China's 66 billion trees in deserts are absorbing more CO2 and growing faster than natural ones

A study has found that trees planted by China in the past 48 years to contain the spread of two major deserts are growing faster than trees in natural forests. The country has planted 66 billion trees since 1978 as part of its "Great Green Wall" project. The work is aimed at slowing down the spread of the Gobi and Taklamakan deserts. It plans to plant 34 billion more trees by 2050. Scientists decided to study how these trees were different from the ones growing in forests. The ones planted were found to absorb large amounts of CO2, and their leaf area increased 66 per cent faster than natural ones.

Researchers don't know exactly how these trees differ from the natural ones. Yuhang Luo, first author of the study, told Live Science that "most global ecosystem models do not distinguish between forest types", and so they wanted to understand whether species diversity, density and the age of a tree affect how it responds to CO2 and climate change.

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Planted trees grew 66% faster than natural trees

Using satellite data, the team tracked leaf area index to determine how fast these trees grew. The index is a measure of canopy density and a key driver of carbon uptake. The results showed a stark contrast between them, with planted trees increasing their leaf area 66% faster than natural ones. The study states that this is likely because of the difference in their age. The planted trees are younger, and they typically grow faster. The researchers also compared forests of similar age to see if the same held true for them as well. Surprisingly, they still found that the planted ones grew 4.6 per cent.

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Scientists said this is primarily because planted trees grow with human intervention, while trees in forests compete for water and sunlight. Planted trees often include fast-growing species like eucalyptus and poplar. Weeds and other competing vegetation are removed regularly, and they are fertilised as well. So these trees do not have to fight for water and nutrients.

However, once they reach a certain age, that is when the planted trees start declining. They peak around 30 and 40, and then start dropping. Meanwhile, trees in the wild grow slowly but steadily and at an advantage in the long run. "Planted forests can be a powerful short-term tool for carbon uptake, but this advantage is temporary," Luo said, adding that "forests remain irreplaceable."