Tree ferns are older than dinosaurs. And that’s not even the most interesting thing about them

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Gregory Moore, University of Melbourne

With massive fronds creating a luxuriously green canopy in the understory of Australian forests, tree ferns are a familiar sight on many long drives or bushwalks. But how much do you really know about them?

First of all, tree ferns are ferns, but they are not really trees. To be a tree, a plant must be woody (undergo secondary plant growth, which thickens stems and roots) and grow to a height of at least three metres when mature. While tree ferns can have single, thick trunk-like stems and can grow to a height of more than 15 metres, they are never woody.

They’re also incredibly hardy — tree ferns are often the first plants to show signs of recovery in the early weeks after bushfires. The unfurling of an almost iridescent green tree fern fiddlehead amid the sombre black of the bushfire ash is almost symbolic of the potential for bushfire recovery.

Ancient family ties

Tree ferns are generally slow growing, at rates of just 25-50 millimetres height increase per year. This means the tall individuals you might spot in a mature forest may be several centuries old.

However, in the right environment they can grow faster, so guessing their real age can be tricky, especially if they’re growing outside their usual forest environment.

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As a plant group, tree ferns are ancient, dating back hundreds of millions of years and pre-dating dinosaurs.

They existed on earth long before the flowering or cone-bearing plants evolved, and were a significant element of the earth’s flora during the Carboniferous period 300-360 million years ago, when conditions for plant growth were near ideal. This explains why ferns don’t reproduce by flowers, fruits or cones, but by more primitive spores.

A shoot of the Dicksonia antarctica, ready to unfurl.
JJ Harrison/Wikimedia, CC BY-SA

In fact, fossilised tree ferns and their relatives called the fern allies laid down during the carboniferous then have provided much of the earth’s fossil fuels dating from that period. And tree ferns were a great food source, with Indigenous people once eating the pulp that occurs in the centre of the tree fern stem either raw or roasted as a starch.

Until recent times, ferns were quiet achievers among plant groups with an expanding number of species and greater numbers. Today, human activities are limiting their success by the clearing of forests and agricultural practices. Climate change is also a more recent threat to many fern species.

Species you’ve probably seen

Two of the more common tree fern species of south eastern Australia are Cyathea australis and Dicksonia antarctica. Both species have a wide distribution, extending from Queensland down the Australian coast and into Tasmania.

They’re often found growing near each other along rivers and creeks. They look superficially alike and many people would be unaware that they are entirely different species at first glance. That is, until you look closely at the detail of their fronds and run your fingers down the stalks.

Tree ferns are a familiar sight on road trips through forests and bushwalks.
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C. australis has a rough almost prickly frond, hence its common name of rough tree fern, and can grow to be 25 metres tall. While D. antarctica, as the soft tree fern, has a smooth and sometimes furry frond and rarely grows above 15 metres.

Both contribute to the lush green appearance of the understory of wet forests dominated by eucalypts, such as mountain ash (Eucalyptus regnans).

Stems that host a tiny ecosystem

The way tree ferns grow is quite complex. That’s because growth, even of the roots, originates from part of the apex of the stem. If this crown is damaged, then the fern can die.

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At the right time of the year, the new fronds unfurl in the crown from a coil called a fiddlehead. The stem of the tree fern is made up of all of the retained leaf bases of the fronds from previous years.

The stems are very fibrous and quite strong, which means they tend to retain moisture. And this is one of the reasons why the stems of tree ferns don’t easily burn in bushfires — even when they’re dry or dead.

Dicksonia antarctica is one of the more common species in Australian forests.
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In some dense wet forest communities, the stems of tree ferns are a miniature ecosystem, with epiphytic plants — such as mosses, translucent filmy ferns, perhaps lichens and the seedlings of other plant species — growing on them.

These epiphytes are not bad for the tree ferns, they’re just looking for a place to live, and the fibrous, nutrient-rich, moist tree fern stems prove brilliantly suitable.

Engulfed by trees

Similarly, the spreading canopies of tree ferns, such as D. antarctica, provide an excellent place for trees and other species to germinate.

That’s because many plants need good light for their seedlings to establish and this may not be available on the forest floor. Seeds, such as those of the native (or myrtle) beech, Nothofagus cunninghamii, may germinate in the crowns of tree ferns, and its roots can grow down the tree fern trunks and into the soil.

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As time passes, the tree species may completely grow over the tree fern, engulfing the tree fern stem into its trunk. Decades, or even centuries later, it’s sometimes still possible to see the old tree fern stem embedded inside.

Still, tree ferns are wonderfully resilient and give a sense of permanence to our ever-changing fire-affected landscapes.

Gregory Moore, Doctor of Botany, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Australia’s smallest fish among 22 at risk of extinction within two decades

Red-finned blue-eye
Bush Heritage Australia / Adam Kerezsy

Mark Lintermans, University of Canberra; Hayley Geyle, Charles Darwin University; Jaana Dielenberg, The University of Queensland; John Woinarski, Charles Darwin University; Stephen Beatty, Murdoch University, and Stephen Garnett, Charles Darwin University

The tragic fish kills in the lower Darling River drew attention to the plight of Australia’s freshwater fish, but they’ve been in trouble for a long time.

Many species have declined sharply in recent decades, and as many as 90 of Australia’s 315 freshwater fish species may now meet international criteria as threatened.

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No Australian fish species is yet listed officially as extinct, but some have almost certainly been lost before scientists even knew they existed. With so many species at risk, understanding which are in greatest peril is a vital first step in preventing extinctions.

This is what our new research has done. We’ve identified 20 freshwater fish species with a 50% or greater probability of extinction within the next two decades, and a further two with a 40-50% chance – unless there’s new targeted conservation action.

The Australian freshwater fishes at greatest risk of extinction.

Slipping through the conservation cracks

Many small-bodied species, including Australia’s smallest fish the red-finned blue-eye, look likely to be lost within a single human generation. These fish have evolved over millions of years.

Twelve of the species identified have only been formally described in the past decade, and seven are still awaiting description.

This highlights the urgent need to act before species are listed under the national legislation that gives fishes their conservation status, and even before they’re formally described.

These processes can take many years, at which point it may be too late for some species.

More than half the species on our list are galaxiids – small, scaleless fish, that live in cooler, upland streams and lakes. Trout, an introduced, predatory species, also favour these habitats, and the trout have taken a heavy toll on galaxiids and many other small species in southern Australia.

Victoria’s Shaw galaxias – one of 14 galaxias species identified at high risk of extinction.
Tarmo Raadik

For example, the Victorian Shaw galaxias has been eaten out of much of its former range. Now just 80 individuals survive, protected by a waterfall from the trout below. We estimate the Shaw galaxias has an 80% chance or more of extinction within the next 20 years.

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Many galaxiids do not thrive or readily breed in captivity, so suitable trout-free streams are essential for their survival.

Improving trout management requires an urgent, sustained conservation effort, including collaborations with recreational fishers, increased awareness and changing values among government and key sectors of society.

Without this, trout will almost certainly cause many native galaxiids to go extinct.

This waterfall in NSW is all that protects the last population of stocky galaxias from the predatory trout below.
Mark Lintermans

Native fish out of their natural place can also be a problem. For example, sooty and khaki grunters – native fishing species people in northern Australia have widely moved – threatening the ancient Bloomfield River cod.

One disaster can lead to extinction

All of the most imperilled species are now highly localised, which means they’re restricted to very small areas. Their distributions range from only four to 44 square kilometres.

A single catastrophic event could completely wipe out these species, such as a large bushfire that fills their streams with ash and robs them of oxygen.

The SW Victoria River blackfish persists as three very small, isolated populations. The main threat to this species is recreational angling.
Tarmo Raadik

For example, until 2019 the Yalmy galaxias had survived in the cool creeks of the Snowy River National Park. But after the devastating Black Summer fires, just two individuals survived, one male and one female, in separate areas.

Millions of years of evolution could be lost if a planned reunion is too late.

One of the key steps to reduce this risk is moving fish to new safe locations so there are more populations. Researchers choose these new locations carefully to make sure they’re suitable for different species.

Climate change is another threat to all identified species, as it’s likely to reduce flows and water quality, or increase fires, storms and flooding. Many species have been forced to the edge of their range and a prolonged drought could dry their remaining habitat.

The short-tail galaxias existed in two small separated populations in creeks of the upper Tuross River Catchment, in the south coast of NSW. One stream dried in the recent drought, and the other was burnt in the subsequent fires.

Luckily the species is still hanging on in the burnt catchment, but only a single individual has been found in the drought-affected creek.

The main threat to the Daintree rainbowfish is loss of stream flow due to drought, climate change and water extraction.
Michael Hammer / Museum and Art Gallery of the Northern Territory, Author provided

Unlisted, unprotected

Our study is part of a larger project to identify plants and animals at high risk of extinction.

We found the extinction risks of the 22 freshwater fish species are much higher than those of the top 20 birds or mammals, yet receive far less conservation effort.

Only three of the highly imperilled fish species are currently listed as threatened under national environmental legislation: the red-finned blue-eye, Swan galaxias and little pygmy perch.

Listing species is vital to provide protection to survivors and can prompt recovery action. Given our research, 19 fish species should urgently be added to the national threatened species list, but conservation action should start now.

The little pygmy perch in the far south-west corner of WA is one of only three of the 22 imperilled species identified that’s formally protected under Australian laws.
Stephen Beatty/Harry Butler Institute, Murdoch University

Small native freshwater fishes are worth saving. They play a vital role in our aquatic ecosystems, such as predating on pest insect larvae, and are part of our natural heritage.

By identifying and drawing attention to their plight, we are aiming to change their fates. We cannot continue with business as usual if we want to prevent their extinctions.

Mark Lintermans, Associate professor, University of Canberra; Hayley Geyle, Research Assistant, Charles Darwin University; Jaana Dielenberg, Science Communication Manager, The University of Queensland; John Woinarski, Professor (conservation biology), Charles Darwin University; Stephen Beatty, Research Leader (Catchments to Coast), Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, and Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.