Articles | Volume 14, issue 5
Biogeosciences, 14, 1039–1054, 2017
Biogeosciences, 14, 1039–1054, 2017

Research article 07 Mar 2017

Research article | 07 Mar 2017

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Matti Räsänen1, Mika Aurela2, Ville Vakkari2, Johan P. Beukes3, Juha-Pekka Tuovinen2, Pieter G. Van Zyl3, Miroslav Josipovic3, Andrew D. Venter3, Kerneels Jaars3, Stefan J. Siebert3, Tuomas Laurila2, Janne Rinne1,2,4,5, and Lauri Laakso2,3 Matti Räsänen et al.
  • 1Department of Physics, University of Helsinki, Finland
  • 2Finnish Meteorological Institute, Helsinki, Finland
  • 3Unit for Environmental Sciences and Management, North-West University, South Africa
  • 4Department of Geosciences and Geography, University of Helsinki, Finland
  • 5Department of Physical Geography and Ecosystem Science, Lund University, Sweden

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.

Short summary
This study presents measurements of carbon dioxide exchange between the atmosphere and a grazed savanna grassland ecosystem for 3 years. We find that the yearly variation in carbon dioxide balance is largely determined by the changes in the early wet season balance (September to November) and in the mid-growing season balance (December to January).
Final-revised paper