Their farms are poor because of the thin topsoil, and the Thulls produce food only through great amounts of back-breaking labor.
The trees are cut, the undergrowth is burned, the thin topsoil planted with corn until the crop fails, the land then grazed by cattle until the rains wash the earth away.
The thin and poor-quality topsoil yielded an initially good harvest, followed by a smaller harvest the second year.
The thin topsoil didn't look sufficient to sustain trees the size of those surrounding the site.
The Mokoron remains were discovered nearly two years ago, after a hurricane turned mountainsides into cascades of mud and water, washing away the thin topsoil.
The desert is the combined result, scientists say, of severe overgrazing that has destroyed the thin topsoil, and a decade of hotter, drier weather, including three straight years of extreme drought.
The ground underfoot was rough and broken, with patches of rock poking through the thin topsoil.
The thin topsoil would wash away, the hills would become bare, and this island of forest would be gone.
Most of the larger varieties support themselves on thin topsoil with buttress roots.
Hot and potent, the October winds scoop the thin topsoil off the African savanna, swirl the dust high into the skies and thrust it west on a journey that can stretch thousands of miles.