Abstract - Plants have co-evolved with the atmosphere and the climate and play essential roles in the global hydrological and carbon cycles. Their physiology is coupled to the atmosphere through processes of turbulent transport or mixing, which supply CO₂ for photosynthesis and remove heat and transpired water vapour from the leaves. This turbulence is chaotic but not random and plant communities or canopies interact with the wind in complex ways to determine the structure of the turbulence that effects the transport.

When canopy winds are strong, the dominant turbulent eddies in the canopy are shear-driven vortices but when winds are light, these are replaced by buoyant plumes. Both types of turbulence cause unexpected behaviour such as counter-gradient diffusion in the canopy-i.e., the flux of heat, water vapour or CO₂ can be in the direction of increasing concentration-and both are linked to the canopy structure.

At a larger scale, whether winds in the canopy are locally strong or light, depends on the structure of the kilometre-scale eddies that fill the atmospheric boundary layer (ABL) above. The ABL is the lowest region of the atmosphere and responds directly to processes on the ground over the diurnal cycle. However, the structure of ABL-scale turbulence, in turn, depends on the average fluxes of heat and momentum carried from the canopy to the air above by the canopy-scale vortices or plumes.

This essential two-way coupling poses a severe challenge to parameterising biosphere-atmosphere exchange in climate and weather models and to interpreting flux tower measurements of carbon exchange.

Most immediately, the interdependence of turbulent eddies ranging from those at leaf scale through canopy scale to ABL-scale means that the control of assimilation and transpiration by biological properties like stomatal conductance, is steadily lost as we move from the single leaf to the plant to the whole canopy and on to landscape scale. This has profound consequences for interpreting laboratory scale physiological measurements.

Biography - John Finnigan received his BSc from the University of Manchester in 1968 and his PhD from the Australian National University in 1978. He joined the CSIRO Division of Environmental Mechanics in 1972 and from 1989 to 1995 he was Head of that Division. In 2001 he founded the CSIRO Centre for Complex Systems Science, which he led until 2013. He is currently a CSIRO Fellow at CSIRO Environment.

He is a Fellow of the Australian Academy of Science, a Fellow of the American Geophysical Union, an Honorary Professor at the ANU School of Biology and at the School of Geophysical Sciences, University of Edinburgh, Scotland, and an Affiliate Scientist at the National Center for Atmospheric Research, Boulder Colorado.

His research activities have spanned Atmospheric Science, from the dynamics of turbulence to the role of biosphere-atmosphere exchange in climate dynamics and now include Complex Systems Science. Currently, as well as continuing work on boundary layer flow over complex topography, he is engaged in research on the ways that human decision making and societal dynamics can be captured quantitatively in models of the human-earth system.