Recovering degraded and secondary forest carbon stock modeled in 2018 in (a) Amazonia, (b) Borneo and (c) Congo (image: Heinrich et al/Nature)
Published on 08/14/2023
By Luciana Constantino | Agência FAPESP – An article published in the journal Nature describes a novel methodology for calculating the carbon absorption capacity of tropical forest regeneration areas. The innovation can contribute to climate change mitigation policies and plans to charge for environmental services.
Led by scientists at Brazil’s National Space Research Institute (INPE) and the University of Bristol in the United Kingdom, the study is the first of its kind conducted on a large scale using remote sensing.
An analysis of satellite data for the period 1984-2012 traced the spatial and temporal patterns of growth in degraded and secondary forests influenced by key environmental and anthropogenic drivers and investigated the age distribution of this vegetation throughout the tropics.
Age-based growth curves were constructed to account for variations in climate, environmental conditions and disturbances caused by human activity, such as burning and logging. As a result, the study quantified carbon sinks in recovering forest areas, defined as secondary forest growing on deforested land and degraded forest areas with partial loss of tree canopy, structure and function owing to logging (mostly illegal), fire and/or extreme weather.
According to the article, recovering forest areas in the world’s three main continuous tropical humid regions – the Amazon (South America), Congo (Central Africa) and Borneo (Southeast Asia) – removed at least 107 million metric tons of carbon from the atmosphere per year and accumulated 3.56 billion tons during the period.
This was sufficient to offset 26% of the carbon emissions due to global deforestation (10.52 billion tons) and anthropogenic degradation (2.91 billion tons).
“The results are important both for national carbon emission inventories submitted to the United Nations and for Brazil’s great potential to attract investment in management of and payment for environmental services,” Luiz Eduardo Oliveira e Cruz de Aragão, last author of the article and head of INPE’s Earth Observation and Geoinformatics Division, told Agência FAPESP.
His remarks were a reference to REDD+ projects, where REDD stands for Reducing Emissions from Deforestation and Degradation, and the plus sign indicates “additional forest-related activities that protect the climate”, especially sustainable management of forests and conservation of forest carbon stocks, according to the UN Framework Convention on Climate Change (UNFCCC). These projects are implemented by developing countries, which receive funding in return for reducing greenhouse gas emissions from deforestation and forest degradation. National inventories are published by countries and submitted to UNFCCC with action plans to reduce emissions.
“Our study produced the first pantropical estimates of above-ground carbon absorption in recovering forest areas. Protection of old-growth tropical rainforests is still the top priority, but we demonstrate the value of sustainably managing the areas that can recover from deforestation and degradation by human activity,” said Viola Heinrich, first author of the article. She recently earned a PhD in physical geography at the University of Bristol’s School of Geographical Science, with Aragão as thesis advisor.
Potential
According to the study, 35% of degraded areas in the three tropical forests had been completely deforested by 2018. If these degraded forests had been conserved, the potential contribution from all recovering forests could have reached 5.89 billion tons of carbon, offsetting 48% of gross emissions from forest losses (12.34 billion tons).
“The methodology used in this study enabled us to find out, for example, whether an area’s potential biomass recovery decreases after a fire. This can help carbon market investors weigh up an area’s regeneration potential. In any event, the more we protect the standing forest, the better,” Ricardo Dal’Agnol, a co-author of the article, told Agência FAPESP. He has a PhD from INPE and is currently investigating forest degradation mapping with remote sensing (LIDAR) and deep learning as a postdoctoral researcher at the University of California Los Angeles (UCLA) and at NASA’s Jet Propulsion Laboratory. He was previously a researcher at INPE and had a postdoctoral scholarship from FAPESP.
FAPESP also supported the study via postdoctoral scholarships in Brazil and abroad awarded to Henrique Luis Godinho Cassol, a researcher at INPE and a co-author of the article.
According to the article, the potential carbon sink to be obtained by protecting the recovery of degraded and secondary forest areas could reach 53 million tons per year in the tropical regions studied.
“Focusing on the protection and restoration of secondary and degraded tropical forests is an efficient solution to build robust mechanisms for sustainable development in tropical countries. It adds monetary value to the environmental services provided by forests, with economic and social benefits for the people who live there,” Aragão said.
Efforts to protect secondary forest and degraded areas should not be allowed to detract from the importance of conserving primary forest areas, which must remain the top priority from the standpoint of climate change mitigation, the researchers stressed.
Carbon sinks
Tropical forests are one of the most important ecosystems for climate change mitigation, alongside oceans and soil. They function as carbon sinks during growth, absorbing and storing carbon, but emit greenhouse gases when degraded or cut down.
In order to prevent a rise in global temperatures of more than 2 °C compared with the pre-industrial period and if possible limit the rise to 1.5 °C, carbon emissions will have to fall at least 45% by 2030 and reach zero by 2050. However, emissions remain on an unsustainable growth trajectory according to the report CO2 Emissions in 2022 issued by the International Energy Agency (IEA).
This detailed region-by-region and fuel-by-fuel analysis drawing on publicly available data highlights the pollution produced by the energy sector, focusing on carbon emissions from the burning of fossil fuels. Global energy-related CO2 emissions rose 0.9% (321 million tons) to a new high of more than 36.8 billion tons in 2022, according to the report.
In Brazil, greenhouse gas emissions rose more in 2021 than in any year in almost two decades, according to the Climate Observatory (Observatório do Clima), a Brazilian network of civil society organizations. Its statistics show that gross emissions of CO2 reached 2.42 billion tons, up 12.2% year over year. The main sources were deforestation, especially in the Amazon, and agriculture.
In March 2021, the group of researchers had already published in Nature Communications a study showing that maintaining the secondary forest areas measured in 2017 in the Amazon could accumulate 19.0 million tons of carbon per year and contribute 5.5% to Brazil’s net emissions reduction target by 2030. Avoiding fires and repeated deforestation could increase secondary forest carbon stock by 8%.
The article “The carbon sink of secondary and degraded humid tropical forests” is at: www.nature.com/articles/s41586-022-05679-w.
Source: https://agencia.fapesp.br/42126
