Phytophthora cinnamomi: extent and impact in Two Peoples Bay Nature Reserve, Western Australia (1983-2024)

Context. Phytophthora cinnamomi has been present in Two Peoples Bay Nature Reserve in Western Australia for decades, with impacts observed in susceptible plant communities. Aims. This study aimed to examine the past and present impact of P. cinnamomi on ecosystems. Methods. The distribution of P. cinnamomi was mapped 1983-1995 and reassessed in 2024. The long-term spread of the pathogen was measured. Plant densities were assessed, dry-weight biomass measured, and visits by avifauna quantified in infested and healthy vegetation. The persistence of chlamydospores was assessed. Key results. Mapping confirmed the widespread distribution of P. cinnamomi in the Reserve, with some areas mapped as disease-free up to 1995 now infested. Phytophthora dieback has spread in Banksia shrubland at an average of 1.5 m/year over a 33-year period. The density of species from the Proteaceae, Fabaceae, Ericaceae, and Hibbertia was significantly reduced; and the biomass of non-sedge species and visits by avifauna lower in infested compared with healthy Banksia shrubland. However, pockets of healthy habitat persist in infested areas and two highly susceptible Ericaceae (Leucopogon glabellus, Styphelia flavescens) were observed in high numbers in infested vegetation. Recovery of chlamydospores confirmed the persistence of the pathogen behind the dieback front. Conclusions. The impact of P. cinnamomi is long term and irreversible, however, some susceptible species may have mechanisms to ensure their persistence through prolific seed production. Implications. Protection of areas of healthy susceptible habitat from the introduction and spread of P. cinnamomi, the implementation of existing control measures and research into alternative measures continue to be a priority.