Vertical point quadrat sampling and an extinction factor to calculate leaf area index

The appropriateness of a correction factor to derive leaf area index (LAI) from contact frequency using vertically-inserted point quadrat sampling was investigated. Point quadrat data were collected in a grid pattern over 72 individual shrubs and grass plots comprising eight common Great Basin scrub species of widely divergent ecology and canopy form. Destructive sampling and intercept measurements were used to determine LAI values. Extinction coefficients were then calculated from paired LAI and contact frequency. For all eight species, this extinction coefficient was statistically equivalent to 0•5 as a result of spherical leaf angle distribution, permitting LAI estimation simply by multiplying contact frequency by 2.