The forests are among the greatest allies against climate change: every year they absorb huge quantities of carbon, subtracting it from the atmosphere.
But a new study published in Nature Ecology and Evolution launches a less visible but crucial alarm: tropical forests are becoming younger, and this “generational change” emits 140 million tons of carbon per year.
According to the research, led by Simon Besnard of the GFZ Helmholtz Center for Geosciences of Potsdam, between 2010 and 2020 the oldest forests of the planet-especially in the Amazon, in the Congo basin and in Southeast Asia-have been progressively replaced by younger populations. Only 1% of the global forest surface has gone from “old” to “young”, but that 1% had a huge impact: it is responsible for over a third of the total carbon loss recorded in the same period.
The secular trees, with more than 200 years of life, hold, in fact, immense amount of carbon. Ancient forests store on average 77.8 tons of carbon per hectare, against 23.8 of young forests. When the older trees are replaced, much of that reserve disperses in the atmosphere, frustrating centuries of natural storage.
Besnard explains: “When considering a forest as a carbon well, the reserve is more important than the well factor”. In other words, the already stored reserves count more than the speed with which the new trees grow.
The paradox of the tropics
While Europe, North America and China record a slow “aging” of the forests, in the tropics the opposite happens: the average age falls. The Amazon, the Congo basin and the South-East Asia-the areas with the greatest biodiversity of the planet-are experiencing a “negative aging”, mainly due to fires and deforestations.
The result? Ever younger forests, therefore more vulnerable, and a clear carbon transfer from the earth’s environment to the atmosphere.
The paradox is evident: young trees grow quickly and absorb more quickly, up to twenty times more than mature forests. But this advantage is not enough. The amount of carbon that can retain is much less, and ancient forests use centuries to accumulate what new populations will never be able to compensate in useful times for climatic policy. The loss of these carbon “slow reserves” makes the global forest system more unstable, more fragile and less effective in mitigating global warming.
Keep it is better than reconstructing
The conclusion of the study is clear: protecting the secular forests is more effective than refreshing after loss. Storing what exists less costs, emits less carbon and guarantees more biodiversity. The 2050 simulations show that, in a conservation scenario, the amount of carbon stored would remain much higher than a “business as usual” scenario. The authors recognize the value of reforestation practices, but recall that planting new trees does not replace the reduction of fossil emissions or the maintenance of forests already standing.
Beyond carbon: the life of forests
A forest is not just carbon. It is habitat, water, ecological balance and support for the communities that live there. The loss of secular forests also means loss of biodiversity, water stability and ecological memory: ancient trees help the natural regeneration of the surrounding forests.
A fundamental question remains open: what happened to the removed biomass? Part of the carbon is released immediately, through fires or deforestation for agricultural purposes. Another part ends in wood products, held back for years or decades. Understanding how much this carbon actually remains “trapped” is still one of the great challenges of climatic research.
