Height differences in two eucalypt provenances with contrasting levels of aridity

Huge investments are fed into repairing the world’s degraded land, placing unparalleled pressure on delivering large quantities of quality seed. One of the most pressing issues is to identify which region to collect seed from and specifically whether local seed has a home-site advantage, particularly given the pressures of climate change. Recent theoretical recommendations have supported supplementing local seed with seed transferred in an arid-to-mesic direction to improve climate resilience of plantings. We tested this recommendation by establishing a reciprocal transplant trial in June 2010 of two seed provenances with contrasting aridity of Eucalyptus socialis, a tree widely used for restoration in southern Australia. We recorded survival and height over five years. 2010 and 2011 were particularly wet years at both sites (>1.8 times historical rainfall), but 2012 to 2015 were consistent with long-term rainfall trends, with the arid site receiving 12-48% less annual rainfall than the mesic site. Only the arid provenance showed a home-site advantage, and only for height after the two wet years followed by the three drier years. Provenances had similar levels of survival at both sites and did equally well at the mesic site. These results only provide initial evidence to support the recommendation that restoration plantings aiming to incorporate climate resilience should include arid-to-mesic transferred seed. Further work is needed to fully explore potential confounding site-specific effects. Supplementing locally collected seeds with arid-to-mesic transferred seed could be important to increase climate resilience of plantings and demands further studies to explore its costs vs. benefits.Martin F. Breed, Nicholas J. C. Gellie, Andrew J. Low