Bushfires are changing the ‘hidden’ understory in Australian forests


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Our research shows that emerging fire regimes are pushing the very character of our forests. Picture: Tom Fairman, University of Melbourne

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Our research shows that emerging fire regimes are pushing the very character of our forests. Picture: Tom Fairman, University of Melbourne

Fire is a natural part of the Australian landscape. But the more frequent fires we’ve seen recently—particularly the high severity bushfires that consume or scorch the canopies of whole forests—are a major concern to our country’s ecosystem health, carbon storage and biodiversity.

We often see devastating footage of those eucalypt forests in flames, but we should also be concerned about the effect of bushfires we can’t always see—sometimes below ground.

More to forests than trees

Most of our understanding of the impacts of fires comes from the trees that form the overstory of these forests.

For example, we know that more frequent severe fires lead to the loss of fire-sensitive trees like alpine ash and a decline in otherwise fire-tolerant snow gum forests.

The overstory—the layer of vegetation formed by the tallest trees in the forest that typically receive the most sunlight and form the upper canopy of the forest—is where most of the carbon is stored and where we find the hollows for animals to live in.

While the overstory is important, there is much more to forests than its trees.

The understory—the shorter trees, shrubs, and plants that grow beneath the overstory—is where we find most of the plant diversity.

And the soil beneath that is where the “hidden” understory resides—the understory species’ seeds lie dormant in the soil seedbank, sometimes for decades—waiting for their opportunity to germinate.

The soil seedbank is a vital extension of aboveground plant diversity.

It represents the legacy of understory plants which may have died long ago, and act as a source of new growth for future generations.

Think of the soil seedbank as an insurance reserve of plant diversity in the event of something calamitous happening to the living understory plants.

In a world of frequent severe fires, that calamity is becoming a reality.

So what happens to these deeper, darker but important parts of the forests in an extreme bushfire? We have started to answer this question in our recent research published in the journal Fire.


Montane forests have higher precipitation, so the forest generally becomes taller, wetter, darker and more dense. Credit: Benjamin Wagner

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Montane forests have higher precipitation, so the forest generally becomes taller, wetter, darker and more dense. Credit: Benjamin Wagner

Into the ‘hidden’ understory

In our two recently published papers, with the other being published in Forest Ecology and Management, our team investigated how the plant understory responds to more frequent, severe fires across a range of forest types.

We looked at the dry shrubby forests at low elevations and the montane forests at high elevations, all the way through to the snow gum forests that fringe Victoria’s alpine peaks.

Montane forests have higher precipitation, so the forest generally becomes taller, wetter, darker and more dense—forming the most extensive zone in the Australian Alps.

More information:
Sabine Kasel et al, Short-Interval, High-Severity Wildfire Depletes Diversity of Both Extant Vegetation and Soil Seed Banks in Fire-Tolerant Eucalypt Forests, Fire (2024). DOI: 10.3390/fire7040148

Emily Duivenvoorden et al, Short-interval, high-severity wildfires cause declines in soil seed bank diversity in montane forests of south-eastern Australia, Forest Ecology and Management (2023). DOI: 10.1016/j.foreco.2023.121627

Journal information:
Forest Ecology and Management




This article was originally published by a phys.org . Read the Original article here. .