Final answer:
Man's presence in the Sahel has contributed to desertification through deforestation, overgrazing of livestock, and soil salinization due to irrigation. These activities have intensified the natural desertification processes of an already vulnerable region.
Step-by-step explanation:
The Sahel region is greatly affected by man's presence, which has accelerated the process of desertification in multiple ways. Factors such as deforestation, resulting in the removal of vegetation that binds the soil together, overgrazing by livestock which reduces the land's ability to regenerate its vegetation, and the buildup of salt in irrigated soils, degrading the soil quality and fertility, all contribute to desertification. Although not solely attributed to human activities, these practices exacerbate the natural tendency towards desertification in the Sahel, which is already prone to changes due to its climate and proximity to the Sahara Desert.