Turning up the heat on the provenance debate: Testing the 'local is best' paradigm under heatwave conditions

A key aspect of successful restoration projects is the sourcing of propagation material suited to the environmental and biotic conditions of the proposed planting site. Traditionally, the use of propagules collected locally has been advocated for revegetation on the assumption that this material is better adapted to local conditions. A rapidly changing climate, however, is challenging the assumption that the use of local genetic stock will provide the best restoration outcome in the long term. We tested the 'local is best' paradigm using open top chambers to simulate the predicted summer temperatures for 2050 in western Sydney, Australia. We compared the establishment success of Eucalyptus tereticornis and Themeda australis, dominant species in Cumberland Plain Woodland, grown from local versus non-local seed. All plants survived an exceptional summer heatwave and few differences between temperature treatments were found. No evidence of local superiority was found for survival or growth of non-reproductive tissues of either species. However, local provenance plants of E.tereticornis suffered significantly greater herbivory in the ambient temperature treatment than one non-local provenance, and local provenance plants of T.australis demonstrated significant superiority to most non-local provenances in all categories of reproductive growth. For both species, the provenances from warmer climates demonstrated comparable, and often better, growth performance than the local provenance plants.