China has been building a ‘Great Green Wall’ of trees and shrubs across its arid and semiarid regions since 1978, in an effort to combat desertification and improve the environment. The project, known as the Three-North Afforestation Program (TNAP), is the largest ecological restoration project in the world, covering the Northeast, the North Central and the Northwest of China.

A new study by Chinese scientists has revealed that TNAP has also created a significant carbon sink, absorbing nearly 5% of the country’s total industrial carbon dioxide emissions between 1978 and 2017. The researchers used remote sensing images, field observations and national forest inventory data to estimate the increase in carbon stocks in biomass, soil and the ‘ecological effect carbon’ - mainly the carbon sequestration derived from the reduction of soil loss due to afforestation.

The study found that the total forested area increased from about 221,000 square kilometers in 1978 to about 379,000 square kilometers in 2017 within the TNAP project areas, and that TNAP contributed to a total carbon sink of 47.06 million tonnes of carbon per year in the past four decades. The carbon sink in above-ground and below-ground biomass increased from 0.843 billion tonnes (10¹⁵ g) in 1978 to 2.080 billion tonnes in 2017. The researchers also highlighted that the ‘ecological effect carbon’ accounted for about 16% of the total carbon sink increase, indicating a critical role of ecological effects in shaping the distribution of carbon stocks in the protective forests.

The researchers said that their study provided a benchmark to evaluate the value of national ecological restoration projects on carbon sink and ecosystem function assessment. They also suggested that the carbon sequestration benefited from the ecological effects of afforestation should not be ignored when estimating carbon sink and parameterizing carbon-related models.

The study, funded by the National Key Research & Development Program of China and the National Natural Science Foundation of China, has been published in Ecological Processes, entitled “A large carbon sink induced by the implementation of the largest afforestation program on Earth.”