The link below is to an article that looks at discovering new flowering plant species while bushwalking in Australia.
Over countless millennia, Aboriginal and Torres Strait Islander peoples have harnessed the tremendous potential of plants, ingeniously using them for medicines, nutrition, to express our culture and to develop innovative technologies.
But as I learn more about First Peoples’ plant knowledge, I’m also better understanding the broader Australian community’s failure to recognise the depth and breadth of our expertise.
Aboriginal people, our culture and deep knowledges are often seen as “in the past”, fixed and stagnant.
Damaging perceptions which cast us as lesser and posit us as a
homogenous peoples, who were limping towards inevitable extinction before
the arrival of a “superior” race, still abound. Such tropes deny our dynamic place in the present day, and our ability to continuously adapt and innovate.
Below I’ve listed five of my favourite indigenous plants and the multiple ways Aboriginal people used them, and continue to do so.
1. Spiny-headed mat-rush (Lomandra longifolia)
Spiny-headed mat-rush is a large tussocky plant found throughout southeastern Australia.
The Wurundjeri people particularly favour this plant for weaving cultural items such as necklaces, headbands, girdles, baskets, mats and bags for carrying foods, as well as for making technologies such as eel traps and hunting nets.
Its seeds are high in protein. They can be collected and pounded into a bread mix, with the core of the plant and the base of the leaves eaten as a vegetable.
Many diverse Aboriginal peoples use the roots to treat bites and stings. The caterpillars of several butterflies, such as the Symmomus Skipper, also rely on this plant for food and habitat.
2. Wallaby grass
There are around 30 types of wallaby grass in Australia. Native grasslands were once the most extensive habitat of Victoria’s western plains, but are now the most endangered plant community.
Grasslands provide food and habitat for a huge diversity of fauna, particularly birds, such as the peregrine falcon, whistling kite and Australian kestrels. Many animals, such as the legless lizard, little whip snake and fat-tailed dunnart, were once commonplace, but are now scarce in this endangered ecosystem.
Wallaby grass seeds make an excellent bread by pounding them into flour. The leaves and stem are also used to make cultural items, such as nets for fishing and hunting.
It’s also incredibly hardy – highly tolerant to frost, heat and drought, and requiring no fertilisers and little water. And it makes an excellent lawn, controlling erosion and weeds.
3. Bulbine lily (Bulbine bulbosa)
In summer, bulbine lily dies back to a dormant bulb, before re-shooting in late autumn. In spring, it displays vibrant yellow flowers.
Bulbine lilies can be found in all states except Western Australia, growing wild in tandem with milkmaids and chocolate lilies in the few areas of Victoria’s undisturbed remnant vegetation.
It’s considered the sweetest tasting of all edible root plants and is available year-round. You can find a plump, round, cream-coloured storage organ (a type of underground stem) under its stalk, which can be eaten after being roasted. Bulbine lily is also nutritious, a good source of calcium and iron.
4. Black kurrajong (Brachychiton populneus)
Aboriginal peoples from many diverse groups favour the fibrous kurrajong bark for making string for fishing lines, nets and bags, as well as body adornments such as headbands.
Flowers turn to fruit in the form of leathery pods. These pods contain highly nutritious yellow seeds, which contain around 18% protein and 25% fat, and high levels of magnesium and zinc.
To eat the seeds, you first must remove toxic yellow hairs surrounding them. They can be eaten raw and roasted, and have a pleasantly nutty flavour. The young roots of this tree also make an excellent food source and can provide water.
5. Black sheoak (Allocasuarina littoralis)
Favouring dry conditions, black sheoak is native to Queensland, Tasmania, NSW and Victoria, and can grow up to eight metres high. It flowers in spring, with either rusty-brown spikes or red flowers that develop into cones.
Its seeds are an important food source for many native birds, including parrots and cockatoos.
Diverse groups of Aboriginal peoples use sheoaks for various purposes. The shoots and cones can be eaten, and sheoak wood can be used to fashion boomerangs, shields, clubs and other cultural implements because the wood is both strong and resists splitting and chipping.
In fact, the earliest evidence of boomerangs, found in the Wyrie Swamp in South Australia, were made from various sheoak species, and were dated at 10,000 years old.
Scientists have been interested in the flora of New Guinea since the 17th century, but formal knowledge of the tropical island’s diversity has remained limited.
To solve this mystery, our global team of 99 scientists from 56 institutions built the first ever expert-verified checklist to the region’s vascular plants (those with conductive tissue).
We found there are 13,634 formally described species of plants in New Guinea, of which a remarkable 68% are known to occur there and nowhere else. This richness trumps both Madagascar (11,488 species) and Borneo (11,165 species), making New Guinea the most floristically diverse island in the world.
From tarantula-like orchids to giant bananas, here we reveal some of the more mysterious plants on our checklist. Sadly, unsustainable logging and climate change threaten the conservation of many New Guinean species, and we highlight urgent solutions.
The majestic flora of New Guinea
New Guinea is a land of evocative contrasts. As the world’s largest tropical island – made up of Papua New Guinea to the east and two Indonesian provinces to the west – its biological diversity spans habitats from fringing mangroves to alpine grasslands.
The flora is diverse, filled with the majestic, stunning, intriguing and bizarre. However, very little is known about the conservation status of many species in New Guinea, which remains relatively unexplored by scientists.
There are the few remaining forests of 60 metres high hoop pine (Araucaria cunninghamii) and klinkii pine (A. hunsteinii), that tower majestically up to 30 metres above the already tall rainforest canopy.
Figs, with their copious sap, are present in diverse forms, from small shrubs to vines, or large canopy trees.
And the strongly irritant black sap of the Semecarpus tree, a distant relative of the American poison ivy, causing severe dermatitis, is something naive botanists must learn to avoid!
Then there’s the Ryparosa amplifolia, a rainforest tree that provides swollen hollow stems for ant colonies to live inside. The tree also produces energy rich “food bodies” – granule-like structures on the leaves that mimic animal tissue and provide the ants with sustenance. In return, the ants act as bodyguards, chasing away insect herbivores, and leaf cleaners.
Some of our most popular foods were domesticated from New Guinea, including sugarcane and bananas. But the giant banana, Musa ingens is a a highlight in montane forests. Its leaves can stretch to a length of 5 metres, the tree can grow more than 20 metres tall, and its fruits are massive.
With more than 2,400 species of native orchid species, New Guinea is one of the most spectacular floral gardens in the world. It includes fascinating species such as Bulbophyllum nocturnum, which is the first and only known example of a night-flowering orchid, and Bulbophyllum tarantula, with appendages that resemble the iconic spider.
An uncertain future
Despite New Guinea’s seemingly high number of plant species, at least 3,000 species remain to be discovered and formally described. This estimate is based on the rate of description of new species in the past decades.
Much of New Guinea, particularly the Indonesian part, has been extremely poorly studied, with very few plant species collected. Even within Papua New Guinea, the distribution of many species is inadequately known. This means our findings should be viewed as a baseline upon which to prioritise further work.
The biggest impact on forest conservation is from logging, both clear-felling and degradation. As land is predominantly under customary ownership, addressing subsistence-related forest loss is a long-term challenge. Climate change adds yet further threats, including increased burning of degraded forest due to drier weather.
This means there’s a high risk of the world losing entire species before they are even known.
To this end, in 2018 the governors of Indonesia’s two New Guinea provinces announced the Manokwari Declaration, a pledge to conserve 70% of forest cover for the western half of the island.
Reversing funding shortfalls and declining engagement
Our work builds on many decades of effort by plant collectors whose countless nights under leaking canvas, grass huts and bark shelters have led to thousands of plant discoveries.
Their stories are astounding. These fearless adventurers have sampled water plants by jumping from helicopters hovering low over Lake Tebera, swam in the Purari River rapids to haul a disabled dugout canoe full of botanists and cargo to safety, and have fallen into beds of stinging plants in the mountains of Wagau without subsequent access to pain relief.
Taxonomy – the discipline of identifying, classifying, and understanding relationships between plants – is the key to unlocking the value of this collecting effort.
Future opportunities for botanical research with local New Guineans at the helm is also vital – only 15% of the scientific publications on the New Guinean flora over the past 10 years involved local co-authors.
Improved collaboration between taxonomists, scientific institutions, governments and New Guinean scientific agencies could address these critical urgent priorities.
Undoubtedly, the conservation of New Guinea’s unique flora will be challenging and require work on many fronts that transcend single disciplines or institutions. From what we know already, a world of botanical surprises awaits in the last unknown.
After all, as 19th century naturalist J.B. Jukes wrote:
I know of no part of the world, the exploration of which is so flattering to the imagination, so likely to be fruitful in interesting results […] and altogether so well calculated to gratify the enlightened curiosity of an adventurous explorer, as the interior of New Guinea.
This article is part of Flora, Fauna, Fire, a special project by The Conversation that tracks the recovery of Australia’s native plants and animals after last summer’s bushfire tragedy. Explore the project here and read more articles here.
Before the summer bushfires destroyed vast expanses of habitat, Australia was already in the midst of a biodiversity crisis. Now, some threatened species have been reduced to a handful of individuals – and extinctions are a real possibility.
The Kangaroo Island dunnart, a small marsupial, was listed as critically endangered before the bushfires. Then the inferno destroyed 95% of its habitat.
Prospects for the Banksia Montana mealybug are similarly grim. This flightless insect lives only on one species of critically endangered plant, at a high altitude national park in Western Australia. The fires destroyed 100% of the plant’s habitat.
And fewer than 100 western ground parrots remained in the wild before last summer, on Western Australia’s south coast. Last summer’s fires destroyed 40% of its habitat.
Fish, crayfish and some frogs are also struggling. After the fires, heavy rain washed ash, fire retardants and dirt into waterways. This can clog and damage gills, and reduces the water’s oxygen levels. Some animals are thought to have suffocated.
Here, dozens of experts tell the stories of the 119 species most in need of help after our Black Summer.
How can I help?
Recovery from Australia’s bushfire catastrophe will be a long road. If you want to help, here are a few places to start.
Also see this list of registered bushfire charities
Australia roared into 2020 as a land on fire. The human and property loss was staggering, but the damage to nature was equally hard to fathom. By the end of the fire season 18.6 million hectares of land was destroyed.
So what’s become of animal and plant survivors in the months since?
Click through below to explore the impact Australia’s summer of fires had on an already drought-ravaged landscape and the work being done to rescue and recover habitats.
No other event in our lifetimes has brought such sudden, drastic loss to Australia’s biodiversity as the last bushfire season. Governments, researchers and conservationists have committed to the long road to recovery. But in those vast burnt landscapes, where do we start?
We are among the wildlife experts advising the federal government on bushfire recovery. Our role is to help determine the actions needed to stave off extinctions and help nature recover in the months and years ahead.
Our first step was to systematically determine which plant and animal species and ecosystems needed help most urgently. So let’s take a closer look at how we went about it.
Sorting through the smoke
One way to work out how badly a species is affected by fire is to look at how much of its distribution – or the area in which it lives – was burnt.
This is done by overlapping fire maps with maps or records showing the species’ range. The greater the overlap, the higher the potential fire impact. But there are several complicating factors to consider:
1. Susceptibility: Species vary in how susceptible they are to fire. For instance, animals that move quickly – such as red-necked wallabies and the white-throated needletail – can escape an approaching fire. So too can animals that burrow deeply into the ground, such as wombats.
Less mobile animals, or those that live in vegetation, are more likely to die. We also considered post-fire recovery factors such as a species’ vulnerability to predators and reproductive rate.
2. What we know: The quality of data on where species occur is patchy. For example, there are thousands of records for most of Australia’s 830 or so bird species. But there are very few reliable records for many of Australia’s 25,000-odd plant species and 320,000-odd invertebrate species.
So while we can estimate with some confidence how much of a crimson rosella’s distribution burned, the fire overlaps for less well-known species are much less certain.
3. The history of threats: The impact of fires on a region depends on the extent of other threats, such as drought and the region’s fire history. The time that elapses between fires can influence whether populations have recovered since the last fire.
For instance, some plants reproduce only from seed rather than resprouting. Fires in quick succession can kill regrowing plants before they’ve matured enough to produce seed. If that happens, species can become locally extinct.
4. Fire severity: Some areas burn more intensely than others. High severity fires tend to kill more animals. They also incinerate vegetation and can scorch seeds lying in the soil.
Many Australian plant species are exquisitely adapted to regenerate and resprout after fire. But if a fire is intense enough, even these plants may not bounce back.
5. Already threatened?: Many species affected by these bushfires were already in trouble. For some, other threats had already diminished their numbers. Others were highly vulnerable because they were found only in very limited areas.
The bushfires brought many already threatened species closer to extinction. And other species previously considered secure are now threatened.
Which species made the list?
With these issues in mind, and with contributions from many other experts, we compiled lists of plant, invertebrate and vertebrate species worst-affected by the 2019-20 fires. A similar assessment was undertaken for threatened ecosystems.
Some 471 plant, 213 invertebrate and 92 vertebrate species have been identified as a priority for interventions. Most had more than half their distribution burnt. Many have had more than 80% affected; some had 100% burnt.
Priority invertebrates include land snails, freshwater crayfish, spiders, millipedes, beetles, dragonflies, grasshoppers, butterflies and bees. Many species had very small ranges.
For example, the inelegantly named Banksia montana mealybug – a tiny insect – existed only in the foliage of a few individuals of a single plant species in Western Australia’s Stirling Range, all of which were consumed by the recent fires.
Some priority plants, such as the Monga waratah, have persisted in Australia since their evolution prior to the break-up of the Gondwanan supercontinent about 140 million years ago. More than 50% of its current range burned, much at high severity. During recovery it is vulnerable to diseases such as phytophthora root rot.
Some priority vertebrates have tiny distributions, such as the Mt Kaputar rock skink that lives only on rocky outcrops of Mt Kaputar near Narrabri, New South Wales. Others had large distributions that were extensively burnt, such as the yellow-bellied glider.
The priority lists include iconic species such as the koala, and species largely unknown to the public, such as the stocky galaxias, a fish that lives only in an alpine stream near Cooma in NSW.
What’s being done
A federal government scheme is now allocating grants to projects that aim to help these species and ecosystems recover.
Affected species need immediate and longer-term actions to help them avoid extinction and recover. Critical actions common to all fire-affected species are:
careful management of burnt areas so their recovery isn’t compromised by compounding pressures
protecting unburnt areas from further fire and other threats, so they can support population recovery
rapid surveys to identify where populations have survived. This is also the first step in ongoing monitoring to track recovery and the response to interventions.
Targeted control of feral predators, herbivores and weeds is also essential to the recovery of many priority species.
In some rare cases, plants or animals may need to be moved to areas where populations were reduced or wiped out. Captive breeding or seed collection can support this. Such restocking doesn’t just help recovery, it also spreads the risk of population loss in case of future fires.
Long road back
The COVID-19 pandemic has led to some challenges in implementing recovery actions. Like all of us, state agency staff, NGOs, academics and volunteer groups must abide by public health orders, which have in some cases limited what can be done and where.
But the restrictions may also have an upside. For instance, fewer vehicles on the roads might reduce roadkill of recovering wildlife.
As states ease restrictions, more groups will be able to continue the recovery process.
As well as action on the ground, much planning and policy response is still required. Many fire-affected species must be added to threatened species lists to ensure they’re legally protected, and so remain the focus of conservation effort.
Fire management methods must be reviewed to reduce the chance of future catastrophic fires, and to make sure the protection of biodiversity assets is considered in fire management planning and suppression.
Last bushfire season inflicted deep wounds on our biodiversity. We need to deal with that injury. We must also learn from it, so we can respond swiftly and effectively to future ecological disasters.
Many species experts and state/territory agency representatives contributed to the analyses of priority species. Staff from the Department of Agriculture, Water and the Environment (especially the Environmental Resources Information Network (Geospatial and Information Analytics Branch), the Protected Species and Communities Branch and the Threatened Species Commissioner’s Office) and Expert Panel members also contributed significantly to this work.
John Woinarski, Professor (conservation biology), Charles Darwin University; Dale Nimmo, Associate Professor in Ecology, Charles Sturt University; Rachael Gallagher, Senior Lecturer/ARC DECRA Fellow, Macquarie University, and Sarah Legge, Professor, Australian National University
Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
If you have a question you’d like an expert to answer, please send it to email@example.com
If carbon dioxide levels were to double, how much increase in plant growth would this cause? How much of the world’s deserts would disappear due to plants’ increased drought tolerance in a high carbon dioxide environment?
Compared to pre-industrial levels, the concentration of carbon dioxide (CO₂) in the atmosphere will have doubled in about 20 to 30 years, depending on how much CO₂ we emit over the coming years. More CO₂ generally leads to higher rates of photosynthesis and less water consumption in plants.
At first sight, it seems more CO₂ can only be beneficial to plants, but things are a lot more complex than that.
Let’s look at the first part of the question.
Even if plants grew twice as fast under doubled CO₂ levels, it would not mean they strip twice as much CO₂ from the atmosphere. Plants take carbon from the atmosphere as they grow, but that carbon is going straight back via natural decomposition when plants die or when they are harvested and consumed.
At best, you might be mowing your lawn twice as often or harvesting your plantation forests earlier.
The most important aspect is how long the carbon stays locked away from the atmosphere – and this is where we have to make a clear distinction between increased carbon flux (faster growth) or an increasing carbon pool (actual carbon sequestration). Your bank account is a useful analogy to illustrate this difference: fluxes are transfers, pools are balances.
The global carbon budget
Of the almost 10 billion tonnes (gigatonnes, or Gt) of carbon we emit every year through the burning of fossil fuels, only about half accumulates in the atmosphere. Around a quarter ends up in the ocean (about 2.4 Gt), and the remainder (about 3 Gt) is thought to be taken up by terrestrial plants.
While the ocean and the atmospheric sinks are relatively easy to quantify, the terrestrial sink isn’t. In fact, the 3 Gt can be thought of more as an unaccounted residual. Ultimately, the emitted carbon needs to go somewhere, and if it isn’t the ocean or the atmosphere, it must be the land.
So yes, the terrestrial system takes up a substantial proportion of the carbon we emit, but the attribution of this sink to elevated levels of CO₂ is difficult. This is because many other factors may contribute to the land carbon sink: rising temperature, increased use of fertilisers and atmospheric nitrogen deposition, changed land management (including land abandonment), and changes in species composition.
Current estimates assign about a quarter of this land sink to elevated levels of CO₂, but estimates are very uncertain.
In summary, rising CO₂ leads to faster plant growth – sometimes. And this increased growth only partly contributes to sequestering carbon from the atmosphere. The important questions are how long this carbon is locked away from the atmosphere, and how much longer the currently observed land sink will continue.
The second part of the question refers to a side-effect of rising levels of CO₂ in the air: the fact that it enables plants to save water.
Plants regulate the exchange of carbon dioxide and water vapour by opening or closing small pores, called stomata, on the surface of their leaves. Under higher concentrations of CO₂, they can reduce the opening of these pores, and that in turn means they lose less water.
This alleviates drought stress in already dry areas. But again, the issue is more complex because CO₂ is not the only parameter that changes. Dry areas also get warmer, which means that more water evaporates and this often compensates for the water-saving effect.
Overall, rising CO₂ has contributed to some degree to the greening of Earth, but it is likely that this trend will not continue under the much more complex combination of global change drivers, particularly in arid regions.
But it is heartening to remember that bushfire can be a boon to some plants and animals. We’re already seeing fresh green shoots as plants and trees resprout. Beetles and other insects are making short work of animal carcasses; they will soon be followed by the birds which feed on them.
Australia’s worsening fire regimes are challenging even these tolerant species. But let’s take a look at exactly how life is returning to our forests now, and what to expect in coming months.
The science of resprouting
Of course, bushfires kill innumerous trees – but many do survive. Most of us are familiar with the image of bright green sprouts shooting from the trunks and branches of trees such as eucalypts. But how do they revive so quickly?
The secret is a protected “bud bank” which lies behind thick bark, protected from the flames. These “epicormic” buds produce leaves, which enables the tree to photosynthesise – create sugar from the sun so the tree can survive.
Under normal conditions, hormones from shoots higher in the tree suppress these buds. But when the tree loses canopy leaves due to fire, drought or insect attack, the hormone levels drop, allowing the buds to sprout.
This summer’s fires left in their wake a mass of decaying animal carcasses, logs and tree trunks. While such a loss can be devastating for many species – particularly those that were already vulnerable – many insects thrive in these conditions.
For example, flies lay eggs in the animal carcasses; when the maggots hatch, the rotting flesh provides an ample food source. This process helps break down the animal’s body – reducing bacteria, disease and bad smells. Flies are important decomposers and their increased numbers also provide food for birds, reptiles and other species.
Then come the birds
Once insects start to move back into an area from forested areas nearby, the birds that eat them will follow.
A CSIRO study after bushfires in Victoria’s East Gippsland in 1983 found several native bird species – flame and scarlet robins, the buff-rumped thornbill and superb fairy-wren – increased quickly to levels greater than before fire. As shrubs in the understorey regrow, other species will move in, slowly increasing biodiversity.
Since the recent bushfire in woodland near Moonbi in New South Wales, numerous bird species have returned. On a visit over this past weekend, I observed currawongs landing in the canopy, saw fairy wrens darting in and out of foliage sprouting from the ground, and heard peep wrens in tufts of foliage on bark and high branches.
Honeyeaters moved between burnt and intact trees on the edge of the blackened forest and butterflies visited new plants flowering after recent rain.
Weeds can help
Weeds usually benefit when fire opens up the tree canopy and lets in light. While this has a downside – preventing native plants from regenerating – weeds can also provide cover for native animal species.
A study I co-authored in 2018 found highly invasive Lantana camara provided habitat for small mammals such as the brown rat in some forests. Mammal numbers in areas where lantana was present were greater than where it was absent.
Is there hope for threatened species?
Generalist species – those that thrive in a variety of environments – can adapt to burnt forest. But specialist species need particular features of an ecosystem to survive, and are far less resilient.
It requires large fires to create a specific habitat: big dead trees provide hollows for shelter and nesting, and insects feeding on burnt wood and carcasses provide a food source.
But for the Leadbeater’s possum to benefit from the fire regime, bushfires should be infrequent – perhaps every 75 years – allowing time for the forest to grow back. If fires are too frequent, larger trees will not have time to establish and hollows will not be created, causing the species’ numbers to decline.
Similarly in NSW, at least 50% and up to 80% of the habitat of threatened species such as the vulnerable rufous scrub-bird was burnt in the recent fires, an environmental department analysis found.
Only time will tell whether biodiversity in these areas is forever damaged, or will return to its former state.
Large fires may benefit some native species but they also provide food and shelter for predatory species, such as feral cats and foxes. The newly open forest leaves many native mammals exposed, changing the foodweb, or feeding relationships, in an ecosystem.
This means we may see a change in the types of birds, reptiles and mammals found in forests after the fires. And if these areas don’t eventually return to their pre-fire state, these environments may be changed forever – and extinctions will be imminent.
The alarming rate of carbon dioxide flowing into our atmosphere is affecting plant life in interesting ways – but perhaps not in the way you’d expect.
Despite large losses of vegetation to land clearing, drought and wildfires, carbon dioxide is absorbed and stored in vegetation and soils at a growing rate.
This is called the “land carbon sink”, a term describing how vegetation and soils around the world absorb more carbon dioxide from photosynthesis than they release. And over the past 50 years, the sink (the difference between uptake and release of carbon dioxide by those plants) has been increasing, absorbing at least a quarter of human emissions in an average year.
So, to put it simply, humans are producing more carbon dioxide. This carbon dioxide is causing more plant growth, and a higher capacity to suck up carbon dioxide. This process is called the “carbon dioxide fertilisation effect” – a phenomenon when carbon emissions boost photosynthesis and, in turn, plant growth.
What we didn’t know until our study is just how much the carbon dioxide fertilisation effect contributes to the increase in global photosynthesis on land.
But don’t get confused, our discovery doesn’t mean emitting carbon dioxide is a good thing and we should pump out more carbon dioxide, or that land-based ecosystems are removing more carbon dioxide emissions than we previously thought (we already know how much this is from scientific measurements).
And it definitely doesn’t mean mean we should, as climate sceptics have done, use the concept of carbon dioxide fertilisation to downplay the severity of climate change.
Rather, our findings provide a new and clearer explanation of what causes vegetation around the world to absorb more carbon than it releases.
What’s more, we highlight the capacity of vegetation to absorb a proportion of human emissions, slowing the rate of climate change. This underscores the urgency to protect and restore terrestrial ecosystems like forests, savannas and grasslands and secure their carbon stocks.
And while more carbon dioxide in the atmosphere does allow landscapes to absorb more carbon dioxide, almost half (44%) of our emissions remain in the atmosphere.
More carbon dioxide makes plants more efficient
Since the beginning of the last century, photosynthesis on a global scale has increased in nearly constant proportion to the rise in atmospheric carbon dioxide. Both are now around 30% higher than in the 19th century, before industrialisation began to generate significant emissions.
Carbon dioxide fertilisation is responsible for at least 80% of this increase in photosynthesis. Most of the rest is attributed to a longer growing season in the rapidly warming boreal forest and Arctic.
So how does more carbon dioxide lead to more plant growth anyway?
Higher concentrations of carbon dioxide make plants more productive because photosynthesis relies on using the sun’s energy to synthesise sugar out of carbon dioxide and water. Plants and ecosystems use the sugar both as an energy source and as the basic building block for growth.
When the concentration of carbon dioxide in the air outside a plant leaf goes up, it can be taken up faster, super-charging the rate of photosynthesis.
More carbon dioxide also means water savings for plants. More carbon dioxide available means pores on the surface of plant leaves regulating evaporation (called the stomata) can close slightly. They still absorb the same amount or more of carbon dioxide, but lose less water.
The resulting water savings can benefit vegetation in semi-arid landscapes that dominate much of Australia.
We saw this happen in a 2013 study, which analysed satellite data measuring changes in the overall greenness of Australia. It showed more leaf area in places where the amount of rain hadn’t changed over time. This suggests water efficiency of plants increases in a carbon dioxide-richer world.
Young forests help to capture carbon dioxide
In other research published recently, we mapped the carbon uptake of forests of different ages around the world. We showed forests regrowing on abandoned agricultural land occupy a larger area, and draw down even more carbon dioxide than old-growth forests, globally. But why?
In a mature forest, the death of old trees balances the amount of new wood grown each year. The old trees lose their wood to the soil and, eventually, to the atmosphere through decomposition.
A regrowing forest, on the other hand, is still accumulating wood, and that means it can act as a considerable sink for carbon until tree mortality and decomposition catch up with the rate of growth.
This age effect is superimposed on the carbon dioxide fertilisation effect, making young forests potentially very strong sinks.
In fact, globally, we found such regrowing forests are responsible for around 60% of the total carbon dioxide removal by forests overall. Their expansion by reforestation should be encouraged.
Forests are important to society for so many reasons – biodiversity, mental health, recreation, water resources. By absorbing emissions they are also part of our available arsenal to combat climate change. It’s vital we protect them.
Vanessa Haverd, Principal research scientist, CSIRO; Benjamin Smith, Director of Research, Hawkesbury Institute for the Environment, Western Sydney University; Matthias Cuntz, Research Director INRAE, Université de Lorraine, and Pep Canadell, Chief research scientist, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO
On Friday I flew in a helicopter over the fire-ravaged Kosciuszko National Park. I was devastated by what I saw. Cherished wildlife species are at grave risk of extinction: those populations the bushfires haven’t already wiped out are threatened by thousands of feral horses trampling the land.
The New South Wales park occupies the highest mountain range in Australia and is home to plants and animals found nowhere else in the world. Many of these species are threatened, and their survival depends on protecting habitat as best we can.
Kosciuszko National Park provides habitat for two species of corroboree frog (critically endangered), the alpine she-oak skink (endangered), broad-toothed rat (vulnerable) and stocky galaxias (a critically endangered native fish), among other threatened species.
As the climate has warmed, the cool mountain habitat of these species is shrinking; bushfires have decimated a lot of what was left. Feral horses now threaten to destroy the remainder, and an urgent culling program is needed.
Not a green leaf in sight
Australia’s plants and ecosystems did not evolve to withstand trampling by hard-hooved animals, or their intensive grazing. Unfortunately, the New South Wales government has allowed the population of feral horses in the park to grow exponentially in recent years to around 20,000.
I flew over the northern part of the park with members of the Invasive Species Council, who were conducting an urgent inspection of the damage. Thousands of hectares were completely incinerated by bushfires: not a green leaf was visible over vast areas. A cataclysm has befallen the western face of the mountains and tablelands around Kiandra and Mount Selwyn.
Further north and east of Kiandra the fires were less intense and burnt patchily. On Nungar Plain the grassland and peat wetlands were only lightly burnt, and the first green shoots were already visible along the wetlands of the valley floor.
At first, I wondered if the fires may have spared two animals which live in tunnels in the vegetation on the sub-alpine high plains: the alpine she-oak skink and broad-toothed rat (which, despite the name is a cute, hamster-like creature).
But not only was their understory habitat burnt, a dozen feral horses were trampling the peat wetlands and eating the first regrowth.
On the unburnt or partially burnt plains a few ridges over, 100 or more horses were mowing down the surviving vegetation.
Precarious wildlife refuges
Next we flew over a small stream that holds the last remaining population of a native fish species, the stocky galaxias. A small waterfall is all that divides the species from the stream below, and the jaws of the exotic trout which live there.
The aftermath of the fires means the last refuge of the stocky galaxias is likely to become even more degraded.
Over the years, feral horses have carved terraces of trails into the land causing erosion and muddying the stream bank. As more horses congregate on unburnt patches of vegetation after the fires, more eroded sediment will settle on the stream bed and fill the spaces between rocks where the fish shelter. Ash runoff entering the stream may clog the gills of the fish, potentially suffocating them.
Many key wetland habitats of the southern and northern corroboree frogs have also been burnt. These striking yellow and black frogs nest in wetland vegetation.
We hovered over a key wetland for the northern corroboree frog that had not been burnt, deep in the alpine forest. A group of feral horses stood in it. They had created muddy wallows, trampled vegetation and worn tracks that will drain the wetland if their numbers are not immediately controlled.
Horses out of control
We saw no dead horses from the air. Unlike our native wildlife, most appear to have escaped the fires.
Flying down the upper Murrumbidgee River’s Long Plain, I saw large numbers of feral horses gathered in yet more wetlands. Displaced by the fires to the south and west, they were already trampling the mossy and heathy wetlands that store and filter water in the headwaters.
The Murrumbidgee River is a key water source for south-east Australia. The horses stir up sediment and defecate in the water. They create channels which drain and dry the wetlands, exposing them to fire.
One-third of Kosciuszko National Park has been burnt out and at the time of writing the fires remain active. Feral horses are badly compounding the damage.
If we don’t immediately reduce feral horse numbers, the consequences for Kosciuszko National Park and its unique Australian flora and fauna will be horrendous.
Responsible managers limit the numbers of livestock on their lands and control feral animals. The NSW government must repeal its 2018 legislation protecting feral horses in Kosciuszko National Park, and undertake a responsible control program similar to those of the Australian Capital Territory and Victorian governments.
Without an emergency cull of feral horses in Kosciuszko National Park, burnt vegetation may not fully recover and threatened species will march further towards extinction.