Open Access

Stephen Bell, Paul Hillier

• Systematic targeted surveys for the vulnerable and poorly conserved Pterostylis chaetophora (family Orchidaceae) were undertaken during peak flowering over ten days in 2018 and 2019 across 720 ha of Columbey National Park (Columbey). The assumed population size of this species in Columbey prior to this study (c. 20 individuals) was found to be unrepresentative of the number of sub-populations (175) and individuals (544) subsequently located along 141 km of search transects. Extrapolation of this result across the full Columbey study area suggests an upper population size of nearly 3000 plants, increasing the total documented New South Wales population 15-fold. The most commonly occupied communities for Pterostylis chaetophora were found to be Floodplain Redgum-Box Forest (57% of individuals and 54% of sub-populations), Lower Hunter Spotted Gum-Ironbark Forest (28% of individuals, 25% of sub-populations), and Seaham Spotted Gum-Ironbark Forest (14% of individuals, 18% of subpopulations). The largest sub-populations (>10 individuals) were in Floodplain Redgum-Box Forest where Eucalyptus moluccana dominated the canopy, followed by Lower Hunter Spotted Gum-Ironbark Forest and Seaham Spotted Gum-Ironbark Forest. All three occupied communities are relatively widespread in the lower Hunter Valley and lower North Coast regions, suggesting that such habitat elsewhere may harbour undetected populations of Pterostylis chaetophora. These results suggest that systematic targeted surveys for other threatened orchids are necessary to fully understand both the magnitude of a species' population and its occupied habitat. Such surveys may ultimately lead to re-assessment of the conservation status of some of these species where, like Pterostylis chaetophora, considerably more populations and individuals are uncovered within secure land tenure.