Measuring light interception is important for understanding the conditions at the surface. Questions which had to be answered: How much of the light is reaching the ground and how much is hitting leaf material in the canopy? How efficient were the trees in filtering the light? This is important for having optimal photosynthetic performance.

Digital hemispherical photographs (Canon EOS 350 fitted with Sigma 8 mm fisheye objective) were taken at the central points of each subplot (n=9), horizontally leveled at 1.3 m height above ground in summer 2009. Auto Exposure Bracketing (AEB) at +/- 2 stops. The photos were analyzed with the software Hemisfer from P. Schleppi et al (2005). LAI was calculated on plot level including 9 pictures. Correction is applied for slope, non-linearity and clumping. Measurement of Photosynthetically Active Radiation (PAR) above and below canopy. PAR is between 400 and 700 nm wavelength. Term used: LI = (PAR above canopy - PAR below canopy) / (PAR above canopy). LI was calculated on plot level including 9 pairs of measurements. PAR is measured as photon flux density (μ mol m-2 s-1).

Comparative study sites of the BEF-China Experiment.

As plants are thought to compete for light, LAI gives a measure on how well the plot can exploit the resource light.