The role of plant provenance in restoration ecology under climate change

The rapidly changing climate poses a challenge for many land management and conservation activities. In particular, the need to ensure future sustainability of revegetated communities has focused attention on the critical decision as to where to source seed (and other propagules). Traditionally, industry 'best' practice has adhered to the principle of sourcing propagation material locally. This practice has been based on a perception that locally-sourced material is adapted to local conditions and will therefore confer superior plant performance. Additionally, the use of local provenance is often considered desirable as a means of 'preserving' the genetic integrity of local populations, reducing risks of outbreeding depression. In situations where source populations are small and inbred and where the environment is rapidly changing (a situation we are currently facing), this 'local is best' practice needs to be challenged. Moreover, sourcing seed from genetically-impoverished populations with little adaptive potential is increasingly being viewed as more detrimental to restoration success than potential outbreeding depression. Improved seed-sourcing guidelines, developed in the context of changing environmental conditions and based on empirical evidence, are urgently needed to support restoration projects that are sustainable in the long term. This thesis explores the 'local is best' paradigm using field and glasshouse experiments. In Chapter 2, I describe a common garden experiment comparing the establishment success of different provenances (one local vs four non-local provenances) of six widespread species (Acacia falcata, Bursaria spinosa ssp. spinosa, Eucalyptus crebra, E. tereticornis, Hardenbergia violacea and Themeda australis), all community dominants and / or widely used in restoration projects on the Cumberland Plain, western Sydney. In Chapter 3, I describe an experiment designed to test the establishment success of four provenances each of E. tereticornis and T. australis under both current and simulated future temperature conditions for 2050 in western Sydney. In Chapter 4, I describe a glasshouse experiment comparing the survival and early growth rates of three provenances each of Acacia falcata and Eucalyptus crebra under ambient and elevated CO2. In Chapter 5, I describe the results of a survey (conducted in New South Wales) investigating understanding of local provenance issues among restoration practitioners. The overall results and conclusions of the research are summarized in the final Chapter. Little evidence was found that local provenance plants had superior establishment success in the field studies. In the glasshouse experiment, intraspecific variation was found between the provenances for both species, regardless of the CO2 treatment. The results of the survey identified several inconsistencies of practice and belief within the restoration industry and that the definition of 'local provenance' is very flexible. The majority of respondents are in favour of a review of seed-sourcing policy/guidelines to allow for the inclusion of non-local provenance material. Overall, this research provides empirical support to challenge the validity of the strict adherence to the 'local is best' paradigm in general, but particularly on the Cumberland Plain, and underpins the need for improved seed sourcing guidelines.