The widely celebrated Miyawaki method of creating dense urban “mini-forests” may not deliver many of the environmental benefits often associated with it, according to a new scientific review that questions the evidence behind the globally popular reforestation approach.
The study, published in the Journal of Applied Ecology, examined 51 scientific papers on the Miyawaki method and found that most claims surrounding rapid growth, biodiversity improvement, and carbon sequestration lack strong empirical backing.
Originally developed in the 1970s by Japanese botanist Akira Miyawaki, the method involves densely planting native tree saplings after intensive soil preparation. Supporters say the close spacing forces trees to compete for sunlight, resulting in faster growth and quicker forest regeneration.
In recent years, the method has gained international popularity, particularly in urban greening projects where small plots are transformed into compact forests. Governments, companies, schools, and environmental groups across the world have promoted Miyawaki forests as a fast and effective climate solution.
But researchers behind the new review say the science supporting those claims remains surprisingly weak.
The study’s lead authors, Narkis S. Morales of the Bioeconomy Science Institute in New Zealand and Ignacio C. Fernández of Adolfo Ibáñez University in Chile, found that only 41 percent of the reviewed studies included quantitative assessments. Even fewer followed rigorous scientific standards: only 33 percent used control comparisons, while just 14 percent included replication, both considered essential for reliable ecological research.
Researchers said many widely circulated claims about Miyawaki forests appear to originate from “grey literature,” including promotional materials and non-peer-reviewed reports, rather than robust scientific studies.
Among the most repeated claims is that Miyawaki forests grow up to ten times faster and reach maturity within 20 to 30 years. The researchers found only partial evidence supporting faster growth, while the maturity claim had virtually no empirical support.
The review also challenged claims surrounding carbon storage. Although several papers promoted Miyawaki forests as effective carbon sinks, only two studies directly measured carbon stocks, and neither found statistically significant advantages compared to conventional restoration approaches over longer periods.
The researchers warned that promoting expensive restoration techniques without sufficient evidence could undermine public trust and lead to inefficient use of public funds.
Fernández said he and Morales became interested in studying the method after seeing multiple Miyawaki projects funded by local authorities around Santiago. The pair questioned whether governments were investing wisely in projects with large environmental promises but limited supporting data.
Experts not involved in the study echoed similar concerns. Karen D. Holl, a reforestation expert at University of California, Santa Cruz, said she had frequently encountered claims that the Miyawaki method could improve biodiversity and carbon capture despite seeing little rigorous comparative research.
She described the method as potentially “cost-prohibitive” for large scale forest restoration and emphasized the need for restoration projects to be tested against alternative methods and no intervention controls before widespread adoption.
The study does not argue against the Miyawaki method entirely. Instead, the researchers caution against applying a technique developed for specific ecological conditions universally across different climates and ecosystems.
In Mediterranean regions such as central Chile, for example, plants often cooperate rather than compete for resources due to dry conditions, potentially contradicting one of the core assumptions behind dense Miyawaki planting.
“We are not against the Miyawaki method,” Fernández said. “But we are worried that a method designed for specific conditions is being applied everywhere.”
The findings arrive as cities and governments worldwide increasingly invest in urban greening projects to combat rising temperatures, pollution, and biodiversity loss. Researchers say the study highlights the importance of ensuring restoration efforts are guided by scientific evidence rather than viral popularity or marketing-driven environmental claims.