Growth, Photosynthesis, and Cold Tolerance of Eucalyptus benthamii Planted in the Piedmont of North Carolina

Inadequate cold tolerance of Eucalyptus spp. has limited a broader deployment beyond subtropical regions of the United States. We examined growth, photosynthetic rate, and cold tolerance of a cold-hardy Eucalypt (Eucalyptus benthamii) planted in North Carolina and compared the results with native Pinus taeda. After two growing seasons, E. benthamii surpassed P. taeda in both height (5.06 m, 1.34 m) and diameter (5.0 cm, 0.7 cm) growth, respectively. From April through November, E. benthamii’s mean photosynthetic rate (Ps) (13.82 µmol CO2 m−2s−1) was more than twice that of P. taeda (6.21 µmol CO2 m−2s−1). Similarly, mean Ps during winter months was 6.09 µmol CO2 m−2s−1 for E. benthamii compared to 2.73 µmol CO2 m−2s−1 for P. taeda. Laboratory assessments of cold tolerance demonstrated that, unlike P. taeda, E. benthamii had a limited ability to acclimate to seasonal temperature changes. The coldest temperature (Tm) where >50% of the tissue was damaged and recovery unlikely for E. benthamii was −13.4°C for leaves and −14.3°C for stems, whereas for P. taeda it was −29.9°C for leaves and −36.5°C for stems. The exceptional productivity of E. benthamii was not without trade-offs as all trees died after experiencing air temperatures of −12.8°C on January 7, 2014.