By analysing over 100,000 field measurements as well as environmental data, an international research team has created maps that show how and when naturally regrowing forests bind most carbon.
To fulfil climate goals and avoid the most serious consequences of global heating, we need to both reduce emissions of greenhouse gases and remove carbon dioxide that is already in the atmosphere. Naturally regrowing forests, known as secondary forests, constitute one of the most cost-effective and large-scale solutions. The role these naturally regrowing forests can play largely depends on where they are located and how old they are.
A new study published in the research journal Nature Climate Change shows that 20 to 40- year-old secondary forests can remove carbon dioxide up to eight times faster per hectare than newly planted forests. The largest removal of carbon occurs in areas with tropical rainforests.
"Our study shows that secondary forests are one of the most cost-effective and scalable solutions we have to remove carbon dioxide from the atmosphere. But in order to reach their full potential before 2050, we must act quickly - every year we wait reduces their climate benefits," says Thomas Pugh, a researcher in physical geography at Lund University.
The researchers estimate that if new forests are allowed to start growing freely immediately they could, all told, remove up to 20 billion tonnes of carbon from the atmosphere by 2050 - equivalent to more than half the world's annual emissions of carbon dioxide.
The study also shows that older secondary forests are often underestimated by politicians and decision-makers. Many countries' calculations are based on the standard values of the UN's climate change panel, IPCC. These values do not capture the considerable variations between different areas and forest ages. The research team found that their data often shows significantly higher carbon removal in older forests than was previously assumed.
"A key challenge is that many secondary forests never become sufficiently old to achieve their maximum carbon-binding capacity. In the Amazonas, half of secondary forests are felled within eight years, and in Costa Rica the average age at felling is only 20 years," says Thomas Pugh.
The researchers emphasise that protection of secondary forests does not replace the preservation of primeval forests, which are invaluable for both the climate and biodiversity. However, the results show that secondary forests can be used more effectively to remove carbon dioxide - but only if they are allowed to grow undisturbed and are not felled prematurely.
"Protecting young secondary forests can provide faster and greater climate benefits than only focusing on planting new forests. However, this protection must be carried out in close cooperation with local communities, because many people depend on the forests for their livelihoods," says Thomas Pugh.
