Annual Net Ecosystem Production Research Articles

Net ecosystem productivity of Panjin Phragmites australis wetland during 1971 to 2020 and its impact factors.

Coastal estuarine wetland ecosystem has strong ability for carbon (C) storage and sequestration. Accurate assessment of C sequestration and its environmental impact factors is the basis of scientific protection and mana-gement of coastal estuarine wetlands. Taking the Panjin reed (Phragmites australis) wetland as the object, we used terrestrial ecosystem model, together with Mann-Kendall mutation test, statistical analysis methods, and scenario simulation experiment, to analyze the temporal characteristics, stability, changing trend of net ecosystem production (NEP) of wetlands and the contribution rate of environmental impact factors to NEP during 1971 to 2020. The results showed that the annual average NEP of Panjin reed wetland was 415.51 g C·m-2·a-1 during 1971 to 2020, with a steady increase rate of 1.7 g C·m-2·a-1, which would still have a continuous increasing trend in the future. The annual average NEP in spring, summer, autumn, and winter was 33.95, 418.05, -18.71, and -17.78 g C·m-2·a-1, with an increase rate of 0.35, 1.26, 0.14 and -0.06 g C·m-2·a-1, respectively. In the future, NEP would show an increasing trend in both spring and summer, but a declining trend in both autumn and winter. The contribution rates of environmental impact factors to NEP of Panjin reed wetland depended on temporal scale. At the interannual scale, the contribution rate of precipitation was the highest (37.1%), followed by CO2 (28.4%), air temperature (25.1%) and photosynthetically active radiation (9.4%). Precipitation mainly affected NEP in both spring and autumn with the contribution rates of 49.5% and 38.8%, while CO2 concentration (36.9%) and air temperature (-86.7%) were dominant in summer and winter, respectively.

Estimation of Net Ecosystem Productivity on the Tibetan Plateau Grassland from 1982 to 2018 Based on Random Forest Model

The Tibetan Plateau (TP) is one of the most important areas for the study of the carbon budgets of terrestrial ecosystems. However, the estimation of the net ecosystem productivity (NEP) remains uncertain in this region due to its complex topographic properties and climatic conditions. Using CO2-eddy-covariance-flux data from 1982 to 2018 at 18 sites distributed around the TP grassland, we analyzed the spatial–temporal patterns of the grassland NEP and its driving factors from 1982 to 2018 using a random forest (RF) model. Our results showed that the RF model captured the size of the carbon sink (R2 = 0.65, p < 0.05) between the observed and simulated values for the validation samples. During the observation period, the grassland acted as a carbon sink of 26.2 Tg C yr−1 and increased significantly, by 0.4 g C m−2 yr−1. On a regional scale, the annual NEP gradually increased from the northwest to the southeast, and a similar pattern was also observed in the long-term trends. Furthermore, the moisture conditions, such as the specific humidity and precipitation, were proven to be the main driving factors of the carbon flux in the southeastern areas, while the temperature predominantly controlled the carbon flux in the northwest. Our results emphasize the net carbon sink of the TP and provide a reliable way to upscale NEP from sites.

Changes and net ecosystem productivity of terrestrial ecosystems and their influencing factors in China from 2000 to 2019.

Changes in net ecosystem productivity (NEP) in terrestrial ecosystems in response to climate warming and land cover changes have been of great concern. In this study, we applied the normalized difference vegetation index (NDVI), average temperature, and sunshine hours to drive the C-FIX model and to simulate the regional NEP in China from 2000 to 2019. We also analyzed the spatial patterns and the spatiotemporal variation characteristics of the NEP of terrestrial ecosystems and discussed their main influencing factors. The results showed that (1) the annual average NEP of terrestrial ecosystems in China from 2000 to 2019 was 1.08 PgC, exhibiting a highly significant increasing trend with a rate of change of 0.83 PgC/10 y. The terrestrial ecosystems in China remained as carbon sinks from 2000 to 2019, and the carbon sink capacity increased significantly. The NEP of the terrestrial ecosystem increased by 65% during 2015-2019 compared to 2000-2004 (2) There was spatial differences in the NEP distribution of the terrestrial ecosystems in China from 2000-2019. Taking the line along the Daxinganling-Yin Mountains-Helan Mountains-Transverse Range as the boundary, the NEP was significantly higher in the eastern part than in the western part. Among them, the NEP was positive (carbon sink) in northeastern, central, and southern China, and negative (carbon source) in parts of northwestern China and the Tibet Autonomous Region. The spatial variation of NEP in terrestrial ecosystems increased from 2000 to 2009. The areas with a significant increase accounted for 45.85% and were mainly located in the central and southwestern regions. (3) The simulation results revealed that vegetation changes and CO2 concentration changes both contributed to the increase in the NEP in China, contributing 85.96% and 36.84%, respectively. The vegetation changes were the main factor causing the increase in the NEP. The main contribution of this study is to further quantify the NEP of terrestrial ecosystems in China and identify the influencing factors that caused these changes.

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

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

Spatial and temporal variations of net ecosystem productivity in Xinjiang Autonomous Region, China based on remote sensing.

Net ecosystem productivity (NEP), which plays a key role in the carbon cycle, is an important indicator of the ecosystem's carbon budget. In this paper, the spatial and temporal variations of NEP over Xinjiang Autonomous Region, China from 2001 to 2020 were studied based on remote sensing and climate re-analysis data. The modified Carnegie Ames Stanford Approach (CASA) model was employed to estimate net primary productivity (NPP), and the soil heterotrophic respiration model was used to calculate soil heterotrophic respiration. Then NEP was obtained by calculating the difference between NPP and heterotrophic respiration. The annual mean NEP of the study area was high in the east and low in the west, high in the north and low in the south. The 20-year mean vegetation NEP of the study area is 128.54 gC·m-2, indicating that the study area is a carbon sink on the whole. From 2001 to 2020, the annual mean vegetation NEP ranged between 93.12 and 158.05 gC·m-2, and exhibited an increasing trend in general. 71.46% of the vegetation area showed increasing trends of NEP. NEP exhibited a positive relationship with precipitation and a negative relationship with air temperature, and the correlation with air temperature was more significant. The work reveals the spatio-temporal dynamics of NEP in Xinjiang Autonomous Region and can provide a valuable reference for assessing regional carbon sequestration capacity.

Spatiotemporal Variation Characteristics and Dynamic Persistence Analysis of Carbon Sources/Sinks in the Yellow River Basin

Net ecosystem productivity (NEP) is an important indicator for estimating regional carbon sources/sinks. The study focuses on a comprehensive computational simulation and spatiotemporal variation study of the NEP in the Yellow River basin from 2000 to 2020 using NPP data products from MODIS combined with a quantitative NEP estimation model followed by a comprehensive analysis of the spatiotemporal variation characteristics and dynamic procession persistence analysis based on meteorological data and land use data. The results show that: (1) The total NEP in the Yellow River basin had an overall increasing trend from 2000 to 2020, with a Theil–Sen trend from −23.37 to 43.66 gCm−2a−1 and a mean increase of 4.64 gCm−2a−1 (p < 0.01, 2-tailed). (2) Most areas of the Yellow River basin are carbon sink areas, and the annual average NEP per unit area was 208.56 gCm−2a−1 from 2000 to 2020. There were, however, substantial spatial and temporal variations in the NEP. Most of the carbon source area was located in the Kubuqi Desert and its surroundings. (3) Changes in land use patterns were the main cause of changes in regional NEP. During the 2000–2020 period, 1154.24 t of NEP were added, mainly due to changes in land use, e.g., the conversion of farmland to forests and grasslands. (4) The future development in 83.43% of the area is uncertain according to the Hurst index dynamic persistence analysis. In conclusion, although the carbon−sink capacity of the terrestrial ecosystem in the Yellow River basin is increasing and the regional carbon sink potential is increasing in the future, the future development of new energy resources has regional uncertainties, and the stability of the basin ecosystem needs to be enhanced.

2000-2020年华北地区植被固碳能力时空变化特征及其气象影响分析

PDF HTML阅读 XML下载 导出引用 引用提醒 2000-2020年华北地区植被固碳能力时空变化特征及其气象影响分析 DOI: 10.5846/stxb202110072771 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 以清洁能源淡化海水促进生态修复和应对气候变化的可行路径及综合效益研究(SGGEIG00JYJS2000053);国家重点研发计划项目(2019YFC1510204);国家气象中心预报员专项(Y202116) Spatial and temporal patterns of carbon sequestration and their responses to climatic factors in North China from 2000 to 2020 Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:净生态系统生产力(NEP)是估算植被生态系统碳源／汇的重要指标,开展区域NEP时空变化特征分析,对科学评估植被生态系统固碳能力及其气候变化应对措施具有重要意义。研究基于土壤呼吸模型和TEC模型,利用2000-2020年气象数据和遥感数据,采用线性趋势分析、Hurst指数和相关分析等统计方法,对华北地区固碳能力时空变化特征、影响因素及其未来变化趋势进行分析。结果表明:2000-2020年,华北地区年均NEP为228.8 gC/m2,在空间分布上呈现从西北向东南逐步递增的趋势,总体上表现为净固碳。从变化趋势来看,华北地区生态系统的固碳能力总体呈增加趋势,分布面积占比达到88.8%,达到显著增加趋势的面积比例为54.5%(P<0.05),其中河北北部、北京北部、山西西北部、山东西部等地NEP每年每平方米增加9.0 gC以上。华北大部地区NEP年际波动较小,有79.6%的区域多处于较高稳定、高稳定的等级。从变化趋势来看,华北地区有84.9%区域NEP具有强持续性,且NEP未来仍将持续增加的区域面积占比达到51.4%。华北地区NEP的空间分布和年际变化主要受降水的影响,达到显著相关的区域面积占总面积的44.7%,但与气温、日照呈弱正相关,而且不同区域相关性差异明显。其中降水影响空间格局差异极为明显,华北中北部NEP与降水呈显著正相关,南部呈负相关。 Abstract:Net ecosystem productivity (NEP) is an important index for estimating carbon source/sink of regional vegetation system. Analyzing the distribution characteristics and changing trend of net ecosystem productivity spatially is of great significance to scientifically assess carbon sequestration capacity of ecosystems and formulate policies and measures to cope with climate change. Using the soil respiration model and terrestrial ecosystem carbon flux model (TEC model), combined with MODIS and meteorological data, this paper estimated the NEP in North China from 2000 to 2020. And its spatial distribution characteristics and changing trend were analyzed, using methods of linear regression, the Hurst index, coefficient of variation and other methods. Results showed that: from 2000 to 2020, the annual average NEP in North China was about 228.8 gC/m2. In spatial distribution, the NEP showed an increasing trend from northwest to southeast, representing carbon sink as a whole. From spatial distribution of change trend, the carbon sequestration capacity of North China ecosystems was increasing, especially in the north of Hebei, the north of Beijing, the northwestern Shanxi, the western Shandong with increase of NEP over 9.0 gC/m2. The area of increasing trend with the NEP accounted for 88.8% of the research area, of which 54.5% showed a significantly increasing trend (P<0.05). As for the coefficient of variation (CV), the NEP status in North China presented slight fluctuations with 79.6%% of the area in higher stability and the highest stability. From the NEP change trend analysis, 84.9% of the area in North China was persistent in the future. The NEP in 51.4% of the regions will continue to increase in the future. The spatial distribution and interannual variation of the NEP values were mainly influenced by the values of precipitation, of which 44.7% showed a positive correlation with precipitation. The changes of NEP were slightly positively associated with temperature and sunshine. The responses of NEP in North China to the meteorological factors were diverse in spatial difference of the North China, especially differences by the influence of precipitation. There is a significantly positive correlation between NEP and precipitation in the northern part of North China, and a negative correlation in the south. 参考文献 相似文献 引证文献

Ecological restoration effects of the Beijing–Tianjin Sandstorm Source Control Project in China since 2000

The Beijing–Tianjin Sandstorm Source Control Project (BTSSCP) has been implemented for more than 20 years (2001–2022), and a scientific, accurate, and complete evaluation of its implementation effect is of great significance for the study of ecosystem evolution. In this study, we present a vegetation–water–soil–environment system comprising the net ecosystem productivity (NEP), water conservation (WC), soil erosion (SE), and habitat quality (HQ) to evaluate the spatiotemporal changes and future trends. The results showed that: (1) In areas with high vegetation coverage, only WC was significantly and negatively correlated with SE (−0.68, p less than 0.01). In areas with low vegetation coverage, NEP, WC, and HQ were all significantly negatively correlated with SE. This indicates that SE is a basic function that affects the performance of other ecological services. (2) From 2000 to 2020, the annual maximum average vegetation coverage increased by about 10 %; the annual average NEP increased by about 60 g C/km2, and the annual average SE decreased by about 500 t/km2. Compared with Phase I (2000–2010), the vegetation condition (coverage, NEP) in summer (July–August) was improved by about 10 %, and SE in winter (December–January) decreased by 3 t/km2 per month in Phase II (2010–2020). (3) In terms of future trends, NEP may continue to increase in the grassland area, especially in the Mu Us Sandland, but it may not change significantly in the forest area. Similarly, SE may continue to decrease in grassland-covered areas, but not in forest-covered areas. Most areas of WC could continue to increase, but the HQ will not change significantly. In general, the ecological restoration effects of the BTSSCP have improved significantly. This paper is intended to provide some key information for the management of ecological projects and regional ecological security.

Landscape-variability of the carbon balance across managed boreal forests.

Boreal forests are important global carbon (C) sinks and, therefore, considered as a key element in climate change mitigation policies. However, their actual C sink strength is uncertain and under debate, particularly for the actively managed forests in the boreal regions of Fennoscandia. In this study, we use an extensive set of biometric- and chamber-based C flux data collected in 50 forest stands (ranging from 5 to 211 years) over 3 years (2016-2018) with the aim to explore the variations of the annual net ecosystem production (NEP; i.e., the ecosystem C balance) across a 68 km2 managed boreal forest landscape in northern Sweden. Our results demonstrate that net primary production rather than heterotrophic respiration regulated the spatio-temporal variations of NEP across the heterogeneous mosaic of the managed boreal forest landscape. We further find divergent successional patterns of NEP in our managed forests relative to naturally regenerating boreal forests, including (i) a fast recovery of the C sink function within the first decade after harvest due to the rapid establishment of a productive understory layer and (ii) a sustained C sink in old stands (131-211 years). We estimate that the rotation period for optimum C sequestration extends to 138 years, which over multiple rotations results in a long-term C sequestration rate of 86.5t C ha-1 per rotation. Our study highlights the potential of forest management to maximize C sequestration of boreal forest landscapes and associate climate change mitigation effects by developing strategies that optimize tree biomass production rather than heterotrophic soil C emissions.

Plant functional diversity influences water and carbon fluxes and their use efficiencies in native and disturbed dryland ecosystems

AbstractVegetation is changing rapidly in dryland ecosystems, but critical gaps remain in understanding the long‐term fluxes of carbon (C) and water. We used 6 years of data from two adjacent eddy covariance sites in the Sonoran Desert, a species‐rich woody C3 native shrubland and a species‐poor C4 shrubland converted to buffelgrass savanna. Although emphasis has been given to the physical determinants of productivity in dryland ecosystems, we assessed how PFTs changes influenced (1) water and C fluxes and (2) water‐use (WUEe) and intrinsic C‐use efficiencies (CUEei) in the two sites under the same climatological conditions. We hypothesized that changes in PFTs would alter accessibility, rate and use efficiencies of water and carbon, with poorly known effects on the long‐term fluxes and efficiencies. Annual net ecosystem productivity (NEP) in the shrubland was a C‐source in drier years and a sink in others. However, longer C uptake, greater WUEe and lower CUEei were the crucial drivers for higher and positive NEP (C sink) in the savanna. Annual and seasonal WUEe and CUEei discrepancies indicated the importance of dominant PFTs after disturbance and ecohydrological feedbacks. As the world becomes drier and vegetation disturbance more common, the role of PFT changes should contribute to gaining a clearer understanding of their role in the C and water fluxes of dryland ecosystems.

Seasonal carryover of water and effects on carbon dynamics in a dryland ecosystem

AbstractNet primary productivity in arid and semiarid regions is controlled by water availability for which rainfall has been a commonly used proxy at annual scales. However, the hydrological partitioning occurring through the water balance can also shape both seasonal and annual net ecosystem productivity. In this study, we used 10 years of water and carbon flux measurements in a mixed shrubland watershed of the Chihuahuan Desert to investigate the seasonal variability and controls on net ecosystem production. Over this period, the site exhibited a bimodal rainfall regime with an average of 211 and 67 mm for the wet (July–December) and dry (January–June) periods of the year, respectively. During the wet season, soil infiltration and channel transmission losses led to an average of 35.8 mm of water stored in the subsurface for subsequent dry periods. By contrast, dry seasons consumed 30.3 mm of stored subsurface water to fulfill the ecosystem water demand, particularly during the springtime. In response, gross primary productivity occurred in equal amounts for both seasons, while ecosystem respiration was substantially higher during the wet season. This resulted in the mixed shrubland acting as an annual net sink of carbon (average of 153.2 g C m−2 year−1) of which 65% occurred during the dry season. We determined that the wet season provided water in excess of vegetation demands in that season, a portion of which was stored in the watershed subsurface for subsequent use, leading to a legacy effect. Gross primary productivity during the dry season was dependent on carryover soil moisture accessed by deep‐rooted shrubs. Our coordinated observations of water–carbon dynamics revealed that water availability during the wet season can sustain the annual ecosystem productivity by impacting the subsequent dry season carbon uptake.

Response of carbon budget to climate change of the alpine meadow in Gannan using the CENTURY model

Abstract Alpine meadows have become particularly vulnerable to climate change. Variations in precipitation and temperature affect the ecological production of a region. The matrices for ecosystem change include net primary production (NPP), net photosynthesis (PsnNet), and net ecosystem production (NEP), of which NEP is the most important. Using the CENTURY model for alpine meadows, we investigated the response of NEP to climate change from 1969 to 2018 in Gannan, Gansu Province, China. The distribution pattern of NEP in Gannan was simulated with the model. The Mann–Kendall trend test was used to analyze the interannual variation of NEP for the individual counties and the entire study area over a 50-year period. The results showed the annual NEP distribution pattern varied widely in the region, with the highest NEP values in the southeastern part while the northwestern part showed the lowest. The highest NEP was measured in summer with sufficient precipitation and higher temperatures, whereas the lowest values occurred in winter. The total carbon sequestered in the Gannan alpine meadow over the last 50 years was 43580.9 gC, with the average annual NEP of the alpine meadow being approximately 813.62 gC m−2 year−1. Due to the combined effects of precipitation and temperature variations, NEP exhibits significant seasonal and interannual variations. The simulated NEP values of the seven counties fluctuated over the last 50 years, with each county showing an upward trend and the simulated NEP in the entire Gannan area also showing a clear upward trend that mutated around the year 1990. Both precipitation and temperature were found to be significantly and positively correlated with NEP. Precipitation was a significant driving factor, while temperature interacted with precipitation on the carbon budget. The carbon budget in the alpine meadow was stabilized by increasing precipitation and temperature. Estimates from NEP were in satisfactory correlation with measurements (r2=0.74, n=25 at p&amp;lt;0.01). Our findings provide preliminary understanding of the carbon budget and climatic feedback in Gannan alpine meadows which will help to predict carbon fluxes in the terrestrial biosphere and the impacts of climate change.

Analysis of carbon emissions from land cover change during 2000 to 2020 in Shandong Province, China

Land cover change affects the carbon emissions of ecosystems in some way. The qualitative and quantitative understanding of carbon emissions from human activities (e.g., land cover change, industrial production, etc.) is highly significant for realizing the objective of carbon neutrality. Therefore, this paper used GlobeLand30 land cover maps, annual average normalised difference vegetation index (NDVI) data, annual average net ecosystem productivity (NEP) data and statistical yearbook data from 2000 to 2020 to explore the relationship between land cover change and carbon emissions. Specifically, it included land cover change, carbon storage changes influenced by land cover change, spatial and temporal analysis of carbon sources and sinks, land use intensity change and anthropogenic carbon emissions. The results of the study show that the main land cover changes in Shandong province during 2000–2020 was cultivated land conversion to artificial surfaces. Among them, the area of cultivated land converted to artificial surfaces from 2000 to 2010 was 4930.62 km2, and the proportion of cultivated land converted to artificial surfaces from 2010 to 2020 was as high as 78.35%. The total carbon stock of vegetation affected by land cover change decreased by 463.96 × 104 t and 193.50 × 104 t in 2000–2010 and 2010–2020 respectively. The spatial and temporal distribution of carbon sources and sinks differed more markedly from 2000 to 2020, and land use intensity changes in Shandong Province showed an upward trend. Of the total energy production, industry has the largest energy consumption, followed closely by total energy consumption in transportation, storage and postal services.

Re-assessment of the climatic controls on the carbon and water fluxes of a boreal aspen forest over 1996-2016: Changing sensitivity to long-term climatic conditions.

Recent evidence suggests that the relationships between climate and boreal tree growth are generally non-stationary; however, it remains uncertain whether the relationships between climate and carbon (C) fluxes of boreal forests are stationary or have changed over recent decades. In this study, we used continuous eddy-covariance and microclimate data over 21 years (1996-2016) from a 100-year-old trembling aspen stand in central Saskatchewan, Canada to assess the relationships between climate and ecosystem C and water fluxes. Over the study period, the most striking climatic event was a severe, 3-year drought (2001-2003). Gross ecosystem production (GEP) showed larger interannual variability than ecosystem respiration (Re ) over 1996-2016, but Re was the dominant component contributing to the interannual variation in net ecosystem production (NEP) during post-drought years. The interannual variations in evapotranspiration (ET) and C fluxes were primarily driven by temperature and secondarily by water availability. Two-factor linear models combining precipitation and temperature performed well in explaining the interannual variation in C and water fluxes (R2 > .5). The temperature sensitivities of all three C fluxes (NEP, GEP and Re ) declined over the study period (p < .05), and, as a result, the phenological controls on annual NEP weakened. The decreasing temperature sensitivity of the C fluxes may reflect changes in forest structure, related to the over-maturity of the aspen stand at 100 years of age, and exacerbated by high tree mortality following the severe 2001-2003 drought. These results may provide an early warning signal of driver shift or even an abrupt status shift of aspen forest dynamics. They may also imply a universal weakening in the relationship between temperature and GEP as forests become over-mature, associated with the structural and compositional changes that accompany forest ageing.

Heat and drought impact on carbon exchange in an age-sequence of temperate pine forests

BackgroundMost North American temperate forests are plantation or regrowth forests, which are actively managed. These forests are in different stages of their growth cycles and their ability to sequester atmospheric carbon is affected by extreme weather events. In this study, the impact of heat and drought events on carbon sequestration in an age-sequence (80, 45, and 17 years as of 2019) of eastern white pine (Pinus strobus L.) forests in southern Ontario, Canada was examined using eddy covariance flux measurements from 2003 to 2019.ResultsOver the 17-year study period, the mean annual values of net ecosystem productivity (NEP) were 180 ± 96, 538 ± 177 and 64 ± 165 g C m–2 yr–1 in the 80-, 45- and 17-year-old stands, respectively, with the highest annual carbon sequestration rate observed in the 45-year-old stand. We found that air temperature (Ta) was the dominant control on NEP in all three different-aged stands and drought, which was a limiting factor for both gross ecosystem productivity (GEP) and ecosystems respiration (RE), had a smaller impact on NEP. However, the simultaneous occurrence of heat and drought events during the early growing seasons or over the consecutive years had a significant negative impact on annual NEP in all three forests. We observed a similar trend of NEP decline in all three stands over three consecutive years that experienced extreme weather events, with 2016 being a hot and dry, 2017 being a dry, and 2018 being a hot year. The youngest stand became a net source of carbon for all three of these years and the oldest stand became a small source of carbon for the first time in 2018 since observations started in 2003. However, in 2019, all three stands reverted to annual net carbon sinks.ConclusionsOur study results indicate that the timing, frequency and concurrent or consecutive occurrence of extreme weather events may have significant implications for carbon sequestration in temperate conifer forests in Eastern North America. This study is one of few globally available to provide long-term observational data on carbon exchanges in different-aged temperate plantation forests. It highlights interannual variability in carbon fluxes and enhances our understanding of the responses of these forest ecosystems to extreme weather events. Study results will help in developing climate resilient and sustainable forestry practices to offset atmospheric greenhouse gas emissions and improving simulation of carbon exchange processes in terrestrial ecosystem models.

Carbon fluxes from a spring wheat–corn–soybean crop rotation under no‐tillage management

AbstractThe increase in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production in rainfed cropping systems of the northern Great Plains (NGP) has altered the delivery of ecosystem services from agricultural land. To date, there is limited understanding about how these crops affect the carbon (C) balance of cropping systems in the region when included in a short rotation window. This study sought to quantify C balance of a spring wheat (Triticum aestivum L.)–corn—soybean rotation under no‐tillage management using eddy covariance (EC) techniques. Paired field sites with the same soil type near Mandan, ND, were used for the study. Annual net ecosystem production (NEP) by crop was –34, 120, and 7 g C m–2 y–1 for spring wheat, corn, and soybean, respectively. Carbon removed in grain over the rotation was less than a third of C lost by ecosystem respiration (ER) (210 vs. 674 g C m–2 y–1). After accounting for grain C removal, net ecosystem carbon balance (NECB) was –164, –253, and –121 g m–2 y–1 for spring wheat, corn, and soybean, respectively, with a mean NECB of –179 ± 39 g C m–2 y–1 (P = .043; t test for difference from zero), implying the rotation was a net C source. Time associated with active crop growth each year was 27% for spring wheat, 41% for corn, and 28% for soybean. Management strategies that lengthen the period of biomass growth may mitigate C loss from spring wheat–corn–soybean rotations in the NGP.

An integrated remote sensing and model approach for assessing forest carbon fluxes in China

Forest plays an important role in reducing pressure on the natural environment, weaking the influence of greenhouse effects, and sequestrating atmospheric carbon dioxide. So far, due to the lack of complete understanding of forest ecosystem processes and the limitations on the scope of application of evaluation methods, there are still great uncertainties in the researches on carbon fluxes of forest ecosystems in China at the national level. In this study, an individual tree species FORCCHN model, which could flexibly use the inventory data as the initial field (more accurately) or use the remote sensing information to inverse initial field was applied. The dynamics of key carbon cycle fluxes (net primary productivity (NPP) and net ecosystem productivity (NEP)) and carbon sequestration of forest ecosystems in China from 1982 to 2019 were simulated based on remote sensing data and FORCCHN model. The results showed that forest ecosystems in China had great carbon sequestration potential over the past 39 years. From 1982 to 2019, the NPP of Chinese forests presented a fluctuated increase. Total NPP from 2011 to 2019 ranged from 0.91 PgC·a−1 to 1.14 PgC·a−1. Annual average NEP of forest ecosystems in China from 2011 to 2019 was 0.199 PgC·a−1 (1Pg = 1015 g). Influenced by climate, soil and vegetation, carbon sequestration potential in Chinese forest ecosystems presented obvious regional differences in space. The spatial distribution of NEP gradually increased from Northwest to Southeast China. From 2011 to 2019, forests in Yunnan Province had the strongest carbon storage capacity (72.79 TgC·a−1, 1Tg = 1012 g), followed by forests in Guangxi (18.49 TgC·a−1) and forests in Guangdong (10.01 TgC·a−1). Our results not only address concerns about carbon sequestration but also reflect the importance of Chinese forest resources in the development of the national economy and society.

Nutrient addition enhances carbon sequestration in soil but not plant biomass in a coastal shelter plantation in South China

AbstractCasuarina equisetifolia plantations have been widely established along tropical and subtropical coasts, where they act as a windbreak to shelter coastal areas. These shelter plantations also fulfill another important ecosystem service by sequestering large amounts of carbon (C). However, shelter plantations are usually established on nutrient‐poor sand dunes, which may limit tree growth and therefore C sequestration rates. To assess whether fertilization increases the C sequestration of coastal shelter plantations, we conducted a fertilization experiment in a young C. equisetifolia plantation with four treatments: nitrogen addition (+N), phosphorus addition (+P), nitrogen and phosphorus addition (+NP), and controls (CK). We quantified nutrient availability and annual net ecosystem production (NEP) during the key early establishment phase. Fertilization with +N and +P significantly increased ammonium‐N and extractable P in the surface soils and the N and P concentrations of branches, respectively. Surprisingly, the mean growth rate of C. equisetifolia plantations (24.59 ± 0.66 Mg ha−1 yr−1) was not affected by fertilization. The mean NEP was 6.18 ± 0.49 Mg C ha−1 yr−1, and there was no difference among fertilization treatments. However, soil organic C significantly increased by 41% and 36% with +N and +P, respectively, but not +NP. C. equisetifolia plantations can sequester large amounts of C in biomass on poor soils without the need for additional nutrients, although fertilization may enhance soil C storage. Considering the potential large planting area, we suggest that coastal C. equisetifolia shelter plantations could be an important nature‐based solution for climate change mitigation in coastal regions.

Multi‐Decadal Carbon Cycle Measurements Indicate Resistance to External Drivers of Change at the Howland Forest AmeriFlux Site

AbstractA long‐standing goal of ecology has been to understand the cycling of carbon in forests. This has taken on new urgency with the need to address a rapidly changing climate. Forests serve as long‐term stores for atmospheric CO2, but their continued ability to take up new carbon is dependent on future changes in climate and other factors such as age. We have been measuring many aspects of carbon cycling at an unmanaged evergreen forest in central Maine, USA, for over 25 years. Here we use these data to address questions about the magnitude and control of carbon fluxes and quantify flows and uncertainties between the different pools. A key issue was to assess whether recent climate change and an aging tree population were reducing annual C storage. Total ecosystem C stocks determined from inventory and quantitative soil pits were about 23,300 g C m−2 with 46% in live trees, and 48% in the soil. Annual biomass increment in trees at Howland Forest averaged 161 ± 23 g C m−2 yr−1, not significantly different from annual net ecosystem production (NEP = −NEE) of 211 ± 40 g C m−2 y−1 measured by eddy covariance. Unexpectedly, there was a small but significant trend of increasing C uptake through time in the eddy flux data. This was despite the period of record including some of the most climate‐extreme years in the last 125. We find a surprising lack of influence of climate variability on annual carbon storage in this mature forest.

Comparison of tree-ring and eddy-covariance derived annual ecosystem production estimates for jack pine and trembling aspen forests in Saskatchewan, Canada

Reliable projections of future carbon (C) dynamics are essential to resource management decision making under a changing climate. Additional corroborative data may reduce uncertainty in C flux estimates. Here we use a tree-ring based hybrid biometric modelling approach to estimate annual ecosystem production at jack pine (Pinus banksiana) and aspen (Populus tremuloides and Populus balsamifera) plots co-located with eddy-covariance installations in the boreal forest of Saskatchewan, Canada for a 28 year (1985 to 2012) period. Correspondence between tree-ring and eddy-covariance derived estimates was better for jack pine (14-year overlap, 1999 to 2012) than aspen (16-year overlap, 1997 to 2012), and better for some C fluxes than others. In particular, tree-ring estimates of annual and cumulative net ecosystem production were larger than eddy-covariance derived estimates for the overlapping period. Allometric equations, belowground production, and biomass turnover could neither be confirmed nor ruled out as causes of discrepancy, but a lower stand density and higher carbon use efficiency would together reduce observed differences for aspen. Tree-ring based estimates of biomass increment or net primary production showed good temporal correspondences with both current and previous year eddy-covariance analogues, and net and gross primary production. Similar comparisons for net ecosystem production and heterotrophic respiration had mixed results. This study improves on previous work by comparing independent estimates of the same fluxes quantities and demonstrates the value of tree-ring data for evaluating C flux estimates.