Genetic pollution of native eucalypt gene pools—identifying the risks

Abstract

The contamination of native-eucalypt gene pools via exotic pollen is of concern as (i) pollen dispersal is believed to be much more widespread than seed dispersal, (ii) reproductive barriers are often weak between closely related species, (iii) European settlement has already had a major impact on Australia's eucalypt woodlands and mallee, (iv) there has been a rapid expansion of eucalypt plantations and restoration plantings in Australia and (v) Australia is the custodian of an internationally important genetic resource. Pollen flow between plantation and native eucalypt species has already been reported and implementation of strategies to minimise the risk and consequences of genetic pollution is important if Australian forestry is to be considered sustainable. The risks associated with the introduction of non-native species, provenances and hybrids include direct effects on the gene pool through genetic pollution as well as indirect effects on dependent biodiversity. In many cases, the risk of genetic pollution will be small due to strong barriers to hybridisation between distantly related species, differences in flowering time or poor fitness of hybrids. There is no risk of hybridisation between species from the different major eucalypt genera and/or subgenera (e.g. symphyomyrts, monocalypts, eudesmids, bloodwoods and angophora). The main plantation species are symphyomyrts and within this subgenus, the probability of successful hybridisation generally decreases with increasing taxonomic distance between species. The planting of non-local provenances or improved material within the range of native populations has the potential to have an impact on local gene pools to varying degrees, indicating the requirement for the adoption of management strategies to reduce this risk. Naturally small or remnant populations are at particular risk. A framework for assessment of the risk of genetic pollution is developed herein.