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

Abstract

The endemic argan woodlands cover large parts of South Morocco and create a characteristic landscape with areas of sparsely vegetated and bare soil surfaces between single trees. This unique ecosystem has been under extensive agrosilvopastoral management for centuries and is now at risk of degradation caused by overgrazing and increasing scarcity and variability of rainfall. To investigate susceptibility to wind erosion, we conducted an experimental–empirical study including wind tunnel tests and a drone‐generated digital elevation model and quantified wind‐erodible material on five different associated surface types by means of sediment catchers. The highest emission flux was measured on freshly ploughed surfaces (1875 g m–2 h–1), while older ploughed areas with a re‐established crust produced a much lower emission flux (795 g m–2 h–1). Extensive tillage may have been a sustainable practice for generations, but increasing drought and uncertainty of rainfall now lead to an acute risk of severe soil erosion and dust production. The typical crusted surfaces characterized by residual rock fragment accumulation and wash processes produced the second highest emission flux (1,354 g m–2 h–1). Material collected from tree‐shaded areas (933 g m–2 h–1) was revealed to be a considerable source of organic material, possibly affecting substrate conditions positively on a larger regional scale. The lowest flux was measured on rock fragment‐covered surfaces (301 g m–2 h–1). The data show that open argan woodland may be a considerable source for wind erosion and dust production, depending on surface characteristics strongly related to management. An adapted management must include the conservation of argan trees to offer a promising approach to prevent severe wind erosion and dust production and mitigate possible impacts of land‐use change and climate change related shifts in wind and rainfall patterns. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Spatial distribution of argan tree influence on soil properties in southern Morocco

“…In the past, the high fuel value of argan wood resulted in the deforestation of the argan forest for use in the sugarcane industry or for sale as charcoal (Aït Hssaine, 2002;Faouzi, 2013). Although the argan woodlands have been designated a UNESCO biosphere reserve (Charrouf and Guillaume, 2018), afforestation programmes are ongoing and some felled trees have resprouted, the slow growth of Argania spinosa, the high grazing pressure and ongoing illegal firewood harvesting have led to a degradation of the woodlands that is visible in the architecture or growth form (Culmsee, 2005;Kirchhoff et al, 2019a;Marzolff et al, 2020) and the decrease in forest density (up to 44.5 % decline of wooded area between 1970-2007le Polain de Waroux and Lambin, 2012).…”

Spatial patterns of argan-tree influence on soil quality of intertree areas in open woodlands of South Morocco

“…The parameter Corg shows the most pronounced effects in eastern directions (mostly E, SE) which corresponds to the main wind direction. Marzen et al (2020) found relatively high wind erosion rates under trees using an experimental wind tunnel on one of the here-analysed study sites with the eroded material being mostly tree litter. Sirjani et al (2019) show a negative correlation between Corg content and wind erosion, since higher organic matter often leads to more particle aggregation and more stable aggregates (Tatarko, 2001).…”

“…soils in those regions are generally more vulnerable to erosive processes, which are result and cause for degradation and desertification (Ravi et al, 2010;Marzen et al, 2020;Vásquez-Méndez et al, 2011).…”

“…While the differences between tree or shrub vegetation and their corresponding intertree/intershrub areas have been investigated before, especially in 'fertile island '-research (e.g., Pérez, 2019;Qu et al, 2018;de Boever et al, 2015;Boettcher and Kalisz, 1990;Belsky et al, 1993), the spatial pattern of influence around trees (Zinke, 1962) has been less well researched and not at all for argan trees. In South Morocco, where the geomorphologic processes are highly dynamic (Peter et al, 2014;Kirchhoff et al, 2019b;Aït Hssaine, 2002;Marzen et al, 2020), it is likely that litter and soil particles are dislocated to the intertree areas. The knowledge about this possible dislocation and improvement of soil quality in the intertree areas could enable a better regrowth in these areas (Defaa et al, 2015;Boulmane et al, 2017).…”

Special issue: German Society for Geomorphology

“…Marzen et al ( 2020 ) deployed a portable tunnel wind simulator and dust collectors to explore the susceptibility of different land cover types to erosion by steady‐velocity wind in the Argan woodland of Morocco's Souss basin. They mapped different land cover and surface types on the basis of high‐resolution drone‐based imagery and analysed the corresponding surface and material properties based on field measurements and samples.…”