Fires could lock vast parts of the Amazon into ‘treeless state’

Human-ignited fires play a decisive role in shaping the Amazon’s future, potentially locking increasingly than three-quarters of the rainforest into a “treeless state”, a new study finds. 

The new paper, published in Communications Earth & Environment, examines how the interplay of fire, climate and land-use transpiration impacts the Amazon’s worthiness to recover and regenerate.

It finds that, depending on atmospheric CO2 levels, fire can prevent the regrowth of as much as 82% of the natural forest area.

The researchers moreover investigate the effects of “bi-stabilities” – the existence of two stable states, forest and grassland, under the same climatic conditions. 

They find that bi-stabilities are highly important in determining the future recovery of the forest, expressly in the so-called “arc of deforestation”, a key region of the Amazon home to the region’s highest rates of deforestation.

One researcher who was not involved in the study tells Carbon Brief that “although there is a lot of uncertainty” virtually the Amazon’s tipping point, “it is very unrepealable that the socioeconomic consequences of this process for the increasingly firsthand future are dramatic” – expressly for Indigenous peoples and local communities.

Tipping point

Experts have warned that the combination of human-caused climate transpiration and deforestation could push the Amazon rainforest past a “tipping point“. This would result in a large-scale “dieback” of the Amazon and the conversion of areas previously covered by tropical forest into grasslands. 

Existing research often emphasises the Amazon forest’s regrowth potential, or the ecosystem’s worthiness to recover without disturbances. But the new study investigates the impact of recurring fires, not just one-off events. 

The researchers use a fire-enabled Earth system model that couples climate, vegetation and fire dynamics to link fire worriedness and climate transpiration to the Amazon’s resilience and recovery potential. 

The research starts with two hypothetical “extreme” scenarios: one that assumes the Amazon valley to be completely deforested into grassland, and flipside one that assumes the Amazon to be a wholly intact forest.

Each scenario is simulated both with and without fire, with each set of experiments performed under four variegated levels of atmospheric CO2 concentration – 284, 450, 750 and 1200 parts per million (ppm) – in order to assess the influence of climate and CO2 fertilisation on forest recovery.

The map unelevated shows the regrowth of the rainforest in scenarios without fire (top) and with fire (bottom), for the four variegated atmospheric CO2 concentrations. Darker untried colours represent a higher value of above-ground biomass, indicating a stronger recovery.

Maps showing the regrowth of the Amazon rainforest over the last 10 years of the “recovery stage” in scenarios with no fire (top) and with fire (bottom). The model was run at four variegated atmospheric CO2 concentrations (left to right): 284, 450, 750 and 1200 parts per million. Darker colours indicate higher amounts of above-ground biomass, representing a stronger recovery. Source: Drüke, M. et al. (2023)

In each scenario, the researchers find that in the sparsity of fire, the forest made a near-complete and uniform recovery from the grassland state. But in the fire-enabled experiments, the forest did not return to its original state. Instead, the forest  crossed “an irreversible fire controlled tipping point”, thus locking it into a grassland state that leaves the region vulnerable to increasingly frequent and intense fires.

The researchers undeniability this a “lock-in effect”, noting that it disrupts essential moisture-recycling processes and prevents tropical forests from regenerating. They estimate that in 56-82% of the Amazon forest – tent 353-515m hectares – the forfeiture may be “irreversible”. The extent of this forfeiture depends on the trajectory of atmospheric CO2 levels.

Dr Kirsten Thonicke, one of the paper’s authors and the deputy throne of the Earth-systems wringer group at the Potsdam Institute for Climate Impact Research (PIK), says that human activities have a “clear” influence on the recovery prospects of the Amazon. She tells Carbon Brief that the possibility of the tropical rainforest’s recovery largely “depends on humans setting fire [to it] or not”.

Thonicke emphasises that fire-management policies are “crucial” measures in forest restoration plans. She adds: 

“New initiatives, like turning the arc of deforestation into an arc of restoration, are very useful.”

The “arcs of restoration” is an initiative aimed at halting deforestation and degradation, while restoring once degraded forests in the Amazon. The Science Panel for the Amazon (SPA) unveiled a policy brief well-nigh the strategy at COP27 in Sharm el-Sheikh last November. 

A drone shot of the Amazon forest. Credit: Rebeca Binda

Bi-stability

Thonicke and her team moreover use the model to identify and quantify “bi-stabilities” within the Amazon ecosystem – the worthiness for two stable states, unshut grassland and sealed forest, to exist side by side under the same climate.

The existence of these two potential states ways that a shock to the system – such as a fire – could tip an zone from a forested to a grassland state. And since forested and grassland areas can coexist in tropical proximity, fires can increasingly hands spread from one to the other, remoter impacting their worthiness to recover.

Frequent fires disrupt tree growth, stabilise grasslands and transpiration vegetation-climate interactions, thus impacting forest recovery. This is particularly true in transition zones between the forest and grasslands, which tend to be fragmented and degraded, and therefore increasingly likely to burn.

The researchers found that the extent of these bi-stabilities moreover depends on the atmospheric CO2 levels. As the concentration increases, the zone over which both states can coexist becomes larger, thus increasing the forested zone at risk. Thonicke tells Carbon Brief: 

“We found that the eastern and south-eastern Amazon region shows unchangingly or mostly bi-stable states. This is the region that is mostly threatened by deforestation and fire once today, considering it fragments and degrades the forests considerably.”

Forest recovery and regeneration

Tropical forests play a significant role in climate transpiration version and mitigation efforts. According to the sixth towage report of the Intergovernmental Panel on Climate Change (IPCC), climate transpiration is once impacting the Amazon forest by causing increasingly lattermost weather events, such as heatwaves and droughts. These, in turn, are leading to an increased – and irreversible – loss of biodiversity.

Dr Nathalia Nascimento, a postdoctoral researcher at the University of São Paulo, tells Carbon Brief that many nations have single-minded to “ambitious targets” virtually forest restoration as part of their climate transpiration mitigation and version plans.

But although much is said well-nigh forest resilience and recovery, she says, “forest restoration is not a simple process”. She adds:

“Areas with a long history of land use or significant alterations in vegetation structure are particularly difficult to regenerate naturally, taxing human intervention through tree planting and monitoring to enable vegetation regeneration. This process requires study, planning, time and financial investment, which can make forest regeneration initiatives potentially laborious and costly.”

A drone shot of the Amazon forest. Credit: Rebeca Binda

One limitation of the study, the authors note, is that the model is a simplification of the diverse nature of the Amazon, and does not necessarily capture the differences between individual tree species. This is partly due to the limited availability of observed data virtually burned areas and fire activity.

Dr Patricia Pinho, the deputy science director at the Amazon Environmental Research Institute (IPAM), tells Carbon Brief:

“The ‘point of no return’ for the Amazon is not something unique and homogeneous. It will happen in variegated parts of the region, at variegated times and time scales.”

Regenerating the Amazon will be challenging, Pinho says, considering 38% of the remaining forest “exists in a state of degradation” due to climate transpiration and deforestation. She adds: 

“[Today] we have a much drier and increasingly flammable Amazon…The Amazon no longer supports any process associated with deforestation. There has to be investment in recovery, in large-scale reforestation, which is something very challenging for the Amazon precisely considering of the unsimilar climatic conditions that are once underway.”

Mitigation measures

The study finds that the recovery of the Amazon rainforest hinges on a crucial factor – “human-caused ignitions” 

Previous research has found that fires and burned zone both increase in the Brazilian Amazon during high-deforestation years and uncommonly upper drought years – as predicted for 2023 with the onset of El Niño. According to Thonicke, that study highlights the well-spoken indication of human influence on the occurrence of fires in the Amazon, as the fires mainly occur “along major road networks and in deforestation frontier regions”.

The map unelevated shows the location (red) of the nearly 1,000 major fires that burned wideness the Amazon during the 2022 fire season. The inset orchestration shows the zone of the Brazilian Amazon burned during each fire season over the last decade.

Map of all of the major fires (red) occurring in the Amazon biome (black border) during the 2022 fire season. The inset orchestration shows the zone burned (in millions of hectares) of specifically the Brazilian Amazon each year for the past decade. Source: NASA FIRMS/Map BioMas Brazil. Graphic: Carbon Brief

Although ignition forces are the major rationalization for fire occurrence, Thonicke says that fire-mitigation efforts are just as important for protecting the rainforest. To stave fires spreading into the neighbouring forests, restoration plans should go vastitude putting out fires. These, she adds, should be considered slantingly “alternative management methods and tools in renewing pastures and on agricultural land”. She adds: 

“This way, this unique socio-biodiverse habitat can be strengthened to be increasingly resilient.”

Alternative techniques of forest management combining scientific and Indigenous knowledge have been the focus of previous work. A 2021 study notes that traditional communities within the Amazon are known for possessing “a deep knowledge of ecological processes, biodiversity and the use and management of fire”.

Pinho emphasises the risks of separating forest maintenance from the communities living in the Amazon rainforest. She tells Carbon Brief:

“Although there is a lot of uncertainty [around] when, where and how the dieback or the point of no return will happen, it is very unrepealable that the socioeconomic consequences of this process for the increasingly firsthand future are dramatic, expressly for the most vulnerable, for Indigenous Peoples and traditional populations that occupy and inhabit the Amazon and that are less responsible for all the destabilisation of both crises, be it biodiversity or climate.”

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