{'fraction_non_alphanumeric': 0.02068194522079374, 'fraction_numerical': 0.006148686416992733, 'mean_word_length': 5.193771626297578, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Influence of Acacia canopy cover on soil hydraulic properties in an arid zone of Tunisia

Studies in arid regions have shown that scattered trees play an important role in reducing the negative effects of climate and soil aridity. They strongly influence the environmental conditions under their canopies. Scattered trees often function as 'fertility islands', in that they provide favourable conditions for the recruitment of other plants. The most critical factor controlling plant productivity in arid regions is water availability in the soil. Hence, understanding the soil-water relationships of nursed ecosystems is of crucial importance. The objective of this study was to investigate the facilitating role of Acacia trees on the herbaceous layer in a forest steppe ecosystem in the Bou Hedma National Park in central Tunisia. To identify the soil-water relations, the soil-water retention curve and the hydraulic conductivity of the upper soil layer (0-10 cm) were determined. Two habitats were distinguished: canopy and interspace, respectively underneath and outside the canopy of Acacia trees. The field saturated hydraulic conductivity (Kfs) was higher underneath compared to outside the canopy (8.03 vs. 5.14 x 10 m s). This could be related to the shift in the wet range of the soil-water retention curve, suggesting Kfs was driven by greater macroporosity. By improving the soil hydraulic properties, Acacia trees have a strong influence on the water availability within the nursed ecosystem. Therefore, scattered trees can play a central role in the restoration of degraded drylands. Differences in hydraulic properties underneath and outside the canopy underline the importance of incorporating the spatial variability when developing hydrological models on a field scale.