A genetic analysis of scattered Yellow Box trees (Eucalyptus melliodora A.Cunn. ex Schauer, Myrtaceae) and their restored cohorts

Scattered trees are highly visible reminders of lost vegetation in many intensively managed agricultural landscapes globally. Despite fragmentation, these trees provide important ecosystem services but are rapidly declining and expected to disappear within 200 years. Consequently, natural regeneration and restoration are required to maintain ecosystem services. But seed sourced for older restoration projects was often collected from too few individuals or small, inbred sites. Consequently, restored sites may have insufficient genetic diversity to underpin genetic and demographic processes and facilitate adaptation to climate change. Yellow Box (Eucalyptus melliodora) is a key species in endangered Box-Gum Grassy Woodlands in southeastern Australia that often now exists as scattered trees. This community has been restored for >20 years and it is now prudent to determine whether plantings that will persist over time have been created. Genetic diversity, mating system and pollen dispersal parameters were evaluated in scattered and restored trees and restored tree seed crops. Although within-site variability was evident, overall genetic diversity was significantly lower in restored trees. Significant genetic differentiation between restored and scattered trees indicated that seed was not necessarily sourced locally. Local (250 m) and distant (1 km) pollen sources were detected in the seed crops but these were often dominated by 3-5 nearby scattered trees. The persistence of some of these Yellow Box sites may be constrained by inbreeding once scattered trees are lost from the surrounding landscape. It is unclear how pervasive these responses are in restoration efforts and further information is needed to prevent the presence of restored sites being equated with persistence.