Influence of Acacia Trees on Near‐Surface Soil Hydraulic Properties in Arid Tunisia

Studies in arid regions have shown that scattered trees strongly influence the environmental conditions under their canopies providing favourable conditions for the recruitment of other plants. The most critical factor controlling plant productivity in arid regions is soil water availability. Hence, understanding the soil-water relationships below-canopy is needed to better comprehend the rehabilitation of degraded land by vegetation. In this study, scattered Acacia raddiana trees of three canopy size classes, were selected to examine their effect on soil physical properties, soil-water retention curve, and saturated and unsaturated hydraulic conductivities of the upper soil layer (0–10 cm). Compared to outside the canopy, below-canopy soils have a higher organic matter content causing a lower bulk density and a higher total porosity. Higher hydraulic conductivities were found below as compared to outside the canopy and the rates increased with increasing canopy size. This could be related to the ratio of water content at field capacity to saturation, suggesting that hydraulic conductivities were mainly driven by macropores and large matrix pores. By improving the near-surface soil hydraulic properties, A. raddiana trees can positively affect the water availability for the below-canopy herbaceous cover which is of crucial importance in water-limited environments.