A genetic, demographic and habitat evaluation of an endangered ephemeral species Xerothamnella herbacea from Australia’s Brigalow belt

Abstract

Little remains of the Brigalow (Acacia harpophylla F.Muell. ex Benth.) woodlands of Australia, primarily due to land clearing for grazing and agriculture. Many threatened species in this region are poorly studied, and the life history traits of some herbaceous species such as ephemeral shoot systems, mean that conservation assessments are difficult. Recent gas pipeline developments have led to an increased need to understand the ecology and genetics of such taxa, in order to advise offset and translocation activities. Xerothamnella herbacea R.Baker is an endangered ephemeral herbaceous species from the Brigalow Belt region, which dies back during prolonged dry conditions. The aim of this study was to map the extent of potentially suitable habitat of this species, including determination of population extent within existing protected area estate. The species population sizes, reproductive activity and evidence of clonal spread, as well as the levels of genetic diversity and inbreeding, across the species range were also assessed to provide guidance for potential translocation and offsetting programs. The genetic results were related to the species suitable habitat distribution to test whether historic or recent habitat fragmentation most explains genetic patterns in this species. Most of the populations of this species were found to be small with less than 100 plants. The species appears not to be limited by its reproductive output, suggesting other factors may limit its abundance. The species populations have moderate to low genetic diversity suggesting the species is genetically viable in the medium term but are inbred which may be partially due to vegetative spread. Geographic proximity does not predict genetic similarity of populations and diversity is not correlated with population size. The results indicate potential translocation or offsetting programs need to account for genetic relationships in their planning. Resprouting ability has potentially assisted the species to slow the pace of genetic diversity loss due to anthropogenic fragmentation.