Orchid losers and winners after fire in West Australian urban bushland: a response continuum deeply integrated with other traits

Context South-western Australia is a global hotspot for plant taxonomic and functional diversity with 450 orchids facing threats from habitat loss, grazing, weeds, fire, and climate change. Aims To develop fire history maps and effective monitoring tools to compare fire ecology of orchids with diverse ecological traits from an isolated urban banksia and eucalypt woodland. Methods A 72-year fire history map was intersected with >1000 orchid locations and transects. Orchid survival, flowering, pollination, and germination were measured post-fire relative to long unburnt areas. Key results There were 58 overlapping major fires (1972–2024), averaging 8.7% of the area annually. Fire history analysis of 17 orchids revealed 5 were intolerant, 6 less productive and 6 benefited from fire. Even the latter could be killed by unseasonal fires. Overall, fire impacts greatly outweighed benefits, as most orchids preferred long-unburnt areas, with maximum diversity and abundance three decades post-fire. Paradoxically, Pyrorchis nigricans was one of three orchids requiring fire to flower, but only thrived decades later. Conclusions Orchids had diverse fire outcomes from catastrophic to beneficial summarised by fire response index (FRI) and fire age safe thresholds (FAST). This continuum was correlated with tuber depth, clonality, dispersion and lifespans of orchids, so is deeply integrated with their biology and ecology. Implications Research in an urban nature reserve provided essential tools for sustainable management of orchids relevant to rare species, such as fire history maps, FRI and FAST. Many orchids prefer long unburnt areas, are intolerant to fire, or can be harmed by aseasonal fires. Thus, fire must be carefully managed in their habitats.