Can Leaf Inclination Angle Distribution and Foliage Clumping of a Mature Evergreen Eucalyptus Woodland Change with Elevated Atmospheric CO2?

Leaves are the primary point of interaction among atmospheric CO₂, energy (light), and plant physiology. Plant productivity (gain) is primarily determined by the amount of leaf area, leaf orientation and distribution in space. While leaf area might not change, the productivity can be still altered by changes in proportions of sunlit and shaded areas which are controlled by leaf orientation and distribution in space. Not much attention has been paid to possible changes in leaf orientation and distribution with elevated CO₂ . We report on first measurements of leaf inclination angle distribution and foliage clumping in a native evergreen Eucalyptus woodland exposed to +150 ppm elevated CO₂ - the EucFACE experiment in Western Sydney, New South Wales, Australia. We found that a spherical leaf angle distribution is not a valid assumption at this site. Our measurements of leaf inclination angles using leveled digital photography indicated an erectophile, highly skewed unimodal leaf inclination angle distribution function. We conclude that despite the measured steeper angles under elevated CO₂ levels, the change is not significant and falls within the expected natural variability and uncertainties connected with the measurement method. The lack of clear response of leaf orientation and foliage clumping to elevated CO₂ levels indicates that the previously produced datasets of leaf inclination angles available in public repositories such as TRY and foliage clumping maps obtained with Earth Observation data may be suitable while modeling carbon and water cycles under climate change.