ESTIMATION OF TREE CANOPY LEAF-AREA INDEX BY GAP FRACTION ANALYSIS

We estimated leaf area index (LAI) in a needle-leaved forest and a bro ad-leaved orchard using four instruments which measure fractional ligh t penetration through the canopy. Gap fraction data were analyzed by a one-dimensional inversion model or by using the Beer-Lambert Law. Ins trument and analytical technique both had a strong influence on calcul ated LAI. There was no consistent pattern of LAI results among instrum ents so no simple cross-calibration can be offered. Three of the four instruments accurately estimated orchard LAI when used with one or the other analytical technique. In addition to performance, practical con siderations including cost, sampling, and data analysis were also comp ared among the instruments. Because the instruments do not provide con sistently accurate LAI estimates, LAI should be independently corrobor ated before use in any particular situation. These instruments may be most useful for relative LAI comparisons in a specific canopy type whe n a single combination of instrument and analytical technique is emplo yed.