Climate change: effect on forests could last millennia, ancient ruins suggest


Jonathan Lenoir, Author provided

Jonathan Lenoir, Université de Picardie Jules Verne (UPJV) and Tommaso Jucker, University of Bristol

Forests are home to 80% of land-based biodiversity, but these arks of life are under threat. The rising average global temperature is forcing tiny plants like sidebells wintergreen on the forest floor (known as the understory) to shift upslope in search of cooler climes. Forest plants can’t keep up with the speed at which the climate is changing – they lag behind.

The pace at which forests adapt to changing conditions is so slow that species living in forest understories today are probably responding to more ancient changes in their environment. For instance, the Mormal Forest floor in northern France is, in several places, covered by a carpet of quaking sedge. This long grass-like plant betrays the former settlements of German soldiers who used it to make straw mattresses during the first world war.

Changes in how people managed the land, sometimes dating back to the Middle Ages or even earlier, leave a lasting fingerprint on the biodiversity of forest understories. Knowing how long the presence of a given species can carry on the memory of past human activities can tell scientists how long climate change is likely to have an influence.

A forest carpeted with tall grass.
The wind whispering through Mormal’s sedge evokes the region’s wartime past.
Jonathan Lenoir, Author provided

Ecologists are turning to technologies such as lidar to rewind the wheel of time. Lidar works on the same principles as radar and sonar, using millions of laser pulses to analyse echoes and generate detailed 3D reconstructions of the surrounding environment. This is what driverless cars use to sense and navigate the world. Since the late 1990s, lidar has enabled amazing discoveries, such as the imprints of Mayan civilisation preserved beneath the canopy of tropical forest.

In a new paper, I, along with experts in ecology, history, archaeology and remote sensing, used lidar to trace human activity in the Compiègne Forest in northern France back to Roman times – much later than historical maps could ever do.

Illuminating ghosts from the past

Compared to farm fields, which are ceaselessly disturbed, forest floors tend to be well-preserved environments. As a result, the ground below the forest canopy may still bear the imprints of ancient human occupation.

Archaeologists know this pretty well and they increasingly rely on lidar technology as a prospecting tool. It allows them to virtually remove all the trees from aerial images and hunt artefacts hidden below treetops and fossilised under forest floors.

Using airborne lidar data acquired in 2014 over the Compiègne Forest in northern France, a team of archaeologists and historians found well-preserved Roman settlements, farm fields and roads. Long considered a remnant of prehistoric forest, the Compiègne was, in fact, a busy agricultural landscape 1,800 years ago.

A black-and-white aerial photo of a landscape marked by depressions and boundaries.
Lidar can reveal the terrain hidden beneath forests.
Jonathan Lenoir, Author provided

A closer look at these ghostly images of the Compiègne Forest reveals several depressions within a fossilised network of Roman farm fields. Archaeologists excavated numerous depressions like this across many forests in north-eastern France and found that people from the late iron age and Roman era carved them.

These depressions were made to extract marls (lime-rich mud) to enrich farm fields in carbonate minerals for growing crops and to create local depressions where rainwater collects naturally for livestock to drink. Marling is still a widespread practice in crop production in northern France.

A hillside with a large, white crater in.
A pit for extracting marl in Northern France.
Jonathan Lenoir, Author provided

The long-lasting effects of human activity

These signs of Roman occupation in modern forests provide clues to why some plant species are present where we wouldn’t expect them to be.

On a summer day in 2007 in a corner of the Tronçais Forest in central France, a team of botanists found a little patch of nitrogen-loving species – blue bugle, woodland figwort and stinging nettle – nestled among more acid-loving plants.

Nothing special at first sight. Until archaeologists found that Roman farm buildings had once stood in that spot, with cattle manure probably enriching the soil in phosphorous and nitrogen.

A shrub with bright blue flowers.
Blue bugle heralds an ancient Roman farm.
Kateryna Pavliuk/Shutterstock

If a clutch of tiny plants can betray ancient farming practices dating back centuries or millennia, ongoing environmental changes, such as climate change, will have similarly long-lasting effects. Even if the Earth stopped heating, the biodiversity of its forests would continue changing in response to the warming signal, in a delayed manner, through the establishment of more and more warm-loving species for several centuries into the future.

Just as the Intergovernmental Panel on Climate Change has a mission to provide plausible scenarios on future climate change, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services aims to provide plausible scenarios on the fate of biodiversity. Yet none of the biodiversity models so far incorporate this lag effect. This means that model predictions are more prone to errors in forecasting the fate of biodiversity under future climate change.

Knowing about the past of modern forests can help decode their present state and model their future biodiversity. Now lidar technology is there to help ecologists travel back in time and explore the forest past. Improving the accuracy of predictions from biodiversity models by incorporating lagging dynamics is a big challenge, but it is a necessary endeavour for more effective conservation strategies.


This blog is written by Jonathan Lenoir, Senior Researcher in Ecology & Biostatistics (CNRS), Université de Picardie Jules Verne (UPJV) and Cabot Institute for the Environment member Dr Tommaso Jucker, Research Fellow and Lecturer, School of Biological Sciences, University of Bristol

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

Why I’m mapping the carbon stored in regrowing Amazonian forests

As we navigate our way out of the global medical pandemic, many are calling for a “green economic recovery”. This green recovery should be at the forefront of many discussions as world leaders, policy makers, scientists and organisations are preparing for the 26th Conference of the Parties (COP26) due to take place in November this year in Glasgow, UK. This conference will once again try to unite the world to help tackle the next and even larger global emergency, the Climate Emergency.

In recent years, the conversations around the Climate Emergency have increased dramatically with many individuals, groups, companies and governments aiming to tackle this emergency, in part, through replanting, restoring and reforesting large areas of land.

But what if we let forests regrow back naturally? How much carbon can they absorb from the atmosphere? 

As part of my PhD research at the University of Bristol, I have been looking at naturally regrowing forests in the Brazilian Amazon rainforest. These forests are known as “Secondary forests” and regrow on land that has previously been deforested and used for agricultural or other purposes and has since been abandoned, allowing the natural vegetation to return.

Figure 1: Secondary Forest in the Tapajos region of the Brazillian Amazon (credit Ricardo Dalagnol)

Secondary Forests in the Brazilian Amazon are expected to play a key role in achieving the goals of the Paris Agreement. They have a large climate mitigation potential, given their ability to absorb carbon up to 11 times faster than old-growth forests. However, the regrowth of these secondary forests is not uniform across the Amazon and is influenced by regional and local-scale environmental drivers and human disturbances like fires and repeated deforestations.

I worked with numerous scientists from Brazil and the UK to determine the impact of different drivers on the regrowth rates of the secondary forests, using a combination of satellite data. The key datasets we needed were:

What we did

We combined the satellite data maps and overlayed them to extract information on the carbon stored in relation to the forest age to model the regrowth rate with increasing age. We overlayed the information of key environmental drivers and human disturbances to see if and how these factors impact the regrowth rates.

What we found out

Overall, we found that the environmental conditions in Western Amazon enable secondary forests to regrow faster. Here the land received lots of rainfall and does not experience much drought. In the eastern parts of the Amazon, where the climate is drier and experiences more drought, the regrowth rates were up to 60% lower.

Figure 2: Schematic summary of the main results from the paper, highlighting the spatial patterns of regrowth dependent on both climate and human disturbances. The map in the middle shows the regions of secondary forest in the Brazillian Amazon and the four panels correspond to these regions.

In addition to this, we found that the regrowth rates were reduced even further by as much as 80% in eastern regions if the forests were subject to human activities like burning and repeated deforestations before the land was finally abandoned.

What it all means

Our results show the importance of protecting and expanding secondary forest areas to help us meet the Paris Agreement Targets. Our regrowth models can be used to help determine the contribution of current and future regrowing forests in the Brazilian Amazon in a spatial manner.

We found that in 2017, the secondary forests in the Brazilian Amazon stored about 294 Terragrams Carbon aboveground (that excludes carbon stored in roots and soils). However, this number is equivalent to about 0.25% of the carbon that is already stored in Amazon’s old-growth forests. Limiting carbon emissions through deforestation and degradation through burning of old-growth forests is therefore extremely important to help tackle the Climate Emergency.

We calculated that the annual carbon absorbed by the present secondary forest area in the Amazon is enough to contribute to about 5% of Brazil’s pledged contribution to the Paris Agreement by 2030. This number may seem small, but the area covered by the Amazonian secondary forests is currently equivalent to less than 2% of the whole of Brazil. If the area of secondary forest were to be expanded this would bring with it numerous co-benefits such as generating income to landowners and re-establishing ecosystem services.

In December 2020, many countries submitted updates to their so-called Nationally Determined Contributions (NDC), a country’s individual contributions to the Paris Agreement, this included Brazil. However, Brazil’s updated NDC no longer includes a clear position on reforestation, restoration and eliminating illegal deforestation.

At a time when we have all seen and felt the impacts of a true global emergency such as the COVID-19 pandemic, it becomes easier to imagine the potential impacts of climate change if left at the back of politician’s agendas. In the run up to COP26 it is now more important than ever to raise, not lower ambitions as we continue to tackle the global Climate Emergency.

You can read the full paper and download the data here:


This blog is written by Cabot Institute member Viola Heinrich, School of Geographical Sciences, University of Bristol.

Viola Heinrich

In the Amazon, forest degradation is outpacing full deforestation

Deforestation in the Brazilian Amazon has increased abruptly in the past two years, after having been on a downward trajectory for more than a decade. With the country’s president Jair Bolsonaro notoriously enthusiastic about expanding into the rainforest, new deforestation data regularly makes global headlines.

But what fewer people realise is that even forests that have not been cleared, or fully “deforested”, are rarely untouched. Indeed, just 20% of the world’s tropical forests are classified as intact. The rest have been impacted by logging, mining, fires, or by the expansion of roads or other human activities. And all this can happen undetected by the satellites that monitor deforestation.

These forests are known as “degraded”, and they make up an increasingly large fraction of the world’s remaining forest landscapes. Degradation is a major environmental and societal challenge. Disturbances associated with logging, fire and habitat fragmentation are a significant source of CO₂ emissions and can flip forests from carbon sinks to sources, where the carbon emitted when trees burn or decompose outweighs the carbon taken from the atmosphere as they grow.

Forest degradation is also a major threat to biodiversity and has been shown to increase the risk of transmission of emerging infectious diseases. And yet despite all of this, we continue to lack appropriate tools to monitor forest degradation at the required scale.

A man chainsaws a tree trunk in Amazon rainforest
Degraded – but not deforested.
CIFOR / flickr, CC BY-NC-SA

The main reason forest degradation is difficult to monitor is that it’s hard to see from space. The launch of Nasa’s Landsat programme in the 1970s revealed – perhaps for the first time – the true extent of the impact that humans have had on the world’s forests. Today, satellites allow us to track deforestation fronts in real time anywhere in the world. But while it’s easy enough to spot where forests are being cleared and converted to farms or plantations, capturing forest degradation is not as simple. A degraded forest is still a forest, as by definition it retains at least part of its canopy. So, while old-growth and logged forests may look very different on the ground, seen from above they can be hard to tell apart in a sea of green.

Degradation detectives

New research published in the journal Science by a team of Brazilian and US researchers led by Eraldo Matricardi has taken an important step towards tackling this challenge. By combining more than 20 years of satellite data with extensive field observations, they trained a computer algorithm to map changes in forest degradation through time across the entire Brazilian Amazon. Their work reveals that 337,427 km² of forest were degraded across the Brazilian Amazon between 1992 and 2014, an area larger than neighbouring Ecuador. During this same period, degradation actually outpaced deforestation, which contributed to a loss of a further 308,311 km² of forest.

The researchers went a step further and used the data to tease apart the relative contribution of different drivers of forest degradation, including logging, fire and forest fragmentation. What these maps reveal is that while overall rates of degradation across the Brazilian Amazon have declined since the 1990s – in line with decreases in deforestation and associated habitat fragmentation – rates of selective logging and forest fires have almost doubled. In particular, in the past 15 years logging has expanded west into a new frontier that up until recently was considered too remote to be at risk.

Map of deforestation and degradation in the Brazilian Amazon, 1992-2014.
The Brazilian Amazon, shaded in grey, covers an area larger than the European Union.
Matricardi et al

By putting forest degradation on the map, Matricardi and colleagues have not only revealed the true extent of the problem, but have also generated the baseline data needed to guide action. Restoring degraded forests is central to several ambitious international efforts to curb climate change and biodiversity loss, such as the UN scheme to pay developing countries to keep their forests intact. If allowed to recover, degraded forests, particularly those in the tropics, have the potential to sequester and store large amounts of CO₂ from the atmosphere – even more so than their intact counterparts.

Simply allowing forests to naturally regenerate can be a very effective strategy, as biomass stocks often recover within decades. In other cases, active restoration may be a preferable option to speed up recovery. Another recent study, also published in the journal Science, showed how tree planting and cutting back lianas (large woody vines common in the tropics) can increase biomass recovery rates by as much as 50% in south-east Asian rainforests. But active restoration comes at a cost, which in many cases exceeds the prices that are paid to offset CO₂ emission on the voluntary carbon market. If we are to successfully implement ecosystem restoration on a global scale, governments, companies and even individuals need to think carefully about how they value nature.The Conversation


This blog is written by Cabot Institute member Dr Tommaso Jucker, Research Fellow and Lecturer, School of Biological Sciences, University of BristolThis article is republished from The Conversation under a Creative Commons license. Read the original article.

Tommaso Jucker



Guest blog: Let’s reach the Size of England

The Size of England is an amazing new charity working to raise £13 million to safeguard 13 million hectares of rainforest, which is the size of England, and coincidentally the area of rainforest that is cut down every year globally.

To us, safeguarding is not about owning land – it’s about encouraging those who need the land to use it sustainably and to empower local people and indigenous communities. It’s about establishing local rights to the land and providing alternatives for fuel and initiating tree planting programs to restore habitats.

We know that Size of England can be successful. Last year, the Size of Wales team reached their target of raising £2 million to safeguard 2 million hectares of rainforest. But as you know, we want to raise the game. However in order to do this we need help.

At the moment we are raising money for a start-up fund via a crowdfunding webpage. This is so we can register as a charity and start doing amazing things for the rainforest and the local community. We already have support from brilliant organisations such as Cool Earth, the Prince’s Rainforest Project, WWF and the Crees Foundation, but we can never have enough! We hope, through communication that we can raise the sum whilst also spreading the word of what we want to do, and getting people to ‘like’, ‘follow’ and ‘friend’ the project as it develops.

There are currently three of us, all volunteers with big ideas and ambitions. What we’re asking is can you help the Size of England campaign in other ways? Are you a great fundraiser? Could you improve our website? Have you got legal experience? We’d love to crowd-source skills as well as cash.

Check out our Facebook and Twitter pages. Also take a look at our crowdfunding site if you fancy and pass it on to anyone else who may find it interesting!

Feel free to message me if you have any questions or email me at

This guest blog is written by Olivia Reddy of Size of England.
Olivia Reddy