Trees from below

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Seeing the woods

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Getting a clear picture of how much living matter is in the world's forests and savannas - key data in managing these vital carbon stores - has always been tricky. Satellite technology is changing that.

Forests and savannas are essential for sustaining life as we know it.

These vast and complex areas of vegetation absorb carbon from our atmosphere, strongly influence our climate, host an enormous diversity of plants and animals and are both home to and a vital natural resource for humanity. Yet, economic development continues to have an increasingly negative impact on these vitally important ecosystems.

Clearing these lands for agriculture, construction, and mineral mining contributes around 10 per cent of the world’s carbon emissions (the vast majority come from burning fossil fuels) and leads to biodiversity loss. Nonetheless, says Professor Mathew Williams, Chair of Global Change Ecology, we still struggle to monitor these changes accurately.

“The moist tropical forests of the Amazon are well known and important, but here in Edinburgh, we have focused more on the dry tropics, in places such as Africa,” he says. “Covering huge areas, these forests and savannas store vast amounts of carbon and are home to hundreds of millions of people and iconic and precious wildlife.

“We know the dry tropics influence and are influenced by climate change. However, these changes are complicated. In parts of Africa, dry forests are being cleared, but in other areas, savannas are becoming more densely wooded. More trees may increase carbon storage but could reduce biodiversity and harm local people’s livelihoods. We need to understand what causes these complex changes to forests and savannas and what risks this brings.”

Moving heaven and earth

Williams and colleagues from The University of Edinburgh’s Global Change Research Institute have been pioneering new methods to accurately map forest biomass – the mass of living material in a given area or ecosystem at a given time – and building models to predict how forests will change in the future. These methods, which combine exhaustive hands-on fieldwork, the latest satellite technologies and advanced computing, are helping governments and local communities manage their woodlands in a way that mitigates climate change while preserving their natural qualities.

“The first step is to monitor trees on the ground in a given forest, by marking and measuring them by hand, and then returning every few years to check how they’re doing – which ones have grown, which ones have died and which ones people have cut down,” says Williams.

Giraffes on savanna
Giraffes under an acacia tree on an East African savanna

Beginning with a woodland region in Mozambique in 2005, the team has worked with a range of partners, including Edinburgh-based climate change charity the Plan Vivo Foundation, African scientists and hundreds of smallholders to measure and sustainably manage more than 180,000 hectares of land and hundreds of thousands of trees across nine countries in southern and eastern Africa.

Together with satellite radar imaging, field data enables the researchers to build comprehensive maps of Africa’s growing and shrinking forest biomass in near real-time. From this information, they construct sophisticated computer models which simulate how climate change, land use and fire will influence forest ecosystems across the dry tropics in the future.

“Tree planting is seen as a solution to climate change. But it has to be the right tree in the right place at the right time,” says Williams’ colleague Professor of Global Change Mapping, Edward Mitchard. “Planting non-native eucalyptus trees in Africa might capture carbon and generate income for some, but it could also have significant negative effects on natural habitats, water availability and biodiversity.

“Satellite data allows us to see how forests are changing and help diagnose why – whether it be fire, agriculture or urban spread. Our models then predict what will happen to the savannas if we continue to act in this way and what the outcomes will be if lands are managed differently. This work is essential to help guide community preparations for and adaptations to climate change and so ensure livelihoods can be sustained and enhanced.”

Change on a local and global scale

The Edinburgh researchers’ methods and data have helped Mozambique’s government monitor carbon stocks and emissions more accurately, allowing it to set and track its progress towards climate change mitigation goals. The work has also demonstrated the value of specific actions, such as burning grass in woodlands early in the dry season to remove fuel from potentially more damaging wildfires later in the season.

Meanwhile, Williams and his colleagues have supported Plan Vivo to quantify the carbon reduction performance of its community initiatives and allow it to exchange carbon credits with organisations that want to offset their carbon emissions on the voluntary carbon market. Selling these Plan Vivo Certificates (PVCs), which each equate to one tonne of CO2 emissions, has enabled the charity to fund new projects and offset more than 3.5 million tonnes of CO2.

Outside of Africa, the Edinburgh researchers are contributing to joint NASA and European Space Agency (ESA) programmes to develop capacity and satellite tools to monitor forest degradation globally. They are also collaborating with the Brazilian national space agency INPE to help improve predictions of how climate change will affect Brazil’s carbon storage, including for much of the Amazon. These data are vital for international negotiations such as COP26, which takes place in Glasgow in November 2021.

The Amazon rainforest in Brazil
The Amazon rainforest in Brazil

The only certainty is uncertainty

The Edinburgh researchers are also critical partners in the ESA’s first-ever mission to monitor forests. After its launch in 2023, the BIOMASS satellite will measure the amount of biomass and carbon stored above ground in tropical forests over five years. .

For team member Dr Casey Ryan, a Reader in Ecosystem Services and Global Change, the only certainty is that this area of research must continue to grow.

“The methods and models we’ve developed give us an enormous opportunity to visualise different futures and ask vital ‘what if’ questions. However, we know there remains a high degree of uncertainty in the predictions they make,” he says.

“The only way to address this is to map and measure more of the Earth’s forests and savannas. The BIOMASS satellite is a tremendously exciting opportunity to do this from space. At the same time, we’re pleased to continue our work on the ground in a new research project with 41 international partners exploring 600 forest and savanna plots across the dry tropics. This SECO project is the largest of its kind and will help us understand what we need to do to conserve forests from South America to Africa and Asia safely.”

Image credits: trees from below – Jordan Siemens/Getty; giraffes – Pierre-Yves Babelon/Getty; Amazon – Ignacio Palacios