The influence of Saharan agro-pastoralism on the structure and dynamics of acacia stands

Trees play a crucial role in drylands, where they are often considered as keystone species for ecosystems and for local livelihoods. In particular in the Saharan region, Vachellia tortilis subsp. raddiana (ex. Acacia tortilis subsp. raddiana) are multi-purpose acacia trees for people and contribute to the overall ecosystem functioning. Despite progress in research, acacia stands in this region are poorly documented and little is known on their interactions with human Saharan populations. On the basis of a multidisciplinary approach, the aim of this study was to assess the structure and dynamics of Saharan acacia stands in south-western Morocco and the influence of human activities and practices. Interviews and participant observations were performed in two villages and individual acacia trees were measured in contrasting topography, microhabitat and land use situations. The acacia stands were located in cultivated and browsed areas where trees were used and shaped in the framework of human subsistence activities. In this context, the low-density acacia stands (4.8 trees/ha) showed high regeneration (47.8%) and recruitment rates, and low mortality (3.3%). Land use had more effect on stand structures than topography or microhabitat. Tree regeneration and density were especially high in cultivated areas. Most trees showed traces of pruning (60.3% of them) and debarking (33.9%), but with no correlation with tree mortality. Environmental and anthropogenic factors jointly contributed to the structure and dynamics of acacia stands, and no threat to their sustainability was observed. Even though further investigation would be required to better distinguish environmental and anthropogenic factors and to draw long-term conclusions, our results suggest that Saharan agro-pastoralism activities are not necessarily incompatible with acacia tree conservation, contrary to the commonly admitted postulate in Morocco.