Growth, photosynthesis and cold tolerance of Eucalyptus benthamii planted in the Piedmont of North Carolina

Background/Question/Methods

For decades, Eucalyptus sp. have been considered as candidates for use in managed forests in the southeastern United States.  However, efforts have largely been stymied by periodic severe cold damage of experimental plantations; the result is that the only commercially grown Eucalyptus is in middle to southern Florida.  In small plantings, Eucalyptus benthamii growing in Raleigh, N.C., survived the winter of 2010/11 (relatively cold) and survived and even grew throughout the winter of 2011/12 (relatively warm).  Our interest is in assessing the growth, carbon gain, and cold tolerance of E. benthamii in a replicated study planted in the spring of 2012 on a site near Raleigh, NC (35° 36’ N, 77° 56’ W).  Growth was measured after 6 months, and every two weeks starting in December 2012.  Gas exchange (A_max) was measured at least once per month starting in November 2012.  Photosynthetic A_ci and light curves were measured quarterly. Cold tolerance, using the electrolyte leakage method, was measured several times during the winter and spring. Loblolly pine (Pinus taeda), a species well adapted to the region, was also measured in adjacent plots representing an adapted “control” species.

Results/Conclusions

In October, 2013, six months after planting, mean height was 125.37 cm (S.E. = 14.32) and 58 cm (1.71 ) for E. benthamii and loblolly pine, respectively.  As of mid-February, the winter of 2012/13 has been moderate with temperatures on two nights down to -8° C, and ample days with temperatures in the low to mid-teens.    A_max (µmol m² s^-1) of E. benthamii was 15.31, (S.E. = 0.89), 11.27 (0.97), 1.77 (0.43) and 7.77 (1.82) on 12/16 (previous night temp: 3.9°C), 12/12 (11.27°C), 1/23 (-7.8°C) and 1/29 (6.7°C), respectively.  A_max of pine was 8.86, 5.24, 0.17, and 1.82 on the same dates, respectively. In December, loblolly pine shoots were more cold tolerant than E. benthamii, though mature foliage from the two species had indistinguishable and marginal cold hardiness levels (damage estimated at +/- -12°C). However, after a January frost, foliage of E. benthamii showed signs of freezing damage on shoot tips, whereas none was evident on loblolly pine.  E. benthamii may have the capacity to survive winter severity in the Piedmont of North Carolina, but winter growth is dependent on both the depth of cold tolerance and low temperatures as well as the ambient daily mean temperatures.