News/events type: Scientific paper

A surprising new climate benefit is found in tree bark

They’re well known for their carbon storing properties but now scientists have discovered that trees have an additional climate benefit, in their bark.

Professor Yadvinder Malhi, Director of the Leverhulme Centre for Nature Recovery, is among an international team of colleagues who have found tree bark surfaces play an important role in removing methane gas from the atmosphere.

Writing in the journal Nature they say microbes hidden within tree bark can absorb methane – a powerful greenhouse gas – from the atmosphere. Methane is responsible for around 30 per cent of global warming since pre-industrial times and emissions are currently rising faster than at any point since records began in the 1980s.

The team of researchers has shown for the first time that microbes living in bark or in the wood itself are removing atmospheric methane on a scale equal to or above that of soil. They calculate that this newly discovered process makes trees 10 per cent more beneficial for climate overall than previously thought.

Former Environmental Change Institute (ECI) Postdoc Researcher, Dr Allie Shenkin and Prof Malhi used detailed 3D laser scans of trees to estimate the total surface area of bark, both in particular woods and at the planetary scale. Prof Malhi said the tree shape analysis shows that if all the bark of all the trees of the world were laid flat, the area would be equal to the Earth’s land surface.

Prof Malhi said: “Tree woody surfaces add a third dimension to the way life on Earth interacts with the atmosphere, and this third dimension is teeming with life, and with surprises.”

In the study, the researchers investigated upland tropical, temperate and boreal forest trees. They took measurements spanning tropical forests in the Amazon and Panama; temperate broadleaf trees in Wytham Woods, in Oxfordshire, and boreal coniferous forest in Sweden.

Prof Malhi added: “Once again research carried out at the University of Oxford’s Wytham Woods has shown what an important area of study they are and it’s exciting to see they can still reveal surprises of planetary importance.”

Wytham Woods has been owned and maintained by the University of Oxford since 1942. The woods are often quoted as being one of the most researched pieces of woodland in the world, and their 1000 acres are designated as a Site of Special Scientific Interest.

The site is exceptionally rich in flora and fauna, with over 500 species of plants, a wealth of woodland habitats, and 800 species of butterflies and moths.

Prof Myles Allen, Climate programme lead at the ECI, and Head of Atmospheric, Oceanic and Planetary Physics in the Department of Physic provided valuable insights into how best to calculate the climate change implications of this absorption of methane, enabling the additional climate benefit of protecting or restoring trees to be calculated.

Although most methane is removed by processes in the atmosphere, soils are full of microbes that absorb the gas and break it down for use as energy. Soil had been thought of as the only terrestrial sink for methane, but the researchers now show that trees may be as important, perhaps more so.

Lead researcher on the study, Professor Vincent Gauci of the University of Birmingham, said: “The main ways in which we consider the contribution of trees to the environment is through absorbing carbon dioxide through photosynthesis, and storing it as carbon. These results, however, show a remarkable new way in which trees provide a vital climate service.

“The Global Methane Pledge, launched in 2021 at the COP26 climate change summit aims to cut methane emissions by 30 per cent by the end of the decade. Our results suggest that planting more trees, and reducing deforestation surely have to be important parts of any approach towards this goal.”

The methane absorption was strongest in the tropical forests, probably because microbes thrive in the warm wet conditions found there.  On average the newly discovered methane absorption adds around 10% to the climate benefit that temperate and tropical trees provide.

By studying methane exchange between the atmosphere and the tree bark at multiple heights, they were able to show that while at soil level the trees were likely to emit a small amount of methane, from a couple of metres up the direction of exchange switches and methane from the atmosphere is consumed.

In addition, the team used laser scanning methods to quantify the overall global forest tree bark surface area, with preliminary calculations indicating that the total global contribution of trees is between 24.6-49.9 Tg (millions of tonnes) of methane. This fills a big gap in understanding the global sources and sinks of methane.

This new discovery opens up whole new directions of research. It is not known which bark types or trees species are better hosts for these methane-eating microbes, how quickly new trees build a methane-absorbing function, or whether the as yet unmeasured branches of trees are ever stronger methane absorbers.

Read the full paper in Nature: Global atmospheric methane uptake by upland tree woody surfaces

Watch a video explainer from Prof Malhi, Ecosystems Director of the Leverhulme Centre for Nature Recovery here.

We can no longer ignore nature in our political and economic decision-making

Now is the time to put nature at the centre of decision-making, for the sake of our civilization. In a special edition of the Royal Society’s journal, Philosophical Transactions of the Royal Society B, Professor Yadvinder Malhi, Director of the Leverhulme Centre for Nature Recovery at the Environmental Change Institute at the University of Oxford, considers the importance of nature in making decisions.

In a preface to a special feature in the journal, co-written with Prof Gretchen C. Daily, Director of the Center for Conservation Biology at Stanford University, Professor Malhi said:

“The value and importance of the natural world is not sufficiently accounted for in economic or other decision-making processes, and bringing nature into decision-making provides the potential for a systemic solution to this challenge.

“There is powerful evidence and growing recognition that this decline matters – not only because of the intrinsic value of Earth’s biodiversity, but also because the degradation of the web of life threatens human well-being today, social and economic progress, and even the future of our civilisation.”

Professors Malhi and Daily say recent developments and statements have raised awareness of the biodiversity crisis, resulting in high-level calls to “bend the curve” of biodiversity loss within a decade, and to create nature-positive economies and businesses. New policy impetus has come from the adoption of the 2022 Kunming-Montreal Biodiversity Framework, as well as a flurry of new nature-focused legislation at supernational, national, and city levels.

How exactly this can be achieved at scale and across sectors remains a major challenge. However, there has been substantial progress in developing successful demonstrations of integrating nature into decision-making in a variety of sectors and regions.

This special feature examines some of the greatest challenges and most promising solutions for bringing nature into decision-making at scale. Solutions include:

  • Assigning values to nature which are then embedded in key environmental policy instruments: protected areas for nature and payments for ecosystem services.
  • Highlighting the pioneering approach in Costa Rica with a system giving value to standing forests which reversed deforestation.
  • The transnational corporations that are taking nature into account in their decision-making who all share similar critical success factors.
  • The development of national natural capital accounts to increase integration of the values of nature into decision-making.
  • Cities that have enhanced urban nature and reveal what lessons can be learned for replicating and scaling up models of success.
  • Children’s exposure to nature in the school environment showing enhanced benefits for children’s physical and mental health, focus at school, and nurturing of pro-nature attitudes.

The global intertwining between humanity and the biosphere, navigating human actions and societies within a global safe operating space.

Professor Malhi said:

“As a collection, these papers highlight the urgency of bringing nature into decision-making, and also demonstrate the real progress in application of data rich tools that facilitate such decision-making, while at the same time reminding us that there are deeper issuesi  around our relationship with the straining biosphere that need examination and remedying.”

 

Read the feature in full: Bringing nature into decision-making

World’s Most Productive Natural Forests Recently Discovered in West Africa

Whilst most studies on the ecosystem functioning of tropical forests have focussed extensively on Latin America or Asia, researchers in Oxford say comparing findings with studies in Ghana has produced interesting and differing results showing that more studies need to be made in Africa.

Tropical forests cover large areas of equatorial Africa and play a significant role in the global carbon cycle. Scientists from the Leverhulme Centre for Nature Recovery, in the Environmental Change Institute (ECI), in close partnership with collaborators at the Forestry Research Institute of Ghana (FORIG), have been looking at the carbon budget in both the Amazon and West Africa by undertaking detailed field assessments of the carbon budget of multiple forest sites.

The researchers monitored 14 one-hectare plots along an aridity gradient in Ghana. When compared with an equivalent aridity gradient in Amazonia they had previously studied using the same measurement protocol, the studied West African forests generally had higher productivity and more rapid carbon cycling.

Their findings have been published in Nature Communications: Contrasting carbon cycle along tropical forest aridity gradients in West Africa and Amazonia.

Lead author Huanyuan Zhang-Zheng, a postdoctoral researcher at the Centre, said: “Tropical forests are so diverse that we are constantly surprised when opening new study sites. I became fascinated with West African forests because of this study, but I am sure there are more fascinating tropical forests yet to discover. When we’re talking about carbon budgets, you can’t just study a stand of forests and imagine that applies to even nearby forests. Carbon budgets vary greatly from wet to dry regions in the tropics.”

Having studied the carbon budget in the Amazon it was interesting to see that West African forests are more productive, have more photosynthesis and absorb more energy. And we don’t quite understand why this is the case. This is an important region and shouldn’t be ignored. Our new findings were able to tell us a different story than our previous studies in the Amazonia, and has stimulated new questions and new research.

The work carried out is part of the Global Ecosystem Monitoring network (GEM), an international effort to measure and understand forest ecosystem functions and traits, and how these will respond to climate change. GEM was created by the ECI in 2005 under the leadership of Prof Yadvinder Malhi. The GEM network describes the productivity, metabolism and carbon cycle of mainly tropical forests and savannas.

Professor Malhi said: “Ecology is a global science, and equal long-term partnerships are essential to produce both better science and fairer science. This work is the product of decades of long-term partnership between Oxford and institutions in both Africa and South America, work that seen many local students trained and graduating and contributed to building local capacity in environmental science”.

The study is also a fruit of successful collaboration with the Forestry Research Institute of Ghana – CSIR, many scientists from which made fundamental contributions to the study and are coauthors of the publication. One of the lead Ghanaian collaborators, Said Akwasi Duah-Gyamfi, Senior Research Scientist, CSIR-Forestry Research Institute of Ghana, said: “It was a wonderful experience to be part of the research team, and most importantly to explore and generate knowledge on topical issues about forests in Africa.”

Read the paper in full: Contrasting carbon cycle along tropical forest aridity gradients in W Africa and Amazonia

Read more about GEM: The Global Ecosystems Monitoring network: Monitoring ecosystem productivity and carbon cycling across the tropics

Replanting logged forests with diverse mixtures of seedlings accelerates restoration

Satellite observations of one of the world’s biggest ecological experiments on the island of Borneo have revealed that replanting logged forests with diverse mixtures of seedlings can significantly accelerate their recovery.

The experiment was set up by Professor Andy Hector and colleagues over twenty years ago as part of the SE Asia Rainforest Research Partnership (SEARRP). This assessed the recovery of 125 different plots in an area of logged tropical forest that were sown with different combinations of tree species. The results revealed that plots replanted with a mixture of 16 native tree species showed faster recovery of canopy area and total tree biomass, compared to plots replanted with 4 or just 1 species. However, even plots that had been replanted with 1 tree species were recovering more quickly than those left to restore naturally.

Lead Scientist of the study, Professor Andy Hector said:

“Our new study demonstrates that replanting logged tropical forests with diverse mixtures of native tree species achieves multiple wins, accelerating the restoration of tree cover, biodiversity, and important ecosystem services such as carbon sequestration.”

Greater diversity gives greater resilience

According to the researchers, a likely reason behind the result is that different tree species occupy different positions, or ‘niches’, within an ecosystem. This includes both the physical and environmental conditions that the species is adapted to, and how it interacts with other organisms. As a result, diverse mixtures complement each other to increase overall functioning and stability of the ecosystem. For instance, some tropical tree species are more tolerant of drought because they produce a greater amount of protective chemicals, giving the forest resilience to periodic times of low rainfall. In turn, a diverse mix of trees can support a much wider range of animal life. For instance, hornbills specifically require large mature trees with holes where the females can nest.

Professor Hector added:

“Having diversity in a tropical forest can be likened to an insurance effect, similar to having a financial strategy of diverse investment portfolios.”

 

One of the world’s biggest ecological experiments

Tropical forests cover just 6% of the planet’s land surface but are home to around 80% of the world’s documented species (WWF), and act as major carbon sinks. However, these critical habitats are disappearing at an alarming rate, chiefly due to logging for timber and conversion to palm oil plantations. Between 2004 and 2017, 43 million hectares of tropical forest were lost – an area roughly the size of Morocco (WWF).

Restoring logged tropical forests is a crucial component of efforts to tackle both the nature and climate crises. Up to now, however, it has been unclear whether this is best achieved through allowing forests to restore themselves naturally (using dormant seeds in the soil) or through active replanting.

To investigate this, the researchers collaborated with local partners to set up the Sabah Biodiversity Experiment on 500 hectares of logged forest in the Malaysian state of Sabah on the island of Borneo. This was divided into 125 experimental plots that were either left to recover naturally or planted with mixtures of either 1, 4, or 16 tree species that are frequently targeted for logging. The 16 species included several endangered species and the worlds’ tallest species of tropical tree (Shorea faguetiana) which can reach over 100 m in height. The first trees were planted in 2002, with nearly 100,000 planted in total over the following years.

The recovery of the plots was assessed by applying statistical models to aerial images captured by satellites. Within a few years, it became apparent that those with 1 species did worse than those planted with a mixture of 4 species, and those enriched with 16 species did best of all.

Lead author Ryan Veryard said:

“Importantly, our results show that logged forest can recover so long as it is not converted to agricultural uses like oil palm plantation. They also emphasise the need to conserve biodiversity within undisturbed forests, so that we can restore it in areas that have already been logged.”

The Sabah Biodiversity Experiment team are now starting a new three-year project funded by the UK Natural Environmental Research Council to take a census of all the surviving trees in the experiment. This will be combined with a wider range of remote sensing methods (including lidar sensors carried by a helicopter and smaller sensors carried by drones) to give a more comprehensive analysis of forest health.

Read more about this research, published in Science Advances, here