In an article published online in the journal Forest Ecology and Management, U.S. Forest Service researcher Christina Stringer and collaborators provide the first comprehensive estimate — 14 million megagrams (Mg) or almost 31 trillion pounds — of the carbon sequestered in the mangrove forests of the Zambezi River Delta in Mozambique.
More important than the number itself is the ability to precisely calculate carbon stocks of mangrove forests, a task which until recently has proven difficult and elusive. In the article, Stringer and her collaborators describe the inventory approach they used to arrive at the estimate. Both rigorous and practical, the approach can be applied to other mangrove forests in Africa to provide the carbon quantifications required for participation in incentive programs for climate change mitigations.
The tangled mangrove forests that grow in tropical and subtropical coastal areas represent less than one percent of the world’s tropical forest area, yet they sequester higher levels of carbon than any other forest ecosystem, for instance storing up to three times more carbon per area than typical upland tropical forests. This means that these forests also release outsize amounts of carbon into the atmosphere when they’re destroyed.
Mangrove forests are a prime target for mitigation for programs such as the United Nations Collaborative on Reducing Emissions from Deforestation and Degradation in Developing Countries (UN-REDD and REDD+), which offer financial incentives for developing countries to reduce deforestation. Though the programs have focused on terrestrial forests, the large capacity for carbon storage of mangrove forests coupled with the accelerating destruction of these ecosystems worldwide has sparked interest in including them in REDD+ programs, which require precise, quantified data on forest carbon stocks.
Africa contains about 20 percent of the world’s mangrove forests, with Mozambique second to Nigeria in total area of mangrove cover. The Zambezi River Delta, which forms the second largest continuous mangrove habitat in Africa, is also home to many small communities of people who depend on the forests and near-shore fisheries for their livelihoods, making it an area of great interest for conservation.
Over the past two years, Stringer, research hydrologist with the Forest Service Southern Research Station Center for Forested Wetlands Research, and SRS team leader Carl Trettin, a co-author on the article, worked with collaborators in Mozambique to set up inventory plots in remote swampy mangrove forests, using a Spatial Decision Support System developed by university collaborators to locate plots on the ground in five different canopy height classes derived from global remote-sensing data sets.
They found that ecosystem carbon density ranged from 373.8 to 620.8 Mg per hectare, with overstory biomass the dominant above-ground carbon pool. Soil carbon was the largest carbon pool accounting for 45 to 73 percent of the carbon in each of the height classes.
“This project represents the first comprehensive mangrove forest inventory in East Africa,” said Stringer. “This approach resulted in very precise estimates, with uncertainties falling well within the international guidelines of programs such as REDD+.”
The results of the study will provide a baseline for REDD+, be included in the national forest inventory being conducted by the government of Mozambique, and provide the foundation for a new Blue Forests project implemented by the World Wildlife Fund-Mozambique with funding from the Global Environmental Facility.
The project was made possible through funding by U.S. Agency for International Development (USAID) under the USAID Mozambique Global Climate Change Sustainable Landscape Program. Linking Forest Service capabilities in research to address issues in developing countries is coordinated through the Forest Service International Programs office.
For more information, email Christina Stringer at firstname.lastname@example.org