Prediction of leaf area index in eucalypt plantations: effects of water stress and temperature

A calibration curve was established to convert plant area index of Eucalyptus nitens (Deane and Maiden) Maiden, assessed with a Li-Cor LAI-2000, to leaf area index, LAI. Based on a comparison of this calibration curve with existing calibration curves for other species, we concluded that a generic calibration curve may be applicable for the assessment of LAI eucalypt plantations. The Li-Cor LAI-2000 measurements were used to correlate the equilibrium LAI of E. nitens plantations with mean annual temperature. These and other data were then combined to develop relationships between LAI both E. nitens and E. globulus Labill. plantations and mean annual temperature and water stress. In plantations of both species, LAI declined linearly with water stress. However, marked differences in the effect of suboptimal growth temperatures on LAI were observed between species: on cold sites, LAI of E. nitens was markedly higher than LAI of E. globulus. A simple analytic model of net primary production (NPP) was developed. In this model, increasing LAI increased light interception and hence dry matter production, but simultaneously increased canopy respiration. Consequently, for a given light utilization coefficient, there was a value of LAI that maximized NPP. The model was parameterized for E. globulus and used to investigate the influences of water stress and mean annual temperature on LAI through their effects on light utilization coefficient. The model indicated that the value of LAI that was predicted to maximize NPP under various water and temperature stress regimes was similar to the value of LAI observed in the field under similar conditions only if leaf longevity was linked to water and temperature stress.