Non-destructive measurement of leaf area in olive ( Olea europaea L.) trees using a gap inversion method

Abstract

Leaf Area Index (LAI) data are required to characterise evaporation and assimilation rates from canopies. The LAI of a canopy of trees can be estimated from the transmittance of radiation at various angles. A commercial sensor for LAI determination (Plant Canopy Analyzer LI-COR LAI-2000) was tested for olive trees ( Olea europaea L.) during 1992 and 1993 in Cordoba, Spain. Plant leaf area of single olive trees was measured destructively and compared with indirect measurements with the PCA. A simulation model was constructed to test sampling strategies to determine plant area index (PAI) with the PCA in tree orchards. Plant areas and area densities of isolated olive trees in the field were accurately determined using the PCA. The PAI in arrays of young potted olive trees was also measured adequately. Measurements in an olive orchard and results of the simulation model of the PCA indicated that the PCA alone will underpredict PAI by around 30% in olive orchards or arrays of trees with similar geometry. Accurate PAI determination may be obtained in some cases by using the PCA to calculate the PA of single trees. Alternatively, PAI may be calculated as the weighted average of the maximum and minimum values of PAI in the orchard using the ground cover as a weighting factor. PAI estimates will be very close to LAI in olive orchards as the fraction of total area corresponding to leaves exceeds 90% in olive trees grown in the field.