Nav: Home

Nitrogen-fixing trees help tropical forests grow faster and store more carbon

February 13, 2020

(Millbrook, NY) Tropical forests are allies in the fight against climate change. Growing trees absorb carbon emissions and store them as woody biomass. As a result, reforestation of land once cleared for logging, mining, and agriculture is seen as a powerful tool for locking up large amounts of carbon emissions throughout the South American tropics.

But new research published in Nature Communications shows that the ability of tropical forests to lock up carbon depends upon a group of trees that possess a unique talent - the ability to fix nitrogen from the atmosphere.

The study modeled how the mix of tree species growing in a tropical forest following a disturbance, such as clearcutting, can affect the forest's ability to sequester carbon. The team found that the presence of trees that fix nitrogen could double the amount of carbon a forest stores in its first 30 years of regrowth. At maturity, forests with nitrogen fixation took up 10% more carbon than forests without.

Sarah Batterman, a Research Fellow at Cary Institute of Ecosystem Studies and coauthor on the paper, explains, "We want to use this work to guide tropical reforestation to optimize carbon uptake and resiliency. This requires understanding what mix of trees is needed to maximize long-term carbon storage while withstanding future climatic conditions. Our findings suggest that nitrogen-fixing trees are a key ingredient in the reforestation recipe."

Nitrogen-fixing plants partner with soil microbes to turn atmospheric nitrogen gas into a form of nitrogen that is available to fuel plant growth. Through these interactions, nitrogen fixers are able to self-fertilize. This adaptation gives them an edge in recently cleared, early succession tropical soils that are nitrogen-poor. Fixers also help fertilize nearby plants when they shed their leaves and return nitrogen to the soil.

In the tropics, nitrogen-fixing trees are common, but they can be relatively rare in newly recovering forests. Their large, nutrient-packed seeds are often dispersed by wildlife. Having animal dispersed seeds is a disadvantage in the early stages of forest regrowth, when animals that once lived in the forest have not yet returned. Planting fixers as part of reforestation efforts could boost forest development and carbon accumulation.

Batterman says, "To understand the function of nitrogen-fixing trees in a tropical forest, we need to isolate their effects. We can't do that in a real forest because adding or removing trees would alter other aspects of the ecosystem, such as light availability, which would skew findings. It would also take decades to centuries to measure. Instead, we developed a model to quantify ecosystem processes, like nitrogen cycling, that affect forest growth and carbon sequestration."

Using data collected at 112 tropical forest plots in Panama - a record which includes data on over 13,000 individual trees ranging in age from five to 300 years post-disturbance - the research team developed a model that represents interactions among soil, plants, and nutrients at the scale of individual trees. The model accounts for competition between plants for light and nutrients, nutrient cycling between plants and the soil, and tree-level nitrogen fixation.

Trees were classified into four groups that are unique to different stages of forest regrowth, including early-, mid-, and late-successional species, plus nitrogen fixers. By changing the ability of trees to fix nitrogen in their model, the team was able to predict how fast carbon accumulated in a forest and how much carbon it was able to store.

Batterman explains: "Forests with nitrogen-fixing trees grow more rapidly in early succession and have a higher carbon storage potential than forests without nitrogen fixers. They also recover faster when confronted with disturbances."

To quantify nitrogen cycling in tropical forests, many existing models use ecosystem-wide parameters such as evapotranspiration and net primary production to estimate nitrogen fixation fluxes. These models tend to overestimate the amount of nitrogen in the system.

Lead author Jennifer Levy-Varon, who worked on the study while a Postdoctoral Research Associate at Princeton University, says, "Our model is unique because instead of looking at ecosystem-wide processes and using those to estimate nitrogen fluxes, we're honing in on individual trees. This gives us a more accurate understanding of nitrogen-fixers' contributions to the forest nitrogen budget and associated carbon sequestration."

To put the importance of nitrogen-fixing trees in context, the team used their model to predict how much additional carbon could be stored in reforested areas in tropical countries based on acreage pledged under the Bonn Challenge.

"The Bonn Challenge is an international effort to reforest 350 million hectares of land by 2030. We found that by including nitrogen-fixing trees in these efforts, tropical countries could sequester an additional 6.7Gt of carbon dioxide over the next 20 years. To give that number some context, 6.4Gt was the total amount of CO2 equivalents emitted in the US in 2017. It's comparable to driving 15.6 trillion miles, which is about 5 years of US vehicle emissions." says Batterman.

Coauthor Lars Hedin, Professor of Ecology and Evolutionary Biology at Princeton University, concludes, "This model gets us closer to understanding the importance of tropical forests in the global carbon cycle, and their role in removing the greenhouse gas carbon dioxide from the atmosphere."
-end-
Read the full study: https://www.nature.com/articles/s41467-019-13656-7.pdf

Investigators

Jennifer H. Levy-Varon - Princeton Environmental Institute, Princeton University; Department of Ecology and Evolutionary Biology, Princeton University
Sarah A. Batterman - Department of Ecology and Evolutionary Biology, Princeton University; School of Geography and Priestley International Centre for Climate, University of Leeds; Smithsonian Tropical Research Institute; Cary Institute of Ecosystem Studies
David Medvigy Department of Geosciences, Princeton University; Department of Biological Sciences, University of Notre Dame
Xiangtao Xu - Department of Geosciences, Princeton University; Department of Ecology and Evolutionary Biology, Cornell University
Jefferson S. Hall - ForestGEO, Smithsonian Tropical Research Institute
Michiel van Breugel - Smithsonian Tropical Research Institute; Yale-NUS College, Singapore and Department of Biological Sciences, National University of Singapore
Lars O. Hedin - Princeton Environmental Institute, Princeton University; Department of Ecology and Evolutionary Biology, Princeton University

Acknowledgements

Funding for this research was made possible in part by the Carbon Mitigation Initiative and the Grand Challenges Program at Princeton University, the United Kingdom Natural Environment Research Council, ForestGEO, the Heising-Simons Foundation, HSBC, Stanley Motta, Small World Institute Fund, the Hoch family, National Science Foundation (NSF grant EAR-1360391), National University of Singapore, STRI, and Yale-NUS College.

This work is a contribution of the Agua Salud Project, a collaboration between the Smithsonian Tropical Research Institute (STRI), the Panama Canal Authority (ACP), and the Ministry of the Environment of Panama (MiAmbiente).

Cary Institute of Ecosystem Studies is an independent nonprofit center for environmental research. Since 1983, our scientists have been investigating the complex interactions that govern the natural world and the impacts of climate change on these systems. Our findings lead to more effective management and policy actions and increased environmental literacy. Staff are global experts in the ecology of: cities, disease, forests, and freshwater.

Cary Institute of Ecosystem Studies

Related Climate Change Articles:

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.
Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.
Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.
Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.
A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.
Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
More Climate Change News and Climate Change Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.