Study: Planting new forests is part of but not the whole solution to climate change

June 22, 2020

The large-scale planting of new forests in previously tree-free areas, a practice known as afforestation, is hailed as an efficient way to remove excess carbon dioxide from the atmosphere - a so-called natural climate solution.

But a new study led by a Colorado State University biology researcher finds that the carbon-capture potential of afforestation may be overestimated. The study, published online June 22 in Nature Sustainability, contends that ratios of soil organic carbon underneath afforested areas vary greatly across different ecosystems and climates, and these variations depend on factors like tree species, land-use history and soil type.

These results, based on over 11,000 soil samples taken across control and afforested plots in northern China, indicate that natural climate solutions alone are not enough to meet global climate mitigation goals.

"We hope that people can understand that afforestation practices are not one single thing," said Anping Chen, a research scientist in the CSU Department of Biology and a lead author on the study. "Afforestation involves many technical details and balances of different parts, and it cannot solve all our climate problems." Chen helped launch the ambitious study while a graduate student at Princeton University about a decade ago.

Inspired to find better data

The research was inspired by a 2010 workshop at Princeton, which led to a high-profile publication on the global forest carbon sink in Science by U.S. Forest Service scientist Yude Pan. In the absence of better data sources, the scientists had used a fixed ratio between tree biomass and soil carbon to estimate total soil organic carbon stocks - a measure that Chen and and Peking University collaborator Shilong Piao suspected was not accurate. This method can be even more problematic, Chen said, for estimating afforestation carbon sequestration potential because land-use changes are often associated with soil disturbances.

As Chen and Piao sat in the workshop, they decided to try and find a new way to estimate below-ground soil carbon changes, and designed a field study to investigate their hypotheses.

In 2012-13, researchers from the U.S. and China led by Chen and Piao collected comparative soil samples at various depths from 619 pairs of afforested plots and control plots across northern China. The Chinese government has run extensive afforestation campaigns as both climate mitigation strategies as well as an attempt to reduce dust from the Gobi desert.

The researchers found that in carbon-poor soils, afforestation did increase soil organic carbon density. But in soils already rich in carbon, they found that carbon density decreased. Their findings concluded that fixed biomass-to-soil organic carbon ratios assumed in previous studies might be overestimating the overall soil organic carbon enhancement features of afforestation practices in general.

The results have implications for forest managers and policymakers. For example, a site that's already above a certain threshold of soil organic carbon underground may be best left alone for natural forest regeneration rather than planted with trees, Chen said.

"Our results strongly suggest that estimated afforestation carbon sink potentials that do not account for background soil carbon stocks or the potentially negative effects of afforestation is overly optimistic," the authors wrote. "These findings also indicate that the assumption of a fixed ratio between soil and biomass carbon, which has been widely used in previous studies for estimating soil carbon stocks, is unreliable."
-end-
The paper is titled "Divergent responses of soil organic carbon to afforestation."

Colorado State University

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.