Suppression of Seedling Survival and Recruitment of the Invasive Tree Prosopis juliflora in Saudi Arabia through Its Own Leaf Litter: Greenhouse and Field Assessments

Abstract

Many studies have focused on how leaf litter depth affects seed germination and seedling growth because the seedling stage is the most vulnerable portion of a plant’s life cycle. Invasive plants with the most severe ecological consequences are those that modify ecosystems, and this can occur through the formation of thick litter layers which can suppress the emergence, survival, and recruitment of native plant seedlings; in addition, in some cases, these litter layers can suppress invasive plant seedling recruitment. Prosopis juliflora is a thorny shrub that is native to arid and semi-arid portions of North America, parts of South America, and the Caribbean. It has invaded millions of hectares around the world, including Saudi Arabia. The objective of this study is to evaluate whether P. juliflora leaf litter reduces the recruitment of its own seedlings under greenhouse and field conditions in Saudi Arabia. In both the greenhouse and the field, the number of days to first emergence increased and germination percentage decreased with increasing litter depth. With the 1, 2, and 4 cm litter depth treatments, the number of viable seeds generally decreased, with no emergence, germination, or viable seeds detected for the 8 cm litter depth treatment. Results of this study reveal that increasing the depth of P. juliflora leaf litter suppresses the survival and recruitment of its own seedlings. Future search should assess the actual mechanisms through which P. juliflora seeds are suppressed, the role of allelopathic compounds in this process, and whether viable seeds are dormant and will persist in the soil seed bank.