High adult mortality and failure of recruitment in a population of Banksia spinulosa following high‐intensity fire

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ABSTRACT Serotinous plants that both release seed and resprout after fire are thought to be resistant to wildfires within the range of intensities that have been experienced up until now. However, the frequency and scale of intense wildfires is increasing under climate change. We studied annual flowering and fruit‐set in a large population of Banksia spinulosa plants in south‐eastern Australia from the early 1990s to 2006. The results led us to predict that there would be little recruitment from seedlings after the next fire but good resprouting from very long‐lived lignotubers. Our study population burned in the widespread, high‐intensity wildfires of December 2019, providing an opportunity to test the hypothesis. Most above‐ground stems and cones were reduced to ash, and only 15 cones (on 10 plants) remained after the fire. We found no seedlings in the 0.3 ha site that had initially contained over 350 adult plants. Little natural mortality had been observed pre‐fire, but by 5 months after the fire, nearly 25% of lignotubers had failed to resprout. We conclude that even common and widespread resprouting species will suffer population decline and reduced genetic diversity as high‐intensity fires become more extensive and frequent.

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