Test of accuracy of LAI estimation by LAI-2000 under artificially changed leaf to wood area proportions

The accuracy of LAI-2000 Plant Canopy Analyzer for leaf(LAI) and plant (PAI) area indexes measurements was tested in 20-year-old Norway spruce stand using the reduction of canopy biomass. Needle and branch areas were reduced progressively upward every one meter. Values of effective leaf area index (LAI(e)), as an uncorrected product of LAI-2000, were compared with directly estimated LAI and PAI values after each reduction step. LAI-2000 underestimates PAI and LAI values according to LAI-2000 rings readings, and varied proportions between leaf and wood areas. The values of LAI(e) have been increased with decreasing of the view angle of the relevant LAI-2000 rings. Therefore, the underestimation of LAI becomes smaller when the readings near the horizon are masked. More accurate results, for projected LAI (LAI(p)) calculation, are produced by LAI-2000 when some dense grids of measurement points and the most vertical ring readings (0 - 13 degrees) are used. Correction factor 1.6 is possible to use for unreduced canopy hemi-surface LAI estimation, when the last rings (i.e. 5(th) and 4(th) rings, 47 - 74 degrees) are excluded. Correction factor of 1.25 can be used to compute LAI(p) if the angle readings under 43 degrees are also masked.