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Weeds and Bushcare Issues

PLANT WHAT NATIVE WHERE?
Does 'provenance' matter?

Bob Makinson, conservation botanist at the Sydney Royal Botanic Gardens, delivered an excellent presentation on April 2, 2009, on reasons why the provenance, or source, of plant material is important for all of us working towards restoring the health of the bush in the Blue Mountains.

photo: Gil Appleton

Adding plants or seeds from another source may be necessary to help restore a local patch or species to healthy size, but there are some risks. Infra-species crossing (same species, different provenance) can cause changes in genetic diversity. This may have positive or negative effects on the offspring, including reduced seed-set or less fit progeny. Occasionally, different provenances of the same species cannot interbreed, so mixing them may even retard restoration.

Threatened species are a special case, and the consequences of a wrong decision are greater. Collection or translocation of seed or whole plants of these species should only be done with expert involvement.

For most 'ordinary' species, Bob pointed to recent research results which add to the 'Rules of Thumb' which many of us already practice.

For the Blue Mountains, his main messages were:

• Plant material ideally to be sourced from within 5km (flexible) at a similar altitude, and from similar habitat and soil-type.
• Review history of source area – is it regrowth, perhaps from a limited genetic base?
• Review knowledge of the species (e.g. breeding system).
• Review your goals –survivorship rate of planted material is important, but the goal is long-term viable populations, with 'fit' offspring, the right pollinators and dispersers, and enough genetic variability to allow future adaptation.
• Source seed from populations of over 200, as smaller populations may have a narrow genetic base and produce poor seed.
• If trying to establish connectivity between remnants, minimise distances to maximise gene flow.

Inter-species hybridization is more common in some genera, Eucalypts and Grevilleas being prone to it. If you have very rare species nearby, seek advice on the risk of impact on the wild plants. Gene flow from large revegetation plots of eucalypts to wild plants is increasingly common. We should keep in mind that the World Heritage status of the Blue Mountains relies largely on the abundant species of Eucalypts, and protecting their genetic integrity is important. Bob pointed to a good review paper on this issue, with pre-planting risk assessment rules that can greatly reduce the problem.

The good news in terms of the effect of climate change on restored native bushland in the Blue Mountains was that we may be buffered to some extent – Bob suggested that our topography will modify the mega-climate changes that are expected, and we have robust native communities and massive conserved areas. (Bushcare volunteers can take some credit for those last two factors). We also do not expect very large plantations of introduced Eucalypts (3 million hectares of Eucalypt plantations are planned for Australia by 2020).

Bob quoted a modified version of the doctors' oath – “first do no (more) harm”. Nevertheless, he also stressed that we should not let fear of provenance problems, or of climate change, paralyse our restoration efforts. In the context of the Blue Mountains, making sure we adhere to good practices with plant provenance is a way to avoid harm.

The talk led to a lively forum involving the audience of volunteers, students, nursery representatives, professionals and concerned residents.

Several research papers relevant to the talk are available at the Bushcare office.

Listen to Bob Makinson's Talk

If you have fast Broadband and a sizeable bandwidth allowance, you can listen to Bob's talk and the questions that followed. The mp3 files are listed below for immediate listening or download.