Fire is increasingly occurring outside of historical fire seasons due to climate change and human activity. Managing fire regimes is a critical environmental challenge to reduce risks to biodiversity.
Researchers at the Harry Butler Institute have discovered how unseasonal fires impact plant life cycles and leave ecosystems vulnerable to poor post-fire recovery.
“In many ecosystems around the world, fire is increasingly occurring outside of historical fire seasons owing to climate change lengthening fire seasons and other human activity triggering year-round ignitions,” explained Dr Joe Fontaine, who leads fire research at Murdoch University.
While many plant species have evolved alongside fire for millennia, they are often adapted to particular fire regimes, including fire in certain seasons.
“When that changes in a relatively short period, they don’t have the benefit of time to adapt.”
To investigate the effects of this, the team sowed non-dormant seeds of nine native plant species from Banksia woodlands - Acacia, Allocasuarina, Banksia, Eucalyptus, Hakea, Kennedia and Melaleuca species - monthly from May to October.
These species cover a range of plant families and functional types to emulate a biodiverse setting.
“By sowing seeds at different times, from the end of dry season through to the end of wet season, we emulated post-fire recruitment opportunities in different seasons,” said Dr Fontaine.
“After sowing them, we monitored seedling emergence and survival for two years and also looked at what happened to seeds that failed to germinate and remained on the soil surface over the following summer.”
As expected, seedling emergence was best from May and June sowings, with seeds cued to germinate with the first winter rains.
Seedling survival over the first summer was also best from seeds sown in May and June. Seedlings from these sowings mostly emerged late July-early August, providing them the longest establishment period before summer drought.
“The few seedlings that emerged in October from seeds sown earlier in spring had little time to establish before summer and were all dead shortly after emergence.”
The findings align with field evidence from southwestern Australia and other winter rainfall ecosystems globally show that maximum regrowth is expected following summer and autumn fire and lower regrowth may be expected from winter and spring wet season fire.
“As climate and fire regimes change globally, understanding the vulnerability of key plant population processes to fire seasonality can help us predict changes in plant populations and communities and identify species that may be most sensitive,” said Dr Fontaine.