19 Apr 2021

19 Apr 2021

Review status: this preprint is currently under review for the journal SOIL.

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

Mario Kirchhoff1, Tobias Romes1, Irene Marzolff2, Manuel Seeger1, Ali Aït Hssaine3, and Johannes B. Ries1 Mario Kirchhoff et al.
  • 1Department of Physical Geography, Trier University, Trier, 54286, Germany
  • 2Department of Physical Geography, Goethe University Frankfurt am Main, Frankfurt am Main, 60438, Germany
  • 3Department of Geography, Université Ibn Zohr, Agadir, 80060, Morocco

Abstract. The endemic argan tree (Argania spinosa) populations in South Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth, but show lower soil quality than their neighbouring tree areas. Hypothetically, spatial differences of soil quality of the intertree area should result from translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas.

385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) as well as the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) and analysed for soil moisture, pH, electrical conductivity, percolation stability, total nitrogen content, content of soil organic carbon and C / N ratio. 74 tension-disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity.

We found that the tree influence on its surrounding intertree area is limited, with e.g., Corg- & N-content decreasing significantly from tree trunk to tree drip line. However, intertree areas near the tree drip line differed significantly from intertree areas between two trees, yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil moisture was highest in the north due to shade from the midday sun, the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line.

Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil moistures, N- or Corg-content to ensure seedling survival.

Mario Kirchhoff et al.

Status: open (until 06 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on soil-2021-32', Anonymous Referee #1, 22 Apr 2021 reply

Mario Kirchhoff et al.

Mario Kirchhoff et al.


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Short summary
This study found that the influence of argan trees on soil quality in South Morocco is mostly limited to the area covered by the tree crown. However, the tree influences the bare soil outside the crown positively in specific directions because wind and water can move litter and soil particles from under the tree to the areas between the trees. These findings based on soil samples around argan trees could help structure reforestation measures.