Very high CO<sub>2</sub>exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Tagesson, Torbern; Ardö, Jonas; Guiro, Idrissa; Cropley, Ford; Mbow, Cheikh; Horion, Stéphanie; Ehammer, Andrea; Mougin, E.; Delon, Claire; Galy‐Lacaux, Corinne; Fensholt, Rasmus

doi:10.1080/00167223.2016.1178072

Cited by 22 publications

(22 citation statements)

References 90 publications

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“…The annual NEE sum and its inter-annual variation at our site differ significantly from the results reported by a previous study at a grazed savanna grassland in Dahra, Senegal (Tagesson et al, 2015(Tagesson et al, , 2016b. The Dahra site had a peak MODIS LAI (MOD15A2) of between 1.4 and 2.1 and a mean annual precipitation of 524 mm, which are similar to the Welgegund site.…”

Section: Comparison To Other Sitescontrasting

confidence: 53%

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Räsänen¹,

Aurela²,

Vakkari³

et al. 2017

Biogeosciences

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Abstract. Tropical savannas and grasslands are estimated to contribute significantly to the total primary production of all terrestrial vegetation. Large parts of African savannas and grasslands are used for agriculture and cattle grazing, but the carbon flux data available from these areas are limited. This study explores carbon dioxide fluxes measured with the eddy covariance method for 3 years at a grazed savanna grassland in Welgegund, South Africa. The tree cover around the measurement site, grazed by cattle and sheep, was around 15 %. The night-time respiration was not significantly dependent on either soil moisture or soil temperature on a weekly temporal scale, whereas on an annual timescale higher respiration rates were observed when soil temperatures were higher. The carbon dioxide balances of the years 2010-2011, 2011-2012 and 2012-2013 were −85 ± 16, 67 ± 20 and 139 ± 13 gC m −2 yr −1 , respectively. The yearly variation was largely determined by the changes in the early wet season fluxes (September to November) and in the mid-growing season fluxes (December to January). Early rainfall enhanced the respiratory capacity of the ecosystem throughout the year, whereas during the mid-growing season high rainfall resulted in high carbon uptake.

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Section: Comparison To Other Sitescontrasting

confidence: 53%

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Räsänen¹,

Aurela²,

Vakkari³

et al. 2017

Biogeosciences

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Section: Seasonal Dynamics and Inter-annual Variability Of Ec Gpp Pamentioning

confidence: 95%

“…However, Dahra had the highest average EC GPP during the growing season (8.6 g C m −2 d −1 ) despite having similar climatic and subsurface conditions as the other two sites (Table 1). A recent study by Tagesson et al [70] provided two plausible reasons for the higher photosynthetic capacity at Dahra: (1) A total of 80% of the vegetative cover at Dahra is comprised of herbaceous C 4 plants, signifying a higher concentration of plants that are more productive under optimal climatic conditions (i.e., during the growing season); and (2) intense grazing disturbance causes plants to develop strategies that allocate more C to leaves thereby increasing their leaf area index and leading to increase in absorbed photosynthetically active radiation and C assimilation. A third plausible reason for the high EC GPP at Dahra is linked to the increase in relative humidity which ranges from 9% in the dry season to 63% in the growing season (Table 1).…”

Section: Seasonal Dynamics and Inter-annual Variability Of Ec Gpp Pamentioning

confidence: 99%

Evaluating Water Controls on Vegetation Growth in the Semi-Arid Sahel Using Field and Earth Observation Data

et al. 2017

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Water loss is a crucial factor for vegetation in the semi-arid Sahel region of Africa. Global satellite-driven estimates of plant CO 2 uptake (gross primary productivity, GPP) have been found to not accurately account for Sahelian conditions, particularly the impact of canopy water stress. Here, we identify the main biophysical limitations that induce canopy water stress in Sahelian vegetation and evaluate the relationships between field data and Earth observation-derived spectral products for up-scaling GPP. We find that plant-available water and vapor pressure deficit together control the GPP of Sahelian vegetation through their impact on the greening and browning phases. Our results show that a multiple linear regression (MLR) GPP model that combines the enhanced vegetation index, land surface temperature, and the short-wave infrared reflectance (Band 7, 2105-2155 nm) of the moderate-resolution imaging spectroradiometer satellite sensor was able to explain between 88% and 96% of the variability of eddy covariance flux tower GPP at three Sahelian sites (overall = 89%). The MLR GPP model presented here is potentially scalable at a relatively high spatial and temporal resolution. Given the scarcity of field data on CO 2 fluxes in the Sahel, this scalability is important due to the low number of flux towers in the region.

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“…Total precipitation is expected to decrease in the western parts and to increase in the central and eastern parts of the Sahel, although a high variability remains among the different climate model predictions (Biasutti, 2019;Pascale et al, 2016). Furthermore, an increase in rain event intensity, coupled with a decrease in frequency, has been observed in recent years (Panthou et al, 2014;Taylor et al, 2017) and is projected for the coming century (Dunning et al, 2018). Even though the region has a long history of adapting to drastic changes in rainfall (Mortimore, 2010), it is still uncertain how current and future changes in rainfall regimes will impact the plant functional responses in the Sahel and in drylands in general.…”

Section: Introductionmentioning

confidence: 99%

Contrasting responses of woody and herbaceous vegetation to altered rainfall characteristics in the Sahel

et al. 2021

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Abstract. Dryland ecosystems are a major source of land cover, account for about 40% of Earth's terrestrial surface and net primary productivity, and house more than 30 % of the human population. These ecosystems are subject to climate extremes (e.g. large-scale droughts and extreme floods) that are projected to increase in frequency and severity under most future climate scenarios. In this modelling study we assessed the impact of single years of extreme (high or low) rainfall on dryland vegetation in the Sahel. The magnitude and legacy of these impacts were quantified on both the plant functional type and the ecosystem levels. In order to understand the impact of differences in the rainfall distribution over the year, these rainfall anomalies were driven by changing either rainfall intensity, event frequency or rainy-season length. The Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model was parameterized to represent dryland plant functional types (PFTs) and was validated against flux tower measurements across the Sahel. Different scenarios of extreme rainfall were derived from existing Sahel rainfall products and applied during a single year of the model simulation timeline. Herbaceous vegetation responded immediately to the different scenarios, while woody vegetation had a weaker and slower response, integrating precipitation changes over a longer timeframe. An increased season length had a larger impact than increased intensity or frequency, while impacts of decreased rainfall scenarios were strong and independent of the season characteristics. Soil control on surface water balance explains these contrasts between the scenarios. None of the applied disturbances caused a permanent vegetation shift in the simulations. Dryland ecosystems are known to play a dominant role in the trend and variability of the global terrestrial CO2 sink. We showed that single extremely dry and wet years can have a strong impact on the productivity of drylands ecosystems, which typically lasts an order of magnitude longer than the duration of the disturbance. Therefore, this study sheds new light on potential drivers and mechanisms behind this variability.

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Very high CO₂exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Cited by 22 publications

References 90 publications

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Evaluating Water Controls on Vegetation Growth in the Semi-Arid Sahel Using Field and Earth Observation Data

Contrasting responses of woody and herbaceous vegetation to altered rainfall characteristics in the Sahel

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Very high CO2exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Cited by 22 publications

References 90 publications

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Evaluating Water Controls on Vegetation Growth in the Semi-Arid Sahel Using Field and Earth Observation Data

Contrasting responses of woody and herbaceous vegetation to altered rainfall characteristics in the Sahel

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Very high CO₂exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem