Short rotation Eucalyptus plantations offer great potential for increasing wood-fiber production in the southern United States. Eucalyptus plantations can be highly productive (>35 m 3 ha À1 year À1), but they may use more water than intensively managed pine (primarily Pinus taeda L.) plantations. This has raised concern about how expansion of Eucalyptus plantations will affect water resources. We compared tree water use, stem growth, and WUE (kg wood per m 3 water transpired) in adjacent nine-year-old Eucalyptus benthamii and P. taeda plantations with similar stand density and leaf area. Sap flux (F d , g cm À2 s À1) was measured continuously over one year using thermal dissipation probes. Stem biomass, stem growth, tree water use (E t, L day À1), canopy transpiration per unit leaf area (E l , mmol m À2 s À1), and canopy stomatal conductance (G s , mmol m À2 s À1) were quantified. Eucalyptus had higher daily F d (196.6 g cm À2 day À1) and mean daily E t (24.6 L day À1) than pine (105.8 g cm À2 day À1 , 15.2 L day À1). Eucalyptus exhibited a seasonally bimodal pattern in daily E t that did not occur in pine. Monthly E t was 23-51% higher in Eucalyptus and differences between species were greatest in the spring and fall. Annual E t was 32% higher in Eucalyptus (9.13 m 3 H 2 O year À1) than pine (5.79 m 3 H 2 O year À1). Annual stem biomass increment was greater in Eucalyptus (Eucalyptus: 22.9; pine: 11.8 kg tree À1 year À1), and Eucalyptus had greater WUE (Eucalyptus: 2.86; pine 1.72 kg biomass m À3 H 2 O year À1). Pine exhibited a lower seasonal minimum and higher seasonal maximum leaf area index (LAI). At low LAI, there was no significant difference between species in E l or G s ; however, at maximum LAI, pine E l and G s were 46 and 43%, respectively of rates observed in Eucalyptus. The species differed in G s response to vapor pressure deficit (D). At a similar reference G s (G s,ref at D = 1 kPa), pine exhibited greater stomatal sensitivity to D. These results suggest that (1) Eucalyptus trees had higher sap flux and total water use than pine, (2) Eucalyptus had greater stem growth and WUE, and (3) species differences in water use were driven primarily by differences in E l and G s .

In recent Eucalyptus cold-tolerance trials, E. benthamii has shown good growth rates as well as cold tolerance for USDA Plant Hardiness Zones 8 and 9. This study developed growth and yield models for E. benthamii in the southeastern United States. A network of 182 temporary sample plots of E. benthamii ranging in age from 1.5 to 13.3 years was established, and inventory data were collected. Site quality was determined by fitting a polymorphic site index curve, whereas a function for stand basal area based on age, dominant height, and site occupancy was fitted. Stand-level volume and dry-weight biomass prediction equations were fitted as a function of dominant height and basal area. Based on the growth and yield model results, mean annual increments ranged from 26.4 m3 ha–1 year–1 at rotation age 6 years on the best sites to 13.7 m3 ha–1 year–1 at rotation age 10 years on the poorest sites. This is the first published set of management-oriented models for land managers considering planting E. benthamii in the southeastern United States.

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