Articles | Volume 13, issue 8
Biogeosciences, 13, 2387–2403, 2016

Special issue: OzFlux: a network for the study of ecosystem carbon and water...

Biogeosciences, 13, 2387–2403, 2016

Research article 26 Apr 2016

Research article | 26 Apr 2016

The contribution of trees and grasses to productivity of an Australian tropical savanna

Caitlin E. Moore1, Jason Beringer2,1, Bradley Evans3,4, Lindsay B. Hutley5, Ian McHugh1, and Nigel J. Tapper1 Caitlin E. Moore et al.
  • 1School of Earth, Atmosphere and Environment, Monash University, VIC, 3800, Clayton, Australia
  • 2School of Earth and Environment, University of Western Australia, WA, 6009, Crawley, Australia
  • 3Department of Environmental Sciences, The University of Sydney, NSW, 2015, Eveleigh, Australia
  • 4Terrestrial Ecosystem Research Network Ecosystem Modelling and Scaling Infrastructure, The University of Sydney, NSW, 2015, Eveleigh, Australia
  • 5School of Environment, Research Institute for the Environment and Livelihoods, Charles Darwin University, NT, 0909, Casuarina, Australia

Abstract. Savanna ecosystems cover 20 % of the global land surface and account for 25 % of global terrestrial carbon uptake. They support one fifth of the world's human population and are one of the most important ecosystems on our planet. Savanna productivity is a product of the interplay between trees and grass that co-dominate savanna landscapes and are maintained through interactions with climate and disturbance (fire, land use change, herbivory). In this study, we evaluate the temporally dynamic partitioning of overstory and understory carbon dioxide fluxes in Australian tropical savanna using overstory and understory eddy covariance measurements. Over a 2-year period (September 2012 to October 2014) the overall net ecosystem productivity (NEP) of the savanna was 506.2 (±22 SE) g C m−2 yr−1. The total gross primary productivity (GPP) was 2267.1 (±80 SE) g C m−2 yr−1, of which the understory contributed 32 %. The understory contribution was strongly seasonal, with most GPP occurring in the wet season (40 % of total ecosystem in the wet season and 18 % in the dry). This study is the first to elucidate the temporal dynamics of savanna understory and overstory carbon flux components explicitly using observational information. Understanding grass productivity is crucial for evaluating fuel loads, as is tree productivity for quantifying the tree carbon sink. This information will contribute to a significant refinement of the representation of savannas in models, as well as improved understanding of relative tree-grass productivity and competition for resources.

Short summary
Savannas cover 20 % of the global land surface and account for 25 % of global terrestrial carbon uptake. They support 20 % of the world’s human population and are one of the most important ecosystems on our planet. We evaluated the temporal partitioning of carbon between overstory and understory in Australian tropical savanna using eddy covariance. We found the understory contributed ~ 32 % to annual productivity, increasing to 40 % in the wet season, thus driving seasonality in carbon uptake.
Final-revised paper