Carbon balance of a grazed savanna grassland ecosystem in South Africa

Räsänen, Matti; Aurela, Mika; Vakkari, Ville; Beukes, J. P.; Tuovinen, Juha‐Pekka; Zyl, P. G. van; Josipovic, Miroslav; Venter, Andrew D.; Jaars, Kerneels; Siebert, Stefan; Laurila, Tuomas; Rinne, Janne; Laakso, Lauri

doi:10.5194/bg-14-1039-2017

Cited by 34 publications

(30 citation statements)

References 38 publications

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“…In this study, a marked inter-annual variation of NPP was observed in the savanna ecosystem ( Fig. 3) consistent with the findings from other savannas (Moore et al, 2018a;Räsänen et al, 2017) and biomes (Knapp and Smith, 2001;Yang et al, 2011a). These results suggest that carbon accumulation fluctuates with annual precipitation.…”

Section: Inter-annual Variation Of Nppsupporting

confidence: 91%

Response of net primary productivity to precipitation exclusion in a savanna ecosystem

Jin

Liu

et al. 2018

Forest Ecology and Management

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Declines in precipitation are expected to affect plant performance and ecosystem carbon uptake. The response of ecosystem productivity to declines in precipitation and potential underlying mechanisms have been well studied in many biomes; however, little is known about the role of declines in precipitation and the involved mechanisms in savanna ecosystems. In a 4-year field precipitation manipulation experiment, we simulated four levels of precipitation exclusion (control, 30%, 50% and 70%) to assess the effects of declines in precipitation on net primary productivity (NPP) in a savanna ecosystem in southwestern China. NPP was strongly correlated with soil water content during the experimental period. Precipitation exclusion significantly decreased the NPP of the entire vegetation including trees, shrubs, perennials and litterfall but significantly increased the NPP of annuals. Our results suggested that precipitation exclusion can reduce the productivity of savannas and that plant functional types differ in sensitivity to precipitation exclusion. These findings imply that future declines in precipitation in savanna regions may negatively impact carbon accumulation and may induce shifts in plant functional types to buffer the effects of declines in precipitation on productivity and stabilize ecosystem function in savannas.

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Section: Inter-annual Variation Of Nppsupporting

confidence: 91%

Response of net primary productivity to precipitation exclusion in a savanna ecosystem

Jin

Liu

et al. 2018

Forest Ecology and Management

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“…including the statistical measurement error (Emeas) inherent in EC measurements and the error caused by gap filling of missing data (Egap) was estimated as follows (Räsänen et al, 2017):…”

Section: Appendix B: Uncertainty Analysis Of Neementioning

confidence: 99%

Greenhouse gas and energy fluxes in a boreal peatland forest after clearcutting

Korkiakoski¹,

Tuovinen²,

Penttilä³

et al. 2018

Preprint

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Abstract. The most common forest management method in Fennoscandia is rotation forestry including clearcutting and forest regeneration. In clearcutting, stem wood is removed and the logging residues are either removed or left on site. Clearcutting changes the microclimate and vegetation structure at the site, both of which impact the site's carbon balance. Peat soils with poor aeration and high carbon (C) densities are especially prone to such changes, and significant changes in C stocks and greenhouse gas exchange can be expected. We measured carbon dioxide (CO2) and energy fluxes with the eddy covariance method for two years (April 2016&#8211;March 2018) on a peatland drained for forestry. After the clearcutting, we observed a significant rise (23&#8201;cm) in the water table level. The site was also a large CO2 source (first year: 3086&#8201;&#177;&#8201;120&#8201;g&#8201;CO2&#8201;m&#8722;2yr&#8722;1, second year: 2072&#8201;&#177;&#8201;141&#8201;g&#8201;CO2&#8201;m&#8722;2&#8201;yr&#8722;1) after the clearcutting. These large CO2 emissions resulted from the collapse of gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation. During the second summer (June&#8211;August) after the clearcutting, GPP had already increased by 96&#8201;% and total ecosystem respiration decreased by 14&#8201;% from the previous summer. As a result, net CO2 emissions decreased during the second summer after clearcutting compared to the first one. The Bowen ratios were different in 2016 and 2017, starting at 2.6 in May 2016 and decreasing to less than 1.0 in August 2016, while in 2017 it varied mostly within 0.6&#8211;1.0. This was due to a 33&#8201;% decrease in the sensible heat flux and a 40&#8201;% increase in the latent heat flux from the 2016 values, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO2 and energy fluxes, we measured methane (CH4) and nitrous oxide (N2O) fluxes with manual chambers. After the clearcutting, the site turned from a small CH4 sink into a small source and from N2O-neutral to a significant N2O source. Compared to the large CO2 emissions, the global warming potential (GWP100) of the CH4 emissions was negligible. Also, the GWP100 due to increased N2O emissions was less than 10&#8201;% of that of the CO2 emission change.

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“…, Flanagan and Adkinson , Bradford and Crowther , Skinner , Rasanen et al. ), which could provide an improved understanding of hay production efficiency under rainfed conditions.…”

Section: Introductionmentioning

confidence: 99%

“…Ecosystem C fluxes, expressed as NEP:GEP ratio, could be used to quantify temporal variations in CUE as a fieldor farm-scale ecophysiological parameter for studying the proportion of C absorbed from the atmosphere for C accrual and hay production between contrasting pastures (Bradford and Crowther 2013). Moreover, these hayed agroecosystems may differ in their magnitudes and dynamics of photosynthetic surface and nitrogen (N) content (Lemaire et al 2007, Alberti et al 2010, Flanagan and Adkinson 2011, Bradford and Crowther 2013, Skinner 2013, Rasanen et al 2017, which could provide an improved understanding of hay production efficiency under rainfed conditions.…”

Section: Introductionmentioning

confidence: 99%

Carbon use efficiency of hayed alfalfa and grass pastures in a semiarid environment

2018

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Management, environment, and agroecosystem type are key factors influencing photosynthetic carbon (C) uptake and C use efficiency (CUE), calculated as the ratio of net ecosystem production to gross ecosystem production (NEP:GEP). Current literature has mainly emphasized annual C balance in studies involving multiple years with continuous monitoring of ecosystem C fluxes, yet CUE has not been thoroughly analyzed during the growing season, particularly in paired comparisons of contrasting types of pasture under semiarid conditions. From 2009 through 2013, we used eddy covariance method to determine daily, seasonal, and annual C budgets in rainfed alfalfa (Medicago sativa L.) and grass ecosystems subjected to periodic harvest (haying) near Mandan, North Dakota, USA. We found consistently higher magnitudes of C fluxes (ecosystem respiration [ER], NEP, GEP) and hay production in alfalfa than grassland. Leaf area and canopy nitrogen content per unit land area were key driving factors for daily, seasonal, and annual differences in C fluxes between agroecosystems. Net ecosystem C balance indicated C losses occurred through haying in both ecosystems, though no changes in soil C stocks were detected in either ecosystem over the course of the study. Mean NEP:GEP ratios (±standard error) during periods of steady carbon dioxide (CO2) uptake before and after haying were 0.43 ± 0.01 and 0.26 ± 0.03 for alfalfa and grassland, respectively, implying more efficient C use in the former. Moreover, alfalfa had consistently greater CUE than grassland despite variations in sunlight, temperature, and precipitation within and between growing seasons. Ratios of ER to GEP were also repeatedly lower in alfalfa than grassland in all five growing seasons. Under drought conditions, we infer alfalfa roots accessed water in the soil profile unavailable to more shallow‐rooted grass species. Overall, hayed alfalfa was more efficient and tolerant than grassland in assimilating and using atmospheric CO2 under variable intra‐ and inter‐seasonal conditions. Outcomes from this study suggest the inclusion of alfalfa in unirrigated crop rotations can sustain high CUE, C uptake, and hay production while mitigating C losses in a semiarid environment.

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Carbon balance of a grazed savanna grassland ecosystem in South Africa

Cited by 34 publications

References 38 publications

Response of net primary productivity to precipitation exclusion in a savanna ecosystem

Response of net primary productivity to precipitation exclusion in a savanna ecosystem

Greenhouse gas and energy fluxes in a boreal peatland forest after clearcutting

Carbon use efficiency of hayed alfalfa and grass pastures in a semiarid environment

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