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

Abstract

Abstract. The endemic argan tree (Argania spinosa) populations in southern 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; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 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., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) 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 water content 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. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. 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 water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.

The size of clearings for charcoal production in miombo woodlands affects soil hydrological properties and soil organic carbon

“…Mean steady-state infiltration capacity in small clearings was almost three times higher than in the large clearing, supporting the conclusions of previous studies on the hydrological impacts of gaps in the tree canopy in other systems such as agroforestry parklands (Bargués-Tobella et al, 2014. The difference in soil hydrological properties between large and small clearings in our study can be explained in part by a tree proximity effect (Kirchhoff et al, 2021;Yadessa et al, 2001;Zinke, 1962). As well as the influence trees have on the area under their canopy, they may also impact neighboring open areas through the activity of their roots, which extend beyond the canopy edge (Bargués-Tobella et al, 2014;Benegas, 2013;Dunkerley, 2000;Lyford & Qashu, 1969).…”

Estimation of Surface Soil Nutrient Content in Mountainous Citrus Orchards Based on Hyperspectral Data

“…During the collection process, particular attention was paid to the representativeness of the samples. Sampling points were chosen at the dripline of tree canopies to ensure that the collected soil samples truly reflected the soil characteristics of the area [16]. Additionally, to avoid interference from fertilization, sampling was deliberately avoided in fertilized areas.…”

Monitoring Dryland Trees With Remote Sensing. Part A: Beyond CORONA—Historical HEXAGON Satellite Imagery as a New Data Source for Mapping Open-Canopy Woodlands on the Tree Level

“…But tree count is clearly too simple an indicator for forest dynamics when trees are at risk of unsustainable use due to high demands on livestock forage, firewood and charcoal. Tree canopy cover-composed of individual tree-crown sizes-is more interesting, because soil conditions under the crown differ significantly from the area between the tree crowns and would thus give an indication about relative differences in e.g., soil water content, soil organic carbon or aggregate stability (Kirchhoff et al, 2019;Kirchhoff et al, 2021).…”