land use from theory to practice. This will provide technological guidance for land use planning, city planning, and so forth.
... Wood harvest might introduce a large carbon uptake signal in atmospheric inversion models as the harvested carbon is likely transported and decays far away from the producing area 36 . Therefore, the carbon sink signal derived from eddy-flux and atmospheric inversion approaches might be high in timber-producing regions 37,38 , which is typical in the southern and southeast China where the Fast-Growing and High-Yielding Timber Base Construction Program has been implemented targeting at timber production 35 . We quantified the carbon stored in the wood product pool and the additional carbon that can be sequestrated by implementing appropriate forest management practices. ...
... Forest ecosystems, which cover about 30 % of the global land area (Forzieri et al., 2022), are one of the main terrestrial carbon sinks (Mathias and Trugman, 2022;Pan et al., 2011) through photosynthesis (Beer et al., 2010). China's forest ecosystems, with an area of approximately 1.95 × 10 6 km 2 , are mainly distributed in the subtropical regions, which are an important component of the global forest ecosystem and crucial to the global and regional climate system Yu et al., 2014). However, China is still one of the world's top emitters of greenhouse gases that directly contribute to global warming (Friedlingstein et al., 2022;Yu et al., 2014). ...
... China's forest ecosystems, with an area of approximately 1.95 × 10 6 km 2 , are mainly distributed in the subtropical regions, which are an important component of the global forest ecosystem and crucial to the global and regional climate system Yu et al., 2014). However, China is still one of the world's top emitters of greenhouse gases that directly contribute to global warming (Friedlingstein et al., 2022;Yu et al., 2014). Gross primary productivity (GPP) is an important indicator reflecting ecosystem carbon sequestration capacity, which drives terrestrial carbon sequestration and partially offsets anthropogenic CO 2 emissions. ...
... Gross primary productivity (GPP) is an important indicator reflecting ecosystem carbon sequestration capacity, which drives terrestrial carbon sequestration and partially offsets anthropogenic CO 2 emissions. Therefore, precise quantification of China's subtropical forest GPP and understanding of its driving mechanisms are of great importance for scientists and policy makers to mitigate climate change and carbon emissions with the carbon sink potential of Chinese subtropical forests Yu et al., 2014). ...
The subtropical forests of China play a pivotal role in the global carbon cycle and in regulating the global climate. Quantifying the individual and combined effects of forest cover change (FCC), vegetation structural change (e.g. leaf area index (LAI)), CO 2 fertilisation, and climate change (CC) on the annual gross primary productivity (GPP) dynamics of different subtropical forest types are essential for mitigating carbon emissions and predicting future climate changes, but these impacts remain unclear. In this study, we used a processed-based model to comprehensively investigate the impacts of these factors on GPP variations with a series of model experiments in China's subtropical forests from 2001 to 2018. Simulated GPP showed a significant increasing trend (20.67 g C m −2 yr −1 , p < 0.001) under the interaction effects of FCC, LAI change, rising CO 2 , and CC. The CO 2 fertilisation (6.84 g C m −2 yr −1 , p < 0.001) and LAI change (3.79 g C m −2 yr −1 , p = 0.004) were the two dominant drivers of total subtropical forest GPP increase , followed by the effects of FCC (0.52 g C m −2 yr −1 , p < 0.001) and CC (0.92 g C m −2 yr −1 , p = 0.080). We observed different responses to drivers depending on forest types. The evergreen broad-leaved forests showed the maximum carbon sequestration rate due to the positive effects of all drivers. Both the FCC (0.19 g C m −2 yr −1 , p < 0.05) and CC (1.22 g C m −2 yr −1 , p < 0.05) significantly decreased evergreen needle-leaved forest GPP, while their negative effects were almost offset by the positive impact of LAI changes. Our results indicated that LAI outweighed FCC in promoting GPP, which is an essential driver that needs to be accounted for in studies and ecological and management programmes. Overall, our study offers a novel perspective on different drivers of subtropical forest GPP changes and provides valuable information for policy makers to better manage subtropical forests to mitigate climate change risks.
... Subtropical forests, renowned for their high carbon sink capacity (Wei & Xia, 2024;Yu et al., 2014), are projected to face an increased risk of more frequent droughts (IPCC, 2022). Subtropical forest canopy trees exhibit higher drought resistance than other biomes (Huang & Xia, 2019), benefiting from sufficient rainfall and wellestablished root systems (Pivovaroff et al., 2021). ...
Subtropical forests, recognized for their intricate vertical canopy stratification, exhibit high resistance to extreme drought. However, the response of leaf phenology to drought in the species‐rich understory remains poorly understood. In this study, we constructed a digital camera system, amassing over 360,000 images through a 70% throughfall exclusion experiment, to explore the drought response of understory leaf phenology. The results revealed a significant advancement in understory leaf senescence phenology under drought, with 11.75 and 15.76 days for the start and end of the leaf‐falling event, respectively. Pre‐season temperature primarily regulated leaf development phenology, whereas soil water dominated the variability in leaf senescence phenology. Under drought conditions, temperature sensitivities for the end of leaf emergence decreased from −13.72 to −11.06 days °C ⁻¹ , with insignificance observed for the start of leaf emergence. Consequently, drought treatment shortened both the length of the growing season (15.69 days) and the peak growth season (9.80 days) for understory plants. Moreover, this study identified diverse responses among intraspecies and interspecies to drought, particularly during the leaf development phase. These findings underscore the pivotal role of water availability in shaping understory phenology patterns, especially in subtropical forests.
... At present, plants are the main means of controlling carbon neutrality [8], plants absorb carbon dioxide in the atmosphere through photosynthesis [9], convert it into organic matter, and convert the absorbed carbon into biomass [10], such as trees, leaves, roots, etc., and store a lot of carbon in the plant body. For example, forest carbon sequestration [11], through forest restoration and afforestation projects, has increased a large amount of forest [12] and vegetation cover globally and improved the carbon sequestration capacity of plants [13]. In addition to forests, other types of vegetation, such as grasslands, wetlands, and farmland, release organic matter through their roots as they grow, which can improve the texture and structure of the soil, promote more carbon storage, and reduce the concentration of carbon dioxide in the atmosphere. ...
... For carbon dioxide, some plants can be used as indicator plants to indirectly reflect the content or concentration of carbon dioxide in the environment because of their physiological characteristics or reaction mechanisms [13]. These plants usually exhibit special physiological or morphological changes in high carbon dioxide concentrations. ...
... Marine carbon neutral governance aims to protect Marine ecosystems, promote Marine carbon uptake and storage, and reduce climate change impacts such as ocean acidification and sea level rise. In continental areas, forests can greatly increase carbon storage in continental areas;Water areas such as lakes and rivers can increase aquatic plant cover to enhance the carbon fixation capacity of water bodies; In desert areas, some drought-tolerant plants, such as cactus and desert willow, are adapted to dry environments and can grow in poorer soils [13]. These plants are able to fix carbon under extreme conditions and can be used to prevent soil erosion and increase carbon storage by growing adaptable plants. ...
The sustainability of life on Earth is facing an escalating threat from climate change. The greenhouse effect, which is one of the primary causes of this perilous change, has resulted in detrimental consequences such as ocean acidification, biodiversity loss, climate disasters, and adverse economic and social impacts. As climate change continues to progress, its effects are expected to broaden and intensify. Consequently, countries and the international community are collaborating to mitigate climate change and promote measures for carbon neutrality and sustainable development. By achieving carbon neutrality, the world can decelerate the rate of climate change and biodiversity, foster sustainable development, and establish a healthier and more sustainable environment.Among the various methods employed to attain carbon neutrality, plant carbon sequestration stands out as a primary approach. Studying the impact and potential of plants in achieving carbon neutrality holds immense significance. In this review, I provide a comprehensive overview of the current state of plant carbon sequestration from diverse perspectives, explore the role of different plants in accomplishing carbon neutrality, and analyze the future potential of plants in mitigating the greenhouse effect and addressing climate change. Simultaneously, this review delves into the feasibility and relevant measures of integrating plants with other fields to collectively combat the greenhouse effect and promote carbon neutrality.
... Wood harvest might introduce a large carbon uptake signal in atmospheric inversion models as the harvested carbon is likely transported and decays far away from the producing area 36 . Therefore, the carbon sink signal derived from eddy-flux and atmospheric inversion approaches might be high in timber-producing regions 37,38 , which is typical in the southern and southeast China where the Fast-Growing and High-Yielding Timber Base Construction Program has been implemented targeting at timber production 35 . We quantified the carbon stored in the wood product pool and the additional carbon that can be sequestrated by implementing appropriate forest management practices. ...
Forest carbon sequestration capacity in China remains uncertain due to underrepresented tree demographic dynamics and overlooked of harvest impacts. In this study, we employ a process-based biogeochemical model to make projections by using national forest inventories, covering approximately 415,000 permanent plots, revealing an expansion in biomass carbon stock by 13.6 ± 1.5 Pg C from 2020 to 2100, with additional sink through augmentation of wood product pool (0.6-2.0 Pg C) and spatiotemporal optimization of forest management (2.3 ± 0.03 Pg C). We find that statistical model might cause large bias in long-term projection due to underrepresentation or neglect of wood harvest and forest demographic changes. Remarkably, disregarding the repercussions of harvesting on forest age can result in a premature shift in the timing of the carbon sink peak by 1–3 decades. Our findings emphasize the pressing necessity for the swift implementation of optimal forest management strategies for carbon sequestration enhancement.
... Terrestrial ecosystems play a fundamental role in counteracting increasing CO 2 concentrations in Earth's atmosphere 1,2 . The net uptake of CO 2 by terrestrial ecosystems shows a geographical pattern (denoted here by net ecosystem productivity, NEP), with a peak in NEP in subtropical and temperate forests 3 . Similar to latitude, the elevation gradient has long been considered to exert an important physical control on vegetation, which can be traced back to Alexander von Humboldt in the nineteenth century 4 , or even earlier. ...
The elevation gradient has long been known to be vital in shaping the structure and function of terrestrial ecosystems, but little is known about the elevation-dependent pattern of net CO2 uptake, denoted by net ecosystem productivity (NEP). Here, by analyzing data from 203 eddy covariance sites across China, we report a negative linear elevation-dependent pattern of NEP, collectively shaped by varying hydrothermal factors, nutrient supply, and ecosystem types. Furthermore, the NEP shows a higher temperature sensitivity in high-elevation environments (3000–5000 m) compared with the lower-elevation environments (<3000 m). Model ensemble and satellite-based observations consistently reveal more rapid relative changes in NEP in high-elevation environments during the last four decades. Machine learning also predicts a stronger relative increase in high-elevation environments, whereas less change is expected at lower elevations. We therefore conclude a varying elevation-dependent pattern of the NEP of terrestrial ecosystems in China, although there is significant uncertainty involved.
... Climate change has a profound impact on the growth dynamics of tree species and forest carbon sequestration capacity (IPCC, 2021). Subtropical forests in middle and low latitudes have an advanced ability to absorb carbon dioxide (Yu et al., 2014), but their structure, species composition, and functioning have recently undergone significant changes . Therefore, understanding the relationship between tree growth and environmental factors is essential for evaluating the carbon sequestration potential and ensuring the ecological functioning and services of subtropical forest ecosystems. ...
... Subtropical evergreen broad-leaved forests (EBFs) are mainly found in the subtropical region of southern China with its humid monsoon climate, where they represent the dominant forest type , covering approximately a quarter of the country's land area (Huang et al., 2012;Song et al., 2022). EBFs constitute 6 % of the global forest area and contribute to 8 % of the global net ecosystem productivity (Yu et al., 2014;Keenan et al., 2015). In the Ailao Mountains of central Yunnan province in southwestern China, the mid-montane moist EBF provides a unique research site that shares similar ecological traits compared with lowland subtropical EBFs (Song et al., 2017), but occurs in warm-temperate to temperate climates (Zhu, 2016). ...
