Forest restoration also produced meaningful gains, particularly on properties where most of the original forest had already disappeared. Across the full study area, however, restoring forest on agricultural land was less effective when used on its own — and it was the most expensive of the strategies the team evaluated.

The findings suggest conservation funding should be tailored to the conditions of individual landscapes rather than relying on a single approach everywhere.

Why did no single strategy suffice?

None of the interventions, taken alone, reversed the overall losses of biodiversity and carbon across the study area.

"Net gains in biodiversity and carbon storage were only achieved when both avoidance interventions were implemented. However, combining all three interventions delivered even greater gains," Dr. Miranda said. "Combined interventions will be even more important as climate change progresses, especially as forest restoration can be particularly vulnerable to wildfires."

That conclusion carries weight for policy. Both global environmental commitments and Brazilian federal and state policies currently emphasize large-scale forest restoration. The study indicates that restoration works best alongside protection, not as a substitute for it.

"Restoration is essential where forests have been lost across large areas. But our study shows that investing in new forests makes little sense if, at the same time, we fail to protect existing forests," said co-author Dr. Joice Ferreira, senior researcher at Embrapa and principal investigator of the 'Capoeira' restoration research program. "Otherwise, we are pouring money into a leaky pot — restoring forests in one place while others are being degraded and lost."

She added: "What we urgently need to do is integrate these policy agendas, ensuring that forest restoration goes hand in hand with protection of the forests we still have."

What about wildfires and El Niño?

The urgency is heightened this year. El Niño events, combined with climate change, produce longer, hotter and more intense dry seasons across the Amazon's "arc of deforestation," greatly increasing the extent and severity of forest fires.

"These findings highlight the need to put in place policies and resources to prevent and tackle the wildfires that disturb and degrade tropical forests," said Professor Jos Barlow of Lancaster University, senior author of the study. "This is all the more urgent in this El Niño year."

Who else shares responsibility?

The researchers argue that responsibility extends beyond governments and conservation organizations. Industries and markets tied to commodities produced in areas experiencing forest loss and degradation may also need to act.

"There is a need for the companies and markets that benefit from nationally and globally traded commodities like soy and beef to take responsibility not only for deforestation, but also the degradation of remaining forests that is inextricably linked to these production systems," said co-author Dr. Toby Gardner, Senior Research Fellow at the Stockholm Environment Institute and co-founder of the supply chain sustainability initiative Trase.

What are the study's limits?

The research focused on two regions of the Amazon, so the findings may not transfer directly everywhere. Still, the scientists say the conclusions likely apply to tropical deforestation frontiers elsewhere in the world, and could inform conservation policy beyond tropical regions.

The paper, "Protecting tropical forests is more cost-effective for biodiversity and climate than restoration," appears in Science, volume 393, issue 6817. The research was convened by the Sustainable Amazon Network (Rede Amazonia Sustentavel) and funded by sources including the UK's Global Centre on Biodiversity for Climate and Brazil's National Council for Scientific and Technological Development (CNPq).