Gene pool management of plantation eucalypts for the mid East Coast of Australia

Mixing of historically isolated species or populations due to human activity may have significant evolutionary and ecological consequences. The increase in establishment of eucalypt plantations in Australia over the past twenty years has raised concern over the potential impact on areas of native forest. Many forestry companies and management authorities are utilising sustainable forestry practices including gene pool management in their operations. Gene pool management involves a balance between the protection of the genetic diversity of native eucalypt populations and the benefits of planting eucalypts within certain ecosystems. Research into aspects of gene pool management of eucalypts (including implementation of risk management strategies to reduce genetic pollution) is well advanced for species and plantations in temperate regions. However, little research has been conducted in tropical and subtropical regions. Due to differences in the biological systems (e.g. pollination vectors) of tropical/subtropical and temperate eucalypt species, results of gene flow studies in temperate ecosystems may not be relevant to tropical/subtropical species. This study is one of the first to address gene flow issues for eucalypt plantations in tropical and subtropical regions. Three aspects relating to eucalypt gene pool management were explored: 1) population genetic structure; 2) direct measures of gene flow by pollen; and 3) risk of genetic pollution from eucalypt plantations. Assessment of chloroplast diversity in Eucalyptus grandis found that populations were not highly differentiated and showed little population structure, despite a large disjunction between northern and southern populations. This result was similar to previous studies and suggests that geographic isolation of northern populations may be relatively recent. Populations were grouped into three geographic regions. Pollen dispersal was measured in a population of E. grandis by paternity assignment using microsatellite markers. Pollen movement averaged a distance of 58 m with the longest pollen movement detected at 192 m. A large proportion of pollinations (46%) were the result of pollen immigration from outside the population, indicating the potential for genetic pollution when suitable measures to reduce gene flow are absent. The risk of genetic pollution from eucalypt plantations was assessed in the Hunter Valley where there is concern for a threatened population of Eucalyptus camaldulensis. Case studies of two plantations in the area suggest that pollen movement from plantations to native forest areas is probable, with E. camaldulensis hybrids deployed in plantations being the most likely source of genetic pollution. Strategies to reduce the risk of gene flow from eucalypt plantations are discussed.