Comparison of direct and indirect leaf area index measurements of Pinus radiata D. Don

► Individual-tree leaf area models for radiata pine were independent of stocking. ► Stand leaf area index (LAI) was best estimated by an LAI-2000. ► Hemispherical image analysis was useful but inferior to the LAI-2000. ► Stems ha−1 affected the relationship between directly and indirectly measured LAI. Direct assessments of leaf area index (LAI) based on destructive sampling were modelled as a function of ground-based optical estimates and stand conditions over a wide range of LAI in two experiments in P. radiata plantations in New Zealand. Among optical methods assessed, estimates from a Licor LAI-2000 were most correlated with directly measured LAI, followed by hemispherical images processed with Gap Light Analyzer software and then the same images processed by Hemiview software. Optimal models for all three optical methods included stemsha−1, which increased the ratio between measured and estimated LAI. The ratio was also higher for small estimates of LAI than for large ones. The models had r2 values of 0.89, 0.72 and 0.58 respectively. It was concluded that the modelling approach provided radiata pine plantation managers with robust models for rapid assessment of LAI within the range of stockings examined.