Recent studies reveal that the average size of trees in the Amazon rainforest has increased steadily over the past decades. This growth is attributed primarily to rising atmospheric carbon dioxide (CO2) levels. The findings show important ecological dynamics and the role of the Amazon as a global carbon sink.
Study Overview and Methodology
An international team of about 100 scientists from over 60 universities conducted a comprehensive study titled ‘Increasing tree size across Amazonia’. They monitored 188 permanent forest plots, each averaging 12,000 square metres, across the Amazon basin. The data collection period varied, with some plots observed for up to 30 years. Researchers measured tree diameters and found an average increase of 3.3% per decade in tree size.
Carbon Fertilisation Effect
The primary cause of increased tree size is the rise in atmospheric CO2, which has grown by nearly 20% in the last 30 years. Higher CO2 levels enhance photosynthesis, a process called the carbon fertilisation effect. This effect accelerates plant growth by enabling trees to convert more CO2 into biomass. As a result, Amazonian trees are growing larger than usual, deviating from the typical balance where saplings replace fallen mature trees without changing average tree size.
Significance for Carbon Sequestration
Larger trees can absorb and store more carbon, strengthening the Amazon’s role as a carbon sink. This is crucial in mitigating climate change. Peter Etchells, a Durham University researcher, emphasised that CO2 acting as a fertiliser boosts tree growth and carbon storage. However, this benefit must be viewed alongside ongoing deforestation threats that undermine these gains.
Impact of Deforestation
Despite the growth benefits, deforestation remains a critical issue. Old-growth trees, some centuries old, store vast amounts of carbon and support biodiversity. New plantations or younger forests cannot replicate these benefits quickly. Rebecca Banbury Morgan from the University of Bristol warned that destruction of natural forests causes irreversible loss of carbon storage and biodiversity.
About the Amazon Rainforest
The Amazon rainforest spans nine South American countries, with Brazil containing nearly 60% of it. Though covering just 1% of Earth’s surface, it houses about 10% of known wildlife species. The World Wildlife Fund lists over 427 mammal species, 1,300 birds, 378 reptiles, and thousands of amphibians and fish. The forest is often called the lungs of the planet for its vital role in absorbing CO2 and releasing oxygen. It stores an estimated 150 to 200 billion tonnes of carbon.
Questions for UPSC:
- Critically analyse the role of the carbon fertilisation effect in global forest ecosystems and its limitations in climate change mitigation.
- What are the ecological and socio-economic impacts of deforestation in tropical rainforests like the Amazon? Explain with suitable examples.
- Comment on the significance of biodiversity conservation in maintaining ecosystem services. How does species loss affect human well-being?
- Explain the concept of carbon sinks and carbon sources. How do forests like the Amazon contribute to the global carbon cycle, and what challenges do they face?
