Carbon Sink Research Articles

Influence of Tree Community Characteristics on Carbon Sinks in Urban Parks: A Case Study of Xinyang, China

Influence of Tree Community Characteristics on Carbon Sinks in Urban Parks: A Case Study of Xinyang, China

Widespread slow growth of acquisitive tree species.

Trees are an important carbon sink as they accumulate biomass through photosynthesis1. Identifying tree species that grow fast is therefore commonly considered to be essential for effective climate change mitigation through forest planting. Although species characteristics are key information for plantation design and forest management, field studies often fail to detect clear relationships between species functional traits and tree growth2. Here, by consolidating four independent datasets and classifying the acquisitive and conservative species based on their functional trait values, we show that acquisitive tree species, which are supposedly fast-growing species, generally grow slowly in field conditions. This discrepancy between the current paradigm and field observations is explained by the interactions with environmental conditions that influence growth. Acquisitive species require moist mild climates and fertile soils, conditions that are generally not met in the field. By contrast, conservative species, which are supposedly slow-growing species, show generally higher realized growth due to their ability to tolerate unfavourable environmental conditions. In general, conservative tree species grow more steadily than acquisitive tree species in non-tropical forests. We recommend planting acquisitive tree species in areas where they can realize their fast-growing potential. In other regions, where environmental stress is higher, conservative tree species have a larger potential to fix carbon in their biomass.

Global greenhouse gas reconciliation 2022

Abstract. In this study, we provide an update on the methodology and data used by Deng et al. (2022) to compare the national greenhouse gas inventories (NGHGIs) and atmospheric inversion model ensembles contributed by international research teams coordinated by the Global Carbon Project. The comparison framework uses transparent processing of the net ecosystem exchange fluxes of carbon dioxide (CO2) from inversions to provide estimates of terrestrial carbon stock changes over managed land that can be used to evaluate NGHGIs. For methane (CH4), and nitrous oxide (N2O), we separate anthropogenic emissions from natural sources based directly on the inversion results to make them compatible with NGHGIs. Our global harmonized NGHGI database was updated with inventory data until February 2023 by compiling data from periodical United Nations Framework Convention on Climate Change (UNFCCC) inventories by Annex I countries and sporadic and less detailed emissions reports by non-Annex I countries given by national communications and biennial update reports. For the inversion data, we used an ensemble of 22 global inversions produced for the most recent assessments of the global budgets of CO2, CH4, and N2O coordinated by the Global Carbon Project with ancillary data. The CO2 inversion ensemble in this study goes through 2021, building on our previous report from 1990 to 2019, and includes three new satellite inversions compared to the previous study and an improved managed-land mask. As a result, although significant differences exist between the CO2 inversion estimates, both satellite and in situ inversions over managed lands indicate that Russia and Canada had a larger land carbon sink in recent years than reported in their NGHGIs, while the NGHGIs reported a significant upward trend of carbon sink in Russia but a downward trend in Canada. For CH4 and N2O, the results of the new inversion ensembles are extended to 2020. Rapid increases in anthropogenic CH4 emissions were observed in developing countries, with varying levels of agreement between NGHGIs and inversion results, while developed countries showed a slowly declining or stable trend in emissions. Much denser sampling of atmospheric CO2 and CH4 concentrations by different satellites, coordinated into a global constellation, is expected in the coming years. The methodology proposed here to compare inversion results with NGHGIs can be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objectives of their pledges. The dataset constructed for this study is publicly available at https://doi.org/10.5281/zenodo.13887128 (Deng et al., 2024).

Ecological Impact of Spartina alterniflora Control Methods on Tiaozini Wetland Against the Background of Carbon Neutrality

The Tiaozini wetland is an important part of the Yancheng Coastal Wetland, which is a World Natural Heritage Site. With the invasion of Spartina alterniflora, the ecology of the wetland has been severely damaged. The local government has carried out an ecological project to remove Spartina alterniflora, but the long-term influence of ecological projects is unknown. In order to explore the overall impact of ecological restoration projects, the soil at different depths (0~20 cm, 20~40 cm, 40~60 cm) was collected in the plowing area, flooding area, and suaeda area of the Tiaozini wetland. Then, the physicochemical properties and the microbial community of the soil were comprehensively analyzed. The Tiaozini wetland has made satisfactory progress in controlling Spartina alterniflora. And the results show that Tiaozini wetland still plays an important role in carbon sequestration, with the soil organic carbon density ranging from 34.23 ± 0.02 kg/m2 to 56.07 ± 0.04 kg/m2, which makes it an important blue carbon sink. The high salinity and invasion of Spartina alterniflora inhibit soil nitrogen, phosphorus cycling, and soil enzyme activities. In addition, plowing destroys the microbial structure and reduces the biodiversity of the soil. While the integrated management method has little negative impact on the microbial communities of soil, the invasion of Spartina alterniflora can lead to the accumulation of heavy metals in the environment. Accordingly, this paper further reveals that regional heavy metals are all lower than the background value, but the (potential ecological risk factor of heavy metals) of Cd reached 21.35, indicating a high risk. Furthermore, this paper provides a scientific basis for the government to control Spartina alterniflora, as well as focusing on the overall impact of treatment methods on environmental factors and microorganisms.

Spatiotemporal Evolution and Influencing Factors of Carbon Footprint in Yangtze River Economic Belt

As an important engine of China’s development, the Yangtze River Economic Belt faces the dual contradiction of economic growth and ecological protection. Addressing the insufficient analysis of the spatiotemporal evolution and driving mechanisms of city-level carbon footprints, this study delves into the concept of carbon footprint from the perspective of ecological footprint theory and carbon cycle dynamics. Using ODIAC and NPP data, it systematically evaluates carbon footprints across 130 cities and examines their spatiotemporal evolution and driving factors using kernel density estimation and the Kaya-LMDI model. The results show (1) a significant growth trend in carbon footprint, with rapid expansion from 2000 to 2012, followed by fluctuating growth from 2012 to 2022; (2) a west-to-east “low–high” spatial pattern, where disparities have narrowed but absolute gaps continue to widen, leading to polarization; and (3) economic growth and urban expansion as the primary drivers of carbon footprint growth, while ecological land use pressure and carbon sequestration capacity played a major role in mitigation, with the impact of carbon sequestration foundations remaining limited. This study conducts precise regional carbon sink accounting and offers a new perspective on the quantitative analysis of carbon footprint drivers. The findings provide insights for low-carbon governance and sustainable urban development in the Yangtze River Economic Belt.

Consistency of global carbon budget between concentration- and emission-driven historical experiments simulated by CMIP6 Earth system models and suggestions for improved simulation of CO2 concentration

Abstract. Anthropogenically emitted CO2 from fossil fuel use and land use change is partly absorbed by terrestrial ecosystems and the ocean, while the remainder retained in the atmosphere adds to the ongoing increase in atmospheric CO2 concentration. Earth system models (ESMs) can simulate such dynamics of the global carbon cycle and consider its interaction with the physical climate system. The ESMs that participated in the Coupled Model Intercomparison Project phase 6 (CMIP6) performed historical simulations to reproduce past climate–carbon cycle dynamics. This study investigated the cause of CO2 concentration biases in ESMs and identified how they might be reduced. First, we compared simulated historical carbon budgets in two types of experiments: one with prescribed CO2 emissions (the emission-driven experiment, “E-HIST”) and the other with a prescribed CO2 concentration (the concentration-driven experiment, “C-HIST”). Because the design of CMIP7 is being considered, it is important to explore any differences or implications associated with such variations. The findings of this confirmed that the multi-model means of the carbon budgets simulated by one type of experiment generally showed good agreement with those simulated by the other. However, the multi-model average of cumulative compatible fossil fuel emission diagnosed from the C-HIST experiment was lower by 35 PgC than that used as the prescribed input data to drive the E-HIST experiment; the multi-model average of the simulated CO2 concentration for 2014 in E-HIST was higher by 7 ppmv than that used to drive C-HIST. Regarding individual models, some showed a distinctly different magnitude of ocean carbon uptake from C-HIST because the E-HIST setting allows ocean carbon fluxes to be dependent on land carbon fluxes via CO2 concentration. Second, we investigated the potential linkages of two types of carbon cycle indices: simulated CO2 concentration in E-HIST and compatible fossil fuel emission in C-HIST. It was confirmed quantitatively that the two indices are reasonable indicators of overall model performance in the context of carbon cycle feedbacks, although most models cannot accurately reproduce the cumulative compatible fossil fuel emission and thus cannot reproduce the CO2 concentration precisely. Third, analysis of the atmospheric CO2 concentration in five historical eras enabled the identification of periods that caused the concentration bias in individual models. Fourth, it is suggested that this non-CO2 effect is likely to be the reason why the magnitude of the natural land carbon sink in historical simulations is difficult to explain based on analysis of idealized experiments. Finally, accurate reproduction of land use change emission is critical for better reproduction of the global carbon budget and CO2 concentration. The magnitude of simulated land use change emission not only affects the level of net land carbon uptake but also determines the magnitude of the ocean carbon sink in the emission-driven experiment. This study confirmed that E-HIST enables an evaluation of the full span of the uncertainty range covering the entire carbon–climate system and allows for an explicit simulation of the interlinking process of the carbon cycle between land and ocean. By isolating the forced responses and feedback processes of the carbon cycle processes, the usefulness of C-HIST in elucidating climate–carbon cycle systems and in identifying the cause of CO2 biases was confirmed.

Expanding the potential soil carbon sink: unraveling carbon sequestration accessory genes in vermicompost phages.

The compost microbiome is important in regulating soil carbon sequestration. However, there is limited information concerning phage communities and phage-encoded auxiliary metabolic genes (AMGs) in compost-applied soils. We combined metagenomics and meta-viromes to explore the potential role of bacterial and phage communities in carbon sequestration in the compost microbiome. The experiment comprised swine manure compost (SW) and vermicompost (VE) applied to the soil along with a control treatment (CK). The bacterial community richness decreased after swine manure application and increased after vermicomposting compared to the control treatment. The phage community in the vermicompost-applied soil was dominated (63.1%) by temperate phages. In comparison, the communities of the swine manure compost-applied soil (92.7%) and control treatments (75.4%) were dominated by virulent phages. Phage-encoded carbon sequestration AMGs were detected in all three treatments, with significant enrichment in the vermicompost-applied soil. The average carbon sequestration potential (the coverage ratio of phage AMGs:total genes) of phage AMGs (aceF, GT11, and GT6) in the vermicompost-applied soil (65.18%) was greater than in the swine manure-applied (0) and control soils (50.21%). The results highlight the role of phage-encoded AMGs in improving soil carbon sequestration in vermicompost-applied soil. The findings provide new avenues for increasing soil carbon sequestration.IMPORTANCEThe phage-bacteria interactions have a significant impact on the global carbon cycle. Soil microbial carbon sequestration is a process in combination withcarbon sequestration genes and growth activity. This is the first study aimed at understanding the carbon sequestration potential of phage communities in vermicompost. The results of this study provide variations in carbon sequestration genes in vermicompost microbial communities, and some novel phage auxiliary metabolic genes were revealed to assist bacterial communities to increase soil carbon sequestration potential. Our results highlight the importance of phages in soil carbon sequestration from the perspective of phage-bacterial community interactions.

Volcanic fertilization of Late Triassic lacustrine algal blooms

Although the productivity of modern volcanic soils is well established, the fertilization effects of ancient volcanic ash on aqueous ecosystems remains contentious. Here we demonstrate volcanic fertilization effects on a Late Triassic lacustrine ecosystem based on micropaleontological and geochemical records from the Yanchang Formation of North China. Frequent eruptions of a regional volcanic arc system increased cyanobacterial populations and organic carbon sinking fluxes, as recorded by extreme total organic carbon content (>30 wt.%) and positive organic carbon and negative nitrogen isotopic excursions. In turn, high levels of primary productivity induced intense water-column anoxia, facilitating preservation of organic matter. These findings underscore the potential influences of volcanism on ecological conditions, primary productivity, and carbon sequestration throughout geological history.

Avoiding global deforestation by taxing land in agricultural production: the implications for global markets

The projected growth in population and incomes is expected to create pressure to convert forestland into farmland. At the same time, the increasingly negative climate impacts are expected to generate further pressure to enhance the terrestrial carbon sink. Even though these goals are incompatible as reversing the deforestation trend by afforesting cropland would result in negative market impacts such as higher food prices, using the GTAP and GTM models, we find that these impacts would be relatively small if the goal of preserving 144.2 million hectares of forestland that otherwise would be converted to agricultural land by 2033 is achieved through a tax on land use in agricultural production. As to the economic price for doing so, the avoided deforestation would in most regions of the world result in less agricultural output and higher market prices. This is estimated to impact the well-being of global consumers by $119.7 billion, which translates to a global average cost of $13.78 per person in 2033.

Exploring the frontier of bovine protein production within territorial net zero emission targets.

Exploring the frontier of bovine protein production within territorial net zero emission targets.

Spillover Effects and Influencing Factors of Forest Carbon Storage in the Context of Regional Coordinated Development: A Case Study in Guangdong Province

Clarifying the spatial relationships and impact mechanisms of forest carbon storage is essential for designing carbon sink policies and promoting coordinated regional and sustainable development. Using panel data from 21 cities in Guangdong Province between 2012 and 2021, this study employs the forest accumulation expansion method, exploratory spatial data analysis (ESDA), and spatial econometric models to investigate the distribution, spillover effects, and impact mechanisms of forest carbon storage. The results show the following: (1) During the study period, forest carbon storage in Guangdong Province exhibited a fluctuating upward trend and notable regional disparities, with the highest levels observed in the northern region. (2) Forest carbon storage exhibits spatial correlation characteristics and a positive spillover effect, with a value of 0.2394. (3) Temperature has a negative spillover effect on forest carbon storage, while gross regional product demonstrates a negative direct effect. In contrast, labor and afforestation are key factors that possess significant positive direct and spillover effects. Therefore, in developing forest carbon sinks, it is recommended that the government implement adaptation strategies and strengthen inter-city cooperation to promote sustainable development.

Methane emissions from thermokarst lakes must emphasize the ice-melting impact on the Tibetan Plateau

Thermokarst lakes, serving as significant sources of methane (CH4), play a crucial role in affecting the feedback of permafrost carbon cycle to global warming. However, accurately assessing CH4 emissions from these lakes remains challenging due to limited observations during lake ice melting periods. In this study, by integrating field surveys with machine learning modeling, we offer a comprehensive assessment of present and future CH4 emissions from thermokarst lakes on the Tibetan Plateau. Our results reveal that the previously underestimated CH4 release from lake ice bubble and water storage during ice melting periods is 11.2 ± 1.6 Gg C of CH4, accounting for 17 ± 4% of the annual total release from lakes. Despite thermokarst lakes cover only 0.2% of the permafrost area, they annually emit 65.5 ± 10.0 Gg C of CH4, which offsets 6.4% of the net carbon sink in alpine grasslands on the plateau. Considering the loss of lake ice, the expansion of thermokarst lakes is projected to lead to 1.1–1.2 folds increase in CH4 emissions by 2100. Our study allows foreseeing future CH4 emissions from the rapid expanding thermokarst lakes and sheds new lights on processes controlling the carbon-climate feedback in alpine permafrost ecosystems.

Response mechanism of subtropical forest carbon balance to climate change based on InTEC model

IntroductionSubtropical forests play an important role in the global carbon cycle, and their carbon balance response mechanism to climate change not only has important theoretical value, but also has practical reference significance for forest management and decision-making in response to climate change in similar ecosystems in the future.MethodsTaking Zhejiang Province, China as an example, a series of relevant data were collected, including forest distribution, meteorological data, soil data, nitrogen deposition data, etc. The optimized InTEC model was used for simulation to predict the net ecosystem productivity of forests in Zhejiang Province under different climate scenarios at a hundred year scale in the future, and the temporal and spatial sequence changes were analyzed. Then, combined with the spatiotemporal variation characteristics of meteorological data, analyze the response mechanism of subtropical forest ecosystem carbon cycle to climate change. The age of the Result forest and climate change factors have a significant impact on the forest’s carbon sequestration capacity. In the past forest age stage, the climate factors that had the greatest impact on the net ecosystem productivity of forests were temperature, precipitation, and solar radiation, with correlation coefficients of 0.56, 0.84, and −0.79, respectively. After the forest matures, the correlation between net ecosystem productivity and temperature is the highest and negatively correlated under different climate scenarios. This indicates that there are significant differences in the response of forests to climate change at different times. The response of Discuss forests to climate change varies significantly at different stages, therefore different management measures should be taken according to forest age, especially in subtropical forests. This discovery is of great significance for understanding the influencing factors and driving mechanisms of forest carbon sink function, and also provides a reference for predicting future forest carbon cycle dynamics.

Estimation of carbon stock in the reed wetland of Weishan county in China based on Sentinel satellite series

Reed wetlands in Weishan County, Shandong provinces, are typical and representative wetland ecosystems with exceptional carbon sequestration potential. Evaluating the spatial and temporal characteristics of land use and carbon stock in these reed wetlands, and exploring their carbon sink value is crucial for climate change mitigation and adaptation, and provides a potential to use reed wetlands as a solution for carbon neutrality in China. Using Sentinel active and passive remote sensing data within the Google Earth Engine (GEE) platform, we employed the random forest classification method to identify the land use features in Weishan County. By combining these data with carbon density data obtained from bibliometric sources and the InVEST model, we evaluated the spatial and temporal dynamics of carbon stock in the reed wetlands as well as other land use types. The results indicated that optical data are more effective than radar data for land use classification, achieving the mean value of the overall accuracy of 89%. Reed wetlands contribute significantly to carbon stock, accounting for 28% of the total carbon stock in Weishan County. Other major contributors include forest, water body, agricultural land, artificial land, unused land, and mudflat land. The highest concentration of carbon stock is found along the shores of the four lakes and in the northeastern mountainous areas of Weishan County. The carbon stock capacity of the reed wetland in Weishan County is expected to generate a carbon sink value of 4.95–54 × 108 RMB, up to 1%–12% of the county’s GDP. These findings provide a scientific foundation for subsequent reed restoration and management efforts and offer valuable insights for developing relevant carbon neutrality strategies.

Study on the Realistic Basis and Influencing Factors of China–Russia Forest Carbon Sink Project Cooperation

Current global climate change is becoming increasingly severe, and environmental pollution and ecological damage have become global challenges. Against the backdrop of carbon peak and carbon neutrality, international carbon sink cooperation has become a trend. Forests, as an important carbon sink resource, play a crucial role in mitigating climate change. How to utilize forest resources and achieve forest carbon sink project cooperation has become a hot topic of international concern. This article selects China and Russia as research objects, constructs six latent variables including economic factors, technological factors, natural factors, economic benefits, ecological benefits, and cooperation effects, establishes the Structural Equation Model (SEM), and explores the practical basis and influencing factors of China–Russia forest carbon sink project cooperation. The results show that (1) economic factors and technical factors have a positive impact on economic benefits, and have an indirect impact on the cooperation effect through economic benefits. (2) Natural factors have a positive impact on ecological benefits and have an indirect positive impact on the cooperation effect through ecological benefits; compared with economic benefits, ecological benefits have a more significant impact on the cooperation effect. (3) Natural factors are the main influencing factors of China–Russian forest carbon sink cooperation, followed by economic factors and technical factors. Based on the research results, this article deeply analyzes the main challenges faced by the cooperation between the two sides and puts forward targeted suggestions. In addition, this article also points out the future development prospects of international carbon sink cooperation, aiming to provide scientific basis and support for international carbon sink cooperation.

Spatio-Temporal Variability in CO2 Fluxes in the Atlantic Sector of the Southern Ocean

The Southern Ocean (SO) plays a fundamental role in the planet’s climate system, due to its ability to absorb and redistribute heat and CO2 (an important greenhouse gas). In addition, the SO connects three large oceanic basins the Pacific, the Atlantic, and the Indian Oceans, and it has an important role in the nutrient distribution in these oceans. However, the SO is poorly sampled, with most measurements made in austral spring and summer. The variability in the air–sea CO2 flux is estimated, as well as the role of atmospheric and oceanic variables in this variability. The CO2 fluxes are calculated using the bulk parameterization method, in the Atlantic sector of the Southern Ocean, from 2003 to 2022, using in situ measurements, satellites, and a reanalysis data set. A neural network model is built to produce maps of the partial pressure of CO2 in seawater (pCO2sea). The CO2 flux varies from −0.05 to 0.05 gC m−2 month−1. The Atlantic sector of the SO is a sink of CO2 in summer and spring and becomes a source in austral winter and autumn. The CO2 absorption intensifies from 2003 to 2022 by 7.6 mmol m−2 month−1, due to stronger westerly winds, related to the trend in the positive phase of the Antarctic Oscillation and the extreme El Niño Southern Ocean (ENSO) events (e.g., El Niño and La Niña).

Spatial and Chronological Assessment of Variations in Carbon Stocks in Land-Based Ecosystems in Shandong Province and Prospective Predictions (1990 to 2040)

Analyses of regional carbon stock dynamics, particularly of spatial and temporal dynamics and their relationship with land use transitions, play a key role in the management of terrestrial ecosystem functions and the optimization of land resource allocation. This study focuses on Shandong Province, an important ecological security barrier along the eastern coast of China, to explore carbon stock changes and how land use modifications contributed to the chrono-spatial distribution of carbon stocks from 1990 to 2020, with additional forecasts up to 2040. Based on Natural Variation Conditions, Ecological Variation Conditions, and the City’s Variation Conditions, the results indicate a downward trend in carbon stocks across Shandong Province, from 2661.87 × 106 t in 1990 to 2380.02 × 106 t in 2020. Carbon stocks exhibit a highly uneven spatial distribution, with concentrations being notably higher in the central and eastern regions. Cities are classified based on their carbon stock level: high carbon stock cities (Linyi, Weifang, Yantai), large carbon stock cities (Jinan, Jining, Qingdao, Dezhou, Binzhou, Liaocheng, Taian, Zibo, Dongying), and cities with general carbon stock levels (Weihai, Rizhao, Zaozhuang). The major driver of carbon stock decline is the conversion of ecological lands into urban areas, with cultivated lands and forests being the primary carbon storage contributors. Projections suggest that under the City’s Variation Conditions, carbon stocks will decrease from 2380.02 × 106 t in 2020 to 1654.16 × 106 t by 2040, while Carbon stocks will rise from 2380.02 × 106 t to 2430.56 × 106 t under the Ecological Variation Conditions. A significant disparity in carbon sink potential is found across cities, which are divided into high carbon sink potential cities (Yantai, Dezhou, Weifang, Qingdao, Jinan), large carbon sink potential cities (Binzhou, Weihai, Zibo, Liaocheng, Dongying, Linyi, Taian, Rizhao, Zaozhuang), and general potential cities (Jining, Heze). The insights gained from this study are essential for promoting the conservation of regional terrestrial ecosystems, directing land use policy development, and supporting sustainable development initiatives in Shandong Province.

Thoughts on Promoting Carbon Sink Trading in Zhuzhou City under the Background of Urban Integration

Carbon sequestration trading, as an important market mechanism to address global climate change, is based on the provisions of the United Nations Framework Convention on Climate Change and the Kyoto Protocol. It aims to promote the stability of the global ecological environment by verifying and constraining greenhouse gas emissions. This paper discusses the basic background, practical value, and trading methods of carbon sequestration trading, and puts forward strategies and suggestions for promoting carbon sequestration trading in Zhuzhou City based on its actual situation. Carbon sequestration trading not only promotes sustainable development but also facilitates the compensation of ecological value, providing strong support for the realization of China’s dual carbon goals. Through the research in this paper, the author hopes to provide a reference for the practice of carbon sequestration trading in Zhuzhou City and even the whole country.

Monitoring Canopy Height in the Hainan Tropical Rainforest Using Machine Learning and Multi-Modal Data Fusion

Biomass carbon sequestration and sink capacities of tropical rainforests are vital for addressing climate change. However, canopy height must be accurately estimated to determine carbon sink potential and implement effective forest management. Four advanced machine-learning algorithms—random forest (RF), gradient boosting decision tree, convolutional neural network, and backpropagation neural network—were compared in terms of forest canopy height in the Hainan Tropical Rainforest National Park. A total of 140 field survey plots and 315 unmanned aerial vehicle photogrammetry plots, along with multi-modal remote sensing datasets (including GEDI and ICESat-2 satellite-carried LiDAR data, Landsat images, and environmental information) were used to validate forest canopy height from 2003 to 2023. The results showed that RH80 was the optimal choice for the prediction model regarding percentile selection, and the RF algorithm exhibited the optimal performance in terms of accuracy and stability, with R2 values of 0.71 and 0.60 for the training and testing sets, respectively, and a relative root mean square error of 21.36%. The RH80 percentile model using the RF algorithm was employed to estimate the forest canopy height distribution in the Hainan Tropical Rainforest National Park from 2003 to 2023, and the canopy heights of five forest types (tropical lowland rainforests, tropical montane cloud forests, tropical seasonal rainforests, tropical montane rainforests, and tropical coniferous forests) were calculated. The study found that from 2003 to 2023, the canopy height in the Hainan Tropical Rainforest National Park showed an overall increasing trend, ranging from 2.95 to 22.02 m. The tropical montane cloud forest had the highest average canopy height, while the tropical seasonal forest exhibited the fastest growth. The findings provide valuable insights for a deeper understanding of the growth dynamics of tropical rainforests.

Estimation of Vegetation Carbon Source/sink and Its Response to Land Use Change in the Loess Plateau,A Case Study of Yanhe River Basin

The transformation of ecosystem types caused by land use change plays an extremely important role in the regional carbon cycle. Studying the response of vegetation carbon source/sink systems to land use change is helpful to improve the understanding of the vegetation carbon sink effect in the process of land use change. However, few studies have focused on the response of vegetation carbon sources/sinks to land use change. The CASA model and soil microbial respiration model were combined to estimate the net ecosystem productivity （NEP） of vegetation in the Yanhe River Basin in the Chinese Loess Plateau from 2000 to 2020 based on remote sensing, meteorological, and land use data. The spatiotemporal pattern evolution characteristics of the carbon source/sink and land use were identified using a significance test, univariate linear regression analysis, and land use status transition matrix methods, and the response of the carbon source/sink to land use change was further analyzed. The results showed that from 2000 to 2020, the multi-year average NEP in the Yanhe River Basin showed a spatial distribution pattern of lower in the upstream and higher in the midstream and downstream. The Yanhe River Basin belonged to a weak carbon sink area as a whole, with this type of area accounting for 88.81% of the basin area. The annual NEP of the basin showed a significant increase trend in fluctuations, and the carbon sequestration capacity was gradually improving. The areas with significant and extremely significant increases in annual NEP accounted for 65.78% of the basin area, and the types of annual NEP restoration, basic stability, and degradation accounted for 79.70%, 10.15%, and 10.15% of the basin area, respectively. Over the past 20 years, the land use transformation of Yanhe River Basin mainly included five types, that is, cropland was converted into grassland, woodland, and construction land, and grassland was converted into cropland and woodland. The land use in the Yanhe River Basin was mainly shifting towards promoting the improvement of the carbon sink capacity, and the transformation of land type to woodland had a more significant effect on improving carbon sink capacity. During the five main land use transformation processes in the Yanhe River Basin, the area ratio of NEP recovery-recovery type for cropland shifting to woodland was the highest at 80.78%. The area ratios of NEP recovery-recovery type for grassland shifting to cropland and cropland shifting to grassland were relatively low, at 48.05% and 51.97%, respectively. The stability of NEP restoration when shifting cropland to woodland was the strongest, and the fluctuation of NEP restoration when shifting between cropland and grassland mutually was strong. When adjusting cropland and grassland mutually, attention should be paid to select suitable vegetation types and increase vegetation coverage reasonably to improve carbon sequestration and sink enhancement capabilities, so as to avoid carbon losses during land transformations. The research methods and results in this study can provide reference for land management departments to formulate scientific and reasonable land use decisions to promote vegetation carbon sequestration and sink enhancement.