Forest ecosystem, as a predominant component of terrestrial ecosystems in view of carbon sinks, has a high potential for carbon sequestration. Accurately estimating the carbon sequestration rate in forest ecosystems at provincial level, is a prerequisite and basis for scientifically formulating the technical approaches of carbon neutrality and the associated regulatory policies in China. However, few researches on future carbon sequestration rates (CSRs) for Chinese forest ecosystems for provincial-level regions (hereafter province) have been reported, especially for forest soils. In this study, we quantitatively assessed the carbon sequestration rates of existing forest ecosystems of all the provinces from 2010 to 2060 using the Forest Carbon Sequestration model (FCS), in combination with large quantities of field-measured data in China under three future climate scenarios (RCP2.6, RCP4.5, and RCP8.5). Results showed that CSRs across provinces varied from 0.01 TgC a-1 to 36.74 TgC a-1, with a mean of 10.09 ± 0.43 TgC a-1. Inter-provincial differences have been observed in forest CSRs. Regarding the spatial variations in CSRs on a unit area basis within provinces, the eastern region provinces have a larger capacity for sequestration than the western region, while the western region has greater CSR per unit GDP and per capita. Moreover, there are significant negative correlations between the CSRs per capita in each province and the corresponding GDP per capita, under the assumption that GDP per capita is constant in the future across provinces. In summary, there is a significant regional imbalance in CSR among provinces. Special technological and policy interventions are required to realize carbon sink potential sustainably. An overlap in China’s poorer areas and areas with stronger carbon sinks has indicated that existing policies to support traditional carbon trading are insufficient. Regulatory measures such as “regional carbon compensation” must be adopted urgently in line with the Chinese characteristics, so that people in western or underdeveloped regions can consciously strengthen forest protection and enhance forest carbon sinks through coordinated regional development while ensuring that China’s forests play a greater role in carbon neutrality strategies.
Cropland displacement, as an important characteristic of cropland change, places more emphasis on changes in spatial location than on quantity. The effects of cropland displacement on global and regional food production are of general concern in the context of urban expansion. Few studies have explored scale-effects, however, where cropland is displaced not only within, but also outside, the administrative boundary of a certain region. This study used a spatially explicit model (LANDSCAPE) to simulate the potential cropland displacement caused by urban land expansion from 2020 to 2040 at four scales of the Chinese administration system (national, provincial, municipal, and county levels). The corresponding changes in potential cereal production were then assessed by combining cereal productivity data. The results show that 4700 km2 of cropland will be occupied by urban expansion by 2040, and the same amount of cropland will be supplemented by forest, grassland, wetland, and unused land. The potential loss of cropland will result in the loss of 3.838×106 tons of cereal production, and the additional cropland will bring 3.546×106 tons, 3.831×106 tons, 3.836×106 tons, and 3.528×106 tons of potential cereal production in SN (national scale), SP (provincial scale), SM (municipal scale), and SC (county scale), respectively. Both SN and SC are observed to make a huge difference in cereal productivity between the lost and the supplemented cropland. We suggest that China should focus on the spatial allocation of cropland during large-scale displacement, especially at the national level.
The black soil region of northeast China is a vital food base and is one of the most sensitive regions to climate change in China. However, the characteristics of the crop phenological response and the integrated impact of climate and phenological changes on agricultural productivity in the region under the background of climate change are not clear. The future agricultural risk assessment has been insufficiently quantified and the existing risk level formulation lacks a sound basis. Based on remote sensing products, climate data, and model simulations, this study integrated a logistic function fitting curvature derivation, multiple linear regression, and scenario simulation to investigate crop phenology dynamics and their climate response characteristics in the black soil region. Additionally, the compound effects of climate and phenology changes on agricultural production and possible future risks were identified. The key results were as follows: (1) From 2000 to 2017, 29.76% of the black soil region of northeast China experienced a significant delay in the start of the growing season (SOS) and 16.71% of the total area displayed a trend for the end of the growing season (EOS) to arrive earlier. The time lagged effects of the SOS in terms of the crop response to climatic factors were site and climatic parameter dependent. The influence of temperature was widespread and its effect had a longer lag time in general; (2) Both climatic and phenological changes have had a significant effect on the inter-annual variability of crop production, and the predictive ability of both increased by 70.23%, while the predictive area expanded by 85.04%, as compared to that of climate change in the same period of the growing season; (3) Under the RCP8.5 scenario, there was a risk that the future crop yield would decrease in the north and increase in the south, and the risk area was constantly expanding. With a 2.0℃ rise in global temperature, the crop yield of the southern Songnen black soil sub-region would reduce by almost 10%. This finding will improve our understanding of the mechanisms underlying climate change and vegetation productivity dynamics, and is also helpful in the promotion of the risk management of agrometeorological disasters.
With the continuous enhancement of regional connectivity, the indirect use of land resources through the pathways of trade in goods and services plays an increasingly important role in the overall utilization of land resources. Despite this, relevant research in this field is still in its infancy, and few papers have addressed this issue. This paper uses a multi-regional input-output model to calculate the embodied land in the 30 provinces (autonomous regions and municipalities) and eight regions of China from the perspective of regional trade and further analyzes the spatial pattern of characteristics associated with embodied land flows. The results show that the amount of embodied land occupied by China’s inter-regional trade accounts for 21.39% of the country’s total land, and an average of 38.54% of China’s provincial land demand is met by land exports from other provinces. More than 80% of land consumed by Beijing, Tianjin, and Shanghai is from other provinces. The provinces of Heilongjiang, Inner Mongolia, Xinjiang, and Hebei are the largest net exporters of cultivated land, forest and grazing and aquatic land, fishery land, and built-up land, respectively (the outflows account for 42.26%, 27.53%, 38.66%, and 35.28% of the corresponding land types in the province); and Guangdong, Shandong, and Zhejiang are the main net importers. The flow of agricultural land (cultivated land, forest land, grazing land, and aquatic land) generally shows a shift from west to east and from north to south. The regions in northeast and northwest China have the largest scale of agricultural land outflows, mainly into East and South China. In addition, 8.43% of cultivated land, 7.47% of forest land, 6.41% of grazing land, 6.88% of aquatic land, and 18.35% of built-up land in China are provided for foreign use through international trade. This paper provides feasible ideas and a theoretical basis for solving the contradiction between land use and ecological protection, which could potentially help to achieve sustainable land use in China.
Tidal flats, a precious resource that provides ecological services and land space for coastal zones, are facing threats from human activities and climate change. In this study, a robust decision tree for tidal flat extraction was developed to analyse spatiotemporal variations in the Bohai Rim region during 1984-2019 based on 9539 Landsat TM/OLI surface reflection images and the Google Earth Engine (GEE) cloud platform. The area of tidal flats significantly fluctuated downwards from 3551.22 to 1712.36 km2 in the Bohai Rim region during 1984-2019, and 51.31% of tidal flats were distributed near the Yellow River Delta and Liaohe River Delta during 2017-2019. There occurred a drastic spatial transition of tidal flats with coastline migration towards the ocean. Low-stability tidal flats were mainly distributed in reclamation regions, deltas, and bays near the estuary during 1984-2019. The main factors of tidal flat evolution in the Bohai Rim region included the direct impact of land cover changes in reclamation regions, the continuous impact of a weakening sediment supply, and the potential impact of a deteriorating sediment storage capability. The extraction process and maps herein could provide a reference for the sustainable development and conservation of coastal resources.
Recently, whether drylands of Northwest China (NW) have become wetting has been attracting surging attentions. By comparing the Standard Precipitation Evapotranspiration Indices (SPEI) derived from two different potential evapotranspiration estimates, i.e., the Thornthwaite algorithm (SPEI_th) and the Penman-Monteith equation (SPEI_pm), we try to resolve the controversy. The analysis indicated that air temperature has been warming significantly at a rate of 0.4°C decade?1 in the last five decades and the more arid areas are more prone to becoming warmer. Annual precipitation of the entire study area increased insignificantly by 3.6 mm decade?1 from 1970 to 2019 but NW presented significantly increasing trends. Further, the SPEI_th and SPEI_pm demonstrated similar wetting-drying-wetting trends (three phases) in China’s drylands during 1970-2019. The common periodical signals in the middle phase were identified both by SPEI_th and SPEI_pm wavelet analysis. Analysis with different temporal intervals can lead to divergent or even opposite results. The attribution analysis revealed that precipitation is the main climatic factor driving the drought trend transition. This study hints that the wetting trend’s direction and magnitude hinge on the targeted temporal periods and regions.
Monitoring alpine lakes is important for understanding the regional environmental changes caused by global warming. In this study, we provided a detailed analysis of alpine lake changes in the Tianshan Mountains (TS) and discussed their driving forces based on Landsat TM/ETM+/OLI, WorldView-2, Bing, Google Earth, and ASTER imagery, along with climatic data from 1990 to 2015. The results showed that during the study period, the total number and area of alpine lakes in the eastern TS exhibited an increasing trend, by 64.06% and 47.92%, respectively. Furthermore, the continuous expansion of glacial lakes contributed 95.12% and 94.17% to the total increase in the number and area, respectively, of alpine lakes. Non-glacial lakes exhibited only intermittent expansion. Since the 1990s, the new glacial lakes in the eastern TS have been mainly proglacial and extraglacial lakes. Over the past 25 years, eastern TS has experienced a temperature increase rate of 0.47 °C/10a, which is higher than that in other TS regions. The rapidly warming climate and glacier recession are the primary causes of the accelerated expansion of glacial lakes in the eastern TS.
Understanding the radial growth trends of trees and their response to recent warming along elevation gradients is crucial for assessing how forests will be impacted by future climate change. Here, we collected 242 tree-ring cores from five plots across the Qinghai spruce (Picea crassifolia Kom.) forest belt (2600-3350 m a.s.l.) in the central Qilian Mountains, Northwest China, to study trends in the radial growth of trees and their response to climate factors with variable elevation. All the sampled P. crassifolia chronologies showed an increasing trend in the radial growth of trees at higher altitudes (3000-3350 m), whereas the radial growth of trees at lower altitudes (2600-2800 m) has decreased in recent decades. The radial growth of trees was limited by precipitation at lower elevations (L, ML), but mainly by temperature at higher elevation sites (MH, H, TL). Climate warming has caused an unprecedented increase in the radial growth of P. crassifolia at higher elevations. Our results suggest that ongoing climate warming is beneficial to forest ecosystems at high elevations but restricts the growth of forest ecosystems at low elevations.
Water use efficiency (WUE) is an important variable to explore coupled relationships in carbon and water cycles. In this study, we first compared the spatial variations of annual gross primary productivity (GPP) and evapotranspiration (ET) using four GPP and ET products. Second, we selected the products closest to the flux towers data to estimate WUE. Finally, we quantitatively analyzed the impact of climate change and soil water content on WUE. The results showed that: (1) Four GPP and ET products provided good performance, with GOSIF-GPP and FLDAS-ET exhibiting a higher correlation and the smallest errors with the flux tower data. (2) The spatial pattern of WUE is consistent with that of GPP and ET, gradually decreasing from the northeast to the southwest. Higher WUE values appeared in the northeast forest ecosystem, and lower WUE values occurred in the western Gobi Desert, with a value of 0.28 gC m?2 mm?1. The GPP and ET products showed an increasing trend, while WUE showed a decreasing trend (55.15%) from 2001 to 2020. (3) The spatial relationship between WUE and driving factors reveal the variations in WUE of Inner Mongolia are mainly affected by soil moisture between 0 and 10 cm (SM0-10cm), vapor pressure deficit (VPD), and precipitation, respectively. (4) In arid regions, VPD and precipitation exhibit a major influence on WUE. An increase in VPD and precipitation has a negative and positive effect on WUE, with threshold values of approximately 0.36 kPa and 426 mm, respectively. (5) In humid regions, SM0-10cm, VPD, SM10-40cm, and SM40-100cm exert a significant impact on WUE, especially SM0-10cm, and weakens with increasing soil depths, these differences may be related to physiological structure and living characteristics of vegetation types in different climate regimes. Our results emphasize the importance of VPD and soil moisture in regional variability in WUE.
Revealing the drivers and scale effects of water pollutant discharges is an important issue in the study of the environmental consequences during urban agglomeration evolution. It is also a prerequisite for realizing collaborative water pollutant reduction and environmental governance in urban agglomerations. This paper takes 305 counties in the Yangtze River Delta (YRD) as an example and selects chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) as two distinctive pollutant indicators, using the Spatial Lag Model (SLM) and Spatial Error Model (SEM) to estimate the drivers of water pollutant discharges in 2011 and 2016. Then the Multiscale Geographically Weighted Regression (MGWR) model is constructed to diagnose the scale effect and spatial heterogeneity of the drivers. The findings show that the size of population, the level of urbanization, and the economic development level show global-level increase impacts on water pollutant discharges, while the level of industrialization, social fixed assets investment, foreign direct investment, and local fiscal decentralization are local-level impacts. The spatial heterogeneity of local drivers presents the following characteristics: Social fixed assets investment has a strong promoting effect on both COD and NH3-N discharges in the Hangzhou-Jiaxing-Huzhou region and the coastal area of the YRD; industrialization has a promoting effect on COD discharges in the Taihu Lake basin and Zhejiang province; foreign direct investment has a local inhibitory effect on NH3-N discharge, and the pollution halo effect is more prominent in the marginal areas of the YRD such as northern Jiangsu, northern Anhui, and southern Zhejiang; local fiscal decentralization has a noticeable inhibitory effect on COD discharge in the central areas of the YRD, reflecting the positive impacts on improved local environmental awareness and stronger constraints of multilevel environmental regulations in the urban agglomeration. Therefore, it is recommended to guide greener development to reduce the water pollutant discharge; to embed an environmental push-back mechanism in the fields of industrial production, capital investment, and financial income and expenditure; and to establish a high-quality development pattern of urban agglomerations systematically compatible with the carrying capacity of the water environment.
