SPECIAL—Savanna Patterns of Energy and Carbon Integrated across the Landscape

Jason Beringer School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Jorg Hacker Airborne Research Australia, School of the Environment, Flinders University, Adelaide, South Australia, Australia

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Lindsay B. Hutley School of Environmental and Life Sciences, and School for Environmental Research, Charles Darwin University, Casuarina, Northern Territory, Australia

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Ray Leuning CSIRO Marine and Atmospheric Research, Canberra, Australian Capital Territory, Australia

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Stefan K. Arndt Department of Forest and Ecosystem Science, The University of Melbourne, Melbourne, Victoria, Australia

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Reza Amiri School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Lutz Bannehr Hochschule Anhalt (FH), FB AFG, Institut für Geoinformation und Vermessung, Dessau-Roßlau, Germany

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Lucas A. Cernusak School of Environmental and Life Sciences, and School for Environmental Research, Charles Darwin University, Casuarina, Northern Territory, Australia

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Samantha Grover School of Environmental and Life Sciences, and School for Environmental Research, Charles Darwin University, Casuarina, Northern Territory, Australia

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Carol Hensley School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Darren Hocking School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Peter Isaac School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Hizbullah Jamali Department of Forest and Ecosystem Science, The University of Melbourne, Melbourne, Victoria, Australia

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Kasturi Kanniah School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia, and Department of Remote Sensing, Faculty of Geoinformation Science and Engineering, University Technology Malaysia, Johor, Malaysia

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Stephen Livesley School of Geography and Environmental Science, Monash University, Clayton, and Department of Forest and Ecosystem Science, The University of Melbourne, Melbourne, Victoria, Australia

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Bruno Neininger MetAir AG, and Zurich University of Applied Sciences, Zurich, Switzerland

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Kyaw Tha Paw U Department of Land, Air and Water Resources, University of California, Davis, Davis, California

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William Sea CSIRO Marine and Atmospheric Research, Canberra, Australian Capital Territory, Australia

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Dennis Straten Department of Remote Sensing, Faculty of Geoinformation Science and Engineering, University Technology Malaysia, Johor, Malaysia

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Nigel Tapper School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Richard Weinmann School of Environmental and Life Sciences, and School for Environmental Research, Charles Darwin University, Casuarina, Northern Territory, Australia

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Stephen Wood School of Geography and Environmental Science, Monash University, Clayton, Victoria, Australia

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Steve Zegelin CSIRO Marine and Atmospheric Research, Canberra, Australian Capital Territory, Australia

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Savannas are highly significant global ecosystems that consist of a mix of trees and grasses and that are highly spatially varied in their physical structure, species composition, and physiological function (i.e., leaf area and function, stem density, albedo, and roughness). Variability in ecosystem characteristics alters biophysical and biogeochemical processes that can affect regional to global circulation patterns, which are not well characterized by land surface models. We initiated a multidisciplinary field campaign called Savanna Patterns of Energy and Carbon Integrated across the Landscape (SPECIAL) during the dry season in Australian savannas to understand the spatial patterns and processes of land surface–atmosphere exchanges (radiation, heat, moisture, CO2, and other trace gasses). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux transects, aircraft boundary layer budgets, and satellite remote sensing to quantify the spatial variability across a continental-scale rainfall gradient (transect). We found that the structure of vegetation changed along the transect in response to declining average rainfall. Tree basal area decreased from 9.6 m2 ha−1 in the coastal woodland savanna (annual rainfall 1,714 mm yr−1) to 0 m2 ha−1 at the grassland site (annual rainfall 535 mm yr−1), with dry-season green leaf area index (LAI) ranging from 1.04 to 0, respectively. Leaf-level measurements showed that photosynthetic properties were similar along the transect. Flux tower measurements showed that latent heat fluxes (LEs) decreased from north to south with resultant changes in the Bowen ratios (H/LE) from a minimum of 1.7 to a maximum of 15.8, respectively. Gross primary productivity, net carbon dioxide exchange, and LE showed similar declines along the transect and were well correlated with canopy LAI, and fluxes were more closely coupled to structure than floristic change.

Savannas are highly significant global ecosystems that consist of a mix of trees and grasses and that are highly spatially varied in their physical structure, species composition, and physiological function (i.e., leaf area and function, stem density, albedo, and roughness). Variability in ecosystem characteristics alters biophysical and biogeochemical processes that can affect regional to global circulation patterns, which are not well characterized by land surface models. We initiated a multidisciplinary field campaign called Savanna Patterns of Energy and Carbon Integrated across the Landscape (SPECIAL) during the dry season in Australian savannas to understand the spatial patterns and processes of land surface–atmosphere exchanges (radiation, heat, moisture, CO2, and other trace gasses). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux transects, aircraft boundary layer budgets, and satellite remote sensing to quantify the spatial variability across a continental-scale rainfall gradient (transect). We found that the structure of vegetation changed along the transect in response to declining average rainfall. Tree basal area decreased from 9.6 m2 ha−1 in the coastal woodland savanna (annual rainfall 1,714 mm yr−1) to 0 m2 ha−1 at the grassland site (annual rainfall 535 mm yr−1), with dry-season green leaf area index (LAI) ranging from 1.04 to 0, respectively. Leaf-level measurements showed that photosynthetic properties were similar along the transect. Flux tower measurements showed that latent heat fluxes (LEs) decreased from north to south with resultant changes in the Bowen ratios (H/LE) from a minimum of 1.7 to a maximum of 15.8, respectively. Gross primary productivity, net carbon dioxide exchange, and LE showed similar declines along the transect and were well correlated with canopy LAI, and fluxes were more closely coupled to structure than floristic change.

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