Final answer:
Selvas and Oasis are small green areas of civilization in the Sahara Desert, formed around underground water sources. They have great economic importance and sustain a significant portion of the desert's population through activities like farming and herding.
Step-by-step explanation:
The Saharan Desert is home to several oasis, such as Selvas and Oasis. They are small green areas of civilization formed around underground water sources that reach the surface via wells or springs. These oases, although occupying only a small portion of the desert's landmass, are of great economic importance. They provide sustenance and livelihood to a significant portion of the desert's population, including nomadic groups like the Tuareg and Teda, who engage in activities like farming and herding. These oases serve as limited pasturage areas and facilitate a nomadic lifestyle for the herders. The economic activities in these oasis regions contribute to the overall well-being of the population in the Sahara Desert.