Why can some Sahel areas be described as savanna or scrubland instead of grassland?

In the Sahel, the classification of vegetation as savanna or scrubland rather than grassland is primarily determined by the presence of woody plants and the specific environmental conditions of the region.12

The distinction between these vegetation types is often arbitrary and exists along a dynamic continuum. Several factors influence why certain areas of the Sahel are categorized as savanna or scrubland:1

• Woody Plant Presence: While grasslands are defined by a continuous grass cover, savannas are characterized by that same grass cover being interrupted by trees and shrubs. When these woody components become dominant or are the primary feature, the area may be described as scrubland.13
• Environmental Stress: Scrublands typically occur in semiarid regions where conditions are less optimal for tree growth, often due to low and erratic rainfall or nutrient-poor soils. In the Sahel, the prevalence of thorny shrubs and trees like acacia reflects these harsh, semiarid conditions.32
• Human Influence: Overgrazing by livestock and the clearing of land for firewood and farming have significantly altered the landscape. These activities can deplete grass cover and shift the vegetation profile, sometimes leading to desertification or the encroachment of scrubby, woody vegetation.24
• Soil and Moisture: Soil type and depth influence whether grasses or woody plants thrive. For instance, sandy soils often favor grasses, while deeper or stony soils may support more tree and shrub growth.5

Ultimately, the Sahel acts as a transitional zone where these vegetation types merge, and their specific classification depends on the local balance of climate, soil, and human impact.12