What would happen if we cut down the entire Amazon rainforest? Could it be replaced by an equal amount of reforestation elsewhere?
Removing the entire Amazon rainforest would have myriad consequences, with the most obvious ones possibly not the worst.
Most people will first think of the carbon currently stored in the Amazon, the world’s largest rainforest. But the consequences would be far-reaching for the climate as well as biodiversity and ecosystems — and, ultimately, people.
The overall impact of the Amazon’s complete removal is unthinkable and beyond the power of our current predictive tools. But let’s look at some aspects we can describe.
The Amazon rainforest is estimated to harbour about 76 billion tonnes of carbon. If all trees were cut down and burned, the forest’s carbon storage capacity would be lost to the atmosphere.
Some of this carbon would be taken up by the oceans, and some by other ecosystems (such as temperate or arctic forests), but no doubt this would exacerbate climate warming. For comparison, humans emit about 10 billion tonnes of carbon every year through the burning of fossil fuels.
But the Amazon forest does more than store carbon. It is also responsible for the circulation of huge quantities of water.
This image, captured by NASA’s Aqua satellite in 2009, shows how the forest and the atmosphere interact to create a uniform layer of “popcorn” clouds during the dry season. It is during this period, the time without rain, that the forest grows the most.
If the Amazon’s cloud systems and its capacity to recycle water were to be disrupted, the ecosystem would tip over and irreversibly turn into dry savannah very quickly. Estimates of where this tipping point could lie range from 40% deforestation to just 20% loss of forest cover from the Amazon.
Reforestation elsewhere to achieve the same amount of carbon storage is technically possible, but we have neither the time (several hundred years would be needed) nor the land (at least an equivalent surface area would be required).
Another reason why reforestation is not a remedy is that the water the rainforest circulates — and with it the availability of nutrients — would disappear.
Once you cut the circulation of water through (partial) deforestation, there is a point of no return. The water doesn’t disappear from the planet, but certainly from the forest ecosystems, with immediate and powerful consequences for the world’s climate.
The number of animal species found in the Amazon is even higher, with the largest part made up by insects, representing around 10% of the known insect fauna, as well as a large but unknown number of fungi and microbes.
Once species are lost, they are lost forever, and this would ultimately be the most harmful consequence of cutting down the Amazon. It would possibly be worse than the loss of its role as a massive redistributor and storage of water and carbon.
Last but certainly not least, there are about 30 million people living in and near the Amazon rainforest.
The consequences of losing the forest as a provider of the ecosystem services mentioned above and as a source of food and habitat are unfathomable. The repercussions would reach far into global politics, the global economy, and societal issues.
If you go to the Surrey Hills of northwest Tasmania, you’ll see a temperate rainforest dominated by sprawling trees with genetic links going back millions of years.
It’s a forest type many consider to be ancient “wilderness”. But this landscape once looked very different.
The only hints are a handful of small grassy plains dotting the estate and the occasional giant eucalypt with broad-branching limbs. This is an architecture that can only form in open paddock-like environments – now swarmed by rainforest trees.
These remnant grasslands are of immense conservation value, as they represent the last vestiges of a once more widespread subalpine “poa tussock” grassland ecosystem.
Our new research shows these grasslands were the result of Palawa people who, for generation upon generation, actively and intelligently manicured this landscape against the ever-present tide of the rainforest expansion we see today.
This purposeful intervention demonstrates land ownership. It was their property. Their estate. Two hundred years of forced dispossession cannot erase millennia of land ownership and connection to country.
Myths of “wilderness” have no place on this continent when much of the land in Australia is culturally formed, created by millennia of Aboriginal burning – even the world renowned Tasmanian Wilderness World Heritage Area.
Today, the Surrey Hills hosts a vast 60,000-hectare timber plantation. Areas outside the modern plantations on the Surrey Hills are home to rainforest.
On first seeing the Surrey Hills from atop St Valentine’s Peak in 1827, Henry Hellyer – surveyor for the Van Diemen’s Land company – extolled the splendour of the vista before him:
an excellent country, consisting of gently rising, dry, grassy hills […] They resemble English enclosures in many respects, being bounded by brooks between each, with belts of beautiful shrubs in every vale.
It will not in general average ten trees on an acre. There are many plains of several square miles without a single tree.
And when first setting food on the estate:
The kangaroo stood gazing at us like fawns, and in some instances came bounding towards us.
He went on to note how the landscape was recently burnt, “looking fresh and green in those places”.
It is possible that the natives by burning only one set of plains are enabled to keep the kangaroos more concentrated for their use, and I can in no way account for their burning only in this place, unless it is to serve them as a hunting place.
These ideas are criticised by those who either genuinely believe Aboriginal people merely subsisted on what was “naturally” available to them, or by those with other agendas aimed at denying how First Nations people owned, occupied and shaped Australia.
New research backs up Hellyer
We sought to directly test the observations of Hellyer in the Surrey Hills, using the remains of plants and fire (charcoal) stored in soils beneath the modern day rainforest.
Drilling in to the earth beneath modern rainforest, we found the deeper soils were full of the remains of grass, eucalypts and charcoal, while the upper more recent soil was dominated by rainforest and no charcoal.
We drilled into more than 70 rainforest trees across two study sites, targeting two species that can live for more than 500 years: Myrtle Beech (Nothofagus cunninghami) and Celery-top Pine (Phyllocladus aspleniifolius).
None of the trees we measured were older than 180 years (from 1840). That’s just over a decade following Hellyer’s first glimpse of the Surrey Hills.
Our data unequivocally proves the landscape of the Surrey Hills was an open grassy eucalypt-savanna with regular fire under Aboriginal management prior to 1827.
Importantly, the speed at which rainforest invaded and captured this Indigenous constructed landscape shows the enormous workload Aboriginal people invested in holding back rainforest. For millennia, they used cultural burning to maintain a 60,000-hectare grassland.
Learning from the past
Our research challenges the central tenet underpinning the concept of terra nullius (vacant land) on which the tenuous and uneasy claims of sovereignty of white Australia over Aboriginal lands rests.
More than the political implications, this data reveals another impact of dispossession and denial of Indigenous agency in the creation of the Australian landscape.
Left unburnt, grassy ecosystems constructed by Indigenous people accumulate woody fuels, in Australia and elsewhere.
Forest has far more fuel than grassland and savanna ecosystems. Under the right set of climatic conditions, any fuel will burn and increasing fuel loads dramatically increases the potential for catastrophic bushfire.
When I first came across the kauri pine (Agathis robusta), I certainly wasn’t impressed by their growth. Mixed among other species in a young rainforest plantation, they seemed destined to be left behind by the faster-growing trees (I did think they looked nice, though).
But today I know I judged the kauri unfairly. They can survive for millennia, so they don’t bother doing all their growing in their first couple of decades. But come back 20 years later, and that unassuming tree will be well on its way to being one of the giants of the forest.
By any yardstick, kauri pines are truly unique and impressive. If time is our measure, then the kauri family, Agathis, has endured over epochs, with fossils found in Australia from the early to mid-Jurassic period. Having withstood the rise and fall of the dinosaurs and the evolution and diversification of our flora, 17 species of living fossil trees in the Agathis family remain.
Agathis is an iconic genus of large, ecologically important, and economically valuable conifers that now range over lowland to upper montane rainforests from New Zealand to Sumatra. So, if we judge a plant’s success in terms of its geographical spread or its ability to adapt to a range of conditions, the Kauri family is once again outstanding.
If we measure a plant by appearances, then the tall, robust and handsome Queensland kauri pine remains an impressive – albeit little-known – plant. Reaching up to 50 metres, it emerges above rainforest margins in tropical and subtropical eastern Australia. Its straight, round trunk can grow to 3m in diameter and a combination of smooth mottled bark, coppery new growth and dark green canopy make this tree a world-class ornamental. In parks and gardens across Australia, Kauri pine cuts a fine figure, growing to enormous sizes, even in southern regions.
Our Australian kauri pine, once common in the dry rainforests of Queensland, has become a victim of its own success. A heavy reliance on the highly regarded wood during the earliest stages of the colonial timber industry has left only a few old trees standing, mostly in remote areas or forest reserves. In my role as a research scientist, I have tracked down the kauri’s cousins in the Pacific regions, where the giant pines can now only be found on tops of mountains on remote islands. In New Zealand, the giant kauri that once covered large areas are in danger from the soil-based fungus Phytophora.
Germaine Greer, in her 2014 book White Beech, describes visiting a massive kauri tree on the North Island over 50m tall and 13.5m in girth that is in danger of succumbing to the fungus after a life measured in millennia.
In the South Pacific, the cousins of the Australian kauri have a strong cultural significance and features in the Maori creation myth. The wood from the Southern Kauri (Agathis australis) was used for water craft, and the gum used in traditional tattoos (moko).
Enthusiastic attempts by the Queensland Forest Service to grow the kauri in plantations were devastated by large stick insects. As a result, kauris are now only grown at a very small scale in mixed species rainforest timber plantations, which is where I stumbled upon them.
In about 2002, during my PhD study of young (8-15 years old) rainforest plantations, I first measured kauri as a small tree amongst the well-regarded cabinet timber species of mahoganies and white beech. At first glance, the appeal for me of this Jurassic fossil was merely aesthetic. They were not very impressive in terms of early growth in the plantations; so I focused my attention on the rapid, early growing species.
However, having ignored the kauri for about 10 years, I was astonished (upon return to my old study sites) at how rapidly the kauris had progressed. Not only is this species one of the best performers in terms of diameter growth, but it also has excellent form. It produces straight stems free of large branches that indicates excellent quality logs, for those growers who value wood quality.
My regard for the kauri is now much more than aesthetic; or even as quirky relics from deep time. These trees are showing themselves to be extremely resilient and competitive, under challenging climatic conditions, across a very wide range of sites. They have the capacity to withstand severe storms as well as longer term stresses, such as drought.
I now know that, given the kauri pine can live for many centuries, it is not advisable to measure their value according to the first decade or so of growth, but rather their productivity and resilience across their whole lifespan.
When you cut and burn a tropical forest, you’re left with a barren plain of cracked red mud, incapable of supporting life – the opposite of the teeming, hyperdiverse array of life that was destroyed. Once the trees are gone, the nutrients wash away and the soil degrades into a dense, brick-like layer so hardened that plant roots can’t get through it.
This was the vision of tropical deforestation held in the popular imagination for many years, but the reality is more complex – and more hopeful.
In recent decades, researchers have found that tropical forests are remarkably resilient. As long as some remnants are left when the forest is cleared to provide seeds and refuges for seed dispersers, tropical forests can grow back with astonishing speed.
In a paper published this week in Nature, lead author Lourens Poorter and a team of international collaborators, including me, found that forests in Central and South America can quickly rebound without human intervention on land that has been cleared for cattle grazing or growing crops.
This finding has important implications for climate change because these so-called secondary forests soak up large amounts of carbon from the atmosphere, even without costly reforestation efforts. These regenerating forests are also crucial for protecting biodiversity and all the ecological and social benefits it provides.
Tropical secondary forests – that is, forests that grow after a major clearing, such as a fire, farming or logging – cover an increasing part of the globe. And as their extent expands, so does their potential to shape conservation strategies, both at the local and global scales.
At the U.N. Climate Summit in 2014, 30 nations and a host of NGOs and private companies endorsed the New York Declaration on Forests, a document that advocates halving deforestation by 2020 and ending it completely by 2030.
One of the key points of the declaration calls for the restoration of 150 million hectares (about 375 million acres) of degraded forest land by 2020 and additional restoration in the following decade.
But active forest restoration can be an expensive process, and it may not be cost-effective or even necessary in every case. In landscapes with low levels of degradation, simply protecting young forests and allowing them to develop may be the best strategy.
In our research, my colleagues and I present the largest data set yet assembled to investigate forest regrowth in the New World tropics. The data set spans 45 sites in the lowland tropics from wet forest to dry forest, with a total of 1,478 plots and more than 168,000 individual trees.
It offers an unprecedented, and more hopeful, view of forest recovery.
According to this analysis, tropical secondary forests have enormous potential for removing carbon from the atmosphere. The net carbon uptake for these secondary forests is 11 times that of old-growth forests in the region we studied.
The rate of biomass recovery varies widely across the region, with the fastest regrowth in areas with high rainfall. The median time for a forest to reach 90 percent of old-growth biomass levels was 66 years, but recovery can be much faster in some areas.
Big win for biodiversity
It shouldn’t come as a surprise that tropical forests can grow back after major disturbances. Tropical forests can be affected by a number of different large-scale natural disasters like floods, fires, landslides, major storms and volcanic eruptions.
Even old-growth tropical forests are highly dynamic systems, marked by cycles of tree death and regrowth. The mortality rates for trees larger than 10 centimeters in diameter have been estimated at one percent to two percent per year for forests in the Amazon and Central America. In other words, at the upper end, one in every 50 large trees will fall in the course of a given year.
The gaps in the forest that result from treefalls are rapidly colonized by a riot of vines and fast-growing tree saplings. The heterogeneity of habitats produced by this cycle is a major driver of tropical diversity.
Legacies of ancient human use, stretching back for millennia, have been detected in nearly every “pristine” tropical forest on earth: massive earthworks in the Amazon and modern-day Cambodia; charcoal and pottery fragments in the Congo Basin; and evidence of forest clearing going back nearly 50,000 years in Papua New Guinea.
As long as the cleared areas are modest in size and the period between cycles of cultivation is sufficient for recovery, diverse forests can persist for thousands of years.
Local and global benefits
Tropical secondary forests can – and should – form a substantive part of the long-term global strategy to combat carbon emissions and preserve biodiversity for the future.
Our recent research shows, for example, that in areas where biomass recovery is slow – like the tropical dry forest – we should prevent further forest loss. Where recovery is rapid, we can combine old-growth forest conservation with policies that promote secondary forest formation.
Shifting focus to the conservation of regenerating forests should not take away from the urgent imperative to conserve the remaining uncut tropical forest.
The clearing of old-growth tropical forests is a major source of human-induced greenhouse gas emissions, second only to fossil fuel combustion. Clearly, keeping the carbon that’s currently stored in intact tropical forests from being released to the atmosphere should be a priority.
Old-growth tropical forests also harbor immense biological diversity – including genetic diversity – and if all of the remaining old-growth forests in a landscape are cut, there will be no seed source to promote regeneration.
Conserving secondary forests offers a different, and complementary, set of benefits.
As well as their massive potential for taking up carbon as they grow, secondary forests provide resources and livelihoods for the people who inhabit them.
Secondary forests can harbor a high diversity of ethnobotanically important species that can be used for medicines. They can serve as extractive reserves, where limited harvesting of timber, game animals and other forest products will prevent the exploitation of resources in vulnerable protected areas. They protect watersheds and prevent erosion.
As secondary forests grow back, they eventually come to resemble the forest that was cut, and in the meantime, they knit together the remaining fragments of forest into a more contiguous landscape.
As David Quammen wrote in “Song of the Dodo (1997),” isolated populations of organisms in forests lose connections to the resource base that supports them. Over generations they lose their genetic diversity, making them more vulnerable to inbreeding, disease, and eventual extinction.
Secondary forests offer the hope of reconnecting habitats and creating a more resilient landscape for the future.
So harnessing the power of forest regeneration in the tropics will have benefits both locally – providing resources and restoring ecosystem services – and globally, by sequestering carbon from the atmosphere.
At the Paris Climate Summit, leaders took important steps toward halting deforestation. Promoting forest regrowth is another vital piece of the equation. It’s time for policymakers to recognize the benefits that tropical secondary forests provide, and to shape policies that take advantage of this enormous potential.
If we are to succeed in tackling climate change, it is vital that we preserve the terrestrial carbon locked up in our forests and soils. Even putting the climate benefits aside, the value of our forests is immense. Rainforests cover just 6% of Earth’s surface but are home to 80% of the world’s terrestrial biodiversity, with many species still to be discovered and named.
With the US National Cancer Institute having already commercialised products from rainforest plants, better treatments for many of humanity’s most intractable illnesses may lie hidden in forests that are currently being cut down or burned.
An estimated half a million square kilometres of forest – two and half times the size of Great Britain – were cut down between 2000 and 2010. But while numbers can be hard to visualise, flying above the forests of Sumatra or Kalimantan gives a clear view of the often industrial-scale exploitation that has occurred.
It is a problem of epic scale. No longer is it sweaty men with large saws, a couple of trucks and a bulldozer. When the forests of Southeast Asia are cleared it can be a military-sized operation: thousands of people with hundreds of machines clearing the land of all its biodiversity, stored carbon and unaccountable value. A job that would once have taken months is now over in hours.
The wood from these majestic, unique places goes on to make not only identifiable products like paper, tissue and kitchen towel, but also the cardboard packaging, stickers and paper that surrounds much else of what we buy. And with forests also cleared for agriculture, the palm oil alone produced on previously forested land is found in about half of the products on our supermarket shelves.
Tracking the sources of all these products is hard – so hard that it is tempting just to disengage. But, as with climate change, we can’t abstain from trying just because it’s difficult.
And there are reasons for hope. Over the past five years organisations such as Greenpeace have done an outstanding job in revealing the scourge of landscape-scale deforestation. Their global, highly creative campaigns against companies like Nestle, Mattel and Disney have urged consumers to think hard about the deforestation behind the products on their shelves.
Having had a role to play in some of the regional forest agreements in New South Wales in the 1990s, I know how challenging implementing these commitments would be, even in a developed country like Australia. It is harder still in the muddled, multilayered and complex bureaucracies of many Southeast Asian countries.
The costs for Singaporeans are massive – not only to their health but also to the reputation of the island state. How these fires were set, and who is to blame, is unclear.
The sole benefit of this ongoing tragedy of the commons is that it serves to focus attention on the problem. And there is potential that the upcoming United Nations climate summit in Paris could deliver real progress on avoiding deforestation.
From peat fires to Paris
Several factors are coming together. First, the UN has worked hard on getting major businesses to acknowledge the need to halt deforestation. The New York Declaration on Forests pledges to halve the rate of global forest loss by 2020, and seeks to end it completely by 2030.
Of course, that is weaker than what is required. But at least it is a start, and through signing the declaration, major businesses like McDonalds, WalMart and Unilever have shown their concern and will now have to deliver.
Second, following Greenpeace’s high-profile campaigns, companies that operate in Asia such as Asia Pulp and Paper, Wilmar and others have now made far stronger commitments than the New York Declaration. We should hope fervently that they succeed, because if they can’t find a way to satisfy consumer demand using plantations, there is little hope for native forests.
Third, the Forest Stewardship Council, having played a key role in helping educate consumers, retailers and producers through its certification schemes, recognises that there is now a need to go beyond certification and to ensure responsible forest management is driven by clear principles and a process of constant improvement. Placing a logo on a product and hoping to insulate yourself against criticism is very different to the strategic choice that, as a business, you are committed to eradicating native forest material from your products.
Finally, climate finance targeted at developing countries is beginning to chip away at the economic incentives to exploit forested land. To date, the issue has been impenetrable to anyone lacking the patience to decipher the jargon-laden negotiations behind the UN Reducing Emissions from Deforestation and Forest Degradation (REDD+) program. But with the UN’s renewed focus, the desire of businesses to commit to zero deforestation, and the political need for the Paris talks to deliver tangible progress, a powerful market driver to protecting forests could yet become a reality.
No sensible person wants the things they buy to come with a side serving of environmental destruction. With progress on international policy, effective advocacy, public awareness and business commitments, we may just still be able to protect what’s left of the world’s great tropical rainforests.