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Unique Mapping Tool Brings Unprecedented Look at Land Cover Change in West Africa

They say there are forests in West Africa where spirits abide. Where people walk among woodland burial grounds and speak to the dead. Where life plays out from beginning to end.

Places of myths and taboos, of proverbs and songs, forests have played key roles within the cultural rhythms of West Africans for centuries. According to the native traditions in Ghana, a family would plant a tree in the woods for each child born. Each year then, the development of that son or daughter was measured by the growth of the tree. As the seasons passed and the branches began to bear fruit, it became time for the child to marry. And when the circle of life was complete, it’s said that one’s spirit eternally linked to their own personal birthright tree.

“That’s why when the forests began to disappear, it had huge impacts, socioeconomically, environmentally, even culturally,” says Francis Dwomoh, a native Ghanaian who recently completed his doctoral degree in Geospatial Science and Engineering at South Dakota State University in Brookings, SD. “For us, if you are losing your forests, you’re also losing part of your culture.”

Color photo of scientist Gray Tappan
G. Gray Tappan, a scientist at the U.S. Geological Survey Earth Resources Observation and Science Center, talks about his work in West Africa for an "EROS in Action" video. (Public domain.)

Ghana is in fact losing its forests. By some estimates, the country’s primary rainforest declined by 90 percent in the past half century. Logging, wildfires, agricultural expansion, climate variability, population growth—all have exacted heavy tolls on forest resources, not only in Ghana but throughout the 17 countries that comprise a West African sub-region roughly the size of the United States.

It’s a loss felt at all levels of West African life, from governments facing declining timber exports to local villagers who no longer have ready sources of wood for cooking and housing. But now there are indications that the trend could be reversing, at least in some places. Now it appears that many West African policy and decision makers are looking at new, innovative ways to better nurture and preserve their forests and other natural resources.

A prime example of that innovation—a unique mapping tool created by West Africans and the U.S. Geological Survey’s (USGS) Earth Resources Observation and Science (EROS) Center, with financial support from the U.S. Agency for International Development (USAID).

An unprecedented look at West African land cover

Led by USGS Geographer Gray Tappan at EROS, maps and datasets produced through the West Africa Land Use and Land Cover Trends Project represent an unprecedented look at how land cover has changed in that part of the world over 40 years, both at regional and national scales. This new tool captures where forests have faded away beneath the advance of creeping desertification. Where booming population growth has spurred urban sprawl. Where croplands have replaced woodlands. And in what many view as a positive trend, where the greening of the landscape by new tree growth is now occurring.

Remotely sensed time-series data from Landsat’s rich archive have been crucial in capturing these changes, Tappan said. But the maps and datasets also are products of decades of boots-on-the-ground visual mapping and analysis—much of it done by native West Africans themselves—as well as thousands of aerial photographs.

Tappan and his team understood they could have simply relied on automation to take multispectral information from satellite sensors and use the reflectances they captured to map land cover classes. But the accuracy of such an approach wouldn’t have met their needs, he said.  So, they decided early on to take Landsat images and manually do the mapping “with just good old-fashioned visual analysis,” Tappan said.

It not only dramatically improved the maps’ accuracy, but also brought other important dimensions to them, such as texture, pattern, shape, size, even shadows. For example, roads can be seen coming together at villages in the middle of agricultural areas. “All these other dimensions allowed us to really bring the accuracy way up,” Tappan said.

Tracking change across time

There’s more. The maps and datasets work off three reference time points from Landsat images—1975, 2000, and 2013­—to show changes across time. Rather than being mapped independently from one another, each period is connected to the others in an integrated way, Tappan said. So, if an area shows dense forest today, that dense forest is present 10 years ago. Rock outcrops that appear in 1975 also appear in the same place on the maps in 2000 and 2013.

“You don’t go from a rock outcrop to a savannah in three or four decades. That doesn’t happen,” Tappan said. “Features on the landscape that are stable are stable on the maps. In that way, the mapping technology itself was really good at pulling out the real change.”

Color photograph of Francis Dwomoh
Francis Dwomoh, a postdoctoral fellow in Geospatial Science and Engineering at the South Dakota State University Geospatial Sciences Center of Excellence.(Credit: Young, Steven (Contractor) M. Public domain.)

While other mapping efforts in West Africa have effectively used Landsat images to capture snapshot case studies of conservation issues, forest degradation, and other land cover changes, none tackled multi-date mapping—and the trends picked up by that mapping—at regional and national scales like the effort of Tappan and his team has. That’s got people in West Africa talking.

Presidents and prime ministers across the West Africa sub-region have seen the work of his group, “and have been talking about it, and calling for more monitoring,” Tappan said. Regional West African institutions charged with monitoring such things as food security, sustainability practices for forest and ecosystem services, and the state of the environment are using the maps and datasets.

So are governmental agricultural, environmental, and water resource ministries across the 17 countries. And non-governmental organizations (NGOs) working at local levels with farmers and others to take care of the soil or capture rainfall in vegetation are tuned in to the USGS EROS and West African work as well.

Datasets are "a decision-making tool"

The entirety of the EROS-West Africa work has become “a guide to managing the country’s environmental resources, and a decision-making tool,” Sény Soumah, an agrometeorologist engineer at the National Directorate of Meteorology in Conakry, Guinea, said by email.

In the Republic of Benin, the maps and datasets are exposing trends in and problems with land degradation, said Ogoubiyi Felix Houeto, chief of Benin’s Mapping Division at the National Center for Remote Sensing and Ecological Monitoring. “These data have led to the introduction of a wide-scale reforestation and project management of national forests and community forests through forest plantations and fruit tree plantations,” Houeto said.

Before he came to South Dakota to further his studies, Dwomoh worked at the Forestry Research Institute of Ghana. His research has focused on the changing forests in the West African sub-region—from Ghana to Guinea—and how that impacted the culture, climate, and economy.

“But I did not have access to the historical record of what has been happening, and what has been taking our natural resources,” Dwomoh said. “So, when (the USGS-West African) data came out, to me that was a huge relief. I could look at time series from decades back, look at the change that has occurred in 2000, and even the change that has occurred in 2013.

“I wanted to see where the forest is receding or expanding, and where the savannahs are receding or expanding. And I wanted to bring out other datasets, like climate, population growth, and other socioeconomic data. Then I can get an even better understanding of not only where the changes are occurring, as the maps show, but what is driving those kinds of changes.”

What the maps help to confirm is how much the mushrooming mega-cities in Nigeria have diminished forests and natural resources there, or how farming practices combined with drought and deforestation have degraded fertile lands across West Africa.

In Ghana, where timber demands have resulted in a thinning of forest reserves, climate variability and warming are drying out the grasses and other materials that lie within the newly formed forest openings, making those reserves more susceptible to fire, Dwomoh said. “And within the surroundings of these forest reserves are people who are doing their farming,” he continued. “Fire is the main tool they use to prepare their lands. When they do that, it’s easier for fire to escape into these forest reserves. So that adds then to the problems posed by logging.”

Finding pockets of hope

While the maps and datasets are capturing those devastating impacts, the work of Tappan and his colleagues is also finding pockets of hope across West Africa. Case studies put together by West African team members confirm such successes, like the regreening that’s going on in Niger.

There are vast areas in the southern part of that country where there is far more tree cover now than there was 20, 30, 40 years ago—despite years of failed attempts to plant trees in this semi-arid region of Africa, Tappan said. The difference, he added, is a decision by local farmers “to simply allow Nature to come back.”

Native trees are sprouting spontaneously in fields where their seeds are already in the soil. Now instead of cutting them out to keep the fields clear, farmers are allowing them to take root and grow, perhaps pruning their branches for firewood but not chopping them down completely.

“The survival rates are very high because they are just native trees that are coming back,” Tappan said. “It’s a neat story because it’s not about planting trees, so there’s very little cost as well. And more trees provide all kinds of benefits. They actually increase soil fertility. The farmers see increased crop productivity under canopies of trees. There’s fodder for the animals, and there’s firewood. So, these success stories are really important because they do give hope.”

In the case of Ghana, they will actually end up giving more than that, Dwomoh said. His country is working within the United Nations Framework Convention on Climate Change (UNFCCC) to reduce carbon emissions from deforestation and forest degradation. The payoffs for success in that endeavor are financial rewards from developed countries who are also participating in the UNFCCC.

Hotspots of land cover change

The maps and datasets from Tappan and his colleagues “are very important to us to set the baselines of where we’ve come from” as far as forest regrowth, Dwomoh said. “It helps us know where the hotspots of change are in terms of vegetation loss, and how we can plan to recover those that are lost, or sustain those that are remaining.”

As funding priorities shift, Tappan and EROS will have less of a leadership role in future mapping and datasets. But again, West Africans have been involved in doing the mapping work themselves. Tappan and his colleagues have held workshops that trained representatives from each of the 17 countries on the use of Landsat imagery, and how to characterize and map the landscapes of their countries from the images.

The Africans also have learned how to use actual tools needed to operate within a Geographic information System (GIS) to create land use maps and then update them through time.

Going forward now, an international group called the Permanent Interstate Committee for Drought Control in the Sahel, or CILSS, is taking up the reins of this mapping work, Tappan said. CILSS’ mandate is to carry out food security monitoring, and to lead the fight against the effects of drought and desertification, in West Africa. The EROS-West Africa maps and datasets are a good fit for that effort, Tappan said.

The reality is, both CILSS and decision makers from the West African countries understand very well now that there is a fundamental need to continue to access this land use-land cover information, and to monitor that information over time to measure change, Tappan said.

“As I’ve said, a number of heads of state have seen our work and called for it to continue,” he said. “The idea is to continue the updating of the maps, and the monitoring. There are already commitments from donors to help them make this happen. So, it will be done, mainly headed by CILSS but with partners like the USGS, NASA, and USAID.”

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