Trees are nature’s ready-made answer to carbon capture and storage. Through photosynthesis, trees extract carbon dioxide (CO2) from the atmosphere, convert it to carbon and store it as biomass. The world’s forest ecosystems hold approximately 638 gigatonnes (Gt) of carbon, with 283Gt stored in the forest biomass alone.
In 2017, a study by Cernusak et al. found the world’s terrestrial plants are absorbing and storing approximately 29% of anthropogenic emissions that would otherwise remain in the atmosphere, further contributing to global warming. The majority of these terrestrial carbon sinks occur in tropical wet and moist forests (Figure 1). Namely, the Amazon, the Congo basin and Southeast Asia.
Figure 1 – Approximate carbon storage capacity above and below ground in forest types – taken from USDA – originally adapted from Scharlemann et al.
Tropical deforestation drivers
Over the past 30 years, tropical deforestation has intensified, with forests being cleared for a handful of global commodities: cattle, soy, palm oil, timber paper, and pulp. The leading deforestation driver in Brazil is cattle ranching and in Indonesia, the expansion of palm oil plantations.
Figure 2: The majority of forest loss in the tropics has occurred in Brazil and Indonesia, home to The Amazon and forests of Borneo respectively. Source: Mongabay
In Brazil, approximately 80% of cattle reared remain in the domestic market and 20% of cattle products are exported. In Indonesia, approximately 60% of palm oil demand is for export markets, mainly India, the EU and China.
When it comes to tackling climate change, this is problematic. Though countries are sourcing commodities from areas of deforestation abroad, they are not accounting for the emissions caused by this deforestation in their nationally determined contributions. So far, France has adopted a strategy to halt the import of products containing deforestation by 2030 and the U.K. has just started the process of analysing its footprint of imported deforestation. Many other countries are yet to act.
A tree-o of solutions?
The natural climate solutions proposed to reverse deforestation and reduce atmospheric CO2 are conservation, reforestation and afforestation. Conservation is the preservation and protection of established forests. Reforestation is the replanting of trees in degraded forests. Afforestation is the planting of trees in an area not previously forested.
Scientists remain sceptical whether reforestation and afforestation are as beneficial as keeping old-growth, primary forests standing. Forests that have been standing between 15-800 years are thought to have a positive net carbon balance. Thus, they store more carbon than they release. Further research has found a positive correlation between tree growth and carbon accumulation. The study concludes that old-growth forests are not just static carbon stores, but continue to extract CO2 from the atmosphere as they age. However, Pugh et al. contest this theory. Pugh's research claims the largest carbon sinks are not found in tropical forests, but found in reforested areas previously impacted by humans e.g. logging or mining sites. In these areas, trees are younger, faster growing and more productive.
Research released in July identified potential reforestation and afforestation areas that could increase global forest cover by 25% and provide additional carbon storage of 200Gt at maturity. However, scientists at the University of Bonn questioned the accuracy of the study, as some areas suggested for reforestation were either highly populated or unsuitable for sustained tree growth.
Although scientists and organisations have mixed feelings on which mechanisms are most effective, the sector agrees that forest destruction must stop and regeneration is vital. Last year, 40 scientists united with the Climate and Land Use Alliance to support a statement calling for governments to recognise the vital role forest conservation and restoration must play in climate mitigation.
Reforestation organisations working in the sector believe tree planting is not a solve-all approach, but an interim solution to buy time. This group believe cutting emissions from the burning of fossil fuels must be the primary focus for companies and governments. While this is valid, in my opinion, NCS must come a close second.
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