Spatiotemporal dynamics of land use / land cover and woodland transformation in Bolgatanga, Ghana

In the dry, sun-baked landscapes of West Africa, the ground tells a story of constant change. For decades, scientists have watched how people reshape the earth, turning forests into farms and open fields into towns. This process, known as land-use change, is one of the most visible ways humans interact with their environment. In places where the climate is already harsh and water is scarce, these changes can happen quickly, tipping the balance of nature. To see these shifts clearly, researchers often look down from space. Satellites act as giant cameras, taking pictures of the same spot on Earth over many years. By comparing these images, scientists can measure how much forest has disappeared, how much farmland has grown, and how much the ground has been paved over. This is not just about counting trees; it is about understanding how a growing population and the need for food are rewriting the map of a region.

A recent study focused on Bolgatanga, a municipality in the Upper East Region of Ghana, to trace this transformation over twenty years. The researchers wanted to know exactly how the landscape changed between 2002 and 2022. They used satellite images taken every ten years to create a detailed map of the area. To make sense of the vast amount of data, they employed a computer method called a random forest classifier. Think of this as a smart sorting system that learns to recognize different types of ground cover—like dense woods, open trees, farms, buildings, and bare soil—by studying thousands of examples. The team trained this system using real-world coordinates they collected on the ground and historical maps, ensuring the computer could accurately distinguish between a patch of forest and a field of crops.

The results reveal a dramatic shift in the character of Bolgatanga. Over the two decades, the area covered by towns and cities more than doubled. In 2002, built-up areas made up just under 10 percent of the land. By 2022, that figure had risen to over 20 percent. At the same time, the land used for farming expanded significantly, growing from about 26 percent to 32 percent of the total area. These two forces—urban growth and agricultural expansion—came at a direct cost to the natural vegetation. The combined cover of woodlands, which includes both dense forests and open, scattered trees, shrank by nearly 19 percentage points, dropping from 58 percent to just over 39 percent. The study shows that the loss of trees was not random; it was almost entirely replaced by the need for housing and food.

The researchers also looked at the health of the remaining plants using a measure called the Normalized Difference Vegetation Index, which acts like a report card for plant life. In 2002, the area showed signs of moderate plant vigor, with a good mix of trees and seasonal crops. By 2022, the highest scores for plant health had fallen sharply, mirroring the loss of the woodlands. The landscape had become more uniform, dominated by farms and buildings rather than the varied mix of trees and shrubs that once defined the region. The study notes that this pattern is not unique to Bolgatanga but reflects a broader trend across West Africa, where population growth drives a dual pressure on the land. People need space to live, and they need land to grow food, and both demands are eating into the remaining natural cover.

The study highlights a specific pathway of change that is worth watching. The data suggests that the loss of woodland is not always a sudden event where a forest is cleared all at once. Instead, the researchers observed a gradual degradation. Open woodlands, which are already sparse, often transition into denser, shrubbier growth before eventually being cleared for farming or development. This cycle of disturbance and regeneration happens so quickly that the natural balance is lost. The computer models were highly accurate, correctly identifying land types more than 96 percent of the time in the most recent year, giving the researchers confidence in these findings. However, the study also points out that distinguishing between new buildings and bare ground can be difficult for computers, as both reflect light in similar ways.

The implications of these changes are serious for a region that already faces a hot, dry climate. As the natural woodland cover disappears, the land loses its ability to hold water and support biodiversity. The study concludes that without careful planning, this trajectory will continue. The author suggests that future growth should be directed toward areas that are already degraded or bare, rather than consuming the remaining woodlands. They recommend stronger enforcement of land-use rules and the promotion of farming methods that protect the soil. The story of Bolgatanga is a clear example of how a semi-arid landscape is being reshaped by human needs, a transformation that is now visible from space and requires urgent attention to ensure the land remains productive and resilient for the future.