What happens to species at the rear-edge of their distribution in arid regions? The case of Juniperus thurifera L. in the Aurès Mountains (Algeria)

Algerian populations of Juniperus thurifera are the most restricted in terms of distribution and the least studied among all populations of the entire range of the species in the western Mediterranean region. Although this species is regarded as being of least concern according to the International Union for Conservation of Nature (IUCN), many studies have pointed to the need for its conservation, especially in North Africa, where populations are fragmented and the potential for regeneration is reduced. Understanding the current range of distribution of J. thurifera in Algeria and the environmental factors responsible for this is of key importance for the protection and restoration of these populations. In the present study, a maximum entropy approach (MaxEnt) was used to model the distribution of J. thurifera. Thirty occurrence records were analyzed in combination with climatic, topographic, and anthropogenic predictors at two different spatial resolutions (900 m and 30 m). The best-performing model included climatic, topographic, and anthropogenic predictors, suggesting that the distribution of the species is influenced by a combination of factors, while the performance of climatic and topographic models was similar. The most important predictors of the occurrence of Algerian J. thurifera are water-related factors. However, when considering only topographic variables, altitude has a huge impact. Finally, using improved resolution for modeling distribution enhanced the prediction capability of the model (AUC = 0.942). The findings of the present study confirmed the resilience of J. thurifera, and highlighted the tolerance to drought of Algerian populations.