Plant life history data as evidence of an historical mixed-severity fire regime in Banksia woodlands

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Context: The concept of the fire regime serves as an agreed upon template by which to inform understanding and management of fire-prone ecosystems globally. While observations from satellite imagery or palaeoecological proxy data can provide direct evidence of past fire regimes, they may be limited in temporal and/or spatial scale and are not available for all ecosystems. However, fire-related plant trait and demographic data offers an alternative approach to understand species-fire regime associations at the ecosystem scale.  Aims: We aimed to quantify the life history strategies and associated fire regimes for six co-occurring shrub and tree species from fire-prone, Mediterranean climate Banksia woodlands in southwestern Australia.  Methods: We collected static demographic data on size structure, seedling recruitment, and plant mortality across sites of varying time since last fire. We combined demographic data with key fire-related species traits to define plant life history strategies. We then compared observed life histories with a priori expectations for surface, stand-replacing, and mixed-severity fire regime types to infer historical fire regime associations. Key results: Fire-killed shrubs and weakly serotinous trees had abundant post-fire seedling recruitment, but also developed multi-cohort populations during fire-free periods via inter-fire seedling recruitment. Resprouting shrubs had little seedling recruitment at any time, even following fire, and showed no signs of decline in the long absence of fire likely due to their very long lifespans.  Conclusions: The variation in life history strategies for these six co-occurring species is consistent with known ecological strategies to cope with high variation in fire intervals in a mixed-severity fire regime. While resprouting and strong post-fire seedling recruitment indicate a tolerance of frequent fire, inter-fire recruitment and weak serotiny is interpreted as a bet-hedging strategy to cope with occasional long fire-free periods that may otherwise exceed adult and seed bank lifespans.  Implications: Our findings suggest that Banksia woodlands have evolved with highly variable fire intervals in a mixed-severity fire regime. Further investigations of species adaptations to varying fire size and patchiness can help extend our understanding of fire regime tolerances.

Notes

External Organisations
Murdoch University

Associated Persons
Russell Miller (Contributor)Neal Enright (Contributor); Joseph Fontaine (Contributor)