Summary1. Revegetation can provide major environmental benefits in degraded landscapes, but there is also potential for negative impacts from genetic change in local native populations. Broad areas of revegetation may provide a large source of foreign genes in landscapes where small remnant native populations act as a sink. Genetic change from hybridisation can threaten population persistence and contribute to species extinction through genetic assimilation or demographic swamping. 2. Implementation of revegetation within a risk management framework allows identification of risk factors, analysis and evaluation of risk to inform decision-making and management to minimise and mitigate the risk. Informed analysis and evaluation of genetic risk is important in revegetation because it will be difficult to control or reverse the impacts in natural ecosystems and they are often not expressed until the second generation or later. 3. A risk assessment protocol is presented based on evaluation of factors that influence the likelihood and consequences of adverse genetic change from revegetation arising through pollen dispersal. 4. The assessment is applicable to a broad range of revegetation activities and contributes to the development of informed decision-making processes in implementation of revegetation systems and land use practices that protect and enhance biodiversity in degraded landscapes. 5. Synthesis and applications. Implementation of revegetation programmes within a risk management framework will help to ensure that significant environmental benefits are captured with minimal concomitant negative impacts on the surrounding biodiversity. A genetic risk protocol provides a tool for evaluation of potential adverse genetic impacts on native populations from revegetation and can be implemented in conjunction with weed risk assessment. Risk assessment as an integral part of evaluation of environmental impact for large-scale revegetation programmes will contribute to the development of informed decision-making processes in the implementation of revegetation systems, and ultimately, it will aid in the development of land uses that protect and enhance biodiversity in degraded landscapes.

Historically rare plant species with disjunct population distributions and small population sizes might be expected to show significant genetic structure and low levels of genetic diversity because of the effects of inbreeding and genetic drift. Across the globe, terrestrial inselbergs are habitat for rich, often rare and endemic flora and are valuable systems for investigating evolutionary processes that shape patterns of genetic structure and levels of genetic diversity at the landscape scale. We assessed genetic structure and levels of genetic diversity across the range of the historically rare inselberg endemic Acacia woodmaniorum. Phylogeographic and genetic structure indicates that connectivity is not sufficient to produce a panmictic population across the limited geographic range of the species. However, historical levels of gene flow are sufficient to maintain a high degree of adaptive connectivity across the landscape. Genetic diversity indicates gene flow is sufficient to largely counteract any negative genetic effects of inbreeding and random genetic drift in even the most disjunct or smallest populations. Phylogeographic and genetic structure, a signal of isolation by distance and a lack of evidence of recent genetic bottlenecks suggest long-term stability of contemporary population distributions and population sizes. There is some evidence that genetic connectivity among disjunct outcrops may be facilitated by the occasional long distance dispersal of Acacia polyads carried by insect pollinators moved by prevailing winds. Keywords: gene flow; inselberg; isolation; landscape; phylogeographic structure INTRODUCTION For plant species, demographic and genetic connectivity is affected by seed and pollen dispersal vectors, by a number of life history traits including life form, longevity and the mating system, and by the size and spatial arrangement of populations. Rare plant species and those with specific habitat requirements often have geographically disjunct and small population sizes. For these species, the surrounding landscape typically comprises a matrix of unsuitable habitat that acts as an effective physical barrier to dispersal and the size and spatial arrangement of populations assumes an important role in the structuring and maintenance of genetic diversity. Limitations to connectivity result in a degree of demographic isolation and genetic isolation among populations (Slatkin, 1987), and produce the phylogeographic and genetic structuring observed in many habitat specific, rare, endemics (Yates et al., 2007;Byrne and Hopper, 2008;Butcher et al., 2009). Limited connectivity among disjunct populations can result in reduced levels of genetic diversity as a result of increased levels of inbreeding and via the negative impacts of genetic drift (Slatkin, 1987;Ellstrand, 1992), both of which are further enhanced in small populations. Structuring and maintenance of genetic diversity has a key role in the ultimate persistence of species as they evolve and adapt to changing conditions. As a result of ...

Traditional morphological taxonomic classification is problematic in the Acacia saligna (Labill.) H.L.Wendl. species complex. Reliable identification of entities within the species is essential due to its extensive use both in Australia and overseas, its propensity for weediness, and its ongoing development for use in agroforestry. We used a Bayesian analysis approach to assess genetic structure in populations across the species natural range and to define the natural distributions of various genetic entities. The results indicate that three highly divergent genetic entities are apparent in the A. saligna species complex with further fine-scale genetic subdivision present within two. The three primary genetic entities correspond to the informally described subsp. ‘saligna’ and subsp. ‘pruinescens’ combined, subsp. ‘stolonifera’, and subsp. ‘lindleyi’. Within this primary structure two further entities are apparent; one separating subsp. ‘saligna’/‘pruinescens’ into eastern and western populations and the other distinguishing north-western ‘lindleyi’ populations from the rest of that subspecies distribution. The north-western catchments may have been an important refugium for the species diversity. The results of the study will aid in breeding programs, conservation of natural populations and control of invasive populations of this taxon.

Acacia saligna is a species complex that has become invasive in a number of countries worldwide where it has caused substantial environmental and economic impacts. Understanding genetic and other factors contributing to its success may allow managers to limit future invasions of closely related species. We used three molecular markers to compare the introduced range (South Africa) to the native range (Western Australia). Nuclear markers showed that invasive populations are divergent from native populations and most closely related to a cultivated population in Western Australia. We also found incongruence between nuclear and chloroplast data that, together with the long history of cultivation of the species, suggest that introgressive hybridization (coupled with chloroplast capture) may have occurred within A. saligna. While we could not definitively prove introgression, the genetic distance between cultivated and native A. saligna populations was comparable to known interspecific divergences among other Acacia species. Therefore, cultivation, multiple large-scale introductions and possibly introgressive hybridization have rapidly given rise to the divergent genetic entity present in South Africa. This may explain the known global variation in invasiveness and inaccuracy of native bioclimatic models in predicting potential distributions.

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