Special - The Savanna Patterns of Energy and Carbon Integrated Across the Landscape Campaign

Background/Question/Methods

Savanna ecosystems occur in over 20 countries and cover approximately 15% of the world’s land surface. They consist of a mix of trees and grasses that coexist, but are spatially highly varied in their physical structure, species composition and physiological function. These characteristics alter land–atmosphere exchanges of heat, water, carbon dioxide and other trace gases, which feed back to the climate at multiple scales.  This spatial variation is driven by climate factors (rainfall gradients and seasonality) and disturbances (fire, grazing, herbivory, cyclones). Australian savannas provide significant ecosystem services and further systematic scientific study is needed to sustainably manage these ecosystems.

How do the fluxes of carbon, water and energy vary spatially and temporally across the savanna region and how do we scale from leaf to landscape?

• What are the key differences in climate and ecosystem characteristics (physical structure, species composition, physiological

function) that drive the variability in land surface–atmosphere exchanges?

• How can the fluxes of carbon, water vapour and heat over the various ecosystems as derived from the various measurement

techniques, be combined to form a comprehensive and consistent estimate of the regional fluxes and budgets across the landscape

We undertook an interdisciplinary research effort (SPECIAL) to understand the patterns and processes of carbon, water and energy cycles across northern Australian landscapes across scales from point to region. We quantified the land surface–atmosphere exchanges across the vast region of Australian savannas using a hierarchical, integrated measurement and modelling approach to determine regional greenhouse gas and water budgets. The research team comprised groups from seven institutions and four countries. The research effort comprised of a multi- year measurement and modelling endeavour and culminated in an intensive field program held in September 2008 (late dry season). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux and regional budget measurements, and satellite remotely sensed quantities to quantify the spatial variability utilizing a continental scale rainfall gradient that resulted in a variety of savanna types.

Results/Conclusions

We show that variations in savanna structure, composition and function (i.e. leaf area and function, stem density, albedo, roughness) interact with the overlying atmosphere directly through exchanges of heat and moisture, which alter the overlying boundary layer. The ultimate goal of our research is to be able to produce robust estimates of regional carbon and water cycles to inform land management policy about how they may respond to future environmental changes.