Abstract
Climatic stress and anthropogenic disturbances have caused significant environmental changes in the Sahel. In this context, the importance of soil is often underrepresented. Thus, we analyze and discuss the interdependency of soil and vegetation by classifying soil types and its woody cover for a region in the Senegalese Ferlo. Clustering of 28 soil parameters led to four soil types which correspond with local Wolof denotations: Dek, Bowel, Dior and Bardial. The soil types were confirmed by a Non-metric Multidimensional-Scaling (NMDS) ordination and extrapolated via a Random Forest classifier using six significant variables derived from Landsat imagery and a digital elevation model (out-of-bag error rate: 7.3%). In addition, canopy cover was modeled using Landsat and a Reduced-Major-Axis (RMA) regression (R2 = 0.81). A woody vegetation survey showed that every soil type has its own species composition. However, 29% of Bowel regions are deforested (i.e., degraded) and interviews revealed extensive environmental changes and a strong decline and local extinction of woody species. The differences between the soil types are significant, showing that vegetation changes (i.e., degradation and greening), resilience to climatic stress and human activities largely depend on soil properties. We highlight that spatial heterogeneity is an important aspect when dealing with environmental changes in the Sahel, and local knowledge can be well used to classify spatial units by means of public Earth observation data.
Highlights
The Sahel zone has undergone major environmental changes in the past 50 years (e.g, [1,2,3])
Bowel areas for example contain forested depressions or appear depression-like in Dior areas. Their soil properties are more similar to Bowel than to a Dek, they were included in the Bowel class and only heavy clayey sites were clustered as Dek
We highlighted the importance of soil properties in the context of ecosystem resilience and environmental change
Summary
The Sahel zone has undergone major environmental changes in the past 50 years (e.g, [1,2,3]). Vegetation changes, degradation and re-greening in the Sahel have long been researched and discussed (e.g, [5,8,9,10]) and studies agree that woody vegetation structure plays a decisive role as an indicator for ecosystem health. Rainfall and human management are prominent factors controlling tree and shrub growth, woody cover, species structure as well as its resilience mainly depend on morpho-pedological site conditions and primarily on soil properties [12]. For better understanding of past and ongoing processes, detailed classifications of soil and vegetation units are required
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