Elevational Habitat Associations of Tree Species and Deadwood in Ephemeral Streams of the Namib Desert

ABSTRACT In arid and hyper‐arid regions with prolonged dry spells, plants are often particularly dependent on underground water resources. The distribution patterns of riparian tree species along ephemeral streams offer insights into their strategies to optimally utilize water. Here, we monitored the tree species Faidherbia albida and Vachellia erioloba with drones along the Kuiseb River in the Namib Desert over 6 years, 2020–2025. In addition, Moringa ovalifolia trees were monitored in drainage lines in the Tsondab Valley. We retrieved fine‐grained digital terrain models with 1 m resolution to assess the dependency of tree spatial patterns on the lowest lying areas where water runs through. The spatial habitat associations of tree species were assessed with Berman tests. We further analyzed the distribution patterns of deadwood, relative to elevation, for two study plots in the Kuiseb. Our results show that F. albida grew in lower lying areas nearer the riverbed, as compared to V. erioloba . When both species were highly negatively correlated with elevation in the Kuiseb 1 plot, deadwood amounted to only 0.54%. But when all trees together were positively associated with elevation in the Kuiseb 2 plot, thus growing further up the riverbank, deadwood increased to 12%. Moringa trees in the Tsondab Valley were negatively associated with elevation. They had a preference for low‐lying drainage channels that catch runoff after rainfall. Our research reveals different survival strategies of tree species in streams of the Namib. Vachellia erioloba is known for having up to 70 m deep‐reaching roots, allowing the species to grow more independently from riverbeds. Faidherbia albida has less deep‐reaching roots, making this species more dependent on riverbeds. Moringas prefer drainage lines but they also benefit from storing water in their thick trunks. Overall, our study highlights that topographical variation and heterogeneity in site conditions may strongly affect tree mortality.