When we think of climate change we often think of extreme events like flooding rains and large bushfires. But climate change can also have slower, more subtle impacts on our landscapes.

The life cycle of a plant – for example, how fast it grows, how long it lives, when it reproduces, how many seeds it produces – is intertwined with its local climate.

And even small shifts in temperature and rainfall can delay or shift key life stages.

For example, reduced rainfall in southwestern Australia has been linked to reduced seed production and survival in the shrub Hooker’s banksia (Banksia hookeriana).

In the fire-prone ecosystems of southeastern Australia, fire can kill plants but also often plays a critical role in their regeneration.

Some species require fire to release their seeds into the environment, while others can resprout after fire from protected tissues either along or at the base of their stems.

But the timing of fire, particularly the time between fires, is very important to the survival of many plant species.

What happens to plants when climate and fire change at the same time? 

In our new study, we developed a computer model that allows us to test the combined impacts of changes in a plant’s life cycle and changes in fire patterns on different plant species in simulated environments that are based on reality.

The approach is like a video game: you select your species (character), which has a range of attributes, you then select the landscape you want to explore and, finally, the type of challenge.

Then you run the game (computer model) to see how well, or not, the plant survives.

We chose four species grouped into two fire response strategies.

The desert banksia (Banksia ornata) and the swamp beard-heath (Leucopogon esquamatus) are ‘obligate seeders’, meaning fire will often kill the entire plant.

These plants rely on their seed stocks (either stored in their canopy or in the soil) to regenerate and persist after a fire.

The saw banksia (Banksia serrata) and beaked hakea (Hakea rostrata) also produce seeds, but they can also resprout after fire – speeding up the recovery process because established plants survive.

The beaked hakea (Hakea rostrata) is found in South Australia, Tasmania and Victoria, including the Grampians-Gariwerd region. Picture: Rexness / Wikimedia

Desert banksia (Banksia ornata) relies in seed stocks to regenerate after fire. Picture: Geoff Carle

The swamp beard-heath (Leucopogon esquamatus) is classified as endangered in Victoria. Picture: Daniel Ohlsen / Vic Flora

The saw banksia (Banksia serrata) can resprout from its base after fire. Picture: emilyblackheath / iNaturalist

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We tested scenarios in two landscapes in southeastern Australia – the Blue Mountains (Colomatta) in New South Wales and the Grampians (Gariwerd) in Victoria.

Both landscapes are dominated by woodlands and forests, but they have different plant species compositions and fire regimes.

The Grampians historically has a high fire frequency with a number of large fires in recent decades, while the Blue Mountains has been less fire prone.

The challenges we formulated by combining two important phenomena: changes in the plant’s life cycle because of climate change and climate-related changes in fire patterns in each landscape.

We simulated climate-impacted life cycle changes observed or predicted in a range of species around the world.

This included a plant producing less seed, having higher adult mortality (death) rates, having fewer seedlings survive to maturity or taking longer to reach maturity.

Testing the changes in a computer-simulated environment is the best way to understand these potential impacts before we see them in nature.

It may also give us a head start in reducing the negative effects on plant survival.

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The fire challenges were simulated from six different but plausible climate-change scenarios – including reductions in the time between fires and increases in the area burnt by fire.

We can run any combination of fire and life cycle changes including:

• Testing the impact on our chosen species’ populations in a future climate where they take longer than normal to reach maturity, and the time between fires is reduced.

• Testing the impact on our species’ populations if there's a higher level of adult mortality, but with fire patterns typical of our current climate.

Which species should we be more worried about?

Unfortunately, all of them.

We found that all four species are more likely to decline in the challenges that shifted components of their life cycle – with an increase in adult mortality having the biggest effect.

Increases in forest mortality and canopy die-off events are already occurring because of increased frequency, intensity and duration of drought in parts of southern Australia and elsewhere in the world.

So, while our challenges are hypothetical and happen inside a computer, they aim to represent real events that are already happening.

The desert banksia and the swamp beard-heath, which both rely solely on producing seed, are more vulnerable than the species that could resprout after fire.

This is particularly true when changes in the plant’s life cycle were combined with future climates that shortened the interval between fires.

If the plants took longer to reach maturity, and fires happened more often, this increases the risk that the plants are burnt before producing seeds.

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Our novel approach means we can identify which species are more vulnerable to which facet of change – climate or fire (or both).

It can help target management to protect at-risk species by taking actions like:

• collecting seeds for storage

• actively monitoring plant regeneration after extensive or severe fire

• post-fire reseeding or replanting to ensure population persistence, and/or

• targeted fire suppression to protect priority populations.

Incremental changes in our climate and fire patterns may seem inconsequential in comparison to major natural disaster events.

But our approach tells us that plausible shifts in aspects of a plant's life cycle and predicted shifts in the patterns of fire could have dire consequences for many of our plant species – unless we take steps to manage that risk.