What is desertification primarily the result of?

Desertification is primarily the result of topsoil erosion leading to a permanent reduction in productivity. This process is heavily influenced by both natural factors and human activities, such as deforestation, overgrazing, and poor agricultural practices. When the fertile topsoil is eroded, it significantly diminishes the soil's ability to retain moisture and nutrients, which are essential for plant growth. As a result, the land's productivity declines, making it difficult for vegetation to establish itself, further exacerbating the erosion process and accelerating the desertification cycle.

The other options describe different phenomena or processes that do not accurately encapsulate the primary cause of desertification. For instance, natural processes of succession and the movement of deserts do occur but do not directly address the rapid degradation of productive land into desert landscapes. The formation of dryland ecosystems due to increased temperatures might be related to climate changes, but it does not specifically highlight the human impact and degradation of soil quality that is central to the concept of desertification.