VERTICAL POINT QUADRAT SAMPLING AND AN EXTINCTION FACTOR TO CALCULATELEAF-AREA INDEX

The appropriateness of a correction factor to derive leaf area index ( LAI) from contact frequency using vertically-inserted point quadrat sa mpling was investigated. Point quadrat data were collected in a grid p attern over 72 individual shrubs and grass plots comprising eight comm on Great Basin scrub species of widely divergent ecology and canopy fo rm. Destructive sampling and intercept measurements were used to deter mine LAI values. Extinction coefficients were then calculated from pai red LAI and contact frequency. For all eight species, this extinction coefficient was statistically equivalent to 0.5 as a result of spheric al leaf angle distribution, permitting LAI estimation simply by multip lying contact frequency by 2. (C) 1997 Academic Press Limited.