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

Abstract

ContextThe Southwest Australia Floristic Region (SWAFR) is a global hotspot for plant taxonomic and functional diversity with 450 highly specialised orchids facing threats from habitat loss, grazing, weeds, fire and climate change. AimsTo 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. MethodsA 72-year fire history map was intersected with >1000 orchid locations and 4.5 km of transects to measure effects on abundance and diversity. Orchid survival, size, flowering, pollination and germination were measured post-fire relative to areas unburnt for >22 years. Key resultsThere were 58 overlapping major fires (1972-2024), averaging 8.7% of the 63-ha area annually. Correlating locations of 17 orchids with fire history revealed 5 fire-intolerant and 6 less productive species, while 6 benefited from fire-promoted flowering. Even the latter could be killed by unseasonal autumn fire. Fire decreased or increased pollination, with three orchids dependant on fire. Overall, fire impacts greatly out way benefits, as most orchids preferred long-unburnt areas, with maximum diversity and abundance three decades or more post-fire. Paradoxically, Pyrorchis nigricans required fire to flower, but only thrived in long-unburnt areas. ConclusionsOrchids had diverse fire outcomes from catastrophic to beneficial summarised by fire response indexes (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. ImplicationsResearch 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 SWAFR 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. Data StatementAll data are provided as tables and figures or supplemental tables