Structure of the EucFACE canopy: laser scanning, hemispherical photography, and modelling

Project leader, researchers and collaborators: 
Dr Teresa Gimeno, Prof Matthias Boer, Prof Darius Culvenor CSIRO, Dr Glenn Newnham CSIRO, Dr Craig Barton, Prof David Ellsworth

Funding period: 2012-2015

Project summary: A major uncertainty in the response of forest water use and carbon uptake is the response of the leaf area index (LAI). The expected reduction in leaf-level transpiration rate by elevated CO₂ may not lead to a forest ‘water savings’ if the LAI increases with long-term growth at elevated CO₂. Very little information is available on how mature, native forest vegetation (and especially open woodlands) respond to elevated CO₂ in terms of leaf growth and turnover, which in turn affect LAI.

It is possible to measure LAI non-destructively by measuring the interception of light (or lasers) by the canopy. The Beer-Lambert law connects light interception with LAI,

fAPAR = 1- e^{-K * L}

where fAPAR is the fraction absorbed photosynthetically active radiation (PAR), L is the leaf area index, and K is an ‘extinction coefficient’. The latter depends on the leaf angle distribution (not likely influenced by elevated CO₂), and the degree of clumping of leaves.

We aim to put in place a protocol for long-term monitoring of LAI in each of the six study rings, using canopy photos (from which fAPAR can be estimated), ground-based laser scanning methods (which also give a 3D representation of the canopy), and modelling (to refine the estimate of the extinction coefficient, K).

Our primary goal is to find out whether the leaf area index increases with elevated CO₂ in the EucFACE woodland. Our secondary goals are to increase our understanding of the dynamics of LAI (seasonal, drought-related, etc.) (also a major weakness of vegetation models).