Potential Implications for Expansion of Freeze- Tolerant Eucalyptus Plantations on Water Resources in the Southern United States

The potential expansion of freeze-tolerant (FT) Eucalyptus plantations in the United States has raised concerns about the implications for water resources. Modeling was used to examine the potential effects of expanding the distribution of FT Eucalyptus plantations in US Department of Agriculture Plant Hardiness Zones 8b and greater on water yield (Q). Analyses focused on two scales: the stand scale and the regional scale at the 12-digit Hydrologic Unit Code (HUC) watershed. Results suggested that the stand-level implications of planting FT Eucalyptus on Q could vary by location, the land cover type before Eucalyptus establishment, and the hydrologic conditions of the planting site and surrounding area. Compared with that for some pine plantations, Q at the stand level could be equal to or reduced by as much as to 130 mm year 1 (a reduction of 9 –16% of precipitation) near the end of the rotation or on sites when leaf area index (LAI) is 4 m m 2 and reduced by as much as 500 mm year 1 (a reduction of 33– 63% of precipitation) when LAI is 5 m m . In contrast, at the scale of conversion indicated by an economic analysis as most likely (e.g., 20% conversion of conifer to FT eucalyptus), reductions on Q at the 12-digit HUC scale will be negligible.