Geomorphodynamics in Argan Woodlands, South Morocco

Abstract

The endemic argan tree (Argania spinosa) populations in South Morocco are highly degraded due to their use as a biomass resource in dry years and illegal firewood extraction. The intensification and expansion of agricultural land lead to a retreat of the wooded area, while the remaining argan open woodlands are often overgrazed. Thus, canopy-covered areas decrease while areas without vegetation cover between the argan trees increase. In total, 36 rainfall simulation experiments as well as 60 infiltration measurements were conducted to investigate the potential difference between tree-covered areas and bare intertree areas. In addition, 60 soil samples were taken under the trees and in the intertree areas parallel to the contour lines. Significant differences using a t-test were found between tree and intertree areas for the studied parameters Ksat, Kh, pH, electric conductivity, percolation stability, total C-content, total N-content, K-content, Na-content, and Mg-content. Surface runoff and soil losses were not as conclusive but showed similar trends. The results showed that argan trees influence the soil underneath significantly, while the soil in intertree areas is less protected and more degraded. It is therefore reasonable to assume further degradation of the soil when intertree areas extend further due to lack of rejuvenation of argan trees.

Relative quantification of wind erosion in argan woodlands in the Souss Basin, Morocco

“…During summer and autumn, it may even act as a protection for underlying mineral sediments. Kirchhoff et al (2019a) found that tree-covered areas in argan woodlands show higher values of soil organic matter and lower erodibility compared with inter-tree areas. Our results support this general distinction insofar as soil surface properties and emission fluxes vary only slightly compared with all other surface types.…”

“…The 100m × 100m test site IRG1c is part of a larger research area situated on an alluvial fan, formed by Wadi Irguitène originating from the High Atlas in the north (Kirchhoff et al, 2019a;Kirchhoff et al, 2019b). It belongs to the remaining natural habitat of the argan tree Argania spinosa, which can be assumed to be a paramount keystone species in this environment.…”

“…The specific consideration of tree areas follows Kirchhoff et al (2019a), who found tree cover to be a general feature establishing chemical and physical soil surface traits in argan woodlands. We defined this surface type as the area directly underneath the crown and mapped them automatically from a crown-height model.…”

“…Despite these acknowledgements of the ecological and socio-economic implications and the high level of societal interest and regional and national actions, argan woodlands are severely threatened by degradation processes. The main causes are an extremely diminished rejuvenation of argan populations and overexploitation of adult trees by overgrazing (Lybbert et al, 2010;Le Polain de Waroux and Lambin, 2012;Kirchhoff et al, 2019a). In this vulnerable environment, wind erosion and dust emission are potentially major degradation processes that remain largely unassessed.…”

The Effect of Hydrology on Soil Erosion

“…Kirchhoff et al [15] presented exotic research carried out in a poorly-studied region of Northern Africa, where the endemic argan tree (Argania Spinosa) populations are highly degraded due to their use as a biomass resource in dry years and illegal firewood extraction. In total, 36 rainfall simulation experiments, as well as 60 infiltration measurements, were conducted to investigate the potential difference between tree-covered areas and bare inter-tree spaces.…”