scholarly journals Drought and heatwave impacts on semi-arid ecosystems' carbon fluxes along a precipitation gradient

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190519 ◽  
Author(s):  
Tarek S. El-Madany ◽  
Arnaud Carrara ◽  
M. Pilar Martín ◽  
Gerardo Moreno ◽  
Olaf Kolle ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Ecosystem Respiration ◽  
Carbon Fluxes ◽  
Arid Ecosystems ◽  
Severe Drought ◽  
Precipitation Gradient ◽  
Continental Scale ◽  
Compound Event ◽  
The Impact ◽  
Semi Arid

The inter-annual variability (IAV) of the terrestrial carbon cycle is tightly linked to the variability of semi-arid ecosystems. Thus, it is of utmost importance to understand what the main meteorological drivers for the IAV of such ecosystems are, and how they respond to extreme events such as droughts and heatwaves. To shed light onto these questions, we analyse the IAV of carbon fluxes, its relation with meteorological variables, and the impact of compound drought and heatwave on the carbon cycle of two similar ecosystems, along a precipitation gradient. A four-year long dataset from 2016 to 2019 was used for the FLUXNET sites ES-LMa and ES-Abr, located in central (39°56'25″ N 5°46'28″ W) and southeastern (38°42'6″ N 6°47'9″ W) Spain. We analyse the physiological impact of compound drought and heatwave on the dominant tree species, Quercus ilex. Our results show that the gross primary productivity of the wetter ecosystem was less sensitive to changes in soil water content, compared to the dryer site. Still, the wetter ecosystem was a source of CO 2 each year, owing to large ecosystem respiration during summer; while the dry site turned into a CO 2 sink during wet years. Overall, the impact of the summertime compound event on annual CO 2 fluxes was marginal at both sites, compared to drought events during spring or autumn. This highlights that drought timing is crucial to determine the annual carbon fluxes in these semi-arid ecosystems. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals The European carbon cycle response to heat and drought as seen from atmospheric CO 2 data for 1999–2018

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190506 ◽  
Author(s):  
C. Rödenbeck ◽  
S. Zaehle ◽  
R. Keeling ◽  
M. Heimann
Keyword(s):  
Carbon Cycle ◽  
Elevated Temperatures ◽  
Ecosystem Respiration ◽  
Terrestrial Ecosystems ◽  
Severe Drought ◽  
Natural Ecosystems ◽  
Local Climate ◽  
Climate Conditions ◽  
Continental Scale ◽  
The Impact

In 2018, central and northern parts of Europe experienced heat and drought conditions over many months from spring to autumn, strongly affecting both natural ecosystems and crops. Besides their impact on nature and society, events like this can be used to study the impact of climate variations on the terrestrial carbon cycle, which is an important determinant of the future climate trajectory. Here, variations in the regional net ecosystem exchange (NEE) of CO 2 between terrestrial ecosystems and the atmosphere were quantified from measurements of atmospheric CO 2 mole fractions. Over Europe, several observational records have been maintained since at least 1999, giving us the opportunity to assess the 2018 anomaly in the context of at least two decades of variations, including the strong climate anomaly in 2003. In addition to an atmospheric inversion with temporally explicitly estimated anomalies, we use an inversion based on empirical statistical relations between anomalies in the local NEE and anomalies in local climate conditions. For our analysis period 1999–2018, we find that higher-than-usual NEE in hot and dry summers may tend to arise in Central Europe from enhanced ecosystem respiration due to the elevated temperatures, and in Southern Europe from reduced photosynthesis due to the reduced water availability. Despite concerns in the literature, the level of agreement between regression-based NEE anomalies and temporally explicitly estimated anomalies indicates that the atmospheric CO 2 measurements from the relatively dense European station network do provide information about the year-to-year variations of Europe’s carbon sources and sinks, at least in summer. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals Effects of drought and meteorological forcing on carbon and water fluxes in Nordic forests during the dry summer of 2018

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190516
Author(s):  
Anders Lindroth ◽  
Jutta Holst ◽  
Maj-Lena Linderson ◽  
Mika Aurela ◽  
Tobias Biermann ◽  
...  
Keyword(s):  
Surface Conductance ◽  
Severe Drought ◽  
Water Fluxes ◽  
Multilinear Regression ◽  
Evaporative Demand ◽  
Meteorological Forcing ◽  
Continental Scale ◽  
The Difference ◽  
Effects Of Drought ◽  
The Impact

The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of the variation (77%) was explained by the heterotrophic component. Six out of 11 forests reduced their annual NEP with more than 50 g C m −2 yr −1 during 2018 as compared to the reference year. The NEP anomaly ranged between −389 and +74 g C m −2 yr −1 with a median value of −59 g C m −2 yr −1 . This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals Desertification Control Practices in China

2020 ◽  
Vol 12 (8) ◽  
pp. 3258
Author(s):  
Yanli Lyu ◽  
Peijun Shi ◽  
Guoyi Han ◽  
Lianyou Liu ◽  
Lanlan Guo ◽  
...  
Keyword(s):  
Water Conservation ◽  
Anthropogenic Activities ◽  
Northern China ◽  
Global Scale ◽  
Lessons Learned ◽  
Dust Storms ◽  
Arid Ecosystems ◽  
Desertification Control ◽  
The Impact ◽  
Semi Arid

Desertification is a form of land degradation principally in semi-arid and arid areas influenced by climatic and human factors. As a country plagued by extensive sandy desertification and frequent sandstorms and dust storms, China has been trying to find ways to achieve the sustainable management of desertified lands. This paper reviewed the impact of climate change and anthropogenic activities on desertified areas, and the effort, outcome, and lessons learned from desertification control in China. Although drying and warming trends and growing population pressures exist in those areas, the expanding trend of desertified land achieved an overall reversal. In the past six decades, many efforts, including government policies, forestry, and desertification control programs, combined with eco-industrialization development, have been integrated to control the desertification in northern China. Positive human intervention including afforestation, and the rehabilitation of mobile sandy land, and water conservation have facilitated the return of arid and semi-arid ecosystems to a more balanced state. China’s practices in desertification control could provide valuable knowledge for sustainable desertified land management on a global scale.

Carbon cycle responses of semi-arid ecosystems to positive asymmetry in rainfall

2016 ◽  
Vol 23 (2) ◽  
pp. 793-800 ◽  
Author(s):  
Vanessa Haverd ◽  
Anders Ahlström ◽  
Benjamin Smith ◽  
Josep G. Canadell
Keyword(s):  
Carbon Cycle ◽  
Arid Ecosystems ◽  
Semi Arid

The Impact of Desertification as Revealed by Mapping

1978 ◽  
Vol 5 (1) ◽  
pp. 45-56 ◽  
Author(s):  
John A. Mabbutt
Keyword(s):  
Land Use ◽  
United Nations ◽  
Aridity Index ◽  
Mean Annual Precipitation ◽  
Arid Zones ◽  
Continental Scale ◽  
The United Nations ◽  
The Impact ◽  
Very High ◽  
Semi Arid

Maps prepared for the United Nations Conference on Desertification are critically reviewed and parts of selected maps are illustrated.The World Map of Desertification, called for by the United Nations General Assembly, delineates areas at risk of desertification as determined by bioclimatic stress, the inherent vulnerability of the land, and pressure of land-use. Areas of very high desertification hazard are shown to be those arid and semiarid regions with very heavy pressure of land-use. The threat of desertification is shown to be highest beyond the margins of the full deserts, but the risk extends wherever drought marks the seasonal or periodic extension of aridity. The term ‘drylands’ is used to define areas in which this risk occurs.Alternative maps at global scale include the Climate Aridity Index map based on the Budyko Ratio, which is the ratio between annual net radiation and mean annual precipitation. This allows a more sensitive depiction of aridity gradients and reveals that larger areas are under drought-stress than were previously recognized.The map of Experimental World Scheme of Aridity and Drought Probability uses soil features as an integrative record of past and present environmental conditions, including ‘land aridity’, but is constrained by the concept of soil zonality, without sufficient consideration of topographic and inherited factors which determine soil properties.The map of the Status of Desertification in the Hot Arid Regions shows the existing degree of desertification as judged by the difference between former (in the pristine state) and existing productivity. This is revealed as increasing outwards from the desert cores into the semi-arid lands, but the map does not extend into the sub-humid zone. However, it usefully depicts desertification as an expression of human impact on the land. Only very restricted areas are shown as having undergone very serious or irreversible desertification.Global maps are too generalized to depict actual desertification in quantitative terms, but the continental scale of the unpublished Desertification Hazards Map of Africa North of the Equator allows this to be done, in addition to depiction of the degree of vulnerability to desertification. Areas shown as already degraded occur mainly in the arid zone, whereas those of very high vulnerability lie mainly in the semi-arid zones.The U.N. Conference on Desertification recommended the compilation of an atlas of desertification to depict the state of the world's drylands and to serve as a cartographic basis for planning combative programmes. Regional maps of this kind, as exemplified in the synoptic maps accompanying the Case Studies of Desertification presented to the Conference, range in scale from 1:1,000,000 to 1:100,000—depending on the type of desertification portrayed—with the smaller scales for pastoral lands and more detailed scales for irrigation projects.

scholarly journals Nitrogen addition pulse has minimal effect in big sagebrush (Artemisia tridentata) communities on the Pinedale Anticline, Wyoming (USA)

2018 ◽  
Author(s):  
Christopher W. Beltz ◽  
Megan L. Mobley ◽  
Ingrid C. Burke
Keyword(s):  
Artemisia Tridentata ◽  
Forage Quality ◽  
Single Pulse ◽  
Nitrogen Addition ◽  
Arid Ecosystems ◽  
Available Nitrogen ◽  
Big Sagebrush ◽  
The Impact ◽  
Nitrogen Additions ◽  
Semi Arid

ABSTRACTNitrogen additions are known to elicit variable responses in semi-arid ecosystems, with responses increasing with precipitation. The response of semi-arid ecosystems to nitrogen are important to understand due to their large spatial extent worldwide and the global trend of increasingly available nitrogen. In this study, we evaluated the impact of a single nitrogen addition pulse on a semi-arid big sagebrush (Artemisia tridentata) ecosystem in western Wyoming. This is important given that sagebrush ecosystems are poorly understood, despite their prevalence in the western US. In addition, large-scale nitrogen additions have begun on sagebrush landscapes in Wyoming in order to mitigate population declines in mule deer (Odocoileus hemionus). The study objectives were (1) to evaluate the effectiveness of a nitrogen fertilization pulse in increasing sagebrush biomass and forage quality, and (2) to assess effects of nitrogen addition on soil biogeochemistry and vegetation community structure. We fertilized 15 plots across 5 locations in western Wyoming using a single pulse of urea (5.5g N m−2). In addition, we immobilized available nitrogen through surface hay treatments (250g hay/m2). Nitrogen additions failed to increase growth of sagebrush, alter nitrogen content of sagebrush leaders, or alter greenhouse gas efflux from soils. The plant community also remained unchanged; total cover, species richness, and community composition were all unaffected by our treatment application. Over the two years of this study, we did not find indications of nitrogen limitation of ecosystem processes, despite a wet growing season in 2014. Thus, we have found a general lack of response to nitrogen in sagebrush ecosystems and no treatment effect of a single pulse of N to sagebrush biomass or forage quality.

scholarly journals The impact of spatiotemporal variability in atmospheric CO<sub>2</sub> concentration on global terrestrial carbon fluxes

2018 ◽  
Author(s):  
Eunjee Lee ◽  
Fan-Wei Zeng ◽  
Randal D. Koster ◽  
Brad Weir ◽  
Lesley E. Ott ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Temporal Variability ◽  
Gross Primary Production ◽  
Carbon Fluxes ◽  
Atmospheric Co2 ◽  
Spatiotemporal Variability ◽  
Terrestrial Carbon ◽  
Diurnal Variability ◽  
Co2 Concentrations ◽  
The Impact

Abstract. Land carbon fluxes, e.g., gross primary production (GPP) and net biome production (NBP), are controlled in part by the responses of terrestrial ecosystems to atmospheric conditions near the Earth's surface. The Coupled Model Intercomparison Project Phase 6 (CMIP6) has recently proposed increased spatial and temporal resolutions for the surface CO2 concentrations used to calculate GPP, and yet a comprehensive evaluation of the consequences of this increased resolution for carbon cycle dynamics is missing. Here, using global offline simulations with a terrestrial biosphere model, the sensitivity of terrestrial carbon cycle fluxes to multiple facets of the spatiotemporal variability of atmospheric CO2 is quantified. Globally, the spatial variability of CO2 is found to increase the mean global GPP by 0.2 PgC year−1, as more vegetated land areas benefit from higher CO2 concentrations induced by the inter-hemisphere gradient. The temporal variability of CO2, however, compensates for this increase, acting to reduce overall global GPP; in particular, consideration of the diurnal variability of atmospheric CO2 reduces multi-year mean global annual GPP by 0.5 PgC year−1 and net land carbon uptake by 0.1 PgC year−1. The relative contribution of the different facets of CO2 variability to GPP are found to vary regionally and seasonally, with the seasonal variation in atmospheric CO2, for example, having a notable impact on GPP in boreal regions during fall. Overall, in terms of estimating global GPP, the magnitudes of the sensitivities found here are minor, indicating that the common practice of applying spatially-uniform and annually increasing CO2 (without higher frequency temporal variability) in offline studies is a reasonable approach – the small errors induced by ignoring CO2 variability are undoubtedly swamped by other uncertainties in the offline calculations. Still, for certain regional- and seasonal-scale GPP estimations, the proper treatment of spatiotemporal CO2 variability appears important.

scholarly journals Effect of Fires on Certain Properties of Forest Soils in Western Algeria

2020 ◽  
Vol 23 (3) ◽  
pp. 111-117
Author(s):  
Ayoub Allam ◽  
Amine Habib Borsali ◽  
Abdelkrim Kefifa ◽  
Mohamed Zouidi ◽  
Raphael Gros
Keyword(s):  
Forest Soils ◽  
Forest Fires ◽  
Arid Zone ◽  
Chemical Properties ◽  
Biological Properties ◽  
Basal Respiration ◽  
Arid Ecosystems ◽  
Control Zone ◽  
The Impact ◽  
Semi Arid

AbstractNatural disturbances, such as forest fires, cause significant changes in the structure and functioning of semi-arid ecosystems. After such disturbances, the impact on the soil ecosystem in its entirety is misunderstood. In this study, two years after the last fire, changes in the physicochemical and biological properties of Aleppo pine forest soils in the semi-arid zone were observed. Among all physical properties analysed, only the soil moisture remained significantly lower in the burnt zone in contrast to control zone. Considering the chemical properties, the only negatively affected parameter is the rate of organic matter. In terms of biological properties, results showed that the fire caused a significant decrease in soil microorganisms by decreasing basal respiration and microbial biomass. Conversely, the metabolic quotient recorded higher values in the fire zone than in the control zone. These results indicate that microbial communities in semi-arid soils, already stressed by climatic hazards, are very sensitive to the passage of even low-intensity fires.

scholarly journals Improving Estimation of Gross Primary Production in Dryland Ecosystems by a Model-Data Fusion Approach

2019 ◽  
Vol 11 (3) ◽  
pp. 225 ◽  
Author(s):  
Haibo Wang ◽  
Xin Li ◽  
Mingguo Ma ◽  
Liying Geng
Keyword(s):  
Carbon Cycle ◽  
Arid Region ◽  
Arid Regions ◽  
Meteorological Data ◽  
Gross Primary Production ◽  
Arid Ecosystems ◽  
Desert Ecosystems ◽  
Dryland Ecosystems ◽  
Semi Arid

Accurate and continuous monitoring of the production of arid ecosystems is of great importance for global and regional carbon cycle estimation. However, the magnitude of carbon sequestration in arid regions and its contribution to the global carbon cycle is poorly understood due to the worldwide paucity of measurements of carbon exchange in arid ecosystems. The Moderate Resolution Imaging Spectroradiometer (MODIS) gross primary productivity (GPP) product provides worldwide high-frequency monitoring of terrestrial GPP. While there have been a large number of studies to validate the MODIS GPP product with ground-based measurements over a range of biome types. Few studies have comprehensively validated the performance of MODIS estimates in arid and semi-arid ecosystems, especially for the newly released Collection 6 GPP products, whose resolution have been improved from 1000 m to 500 m. Thus, this study examined the performance of MODIS-derived GPP by compared with eddy covariance (EC)-observed GPP at different timescales for the main ecosystems in arid and semi-arid regions of China. Meanwhile, we also improved the estimation of MODIS GPP by using in situ meteorological forcing data and optimization of biome-specific parameters with the Bayesian approach. Our results revealed that the current MOD17A2H GPP algorithm could, on the whole, capture the broad trends of GPP at eight-day time scales for the most investigated sites. However, GPP was underestimated in some ecosystems in the arid region, especially for the irrigated cropland and forest ecosystems (with R2 = 0.80, RMSE = 2.66 gC/m2/day and R2 = 0.53, RMSE = 2.12 gC/m2/day, respectively). At the eight-day time scale, the slope of the original MOD17A2H GPP relative to the EC-based GPP was only 0.49, which showed significant underestimation compared with tower-based GPP. However, after using in situ meteorological data to optimize the biome-based parameters of MODIS GPP algorithm, the model could explain 91% of the EC-observed GPP of the sites. Our study revealed that the current MODIS GPP model works well after improving the maximum light-use efficiency (εmax or LUEmax), as well as the temperature and water-constrained parameters of the main ecosystems in the arid region. Nevertheless, there are still large uncertainties surrounding GPP modelling in dryland ecosystems, especially for desert ecosystems. Further improvements in GPP simulation in dryland ecosystems are needed in future studies, for example, improvements of remote sensing products and the GPP estimation algorithm, implementation of data-driven methods, or physiology models.

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