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 in 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 in 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 (epsilon), 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 epsilon. 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.

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We examine the effects of spacing and layout on the growth and form of 3-to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2×4 m), triple rows (2×4 m) at 10-m intervals, single rows (2×10 m) and isolated trees (10×10 m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m 2 in block plantings to 150 m 2 in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of aboveground radiation conversion was constant at 0.67 g MJ -1 irrespective of spacing. We estimated that foliar maintenance respiration (R m ) accounted for about 90% of above-ground R m . On a stand basis R m costs block plantings 23.90 t DM ha -1 year -1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha -1 year -1 (40% annual above-ground photosynthetic production) in stands of isolated trees.