Skip to main content

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


Popular posts from this blog

Are you a journalist looking for climate experts? We've got you covered

We've got lots of media trained climate change experts. If you need an expert for an interview, here is a list of Caboteers you can approach. All media enquiries should be made via  Victoria Tagg , our dedicated Media and PR Manager at the University of Bristol. Email victoria.tagg@bristol.ac.uk or call +44 (0)117 428 2489. Climate change / climate emergency / climate science / climate-induced disasters Dr Eunice Lo - expert in changes in extreme weather events such as heatwaves and cold spells , and how these changes translate to negative health outcomes including illnesses and deaths. Follow on Twitter @EuniceLoClimate . Professor Daniela Schmidt - expert in the causes and effects of climate change on marine systems . Dani is also a Lead Author on the IPCC reports. Dani will be at COP26. Dr Katerina Michalides - expert in drylands, drought and desertification and helping East African rural communities to adapt to droughts and future climate change. Follow on Twitter @_k

Urban gardens are crucial food sources for pollinators - here’s what to plant for every season

A bumblebee visits a blooming honeysuckle plant. Sidorova Mariya | Shutterstock Pollinators are struggling to survive in the countryside, where flower-rich meadows, hedges and fields have been replaced by green monocultures , the result of modern industrialised farming. Yet an unlikely refuge could come in the form of city gardens. Research has shown how the havens that urban gardeners create provide plentiful nectar , the energy-rich sugar solution that pollinators harvest from flowers to keep themselves flying. In a city, flying insects like bees, butterflies and hoverflies, can flit from one garden to the next and by doing so ensure they find food whenever they need it. These urban gardens produce some 85% of the nectar found in a city. Countryside nectar supplies, by contrast, have declined by one-third in Britain since the 1930s. Our new research has found that this urban food supply for pollinators is also more diverse and continuous

#CabotNext10 Spotlight on City Futures

In conversation with Dr Katharina Burger, theme lead at the Cabot Institute for the Environment. Dr Katharina Burger Why did you choose to become a theme leader at Cabot Institute ? I applied to become a Theme Leader at Cabot, a voluntary role, to bring together scientists from different faculties to help us jointly develop proposals to address some of the major challenges facing our urban environments. My educational background is in Civil Engineering at Bristol and I am now in the School of Management, I felt that this combination would allow me to build links and communicate across different ways of thinking about socio-technical challenges and systems. In your opinion, what is one of the biggest global challenges associated with your theme? (Feel free to name others if there is more than one) The biggest challenge is to evolve environmentally sustainable, resilient, socially inclusive, safe and violence-free and economically productive cities. The following areas are part of this c