© 1990 Heron Publishing—Victoria, Canada
Plant area index in Eucalyptus globulus plantations determined indirectly by a light interception method
L. C. Gazarini (1), M. C. C. Araújo (2), N. Borralho (2) and J. S. Pereira (1)
1. Department of Forestry, Instituto Superior de Agronomia, Tapada da Ajuda, P-1399 Lisboa codex, Portugal / 2. CELBI, Quinta do Furadouro, P-2510 Obidos, Portugal /
Summary
Plant area index (PAI) was estimated in 3-year-old plantations of Eucalyptus globulus Labill. from (i) allometric relationships obtained from biomass harvesting, and (ii) canopy transmittance measurements. Diffuse
light canopy transmittance was measured with a multi-cone sensor consisting of five inverted cones to scan a hemisphere. Plant
area index was calculated from transmittance measurements by the inversion method assuming an ellipsoidal angle distribution
of uniformly distributed canopy elements, or by application of the Beer-Lambert Law using an empirically determined extinction
coefficient (k) for diffuse light of 0.5. Plant area index values of the experimental plantations varied as a consequence of diffferent
water and mineral nutrient application rates. The PAI estimated from biomass harvesting ranged from 1.61 to 4.04. The estimates
of PAI obtained by the ellipsoidal angle distribution method were significantly different from those based on the allometric
relationships or from transmittance measurements assuming a value of k for diffuse light of 0.5.
