Judith Rosentreter, Yale University; Alberto Borges, Université de Liège; Ben Poulter, NASA, and Bradley Eyre, Southern Cross UniversityMethane — a greenhouse gas far more potent than carbon dioxide — plays a major role in controlling the Earth’s climate. But methane concentrations in the atmosphere today are 150% higher than before the industrial revolution.
In our paper published today in Nature Geoscience, we show as much as half of global methane emissions come from aquatic ecosystems. This includes natural, human-created and human-impacted aquatic ecosystems — from flooded rice paddies and aquaculture ponds to wetlands, lakes and salt marshes.
Our findings are significant. Scientists had previously underestimated this global methane contribution due to underaccounting human-created and human-impacted aquatic ecosystems.
It’s critical we use this new information to stop rising methane concentrations derailing our attempts to stabilise the Earth’s temperature.
From underwater sediment to the atmosphere
Most of the methane emitted from aquatic ecosystems is produced by micro-organisms living in deep, oxygen-free sediments. These tiny organisms break down organic matter such as dead algae in a process called “methanogenesis”.
This releases methane to the water, where some is consumed by other types of micro-organisms. Some of it also reaches the atmosphere.
Natural systems have always released methane (known as “background” methane). And freshwater ecosystems, such as lakes and wetlands, naturally release more methane than coastal and ocean environments.
Human-made or human-impacted aquatic ecosystems, on the other hand, increase the amount of organic matter available to produce methane, which causes emissions to rise.
Significant global contribution
Between 2000 and 2006, global methane emissions stabilised, and scientists are still unsure why. Emissions began steadily rising again in 2007.
There’s active debate in the scientific community about how much of the renewed increase is caused by emissions or by a decline of “methane sinks” (when methane is eliminated, such as from bacteria in soil, or from chemical reactions in the atmosphere).
We looked at inland, coastal and oceanic ecosystems around the world. While we cannot resolve the debate about what causes the renewed increase of atmospheric methane, we found the combined emissions of natural, impacted and human-made aquatic ecosystems are highly variable, but may contribute 41% to 53% of total methane emissions globally.
In fact, these combined emissions are a larger source of methane than direct anthropogenic methane sources, such as cows, landfill and waste, and coal mining. This knowledge is important because it can help inform new monitoring and measurements to distinguish where and how methane emissions are produced.
The alarming human impact
There is an increasing pressure from humans on aquatic ecosystems. This includes increased nutrients (like fertilisers) getting dumped into rivers and lakes, and farm dam building as the climate dries in many places.
In general, we found methane emissions from impacted, polluted and human-made aquatic ecosystems are higher than from more natural sites.
For example, fertiliser runoff from agriculture creates nutrient-rich lakes and reservoirs, which releases more methane than nutrient-poor (oligotrophic) lakes and reservoirs. Similarly, rivers polluted with nutrients also have increased methane emissions.
What’s particularly alarming is the strong methane release from rice cultivation, reservoirs and aquaculture farms.
Globally, rice cultivation releases more methane per year than all coastal wetlands, the continental shelf and open ocean together.
The fluxes in methane emissions per area of coastal aquaculture farms are 7-430 times higher than from coastal habitats such as mangrove forests, salt marshes or seagrasses. And highly disturbed mangroves and salt marsh sites have significantly higher methane fluxes than more natural sites.
So how do we reduce methane emissions?
For aquatic ecosystems, we can effectively reduce methane emissions and help mitigate climate change with the right land use and management choices.
For example, managing aquaculture farms and rice paddies so they alternate between wet and dry conditions can reduce methane emissions.
Restoring salt marsh and mangrove habitats and the flow of seawater from tides is another promising strategy to further reduce methane emissions from degraded coastal wetlands.
We should also reduce the amount of nutrients coming from fertilisers washing into freshwater wetlands, lakes, reservoirs and rivers as it leads to organic matter production, such as toxic algal blooms. This will help curtail methane emissions from inland waters.
These actions will be most effective if we apply them in the aquatic ecosystems that have the greatest contribution of aquatic methane: freshwater wetlands, lakes, reservoirs, rice paddies and aquaculture farms.
This will be no small effort, and will require knowledge across many disciplines. But with the right choices we can create conditions that bring methane fluxes down while also preserving ecosystems and biodiversity.
Judith Rosentreter, Postdoctoral Research Fellow, Yale University; Alberto Borges, Research Director FRS-FNRS, Associate Professor at ULiège, Université de Liège; Ben Poulter, Research scientist, NASA, and Bradley Eyre, Professor of Biogeochemistry, Director of the Centre for Coastal Biogeochemistry, Southern Cross University
In 1992, 1,700 scientists warned that human beings and the natural world were “on a collision course”. Seventeen years later, scientists described planetary boundaries within which humans and other life could have a “safe space to operate”. These are environmental thresholds, such as the amount of carbon dioxide in the atmosphere and changes in land use.
Crossing such boundaries was considered a risk that would cause environmental changes so profound, they genuinely posed an existential threat to humanity.
This grave reality is what our major research paper, published today, confronts.
In what may be the most comprehensive evaluation of the environmental state of play in Australia, we show major and iconic ecosystems are collapsing across the continent and into Antarctica. These systems sustain life, and evidence of their demise shows we’re exceeding planetary boundaries.
We found 19 Australian ecosystems met our criteria to be classified as “collapsing”. This includes the arid interior, savannas and mangroves of northern Australia, the Great Barrier Reef, Shark Bay, southern Australia’s kelp and alpine ash forests, tundra on Macquarie Island, and moss beds in Antarctica.
We define collapse as the state where ecosystems have changed in a substantial, negative way from their original state – such as species or habitat loss, or reduced vegetation or coral cover – and are unlikely to recover.
The good and bad news
Ecosystems consist of living and non-living components, and their interactions. They work like a super-complex engine: when some components are removed or stop working, knock-on consequences can lead to system failure.
Our study is based on measured data and observations, not modelling or predictions for the future. Encouragingly, not all ecosystems we examined have collapsed across their entire range. We still have, for instance, some intact reefs on the Great Barrier Reef, especially in deeper waters. And northern Australia has some of the most intact and least-modified stretches of savanna woodlands on Earth.
Still, collapses are happening, including in regions critical for growing food. This includes the Murray-Darling Basin, which covers around 14% of Australia’s landmass. Its rivers and other freshwater systems support more than 30% of Australia’s food production.
The effects of floods, fires, heatwaves and storms do not stop at farm gates; they’re felt equally in agricultural areas and natural ecosystems. We shouldn’t forget how towns ran out of drinking water during the recent drought.
Drinking water is also at risk when ecosystems collapse in our water catchments. In Victoria, for example, the degradation of giant Mountain Ash forests greatly reduces the amount of water flowing through the Thompson catchment, threatening nearly five million people’s drinking water in Melbourne.
This is a dire wake-up call — not just a warning. Put bluntly, current changes across the continent, and their potential outcomes, pose an existential threat to our survival, and other life we share environments with.
In investigating patterns of collapse, we found most ecosystems experience multiple, concurrent pressures from both global climate change and regional human impacts (such as land clearing). Pressures are often additive and extreme.
Take the last 11 years in Western Australia as an example.
In the summer of 2010 and 2011, a heatwave spanning more than 300,000 square kilometres ravaged both marine and land ecosystems. The extreme heat devastated forests and woodlands, kelp forests, seagrass meadows and coral reefs. This catastrophe was followed by two cyclones.
A record-breaking, marine heatwave in late 2019 dealt a further blow. And another marine heatwave is predicted for this April.
These 19 ecosystems are collapsing: read about each
What to do about it?
Our brains trust comprises 38 experts from 21 universities, CSIRO and the federal Department of Agriculture Water and Environment. Beyond quantifying and reporting more doom and gloom, we asked the question: what can be done?
We devised a simple but tractable scheme called the 3As:
Awareness of what is important
Anticipation of what is coming down the line
Action to stop the pressures or deal with impacts.
In our paper, we identify positive actions to help protect or restore ecosystems. Many are already happening. In some cases, ecosystems might be better left to recover by themselves, such as coral after a cyclone.
In other cases, active human intervention will be required – for example, placing artificial nesting boxes for Carnaby’s black cockatoos in areas where old trees have been removed.
“Future-ready” actions are also vital. This includes reinstating cultural burning practices, which have multiple values and benefits for Aboriginal communities and can help minimise the risk and strength of bushfires.
It might also include replanting banks along the Murray River with species better suited to warmer conditions.
Some actions may be small and localised, but have substantial positive benefits.
For example, billions of migrating Bogong moths, the main summer food for critically endangered mountain pygmy possums, have not arrived in their typical numbers in Australian alpine regions in recent years. This was further exacerbated by the 2019-20 fires. Brilliantly, Zoos Victoria anticipated this pressure and developed supplementary food — Bogong bikkies.
Other more challenging, global or large-scale actions must address the root cause of environmental threats, such as human population growth and per-capita consumption of environmental resources.
We must rapidly reduce greenhouse gas emissions to net-zero, remove or suppress invasive species such as feral cats and buffel grass, and stop widespread land clearing and other forms of habitat destruction.
Our lives depend on it
The multiple ecosystem collapses we have documented in Australia are a harbinger for environments globally.
The simplicity of the 3As is to show people can do something positive, either at the local level of a landcare group, or at the level of government departments and conservation agencies.
We simply cannot afford any further delay.
Dana M Bergstrom, Principal Research Scientist, University of Wollongong; Euan Ritchie, Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University; Lesley Hughes, Professor, Department of Biological Sciences, Macquarie University, and Michael Depledge, Professor and Chair, Environment and Human Health, University of Exeter
Dung beetles play an important role helping clear up all the dung left by other animals in an environment.
In Australia there are approximately 475 native species of dung beetle.
But there’s a problem. Most of them are adapted to deal with marsupial dung. When British colonisers brought livestock down under, they introduced an entirely new type of dung that the native dung beetles were ill-equipped to handle.
Not touching that dung
Cattle dung is wet and bulky. It is very unlike marsupial dung – which is typically small, dry pellets – and so the native dung beetles largely left it alone. As a result, large deposits of cattle dung accumulated in the Australian agricultural landscape.
Besides fouling the land, the dung was an excellent breeding site for bush flies and other nuisance insects, as well as internal parasites that plague the digestive tracts of livestock.
So CSIRO embarked on an ambitious plan to introduce into Australia many dung beetles that were adapted to livestock dung. Starting in 1966, it imported and released 43 species of dung beetles over 25 years.
The beetles came from places such as South Africa, France, Spain and Turkey. The chosen beetles had similar climate requirements and were adapted to wild and domestic livestock, so they could live in Australia and process livestock dung.
What do dung beetles do?
When people think of dung beetles, the popular image that comes to mind is that of an industrious beetle labouring to roll a large ball of dung across the landscape.
These little engineers are actually trying to find a suitable spot to situate the ball, on which they will lay an egg. Their offspring will have food and a safe place to grow up, and generate more dung beetles.
Most species of dung beetles actually tunnel beneath piles of dung and drag bits of it into subterranean chambers, where they then lay their eggs.
The larvae develop over the following weeks to months, eventually emerging as adults and crawling to the surface in search of a mate and another pile of dung to colonise.
The introduced dung beetles
Of the 43 species introduced to Australia by CSIRO, 23 have become established and many are having a positive impact.
The activities of dung beetles helped remove dung from pastures and with it, the breeding site for nuisance flies and internal parasites.
They also improved pasture fertility. They increased the permeability of pasture soils to rainwater which decreased runoff of rainwater laden with nutrients that can pollute waterways.
But it is not known just how widely each of the introduced species has spread. There might be geographical and seasonal gaps in dung beetle activity that could be filled by other species yet to be introduced to Australia.
Working with farming
Dung beetles have been around for tens of millions of years, but their ability to survive in modern agricultural environments may be jeopardised by some farming practices.
Tilling paddocks used in cropping and livestock rotation systems may destroy the developing dung beetle larvae.
Some deworming agents, used by livestock producers to control intestinal parasites, may pass through the livestock and out in their faeces, and might poison the dung beetles colonising the dung.
It should be possible to manage tillage and deworming to minimise harm to the dung beetles, and so maximise their positive impact on the land.
That’s where Dung Beetle Ecosystem Engineers (DBEE) comes in.
In this project, a group of research institutions, producer groups, land management groups and dung beetle entrepreneurs are working together.
The project, now in its second year, is supported by Meat and Livestock Australia and funded by the Rural Research and Development for Profit Program of the Australian Department of Agriculture, Water and the Environment. Charles Sturt University leads the project, with cooperators at CSIRO, University of Western Australia, University of New England, Mingenew-Irwin Group, Warren Catchment Council, Dung Beetle Solutions International, and LandCare Research NZ.
Dung Beetle Ecosystem Engineers aims to:
understand the distribution of dung beetle species previously introduced to Australia, and predict their ultimate spread
evaluate new species of dung beetle for importation and release into Australia
estimate the economic impact of dung beetles on farming systems
develop a database of information on dung beetles in Australasia and educational materials for use by a range of users
work with farming and land management groups to engage landholders in detecting dung beetles and modifying agricultural practices to enhance the success of dung beetles.
At the end of the DBEE project, we will have a better understanding of the role of dung beetles as a farming tool, helping farmers choose agricultural practices that will improve their bottom line.
New dung beetle species will be ready to work for Australia and New Zealand, and a distribution network will enhance their spread to new geographic areas.
DBEE aims bring economic and ecological benefits to the agricultural sector and wider Australian and New Zealand community.
The drought in eastern Australia was a significant driver of this season’s unprecedented bushfires. But it also caused another, less well known environmental calamity this summer: entire hillsides of trees turned from green to brown.
We’ve observed extensive canopy dieback from southeast Queensland down to Canberra. Reports of more dead and dying trees from other regions across Australia are flowing in through the citizen science project, the Dead Tree Detective.
A few dead trees are not an unusual sight during a drought. But in some places, it is the first time in living memory so much canopy has died off.
Ecologists are now pondering the implications. There are warnings that some Australian tree species could disappear from large parts of their ranges as the climate changes. Could we be witnessing the start of ecosystem collapse?
Why are canopies dying now?
Much of eastern Australia has been in drought since the start of 2017. While this drought is not yet as long as the Millennium Drought, it appears to be more intense. Many areas have received the lowest rainfall on record, including long periods of time with no rainfall. This has been coupled with above-average temperatures and extreme heatwaves.
The higher the temperature, the greater the moisture loss from leaves. This is usually good for a tree because it cools the canopy. But if there is not enough water in the soil, the increased water loss can push trees over a threshold, causing extensive leaf “scorching”, or browning. The extensive canopy dieback we have observed this summer suggests that the soil had finally become too dry for many trees.
Are the trees dead?
Brown or bare trees are not necessarily dead. Many eucalypts can lose all their leaves but resprout after rain.
Many parts of eastern Australia are now flushed with green after rain. In these areas, it will be important to assess the extent of tree recovery. If trees are not showing signs of recovery after significant rainfall, they’re unlikely to survive. In some cases carbohydrate reserves – which trees need to resprout new leaves – may be too depleted for trees to recover.
The drought may also hinder post-fire recovery. Most eucalypt forests eventually recover from bushfires by resprouting new leaves. Some forests also recover when fire triggers seedlings to germinate.
But it’s likely that some forests now recovering from fire were already struggling with canopy dieback. So these two disturbances will test how resilient our forests are to back-to-back drought and bushfire.
Trees recovering from drought and/or fire may also enter the “dieback spiral”. The new flush of leaves following rain can make a particularly tasty meal for insects. Trees will then attempt to grow more foliage in response, but their ability to keep producing new leaves gradually declines as they deplete their carbohydrate reserves, and they can die.
Dieback spiral has led to extensive tree loss in the past, including in the New England area of NSW.
Should we be worried?
The capacity of eucalypts to resprout makes them naturally resilient to extended drought. There are some records of canopy dieback from severe droughts in the past, such as the Federation Drought. We assume (although we don’t know for sure) the forests recovered after these events. So they may bounce back after the current drought.
However, it’s hard not to be concerned. Climate change will bring increased drought, heatwaves and fires that could, over time, see extensive losses of trees across the landscape – as happened on the Monaro High Plain after the Millennium Drought.
Australian research in 2016 warned that due to climate change, the habitat of 90% of eucalypt species could decline and 16 species were expected to lose their home environments within 60 years.
Such a change would have huge consequences for how ecosystems function – reducing the capacity for ecosystem services such as carbon storage, altering catchment water resources and reducing habitat for native animals.
Where to from here?
Landholders can help bush on their property recover after drought, by protecting germinating seedlings from livestock and collecting local seed for later revegetation. Trees that appear dead should not be cut down as they may recover, and even if dead can provide valuable animal habitat.
Most importantly, however, we need to monitor trees carefully to see where they’ve died, and where they are recovering. A citizen science project, the Dead Tree Detective, is helping map the extent of tree die-off across Australia.
People send in photos of dead and dying trees – to date, over 267 records have been uploaded. These records can be used to target where to monitor forests during drought, including on-ground assessments of tree health and quantifying the physiological responses of trees to drought stress.
There is no ongoing forest health monitoring program in Australia, so this dataset is invaluable in helping us determine exactly how vulnerable Australia’s forests are to the double whammy of severe drought and bushfires.
Rachael Helene Nolan, Postdoctoral research fellow, Western Sydney University; Belinda Medlyn, Professor, Western Sydney University; Brendan Choat, Associate Professor, Western Sydney University, and Rhiannon Smith, Research Fellow, University of New England
Tree planting has been widely promoted as a solution to climate change, because plants absorb the climate-warming gases from Earth’s atmosphere as they grow. World leaders have already committed to restoring 350m hectares of forest by 2030 and a recent report suggested that reforesting a billion hectares of land could store a massive 205 gigatonnes of carbon – two thirds of all the carbon released into the atmosphere since the Industrial Revolution.
Many of those trees could be planted in tropical grassy biomes according to the report. These are the savannas and grasslands that cover large swathes of the globe and have a grassy ground layer and variable tree cover. Like forests, these ecosystems play a major role in the global carbon balance. Studies have estimated that grasslands store up to 30% of the world’s carbon that’s tied up in soil. Covering 20% of Earth’s land surface, they contain huge reserves of biodiversity, comparable in areas to tropical forest. These are the landscapes with lions, elephants and vast herds of wildebeest.
Savannas and grasslands are home to nearly one billion people, many of whom raise livestock and grow crops. Tropical grassy biomes were the cradle of humankind – where modern humans first evolved – and they are where important food crops such as millet and sorghum originated, which millions eat today. And, yet among the usual threats of climate change and wildlife habitat loss, these ecosystems face a new threat – tree planting.
It might sound like a good idea, but planting trees here would be damaging. Unlike forests, ecosystems in the tropics that are dominated by grass can be degraded not only by losing trees, but by gaining them too.
Where more trees isn’t the answer
Increasing the tree cover in savanna and grassland can mean plant and animal species which prefer open, well-lit environments are pushed out. Studies from South Africa, Australia and Brazil indicate that unique biodiversity is lost as tree cover increases.
This is because adding trees can alter how these grassy ecosystems function. More trees means fires are less likely, but regular fire removes vegetation that shades ground layer plants. Not only do herbivores like zebra and antelope that feed on grass have less to eat, but more trees may also increase their risk of being eaten as predators have more cover.
More trees can also reduce the amount of water in streams and rivers. As a result of humans suppressing wildfires in the Brazilian savannas, tree cover increased and the amount of rain reaching the ground shrank. One study found that in grasslands, shrublands and cropland worldwide where forests were created, streams shrank by 52% and 13% of all streams dried up completely for at least a year.
Grassy ecosystems in the tropics provide surface water for people to drink and grazing land for their livestock, not to mention fuel, food, building materials and medicinal plants. Tree planting here could harm the livelihoods of millions.
Losing ancient grassy ecosystems to forests won’t necessarily be a net benefit to the climate either. Landscapes covered by forest tend to be darker in colour than savanna and grassland, which might mean they also absorb more heat. As drought and wildfires become more frequent, grasslands may be a more reliable carbon sink than forests.
How have we reached the point where the unique tropical savannas and grasslands of the world are viewed as suitable for wholesale “restoration” as forests?
At the root of the problem is that these grassy ecosystems are fundamentally misunderstood. The Food and Agricultural Organisation of the UN defines any area that’s half a hectare in size with more than 10% tree cover as forest. This assumes that landscapes like an African savanna are degraded because they have fewer trees and so need to be reforested. The grassy ground layer houses a unique range of species, but the assumption that forests are more important threatens grassy ecosystems across the tropics and beyond, including in Madagascar, India and Brazil.
“Forest” should be redefined to ensure savannas and grasslands are recognised as important systems in their own right, with their own irreplaceable benefits to people and other species. It’s essential people know what degradation looks like in open, sunlit ecosystems with fewer trees, so as to restore ecosystems that are actually degraded with more sensitivity.
Calls for global tree planting programmes to cool the climate need to think carefully about the real implications for all of Earth’s ecosystems. The right trees need to be planted in the right places. Otherwise, we risk a situation where we miss the savanna for the trees, and these ancient grassy ecosystems are lost forever.
About half of the coastline of Europe, the United States and Australasia is modified by artificial structures. In newly published research, we identified a new effect of marine urbanisation that has so far gone unrecognised.
When we build marinas, ports, jetties and coastal defences, we introduce hard structures that weren’t there before and which reduce the amount of sunlight hitting the water. This means energy producers such as seaweed and algae, which use light energy to transform carbon dioxide into sugars, are replaced by energy consumers such as filter-feeding invertebrates. These latter species are often not native to the area, and can profoundly alter marine habitats by displacing local species, reducing biodiversity, and decreasing the overall productivity of ecosystems.
Incorporating simple designs in our marine infrastructure to allow more light penetration, improve water flow, and maintain water quality, will go a long way towards curbing these negative consequences.
We are used to thinking about the effects of urbanisation in our cities – but it is time to pay more attention to urban sprawl in the sea. We need to better understand the effects on the food web in a local context.
Most animals that establish themselves on these shaded hard structures are “sessile” invertebrates, which can’t move around. They come in a variety of forms, from encrusting species such as barnacles, to tree-shaped or vase-like forms such as bryozoans or sponges. But what they all have in common is that they can filter out algae from the water.
In Australian waters, we commonly see animals from a range of different groups including sea squirts, sponges, bryozoans, mussels and worms. They can grow in dense communities and often reproduce and grow quickly in new environments.
How much energy do they use?
In our new research, published in the journal Frontiers in Ecology and the Environment, we analysed the total energy usage of invertebrate communities on artificial structures in two Australian bays: Moreton Bay, Queensland, and Port Phillip Bay, Victoria. We did so by combining data from field surveys, laboratory studies, and satellite data.
We also compiled data from other studies and assessed how much algae is required to support the energy demands of the filter-feeding species in commercial ports worldwide.
In Port Phillip Bay, 0.003% of the total area is taken up by artificial structures. While this doesn’t sound like much, it is equivalent to almost 50 soccer fields of human-built structures.
We found that the invertebrate community living on a single square metre of artificial structure consumes the algal biomass produced by 16 square metres of ocean. Hence, the total invertebrate community living on these structures in the bay consumes the algal biomass produced by 800 football pitches of ocean!
Similarly, Moreton Bay has 0.005% of its total area occupied by artificial structures, but each square metre of artificial structure requires around 5 square metres of algal production – a total of 115 football pitches. Our models account for various biological and physical variables such as temperature, light, and species composition, all of which contribute to generate differences among regions.
Overall, the invertebrates growing on artificial structures in these two Australian bays weigh as much as 3,200 three-tonne African elephants. This biomass would not exist were it not for marine urbanisation.
How does Australia compare to the rest of the world?
We found stark differences among ports in different parts of the world. For example, one square metre of artificial structure in cold, highly productive regions (such as St Petersburg, Russia) can require as little as 0.9 square metres of sea surface area to provide enough algal food to sustain the invertebrate populations. Cold regions can require less area because they are often richer in nutrients and better mixed than warmer waters.
In contrast, a square metre of structure in the nutrient-poor tropical waters of Hawaii can deplete all the algae produced in the surrounding 120 square metres.
Does it matter?
Should we be worried about all of this? To some extent, it depends on context.
These dense filter-feeding communities are removing algae that normally enters food webs and supports coastal fisheries. As human populations in coastal areas continue to increase, so will demand on these fisheries, which are already under pressure from climate change. These effects will be greatest in warmer, nutrient-poor waters.
But there is a flip side. Ports and urban coastlines are often polluted with increased nutrient inputs, such as sewage effluents or agricultural fertilisers. The dense populations of filter-feeders on the structures near these areas may help prevent this nutrient runoff from triggering problematic algal blooms, which can cause fish kills and impact human health. But we still need to know what types of algae these filter-feeding communities are predominantly consuming.
Our analysis provides an important first step in understanding how these communities might affect coastal production and food webs.
In places like Southeast Asia, marine managers should consider how artificial structures might affect essential coastal fisheries. Meanwhile, in places like Port Phillip Bay, we need to know whether and how these communities might affect the chances of harmful algal blooms.
Martino Malerba, Postdoctoral Fellow, Monash University; Craig White, Head, Evolutionary Physiology Research Group, Monash University; Dustin Marshall, Professor, Marine Evolutionary Ecology, Monash University, and Liz Morris, Administration Manager, Monash University
Climate change and those whose job it is to talk about current and future climate impacts are often classed as the “harbingers of doom”. For the world’s biodiversity, the predictions are grim – loss of species, loss of pollination, dying coral reefs.
The reality is that without human intervention, ecosystems will reshape themselves in response to climate change, what we can think of as “autonomous adaptation”. For us humans – we need to decide if we need or want to change that course.
For those who look after natural systems, our job description has changed. Until now we have scrambled to protect or restore what we could fairly confidently consider to be “natural”. Under climate change knowing what that should look like is hard to decide.
If the Great Barrier Reef still has a few pretty fish and coral in the future, and only scientists know they are different species to the past, does that matter? It’s an extreme example, but it is a good analogy for the types of decisions we might need to make.
In Queensland, the government has just launched the Biodiversity and Ecosystem Climate Adaptation Plan for Queensland focused on what is considered important for making these decisions. The plan is high level, but is an important first step toward preparing the sector for the future.
For the rest of Queensland’s ecosystems the story is much the same as the Great Barrier Reef. There are the obvious regions at risk. Our coastal floodplains and wetlands are potentially under threat from both sides, with housing and development making a landward march and the sea pushing in from the other side. These ecosystems literally have nowhere to go in the crush.
It’s a similar story for species and ecosystems that specialise on cool, high altitude mountaintops. These small, isolated populations rely on cool conditions. As the temperature warms, if they can’t change their behaviour (for instance, by taking refuge in cool spots or crevices during hot times), then it is unlikely they will survive without human intervention such as translocation.
We are all too familiar with the risk of coral reefs dying and becoming a habitat for algae, but some of our less high profile ecosystems face similar transformations. Our tropical savannah woodlands cover much of the top third of Queensland. An iconic ecosystem of the north, massive weed invasions and highly altered fire regimes might threaten to make them unrecognisable.
So where to from here?
From the grim predictions we must rally to find a way forward. Critically for those who must manage our natural areas it’s about thinking about what we want to get out of our efforts.
Conservation property owners, both public (for instance, national parks) and private (for instance, not-for-profit conservation groups), must decide what their resources can achieve. Throwing money at a species we cannot save under climate change may be better replaced by focusing on making sure we have species diversity or water quality. It’s a hard reality to swallow, but pragmatism is part of the climate change equation.
We led the development of the Queensland plan, and were encouraged to discover a sector that had a great deal of knowledge, experience and willingness. The challenge for the Queensland government is to usefully channel that energy into tackling the problem.
One of the clearest messages from many of the people we spoke to was about how biodiversity and ecosystems are valued by the wider community. Or not. There was a clear sense that we need to make biodiversity and ecosystems a priority.
It’s easy to categorise biodiversity and conservation as a “green” issue. But aside from the intrinsic value or personal health and recreation value that most of us place on natural areas, without biodiversity we risk losing things other than a good fishing spot.
Every farmer knows the importance of clean water and fertile soil to their economic prosperity. But when our cities bulge, or property is in danger from fire, we prioritise short-term economic returns, more houses or reducing fire risk over biodiversity almost every time.
Of course, this is not to say the balance should be flipped, but climate change is challenging our politicians, planners and us as the Queensland community to take responsibility for the effects our choices have on our biodiversity and ecosystems. As the pressure increases to adapt in other sectors, we should seek options that could help – rather than hinder – adaptation in natural systems.
Coastal residences may feel that investing in a seawall to protect their homes from rising sea levels is worthwhile even if it means sacrificing a scrap of coastal wetland, but there are opportunities to satisfy both human needs and biodiversity needs. We hope the Queensland plan can help promote those opportunities.
Cath Moran contributed to developing this article.
To the chagrin of the tourist industry, the Great Barrier Reef has become a notorious victim of climate change. But it is not the only Australian ecosystem on the brink of collapse.
Our research, recently published in Nature Climate Change, describes a series of sudden and catastrophic ecosystem shifts that have occurred recently across Australia.
These changes, caused by the combined stress of gradual climate change and extreme weather events, are overwhelming ecosystems’ natural resilience.
Australia is one of the most climatically variable places in the world. It is filled with ecosystems adapted to this variability, whether that means living in scorching heat, bitter cold or a climate that cycles between the two.
Despite land clearing, mining and other activities that transform the natural landscape, Australia retains large tracts of near-pristine natural systems.
Many of these regions are iconic, sustaining tourism and outdoor activities and providing valuable ecological services – particularly fisheries and water resources. Yet even here, the combined stress of gradual climate change and extreme weather events is causing environmental changes. These changes are often abrupt and potentially irreversible.
They include wildlife and plant population collapses, the local extinction of native species, the loss of ancient, highly diverse ecosystems and the creation of previously unseen ecological communities invaded by new plants and animals.
Australia’s average temperature (both air and sea) has increased by about 1°C since the start of the 19th century. We are now experiencing longer, more frequent and more intense heatwaves, more extreme fire weather and longer fire seasons, changes to rainfall seasonality, and droughts that may be historically unusual.
The interval between these events has also shortened, which means even ecosystems adapted to extremes and high natural variability are struggling.
As climate change accelerates, the magnitude and frequency of extreme events is expected to continue increasing.
What is ecosystem collapse?
Gradual climate change can be thought of as an ongoing “press”, on which the “pulse” of extreme events are now superimposed. In combination, “presses” and “pulses” are more likely to push systems to collapse.
We identified ecosystems across Australia that have recently experienced catastrophic changes, including:
kelp forests shifting to seaweed turfs following a single marine heatwave in 2011;
the destruction of Gondwanan refugia by wildfire ignited by lightning storms in 2016;
dieback of floodplain forests along the Murray River following the millennial drought in 2001–2009;
large-scale conversion of alpine forest to shrubland due to repeated fires from 2003–2014;
community-level boom and bust in the arid zone following extreme rainfall in 2011–2012, and
mangrove dieback across a 1,000km stretch of the Gulf of Carpentaria after a weak monsoon in 2015-2016.
Of these six case studies, only the Murray River forest had previously experienced substantial human disturbance. The others have had negligible exposure to stressors, highlighting that undisturbed systems are not necessarily more resilient to climate change.
The case studies provide a range of examples of how presses and pulses can interact to push an ecosystem to a “tipping point”. In some cases, a single extreme event may be sufficient to cause an irreversible regime shift.
In other systems, a single extreme event may only be sufficient to tip the ecosystem over the edge when gradual declines in populations have already occurred. More frequent extreme events can also lead to population collapse if a species does not have enough time to recover between events.
But not all examples can be directly linked to a single weather event, or a series of events. These are most likely caused by multiple interacting climate “presses” and “pulses”. It’s worth remembering that extreme biological responses do not always manifest as an impact on the dominant species. Cascading interactions can trigger ecosystem-wide responses to extreme events.
The cost of intervention
Once an ecosystem goes into steep decline – with key species dying out and crucial interactions no longer possible – there are important consequences.
Apart from their intrinsic worth, these areas can no longer supply fish, forest resources, or carbon storage. It may affect livestock and pasture quality, tourism, and water quality and supply.
Unfortunately, the sheer number of variables – between the species and terrain in each area, and the timing and severity of extreme weather events – makes predicting ecosystem collapses essentially impossible.
Targeted interventions, like the assisted recolonisation of plants and animals, reseeding an area that’s suffered forest loss, and actively protecting vulnerable ecosystems from destructive bushfires, may prevent a system from collapsing, but at considerable financial cost. And as the interval between extreme events shorten, the chance of a successful intervention falls.
Critically, intervention plans may need to be decided upon quickly, without full understanding of the ecological and evolutionary consequences.
How much are we willing to risk failure and any unintended consequences of active intervention? How much do we value “natural” and “pristine” ecosystems that will increasingly depend on protection from threats like invasive plants and more frequent fires?
We suspect the pervasive effects of the press and pulse of climate change means that, increasingly, the risks of doing nothing may outweigh the risks of acting.
The beginning of this century has seen an unprecedented number of widespread, catastrophic biological transformations in response to extreme weather events.
This constellation of unpredictable and sudden biological responses suggests that many seemingly healthy and undisturbed ecosystems are at a tipping point.
Rebecca Harris, Climate Research Fellow, University of Tasmania; David Bowman, Professor, Environmental Change Biology, University of Tasmania, and Linda Beaumont, Senior Lecturer, Macquarie University