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Satellite Tool Will Help Africa Manage Dwindling Mangroves

Mangrove forests thrive in the salty tidal zone between ocean and land. They play an immensely important role in stabilizing the coastline against erosion, moderating storm surges, and as a nursery and sanctuary for hundreds of species of fish, birds, and other animals.

It’s too bad then that in many parts of the world mangrove forests are disappearing faster than they can be surveyed and appreciated for the life-giving services they provide.

Mangroves in Africa have been particularly impacted by human development and many countries may be in danger of losing these vital shoreline woodlands completely, which could threaten food security and expose coastal communities to natural disasters.

“Impoverished fishermen along the coast of tropical African countries like Mozambique and Madagascar may have only a few more years to eke out a profit from one of their nations’ biggest agricultural exports,” says NASA’s Goddard Space Flight Center in a recent news release.

“Within a few decades, they may no longer have a livelihood at all.”

“Mangrove forests–essential breeding grounds for fish and shellfish in these countries–are being destroyed by worsening pollution, encroaching real estate development, and deforestation necessary to sustain large-scale commercial shrimp farming.”

That’s because swampy mangrove forests–essential breeding grounds for fish and shellfish in these countries–are being destroyed by worsening pollution, encroaching real estate development, and deforestation necessary to sustain large-scale commercial shrimp farming, NASA explains.

“The decline of these forests threatens much of Africa’s coastal food supply and economy. The destruction of mangroves–one of Earth’s richest natural resources – also has implications for everything from climate change to biodiversity to the quality of life on Earth.”

But help may be on the way.

Lola Fatoyinbo, an evironmental scientist with NASA’s Jet Propulsion Laboratory (JPL), has helped develop a tool that will help African countries manage their dwindling mangroves.

Growing up in Cotonou, Benin, West Africa, Fatoyinbo passed polluted mangroves daily, NASA says. “Inspired to help save the forests, she began a mission as a graduate student in the United States to gain more insight about African mangroves.”

Her studies have brought Fatoyinbo back to Africa, where she has journeyed along the coastlines to test a new satellite technique for measuring the area, height, and biomass of mangrove forests.

“She developed and employed a method that can be used across the continent, overcoming expensive, ad hoc, and inconsistent modes of ground-based measurement,” NASA says.

Fatoyinbo’s approach recently produced what she believes is the first full assessment of the continent’s mangrove forests.

“We’ve lost more than 50 percent of the world’s mangrove forests in a little over half a century; a third of them have disappeared in the last 20 years alone,” said Fatoyinbo, whose earlier study of Mozambique’s coastal forests laid the groundwork for the continent-wide study.

“Hopefully this technique will offer scientists and officials a method of estimating change in this special type of forest.”

mangrove-forest-picture.jpg

NASA researcher Lola Fatoyinbo (left), seen here in June 2005 on the site where she conducted some of her field measurements, stands among the large branches of a Rhizophora mucronata tree in a mangrove forest on Inhaca Island, Mozambique with one of her research assistants, a student from the University Eduardo Mondlane in Maputo, Mozambique.

Photo courtesy NASA/Temilola Fatoyinbo

Mangroves are the most common ecosystem in coastal areas of the tropics and sub-tropics, NASA says. “The swampy forests are essential–especially in densely-populated developing countries–for rice farming, fishing and aquaculture (freshwater and saltwater farming), timber, and firewood. Some governments also increasingly depend on them for ecotourism.”

The large, dense root systems are a natural obstacle that helps protect shorelines against debris and erosion, NASA explains. “Mangroves are often the first line of defense against severe storms, tempering the impact of strong winds and floods.”

Mangroves also have a direct link to climate, sequestering carbon from the atmosphere at a rate of about 100 pounds per acre per day–comparable to the per acre intake by tropical rainforests (though rainforests cover more of Earth’s surface), NASA adds.

“To my knowledge, this study is the first complete mapping of Africa’s mangroves, a comprehensive, historic baseline enabling us to truly begin monitoring the welfare of these forests,” said Assaf Anyamba, a University of Maryland expert on vegetation mapping, based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Fatoyinbo’s research combines multiple satellite observations of tree height and land cover, mathematical formulas, and ground-truthing data from the field to measure the full expanse and makeup of the coastal forests.

Her measurements yielded three new kinds of maps of mangroves: continental maps of how much land the mangroves cover; a three-dimensional map of the height of forest canopies across the continent; and biomass maps that allow researchers to assess how much carbon the forests store.

Fatoyinbo and colleague Marc Simard of JPL used satellite images from the NASA-built Landsat and a complex software-based color classification system to distinguish areas of coastal forests from other types of forests, urban areas or agricultural fields.

They also integrated data from NASA’s Shuttle Radar Topography Mission (SRTM) to create relief maps of the height of the forest canopy.

Finally, they merged the broad radar maps with high-accuracy observations from a light detection and ranging (commonly called lidar) instrument aboard NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) to obtain accurate height estimates.

“Fatoyinbo double-checked the accuracy of her satellite measurements at the ground level in the only way possible: She went to Africa to measure tree heights and trunk diameters in person,” NASA says.