Mangroves in Mozambique

Travel up a creek to locate a sampling plot. Denise Nicolau, World Wildlife Fund-Mozambique (left) and Semo Mapazi, University of Eduardo Mondlane (right). Photo by Carl Trettin.

September found U.S. Forest Service researchers Carl Trettin and Christina Stringer camping out on the edge of a mangrove swamp in Africa, watching the ocean tides for the best time to take their skiffs out to search for plots to set up for inventory.

They were in Mozambique, which stretches along the eastern coast of Africa and contains an estimated 720,000 to 909,000 acres of mangrove forests, one of the largest continuous mangrove forests in Africa. Trettin and Stringer were there, on the Zambezi Delta, to help figure out just how much carbon is in these forests.

Trettin, leader of the Forest Service Southern Research Station (SRS) Center for Forested Wetlands Research, first came to the Zambezi Delta in late 2011, recruited on the basis of his previous work in the Kingdom of Lesotho on behalf of the Millennium Challenge Corporation to restore mountain wetlands.

“Considering carbon stocks is fundamental to assessing wetland functions and associated ecosystem services, so while the wetlands in the Zambezi Delta are quite different from those in the Lesotho Highlands, the principals are the same,” says Trettin. “We’ll be applying those principals in conjunction with new international protocols for assessing mangrove forests.”

This was Stringer’s first time in Africa. She joined the SRS Forest Wetlands Center this July, bringing a background in research on American mangrove systems. Her new work focuses on carbon cycle science and mangrove ecosystems in Africa.  Stringer marvels at the diversity of mangrove in Africa (nine different species as opposed to the three in the Americas), at the many other plants and animals associated with the African mangrove ecosystems, and at the hardy people living at the swamp’s edge. “It’s so remote there, so inhospitable to humans. Where we’re working there are tiny villages with only tens of people,” says Stringer.  

Trettin and Stringer came out this year to set up monitoring plots identified remotely using a spatial decision support system developed by the University of North Carolina at Charlotte. The program distributed plots according to canopy height across a 300-square kilometer area. Some of the plots turned out to be in places the researchers just couldn’t get to. “We were trying to pole a big skiff up a meter-wide channel to get to some of our plots,” says Trettin. “Meanwhile ocean waves were beating us into the mangroves. We had to adjust some of our plot locations for crew safety.”

The carbon cycle science research is supported with funds from U.S. Agency for International Development through their Mozambique mission and their global Sustainable Wetland Adaptation and Mitigation Program. Linking Forest Service capabilities in research to address science and land management issues in developing countries is coordinated through the agency’s International Program Office. The work to assess the carbon stocks in the Zambezi River Delta is being done in cooperation with World Wildlife Fund (WWF) – Mozambique. 

This is the second year of the WWF project, which is part of the United Nations Reducing Emissions from Deforestation and Degradation (REDD+) program, an effort to create financial value for carbon in forests as incentive to help prevent deforestation and forest degradation. The REDD+ program identified Mozambique as vulnerable to negative impacts from climate change but also well-positioned in terms of forest resources to benefit from REDD+ carbon incentive programs.

In addition to siting plots, Trettin and Stringer are developing methods for taking forest inventory and for measuring carbon stocks of mangrove forests. Ultimately the project will provide an estimate of the carbon pools within the mangroves occurring on the Zambezi Delta as a baseline for REDD+.

“Research shows that the carbon density of mangrove forests is higher than other marine or terrestrial systems,” says Trettin. “But there’s still a lot of uncertainty about how to make the carbon stock estimations needed for REDD+ carbon incentive programs. The protocols we’re developing and evaluating for the first time in the Zambezi Delta will lay the foundation for monitoring change in carbon pools in mangrove forests in Mozambique, Africa, and the world.”

The project works because of a high level of collaboration with a wide range of organizations. “We rely completely on our in-country partners from WWF, the University of Eduardo Mondlane (UEM), and the government of Mozambique,” says Trettin. “In turn, we’ve been able to leverage funds from the National Science Foundation to buy and set up equipment for soil carbon analysis at the university. This opened the doors for us to do cutting edge research in the Delta while building scientific capacity in Mozambique.”

Developing professional capacity is another synergistic outcome of their work. While working in Mozambique, the Forest Service team conducted seminars to instruct students on wetland ecology and carbon cycling.  Students from UEM are also part of the field sampling crew, and several have expressed interest in using aspects of the project for their senior thesis and master’s projects.

For more information, email Carl Trettin at or Christina Stringer at

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