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The risk of pollen-mediated gene flow from exotic Corymbia plantations into native Corymbia populations in Australia

Barbour, RC, Crawford, AC, Henson, M, Lee, DJ, Potts, BM and Shepherd, M 2008 , 'The risk of pollen-mediated gene flow from exotic Corymbia plantations into native Corymbia populations in Australia' , Forest Ecology and Management, vol. 256, no. 1- 2 , pp. 1-19 , doi:

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Sectors of the forest plantation industry in Australia are set to expand in the near future using species or
hybrids of the spotted gums (Corymbia, Section Politaria). Plantations of these taxa have already been
introduced across temperate and subtropical Australia, representing locally exotic introductions from
native stands in Queensland and New South Wales. A literature review was undertaken to provide
insights into the potential for pollen-mediated gene flow from these plantations into native populations.
Three factors suggest that such gene flow is likely; (1) interspecific hybridisation within the genus has
frequently been recorded, including between distantly related species from different sections, (2)
apparent high levels of vertebrate pollinator activity may result in plantation pollen being moved over
hundreds of kilometres, (3)much of the plantation estate is being established among closely related taxa
and therefore few barriers to gene flow are expected. Across Australia, 20 of the 100 native Corymbia taxa
were found to have regional level co-occurrence with plantations. These were located most notably
within regions of north-east New South Wales and south-east Queensland, however, co-occurrence was
also found in south-west Western Australia and eastern Victoria. The native species found to have cooccurrence
were then assessed for the presence of reproductive barriers at each step in the process of
gene flow thatmay reduce the number of species at risk even further. The available data suggest three risk
categories exist for Corymbia. The highest risk was for gene flow from plantations of spotted gums to
native populations of spotted gums. This was based on the expected limited existence of pre- and postzygotic
barriers, substantial long-distance pollen dispersal and an apparent broad period of flowering in
Corymbia citriodora subsp. variegata plantations. The following risk category focussed on gene flow from
Corymbia torelliana C. c. variegata hybrid plantations into native C. c. variegata, as the barriers associated
with the production and establishment of F1 hybrids have been circumvented. For the lowest risk
category, Corymbia plantations may present a risk to other non-spotted gum species, however, further
investigation of the particular cross-combinations is required. A list of research directions is provided to
better quantify these risks. Empirical data will need to be combined within a risk assessment framework
that will not only estimate the likelihood of exotic gene flow, but also consider the conservation status/
value of the native populations. In addition, the potential impacts of pollen flow from plantations will
need to be weighed up against their various economic and environmental benefits.

Item Type: Article
Authors/Creators:Barbour, RC and Crawford, AC and Henson, M and Lee, DJ and Potts, BM and Shepherd, M
Keywords: Biological invasions Exotic species Plantation forestry Off-site impacts Genetic pollution Genetic contamination
Journal or Publication Title: Forest Ecology and Management
ISSN: 0378-1127
DOI / ID Number:
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