Researchers from the Department of Civil Engineering at the University of Hong Kong (HKU) and Southern University of Science and Technology (SUSTech) discovered that excessive tropical forest clearing has caused a two-fold increase in the loss of tropical carbon during the previous two decades.
The tropics are a crucial ecosystem because they store enormous amounts of carbon in their woody vegetation and soil, but since 2001, they have been adversely affected by widespread forest clearing. In the 21st century, the researchers examined the gross forest carbon loss brought on by clearing forests in the tropics (between 23.5° N and 23.5° S, but excluding northern Australia).
They found that due to fast forest loss, the gross annual carbon loss from tropical forests increased by two-fold, from 0.97 gigatons in 2001–2005 to 1.99 gigatons in 2015–2019.
The study has been published in the academic journal Nature Sustainability in an article entitled “Doubling of annual forest carbon loss over the tropics during the early twenty-first century.”
The doubling and acceleration in the loss of forest carbon, including biomass and soil organic carbon, is primarily driven by agricultural expansion which differs from current estimates of land-use change emissions in the assessments of the global carbon budget that shows a flat or decreasing trend. In addition to carbon, conversion of forests to agricultural lands also induces other environmental consequences, like biodiversity extinction and land degradation.Professor Ji CHEN
Given the key role of the tropics in the carbon cycle, the study poses serious implications.
“The findings are critical because they suggest that existing strategies to reduce forest loss are questionable; this failure underscores the importance of monitoring deforestation trends following one of the new pledges made to halt and reverse deforestation by UN climate summit-the twenty-sixth Conference of the Parties (COP26) in Glasgow in November 2021,” said Professor Ji CHEN from HKU’s Department of Civil Engineering.
The largest terrestrial contributor to the global carbon cycle is the tropical forest, which stores around 250 gigatons of carbon in its woody plants and removes roughly 70 gigatons of atmospheric carbon annually through photosynthesis.
Because it results in the loss of carbon-stored biomass and soil, the quick and continuous loss of forests could be disastrous. Additionally, the process of absorbing and storing carbon dioxide is hampered by deforestation.
“The doubling and acceleration in the loss of forest carbon, including biomass and soil organic carbon, is primarily driven by agricultural expansion which differs from current estimates of land-use change emissions in the assessments of the global carbon budget that shows a flat or decreasing trend. In addition to carbon, conversion of forests to agricultural lands also induces other environmental consequences, like biodiversity extinction and land degradation,” said Yu FENG, a PhD candidate of the HKU and SUSTech joint programme.
Agricultural expansion, such as shifting cultivation, especially in Africa, was the primary cause of the majority (82%) of the tropical forest carbon loss.
“While some agricultural lands may reappear as forested due to abandonment or policies, we still observed about 70% of former forest lands converted to agriculture in 2001-2019 remained so in 2020, confirming a dominant role of agriculture in long-term pan-tropical carbon reductions on formerly forested landscapes,” said research team member Dr. Zhenzhong Zeng, Associate Professor at SUSTech.
“The 2014 New York Declaration on Forests promised to halve tropical deforestation by 2020. However, our results demonstrate a failure to the commitment and highlight the colossal challenge posed by the 2021 Glasgow Leaders’ Declaration on Forests and Land Use, which pledges to halt forest loss by 2030,” said Dr. Chunmiao Zheng, Chair Professor at SUSTech and a member of the research team.